Cotton Insect Management With Special Reference to the Boll ...

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Agriculture Handbool< Number 589

Cotton Insect Management With Special Reference to the Boll W^täl

oSpartÄ^ Cotton InsGCt Management With Special Reference to the Boll Weevil

Agricultural Research Service

Agriculture Handbook Number 589

Issued November 1983

Edited by R.L Ridgway, E.P. Lloyd, and W. H. Cross

For sale l)y the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402

ABSTRACT

Ridgway, R. L., E. P. Lloyd, and W. H. Cross, editors. 1983. Cotton insect management with special reference to the boll weevil. U.S. Department of Agriculture, Agriculture Handbook No. 589. 612 p., illus.

This monograph describes the state of the art of management of boll weevils in the United States. It is, therefore, concerned with the biological, economic, and environmental effects of this introduced pest, the problems associated with its control, and alternative approaches to dealing with this pest.

Keywords: cotton losses, cotton culture, Anthonomus grandis, cotton insects, Heliothis spp., simulation models. Boll Weevil Eradication Trial, Optimum Pest Management Trial, insect management, eradication, chemical insecticides, insect growth regulators, pheromones, sterile insect releases, beneficial arthropods, microbial agents

Mention of a proprietary product in this publication does not constitute a guarantee or warranty of the product by the U.S. Department of Agriculture and does not imply its approval by the Department to the exclusion of other products that may also be suitable. Views expressed by the authors are not necessarily those of the U.S. Department of Agriculture.

FOREWORD

Profitable cotton production in the U.S. and effective insect control and management have been particularly closely related since the boll weevil, Anthonomus grandis Boheman, entered the U.S. in 1892. Since that time, much research has been directed toward the boll weevil and other cotton insects. Recently, scientists have conducted expanded field and laboratory investigations to gain increased insight and understanding of the biological, economic, and environmental impacts of alternative options for beltwide cotton insect management. Alternative options or strategies are controversial. To a degree they are controversial because of deep-seated philosophy and/or convictions on the part of individuals and the economic interest groups. In broad terms, one of the most important things that we have learned over the years is that no cotton producer is an island to himself or herself in terms of effective insect management programs. Certainly, all segments of the cotton econoiay are entitled to have access to the knowledge available on the subject and to the privilege of making their own decisions.

A pilot field experiment was conducted in 1971-73 in south Mississippi and Louisiana to determine whether eliminating the boll weevil by properly integrating the use of various techniques was technically and operationally feasible. Although the Technical Guidance Committee for that experiment concluded that it was technically and operationally feasible to eliminate the boll weevil as an economic pest in the United States, a significant number of entomologists opposed the conclusion. The interpretation, therefore, of the results of the pilot field experiment led to divergent views that may be rectified only through further research and joint discussions. It is of interest to note that current authorization in the Agricultural and Consumer Protection Act of 1973 states that "...Secretary is authorized and directed to carry out programs to destroy and eliminate cotton boll weevils in infested areas of the United States...if the Secretary determines that method and systems have been developed to the point that success in eradication of such insects is assured." This authorization stimulated the development of the present boll weevil program with the overall objective of developing sound scientific information which may be utilized in making a recommendation for a beltwide cotton insect management program for the boll weevil infested areas of the Cotton Belt.

During the development of a format for the Biological Evalua- tion Team Report, it became obvious that a number of the topics could be developed into chapters for the publication of a monograph. Enthusiasm for the proposed treatise gained momentum as the potential for such an undertaking was discussed with colleagues, authors, and administrators. There was general agreement that the monograph could add stature and visibility to the comprehensive study while emphasizing areas of interest to a broad base of readers. It was also envisaged that the monograph would be an integral part of the Biological Evaluation Team Report as well as a separate

IV

publication. This sequence of collective thoughts and delibera- tions brought forth "Cotton Insect Management with Special Refer- ence to the Boll Weevil."

The purpose of this monograph is to present the results of research studies related to the biological, economic, and environmental effects of the boll weevil and other cotton insects on the crop with special emphasis on the biological aspects. In view of the emphasis placed on the Optimum Pest Management and Boll Weevil Eradication Trials, it seems appropriate to pay special attention to the biological phases and to provide a summary of the pertinent data together with detailed references.

This monograph is divided into five parts. The introductory chapters provide a historical background, and describe current practices and impacts, as well as concepts for future consideration. The second part provides an indepth discussion of newly developed and existing technology available for practical use now or in the future. In the third part, the supporting components of insect rearing, sampling, and modeling are reviewed. Alternative programs and then impacts are discussed in section four. Finally, in section five, opportunities and constraints of current and future programs are presented.

The authors have paid attention to the more recent and pertinent literature. As in any scientific endeavor, some may chal- lenge the data presented in the monograph. The material is based, however, on such extensive experimental evidence that is not likely to be found incorrect.

Some of the authors project certain management strategies for the boll weevil and other cotton insects. However, it is expected that the results of the research findings present here will not only promote cotton insect strategies but also have application to numerous other crop commodities.

Even though scientists, specialists, consultants, and others representing various segments of the cotton economy may hold diverse views regarding insect management programs for cotton, they should not differ on the desirability of learning the truth. This monograph, authoritatively written by a number of authors and edited by three prominent scientists, presents the facts, assem- bles present knowledge, and indicates areas along which further knowledge must be obtained.

K. R. KELLER Executive Coordinator Boll Weevil Policy Group

ACKNOWLEDGMENTS

The editors of this monograph are very grateful for the assistance of many who contributed to its preparation and publication. Thanks are due to the USDA Boll Weevil Policy Group, Anson R. Bertrand, Harry C. Mussman, and Kenneth R. Farrell, for their support and encouragement as this endeavor was conceived and preparations were begun. Thanks are also due to the authors who prepared their material quickly and cooperated fully with an accelerated review process; to the many anonymous reviewers who provided their comments on a timely basis; to Mrs. Jane Wall, Mrs. Fay Eggers, and Ms. Judith Smith who provided substantial editorial assistance; to Mrs. Marguerite Benedict who prepared the index; and Mr. Edgar Skelton, Mr. Roy Nash, and Mrs. Winnie Daves who supervised the preparation of illustrations and of final copy. In addition, thanks are due to Dr. Kenneth R. Keller, executive coordinator for the Boll Weevil Policy Group, for his assistance in securing anonymous peer reviews and providing strong encouragement throughout its preparation. Special thanks are due Mrs. Sara Smith, Mrs. Dorothy Turner, and Mrs. Marijane Burns for their tireless and persistent efforts as they worked for more than a year in the preparation and revision of this monograph on word processing equipment at Raleigh, NC.

vil

CONTENTS

Foreword iii

Acknowledgments v

Contributors ix

I. Introduction

1. Evolution of Cotton Insect Management in the United States 3

R. L. Ridgway and E. P. Lloyd

2. The Cost of Insecticides Used on Cotton in the United States 29

F. T. Cooke, Jr. and D. W. Parvin, Jr.

3. Ecology of Cotton Insects with Special Reference to the Boll Weevil 53

W. H. Cross

II. Suppression Components

4. Plant Resistance and Modified Cotton Culture 73 L. N. Namken, M. D. Heilman, J. N. Jenkins, and P. A. Miller

5. Entomophagous Arthropods 103 J. R. Abies, J. L. Goodenough, A. W. Hartstack, and R. L. Ridgway

6. Microbial Agents 129 M. R. Bell

7. Boll Weevil Sterility 153 J. E. Wright and E. J. Villavaso

8. Pheromones for Survey, Detection, and Control . . . .179 E. P. Lloyd, G. H. McKibben, J. E. Leggett, and A. W. Hartstack

9. Insect Growth Regulators with Emphasis on the Use of Benzoylphenyl Ureas 207

D. L. Bull, J. R. Abies, and E. P. Lloyd

10. Insecticides for Control of Cotton Insects 237 C. R. Parencia, Jr., T. R. Pfrimmer, and A. R. Hopkins

VIII

III. Support Components

11. Mass Rearing Boll Weevils 265 J. G. Griffin, P. P. Sikorowski, and 0. H. Lindig

12. Sampling Arthropods in Cotton 303 J. W. Smith, W. A. Dickerson, and W. P. Scott

13. Losses in Yield of Cotton Due to Insects 329 P. H. Schwartz

14. Models for Cotton Insect Pest Management 359 A. W. Hartstack and J. A. Witz

IV. Alternative Programs

15. Optimum Pest Management Trial in Mississippi .... 385 J. L. Hamer, G. L. Andrews, R. W. Seward, D. F. Young, Jr., and R. B. Head

16. Analysis of Technology Available for Eradication of the Boll Weevil 409

E. F. Knipling

17. Cotton and Insect Management Simulation Model .... 437 L. G. Brown, R. W. McClendon, and J. W. Jones

18. Impact of Alternative Cotton Insect Management Strategies on Producer Income in Mississippi. . . . 481

E. H. Simpson, III and D. W. Parvin, Jr.

19. Economic Evaluation of the Boll Weevil Eradica- tion Trial in North Carolina, 1978-80 497

G. A. Carlson and L. F. Suguiyama

V. Future Prospects

20. Opportunities for Improving Cotton Insect Manage- ment Programs and Some Constraints on Beltwide Implementation 521

R. E. Frisbie, J. R. Phillips, W. R. A. Lambert, and H. B. Jackson

Index 559

IX

CONTRIBUTORS

J. R. ABLES Cotton Insects Research Agricultural Research Service U.S. Department of Agriculture College Station, TX 77841

G. L. ANDREWS Mississippi Cooperative Extension Service Batesville, MS 38606

M. R. BELL Western Cotton Insects Laboratory Agricultural Research Service U.S. Department of Agriculture Phoenix, AZ 85040

L. G. BROWN Department of Industrial Engineering Mississippi State University Mississippi State, MS 39762

D. L. BULL Cotton Insects Research Agricultural Research Service U.S. Department of Agriculture College Station, TX 77841

G. A. CARLSON Department of Economics and Business North Carolina State University Raleigh, NC 27650

F. T. COOKE, JR. Economic Research Service U.S. Department of Agriculture Stoneville, MS 38776

W. H. CROSS Boll Weevil Research Laboratory Agricultural Research Service U.S. Department of Agriculture Mississippi State, MS 39762

W. A. DICKERSON Boll Weevil Eradication Research Agricultural Research Service U.S. Department of Agriculture Raleigh, NC 27607

R. E. FRISBIE Integrated Pest Management Coordinator Texas A&M University College Station, TX 77843

J. L. GOODENOUGH Pest Control Equipment and Methods Research Agricultural Research Service U.S. Department of Agriculture College Station, TX 77843

J. G. GRIFFIN Boll Weevil Research Laboratory Agricultural Research Service U.S. Department of Agriculture Mississippi State, MS 39762

J. L. HAMER Mississippi Cooperative Extension Service Mississippi State, MS 39762

A. W. HARTSTACK Pest Control Equipment and Methods Research Agricultural Research Service U.S. Department of Agriculture College Station, TX 77843

R. B. HEAD Mississippi Cooperative Extension Service Mississippi State, MS 39762

M. D. HEILMAN Soil and Water Conservation Research Laboratory

Agricultural Research Service U.S. Department of Agriculture Weslaco, TX 78596

A. R. HOPKINS Cotton Production Research Agricultural Research Service U.S. Department of Agriculture Florence, SC 29502

H. B. JACKSON Plant Pest Regulatory Services Clemson University Clemson, SC 29631

J. N. JENKINS Crop Science and Engineering

Research Laboratory Agricultural Research Service U.S. Department of Agriculture Mississippi State, MS 39762

J. W. JONES Department of Agricultural Engineering University of Florida Gainesville, FL 32611

K. R. KELLER Executive Coordinator, Boll Weevil

Policy Group U.S. Department of Agriculture Raleigh, NC 27650

E. F. KNIPLING Agricultural Research Service U.S. Department of Agriculture Beltsville, MD 20705

W. R. A. LAMBERT Entomology Department University of Georgia Tifton, GA 31794

J. E. LEGGETT Cotton Production Research Laboratory Agricultural Research Service U.S. Department of Agriculture Florence, SC 29503

0. H. LINDIG Boll Weevil Research Laboratory Agricultural Research Service U.S. Department of Agriculture Mississippi State, MS 39762

E. P. LLOYD Boll Weevil Eradication Research Agricultural Research Service U.S. Department of Agriculture Raleigh, NC 27607

R. W. McCLENDON Department of Agricultural and

Biological Engineering Mississippi State University Mississippi State, MS 39762

XII

G. H. McKIBBEN Boll Weevil Eradication Research Agricultural Research Service U.S. Department of Agriculture Raleigh, NC 27607

P. A. MILLER National Program Staff Agricultural Research Service U.S. Department of Agriculture Beltsville, MD 20705

L. N. NAMKEN Soil and Water Conservation Research Laboratory


C. R. PARENCIA, JR. Bioenvironmental Insect Control Laboratory Agricultural Research Service U.S. Department of Agriculture Stoneville, MS 38776

D. W. PARVIN, JR. Department of Agricultural Economics Mississippi State University Mississippi State, MS 39762

T. R. PFRIMMER Bioenvironmental Insect Control Laboratory Agricultural Research Service U.S. Department of Agriculture Stoneville, MS 38776

J. R. PHILLIPS Entomology Department University of Arkansas Fayetteville, AR 72701

R. L. RIDGWAY National Program Staff Agricultural Research Service U.S. Department of Agriculture Beltsville, MD 20705

P. H. SCHWARTZ National Program Staff Agricultural Research Service U.S. Department of Agriculture Beltsville, MD 20705

XIII

W. P. SCOTT Bioenvironmental Insect Control Laboratory Agricultural Research Service U.S. Department of Agriculture Stoneville, MS 38776

R. W. SEWARD Mississippi Cooperative Extension Service Batesville, MS 38606

P. P. SIKOROWSKI Department of Entomology Mississippi State University Mississippi State, MS 39762

E. H. SIMPSON, III Department of Agricultural Economics Mississippi State University Mississippi State, MS 39762

J. W. SMITH Bioenvironmental Insect Control Laboratory Agricultural Research Service U.S. Department of Agriculture Stoneville, MS 38776

L. F. SUGUIYÀMA Department of Economics and Business North Carolina State University Raleigh, NC 27650

E. J. VILLAVASO Boll Weevil Research Laboratory Agricultural Research Service U.S. Department of Agriculture Mississippi State, MS 39762

J. A. WITZ Pest Control Equipment and Methods Research Agricultural Research Service U.S. Department of Agriculture College Station, TX 77843

J. E. WRIGHT Boll Weevil Research Laboratory Agricultural Research Service U.S. Department of Agriculture Mississippi State, MS 39762

D. F. YOUNG, JR. Mississippi Cooperative Extension Service Mississippi State, MS 39762

SECTION I INTRODUCTION

Chapter 1

EVOLUTION OF COTTON INSECT MANAGEMENT IN THE UNITED STATES

R. L. Ridgway National Program Staff U.S. Department of Agriculture Agricultural Research Service Beltsville, MD 20705

E. P. Lloyd Boll Weevil Eradication Research Agricultural Research Service U.S. Department of Agriculture Raleigh, NC 27607

ABSTRACT The invasion of the United States by such exotic insects as the boll weevil (Anthonomus grandis Boheman) and the pink bollworm (Pectinophora gossypiella (Saunders)) substantially increased losses in cotton production due to insect pests. The use of inorganic and synthetic organic insecticides provided temporary solutions by controlling both exotic and native insect pests. However, undesirable side effects, such as destruction of natural enemies of insect pests, development of insecticide resistance, and adverse effects on the environment and human health, led to expanded efforts to develop improved methods of control. As a result, entomologists developed two divergent paradigms or strategies for designing technologies for insect control. In one paradigm, emphasis was placed on control actions to be used on a field-by-field basis depending on the time when a certain economic threshold was reached. In the other paradigm, emphasis was placed on suppression of a total insect population, with considerable attention to eradication. However, much of the research conducted to support the two paradigms has resulted in the development of technologies that have application to both approaches.

Two cotton insect management trials conducted during 1978-1980, the Optimum Pest (insect) Manage- ment Trial in Mississippi and the Boll Weevil Eradi- cation Trial in North Carolina, together with accelerated efforts in other States to improve cotton insect control, have now provided a basis for a possible merger of the divergent paradigms. Such a merger could result in the design and implementation of substantially improved cotton insect management programs.

R. L RIDGWAY AND E. P. LLOYD

INTRODUCTION

Significant advances in control of the principal insects attacking cotton including the boll weevil (Anthonomus grandis Bohe- man), bollworm (Heliothis zea (Boddie)), tobacco budworm (H. virescens (F.)), and pink bollworm (Pectinophora gossypiella (Sounders)) have been made in recent years (Newsom and Brazzel 1968, Adkisson 1972, Ridgway 1972a, Newsom 1974, Reynolds et al. 1975, Bottrell and Adkisson 1977, Parencia 1978, Graham 1980, and Phillips et al. 1980). However, a potential for substantial additional advances, particularly in implementation, is now indicated by the results of the large area trials conducted during 1978-80 in Mississippi by the Mississippi Cooperative Extension Service (Andrews 1981); in North Carolina by the Animal and Plant Health Inspection Service of the U.S. Department of Agriculture (USDA) (Ganyard et al. 1981); and by the results of other insect management programs (Phillips et al. 1980). The Mississippi and North Carolina trials and the several alternative boll weevil/cotton insect management programs that were defined for evaluation purposes by the USDA-State Evaluation Teams were designed to provide the basis for selecting the preferred cotton insect management program or programs for use throughout the boll weevil infested areas of the Cotton Belt (Eco- nomics and Statistics Service 1981).

The evolution of cotton insect control in the United States is examined in an attempt to provide a useful perspective from which to evaluate new information now available concerning the selection of improved cotton insect management programs.

Newsom (1974) divided the history of cotton insect management into four periods: (1) the period before the boll weevil entered the United States (before 1892); (2) the initial years of boll weevil infestation (1892-1917); (3) the period when calcium arsenate was used to control the boll weevil (1917-1945); and (4) the period when treatment with synthetic organic insecticide was the principal method used to control cotton insects (after 1945). Later, Perkins (1980a) divided into three parts the period when synthetic organic insecticides were used: (1) euphoria and the crisis of residues (1945-1955); (2) confusion and the crisis of the environment or beginning of new directions (1954-1972), and (3) changing paradigms (after 1968). With some changes in terminology, the periods identified by Newsom (1974) and by Perkins (1980a) plus an additional period, the future, are used here as the framework for a discussion of the evolution of cotton insect management.

BEFORE THE BOLL WEEVIL

The first attempts to grow cotton in the United States were made about 1600, but significant commercial production began in the late 1700's (Handy 1896). At an early date, a number of articles about insect pests of cotton, particularly the cotton leafworm (Alabama argillacea (Hubner)), appeared in southern newspapers

EVOLUTION OF COTTON INSECT CONTROL

^nd magazines, but the literature increased rapidly after a particularly destructive infestation in 1847. The cotton leafworm then continued to be the primary insect pest for a number of years. However, after Paris green was introduced in 1872 for control of the leafworm and was used widely, losses diminished. Later, as cotton production expanded in Texas, the bollworm became recognized as the chief insect pest of cotton (Comstock 1879), and a wide range of possible control measures was suggested such as light traps, poisoned baits, sprays or dusts containing arsenicals, and trap crops. All were of limited effectiveness; however, in seasons of great bollworm abundance, use of arsenicals would "result in saving at least a part of the crop'* (Howard 1896). Therefore, significant losses to the cotton crop due to insect pests occurred in the United States prior to the occurrence of the boll weevil.

INITIAL YEARS OF BOLL WEEVIL INFESTATION

The first report of the occurrence of the boll weevil in the United States was received in the U.S. Department of Agriculture in the fall of 1894. However, a careful survey of the area indicated that the boll weevil had been causing serious damage there since 1892 (Townsend 1895). As time passed and the boll weevil spread north and eastward, it caused serious losses. In 1907, it crossed the Mississippi River, and by 1917 it had infested cotton in most of Georgia. By 1922, the insect had infested cotton in the remaining southeastern States (Hunter and Goad 1923).

Initial attempts to control the boll weevil with insecticides such as Paris green were unsuccessful, and emphasis was placed on cultural control methods such as destruction of volunteer plants, manual collection of fallen infested squares, early stalk destruction, and trap crops (Howard 1896). However, during the early 1900*s some very important research was conducted on the boll weevil and other cotton insects and a fairly effective insect management system was devised (Hunter and Hinds 1905, Hunter and Pierce 1912, and Pierce 1922).

The insect management system articulated by Pierce (1922) included the recommendations for the application of arsenate of lead for control of *'worms,'* presumably the cotton leafworm and bollworm, and numerous cultural methods for control of the boll weevil. Also, the potential of calcium arsenate was recognized even though it was not recommended.

GALGIUM ARSENATE PERIOD

Goad (1918) reported on field experiments in which he found that calcium arsenate gave more effective control of the boll weevil than the other arsenical compounds he tested. Goad and Gassidy

R. L RI DG WAY AND E. P. LLOYD

(1920) recommended the initiation of calcium arsenate treatments when 15-20% of the cotton squares were punctured and continuation of subsequent treatments at 4- or 5-day intervals until the bolls were large enough to be safe from attack. The demonstration of effectiveness of calcium arsenate was a very significant event, but the successful application of calcium arsenate by aircraft in 1922 (Coad et al. 1924) perhaps had greater long-term impact. Several other scientists then confirmed the effectiveness of aerial application of calcium arsenate for control of the boll weevil (Post 1924, Hinds 1925, and Wilson 1926). Control of boll weevils with calcium arsenate made it possible to produce cotton economically in the south and southeastern United States despite the presence of the boll weevil. However, some undesirable side effects were noted. For example, destruction of natural enemies of such insect pests as the bollworm and cotton aphid (Aphis gossypii Glover) increased the incidence of these pests (Ewing and Ivy 1943).

Another significant event, though it was not fully recognized at the time, occurred during the same period. Isley and Baerg (1924) reported on the use of field surveys or "scouting" to assist in making decisions on whether action should be taken to control a cotton insect pest. Scouting became a key component of later pest management programs.

INTRODUCTION OF SYNTHETIC ORGANIC INSECTICIDES

Ivy (1944) evaluated DDT for control of the cotton leafworm and boll weevil but found that it did not provide effective control of either pest. Shortly thereafter. Ivy and Ewing (1946) reported excellent control of the boll weevil with benzene hexachloride (BHC) dust in laboratory and cage tests, and subsequent field tests confirmed the effectiveness of the gamma isomer (Ewing et al. 1947, Gaines and Dean 1947). Then Gaines and Wipprecht (1948) reported that a mixture of gamma BHC, DDT, and sulphur was more effective than calcium arsenate in controlling late-season cotton insects including the boll weevil, bollworm, and spider mites (Tetranychus spp.). Shortly thereafter several other organochlorine insecticides were developed, tested, and recommended for boll weevil control (Gaines 1957). Use of synthetic insecticides and other pesticides on cotton and other commodities increased annually at a very rapid rate (Shepard 1951) until the quantities of insecticide used on cotton began to stabilize in the 1960*s (Ridgway et al. 1978).

During the decade following the introduction of synthetic organic insecticides, the almost complete reliance upon insecticides for control of insects attacking cotton and other crops had an adverse impact on the amount of research directed to the development of alternative approaches to control. However, the importance of selective insecticides and of biological control continued to receive the attention of some scientists (Pickett 1949, Ripper et al. 1948, 1949). Also, during this period, Ewing and Parencia (1950) proposed a community-wide program for boll weevil


suppression based on early-season use of insecticides to kill emerging overwintered weevils. They recognized clearly the value of preserving naturally occurring beneficial arthropods for control of bollworms rather than relying entirely upon the use of broad spectrum insecticides. The program they advocated gave early- season control of the boll weevil, and treatments were terminated early enough so parasites and predators of the bollworm could rebound in time to provide natural control of the bollworm until late-season boll weevil infestations developed and had to be treated again.

BEGINNINGS OF NEW DIRECTIONS

While the introduction of the synthetic organic insecticides provided cotton producers with a highly effective method of controlling their insect pests, the widespread use of these insecticides resulted in the emergence of new problems. For example, the appearance of resistant strains of insects, the disruption of natural control systems that resulted in the elevation of secondary or occasional pests to major pest status, and environmental concerns caused many entomologists to begin considering alternative approaches to insect control that did not rely entirely upon the use of insecticides.

A high level of resistance to chlorinated hydrocarbon insecticides was detected in boll weevil populations in several areas of Louisiana in 1954 (Roussel and Glower 1955). Occurrence of similar resistance in Texas was reported the following year, however, several organophosphorus insecticides and calcium arsenate were reported effective against these populations (Walker et al. 1956). The threat created by the development of insecticide resistance and concerns about the damage caused by the boll weevil resulted in the U.S. Congress directing USDA to review the boll weevil problem and to identify new research approaches. A working group appointed to study the matter concluded that the future of conventional chemicals was seriously threatened and recommended the establishment of a new interdisciplinary laboratory to initiate a broad-based research program designed to find ways of reducing losses to a minimum or of eliminating the problem altogether (USDA 1958). Mean- while, studies underway on integrated biological and chemical control of alfalfa pests were to have significant impact on the future (Stern et al. 1959).

The threat to the cotton industry posed by insecticide resistance was intensified when resistance to DDT was reported in the tobacco budworm (Brazzel 1963) and the bollworm (Graves et al. 1963), and resistance to methyl parathion was reported in the tobacco budworm (Nemec and Adkisson 1969).

Also, the importance of the disruption of natural control systems, particularly through the destruction of natural enemies, was being more widely recognized. Some specific examples were

R. L RI DG WAY AND E. P. LLOYD

documented experimentally when both foliar and systemic insecticides were used to control the boll weevil and cotton fleahopper (Pseudatomoscelis seriatus (Reuter)) (Ridgway et al. 1967, Ridgway 1969) and when foliar applications were used to control Lygus spp. (van den Bosch 1971).

While insecticide resistance was developing within cotton insects and disruption of natural systems was being documented, concerns about the potential adverse environmental and health effects of insecticides were increasing. The publication of "Silent Spring" greatly stimulated expression of that concern (Carson 1962). Also, the adverse environmental effects that occurred when fish kills in the Mississippi River were documented in 1965 had impact on the evolution of cotton insect control. The Congressional hearings that followed this incident (U.S. Congress 1965) resulted in an increase in the appropriations that were to be used in improving methods of controlling insects.

The opposition to the use of DDT increased greatly during the 1960's, and its use on cotton was cancelled on December 31, 1972 (Dunlap 1981). Therefore, this effective and economical insecticide was no longer available for use by growers in the south and southeastern U.S. where it was still useful for the control of the bollworm and tobacco budworm (Anonymous 1975).

The pink bollworm problem was somewhat peripheral to the boll weevil problem, but the basic issues associated with insecticide use were very similar, particularly in the western U.S. Although the pink bollworm first became established in Texas in 1922, it did not become a serious pest until the 1950's (Noble 1969). A comprehensive research program, together with the almost simultaneous development and use of harvest-aid chemicals and mechanical harvesting, resulted in effective cultural control of this insect in those parts of Texas where it had been a serious pest. However, in the mid-1960's the pink bollworm invaded California and Arizona from Mexico (Graham 1980). Shortly thereafter, regulatory actions began limiting the availability of the inexpensive and most effective insecticides. However, the climate favored long-season cotton production and strongly discouraged short-season cultural control of the pink bollworm. Consequently, the spread of the pink bollworm in parts of Arizona and California and the use of large quantities of organophosphate insecticides resulted in that area attaining the distinction of having the highest per acre cost for cotton insect control in the United States during the late I960's (Starbird and French 1972).

Thus, as the I960's came to a close, the combination of insecticide resistance, pest resurgence, and regulatory actions had resulted in substantially increased costs and greatly increased risks for the cotton producer who continued to rely upon insecticides to prevent substantial losses due to insect pests.


PARADIGMS AND EMERGING TECHNOLOGIES

The years after 1968 were marked by the emergence of the two distinct paradigms for insect control research that were to become so important to the evolution of cotton insect management in the United States. These paradigms were discussed in detail by Perkins (1980a) as total population management (TPM) and integrated pest management (IPM). However, they were probably first described by Rabb (1972) who used the terms eradication and population management (Figure 1). Perkins (1980a) notes that both new paradigms were designed to be an alternative to the chemical control paradigm, which had dominated entomological research and practice after 1950. The two paradigms are partially described by the following quotation:

"Carl B. Huffaker and Ray F. Smith, University of California) are not thinking integrated control in the sense that I am. I'm thinking integrated control in the sense that you're taking advantage of the characteristics of different systems and putting them together for total management of a population. They're looking at integrated control . . . (as being) based on assessment of economic threshold levels and not to use control measures until they reach that goal ..." (E. F. Knipling, personal interview, 1976, as reported by Perkins 1980a.)

A somewhat more philosophical description of the contrasts between the paradigms is provided by examining the naturalistic and humanistic presuppositions proposed by Perkins (1980a) for IPM and TPM, respectively, as follows:

"Naturalistic: A belief system that man is a part of the bio- sphere but that he cannot be the total master of it. He may manipulate it for his own benefit, but there are intrinsic limits to his manipulative powers that reside in the properties of the material world.

"Humanistic: A belief system that man is part of the bio- sphere and that he can be master of it. He may manipulate it for his benefit, and there are no intrinsic limits to his manipulative powers that reside in the properties of the material world. The limits, such as they are, are derived from his current ignorance of natural processes."

Although recognition of the IPM and TPM paradigms was useful in designing improved communications, there was also a danger in oversimplifying the situation. For instance, IPM as envisioned by C. B. Huffaker and R. F. Smith is considerably broader than economic thresholds and action on a field-by-field basis (Huffaker and

10 R. L RIDGWAY AND E. P. LLOYD

Eradication Model

Management Model

Target is wide area population

Additional Methods

I Advanced

Population Models

Targets are localized

infestations

Management of Localized Populations

Methods Harmonized with Natural Control

Thresholds Refined I

Temporary Alleviation

Designed for large area communities

Designed primarily for individual grower

Emergency Use of Control Method(s)

Recognition and Preliminary Assessment

of Pest Situation

Figure 1.—Status of the evolution of insect pest control actions (from Rabb 1972).

EVOLUTION OF COTTON INSECT CONTROL 11

Smith 1980), and insect management as envisioned by E. F. Knipling includes strategies other than TPM (Knipling 1978).

The TPM and IPM paradigms can readily be identified with recent activities designed to improve cotton insect control. For example, the TPM paradigm was pursued in the Pilot Boll Weevil Eradi- cation Experiment (PBWEE) in Mississippi in 1971-73 (Lloyd 1972), and the IPM paradigm was pursued in the "Huffaker Project" conducted from 1972 to 1977 (Huffaker and Smith 1980) and, to some extent, in the cotton insect pest management pilot projects conducted in 14 States beginning in 1972 by Extension personnel with funds provided by USDA (Good and Bonell 1976). Disagreements over the interpretation of the results of the PBWEE increased the polariza- tion of viewpoints associated with the two paradigms (Perkins 1980b).

In 1975, the USDA proposed that funds be included in the fis- cal year 1977 budget to conduct the Boll Weevil Eradication Trial (BWET). When the Office of Management and Budget (OMB) reviewed the proposal, it advised USDA that the BWET should be accompanied by (1) a pest management trial; and (2) consideration of continuing current practices. OMB also advised USDA to conduct a comprehensive evaluation of the trials and of the biological, environmental, and economic impacts of alternative boll weevil/cotton insect management programs. Thus, the USDA budget submitted to Congress in January 1976 requested funds to conduct eradication and management trials concurrently. The funds were appropriated; however, the House Agricultural Appropriations Committee instructed USDA not to use these funds in the eradication trial until additional technical advances were made and the affected State governments had authorized the trials. In the fall of 1977, USDA and the House Committee agreed that the trials should proceed. In 1978, the two large areawide trials—BWET and Optimum Pest (insect) Management Trial (OPMT)—were initiated in North Carolina and Mississippi, respectively (USDA 1981).

The components of the BWET included: (1) mandatory participation based on a grower referendum; (2) areawide diapause boll weevil control; (3) monitoring and suppression of boll weevils with pheromone traps; (4) selective use of an insect growth regulator; (5) release of sterile boll weevils; (6) increased field scouting; (7) quarantine procedures; and (8) increased education and technical assistance to growers (Ganyard et al. 1981).

The components of the OPMT included: (1) voluntary participation with full reimbursement to producers for diapause control and pinhead square treatments, i.e., incentive payments; (2) overwintered boll weevil control in the spring as needed; (3) monitoring of the density of boll weevils with pheromone traps; (4) increased field scouting and improved timing of insecticide treatments; and (5) increased education and technical assistance to growers (An- drews 1981).


Thus the conduct of the BWET and OPMT resulted, at least in part, from a policy directive ordering a comparison of the technologies derived from the TPM and IPM paradigms. However, the inclusion of an incentive payment in the OPMT introduced a component that was not a characteristic of the IPM paradigm.

Although the BWET and OPMT were designed to test a number of new technologies for use in two specific areas of the Cotton Belt, additional technologies should be considered when one is designing improved programs applicable to different cotton growing areas. Many of these emerging technologies are becoming available because of the changes in direction of research initiated in the late 1950's by USDA (Hoffmann 1970), because of the expanded public support for research that occurred in the 1960's and early 1970's, and because of increased efforts in the private sector to develop new technologies. Many of the accomplishments of these expanded thrusts are documented in two recent reviews (Knipling 1979, Huf- faker 1980). In addition, major advancements related to cotton insect control have been made in the development of modified cotton cultures (Walker and Niles 1971, Bird et al. 1977, and Heilman et al. 1977); in the improvement of microbial agents (ignoffo et al. 1965, Dulmage 1970, Coppedge et al. 1972, and Yearian and Young 1978); in the augmentation of predators and parasites (Ridgway and Vinson 1977); in the discovery and commercialization of insect pheromones (Mitchell 1981); in the development of insect growth regulators (Lloyd et al. 1977, Ganyard et al. 1978); in the discovery and improvement of autocidal methods (Laster et al. 1976, Earle et al. 1979, and Wright et al. 1980); and in plant growth regulation (Namken and Gausman 1978). Similar advances have also been made in the study of damage thresholds, survey techniques, forecasting, and systems management (Anonymous 1972, DeMichele and Bottrell 1976, Hartstack et al. 1976, Hartstack et al. 1977, Anony- mous 1978, Sterling 1979, Brown et al. 1979, and Gutierrez et al. 1980).

During the 1970*s while the TPM and IPM paradigms were being scrutinized, the chemical insecticide paradigm that began developing in the mid-1950*s was still very much in existence. The petition for an emergency exemption from registration for DDT on cotton filed with the Environmental Protection Agency by the State of Louisiana (Anonymous 1975) and the petition for emergency exemption from registration for the synthetic pyrethroid insecticides filed by eleven States in 1977 (USDA 1977) constituted a continued expression of the importance of insecticides for control of cotton insects. Also, the role of the private consultant became increasingly significant. At the beginning of the decade, in 1970, there were perhaps 500 to 1000 pest control and crop consultants in the U.S. By 1980, the number had increased to about 4000, and this number is likely to increase 4 or 5 fold during the next ten years (Gordon Berg, editor, Ag-Fieldman and Consultants, personal communication). Also, several State consulting associations and a Na- tional Alliance of Independent Crop Consultants were formed during this period.


The advances that were made during the 1970's in the development of improved insect control methods and in their application by both the public and private sectors provide a broad base for designing and implementing improved cotton insect management systems.

THE FUTURE

The conduct of the BWET and OPMT and the evaluation of alternative cotton insect management programs for use in the boll weevil infested areas of the Cotton Belt may provide a unique opportunity to influence scientific change. Kuhn (1970), who utilized the concept of paradigms to analyze scientific and technical change, presented a general model based upon the emergence, use, and eventual discard of paradigms in scientific communications. Perhaps the entomology profession, and particularly that portion of it that will be especially concerned with future directions for cotton insect management, has arrived at a point where the eradication (TPM) and population management (IPM) paradigms described by Rabb (1972) and Perkins (1980a) might be merged into a single paradigm, i.e., areawide population management (Figure 2). Such a merger would appear to be logical since BWET and OPMT had a number of common elements: (1) high percentage of producer participation; (2) intense monitoring of insect populations; (3) application of suppression methods to boll weevil populations in an organized manner; and (4) improved management of local populations of the bollworm and tobacco budworm. However, the successful merger of the paradigms will require the establishment of criteria to be used to determine which strategy, i.e., local population management, areawide management, or eradication, is most appropriate for use against a particular insect pest. For instance, although Rabb (1972) considered eradication an appropriate strategy, he noted that it should be used with considerable caution: "The decision to eradicate ... is a grave responsibility that should be attempted only after careful study involving diverse perspectives has produced convincing evidence that the benefits to be accrued more than balance the resulting ecological impoverishment caused by removal of the pest species." We agree with the need for considerable caution. But when exotic species such as the boll weevil are involved, ecological disruption that might be caused by the suppression methods used and the risk of reinfestation may be of more concern than any ecological disruption that might be caused by removing a single exotic insect species. Other discussions of the pros and cons provide a useful basis for establishing criteria for selecting the preferred insect management strategy (Eden 1978, Knipling 1978, Newsom 1978, and Rabb 1978).

A broad-based commitment to the merger of the TPM and 0PM paradigms and the application of the merged paradigm to cotton insect management could provide a basis for areawide management of the boll weevil throughout much of its range and could also provide the framework for areawide management programs for the pink bollworm, bollworm, and tobacco budworm as applicable emerging technologies

14 R. L RI DG WAY AND E. P. LLOYD

Target is insects migrating or being transported

Target is total population over a large area

Containment

I Eradication

I

Designed to prevent reinfestation

Designed for geographically defined area that can be protected from reinfestation

Additional Methods

Target is a high percentage of a population over a large area

Areawide Population

Management

T Additional Methods

Designed for large area communities'

Targets are localized

infestations

Advanced Population Models I

IVIanagement of Localized Populations

♦ Methods Harmonized with

Natural Control

Thresholds Refined

Temporary Alleviation

Designed primarily for individual grower

Emergency Use of Control Method(s)

C Recognition and Preliminary Assessment

of Pest Situation

Figure 2.—Desired evolution of insect pest control actions (modified from Rabb 1972).


become available. Indeed, the areawide approach may be essential to effective implementation of such new technologies as mating disruption or mass trapping via insect pheromones. In addition, cultural controls, including uniform late planting and use of plant growth regulators for host-plant-specific insects like the boll weevil and pink bollworm, would benefit from an areawide approach. The same would be true for such technologies as autocidal methods and augmentation of natural enemies. Also, implementation of areawide management programs for such exotic insects as the boll weevil and pink bollworms, both of which have a limited host range, could be precursors to eradication of these species from a geographically defined area. At the same time, management of localized populations would continue to be the desired approach for insect pests that only occasionally cause losses.

The design and implementation of desirable cotton insect management programs will require the effective integration of all the groups, organizations, and institutions that can make significant contributions. The importance of such an effort has been emphasized previously, particularly in the matter of biological control of insects (Figure 3, Ridgway 1972b). Some of the institutional arrangements for deploying technologies in various pest management strategies have been identified (Starler and Ridgway 1977). These institutional arrangements include:

-Private producers of technologies selling directly to users. -Private producers of technologies selling directly to users

along with pest management consultant services. -Private consultants purchasing technologies and using them in

private pest management service programs. -Cooperatives producing the technologies, applying them, and

providing pest management services. -Pest management districts (with special taxation and enforce-

ment authorities) purchasing and applying technologies. -State and Federal agencies producing and/or purchasing the

technologies and implementing them.

The knowledge base that has been developed relative to cotton insect management programs provides a rather unique opportunity to develop more effective integration of the efforts of (1) suppliers of insect control materials; (2) private consultants; (3) commercial applicators; (4) education, information, and Extension agencies; and (5) action and regulatory agencies. All of these utilize the results of research to assist the cotton producer (Figure 4). Useful models are provided by the approaches used in the PBWEE in southern Mississippi (Lloyd 1972), in the BWET and OPMT (USDA 1978), in the community programs in Arkansas (Phillips et al. 1980), the High Plains boll weevil containment program, and in county programs facilitated by the Texas Pest Management Associa- tion (Haney and Frisbie 1981).

In view of the technologies that are available and of the successful experiences in implementing many of these technologies.


Figure 3.—Relationship between the various elements associated with the implementation of pest management strategies (from Ridgway 1972b).


RESEARCH (State, Federal and Private Sector)

Figure 4.—Institutions that can contribute to development and implementation of improved cotton insect management practices.


increased emphasis should be placed on the design and implementation of improved cotton insect management programs. Since cotton insect management programs will vary from area to area, no attempt has been made in this introductory chapter to describe specific programs; however, this review of the evolution of cotton insect control in the United States was written, and the monograph on "Cotton Insect Management with Special Reference to the Boll Wee- vil" was assembled to facilitate scientific communication and improved decision making on the selection of such cotton insect programs. Hopefully, as professional entomologists, cotton producers, and policy makers proceed to influence the future direction of cotton insect management, they will critically examine the scientific record, objectively evaluate the most appropriate roles for various institutions, and carefully consider the long range impacts on both agriculture and consumers.


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29

Chapter 2

THE COST OF INSECTICIDES USED ON COTTON IN THE UNITED STATES

F. T. Cooke, Jr. Economic Research Service U.S. Department of Agriculture Stoneville, MS 38776

D. W. Parvin, Jr. Department of Agricultural Economics Mississippi Agricultural and

Forestry Experiment Station Mississippi State University Mississippi State, MS 39762

ABSTRACT Expenditures for cotton insecticides in the United States increased from 96 million dollars in 1971 to 235 million dollars in 1978. However, during about the same period (1971-1977), quantities of insecticides applied to cotton in the United States declined from 73 million pounds of active ingredients to something over 39 million pounds.

This apparent conflict in the data results, at least in part, from the fact that the most common treatment used against the bollworm (Heli- othis zea (Boddie)) and the tobacco budworm (H. virescens (F.)) in the early seventies, toxaphene at 2.0 pounds active ingredients (a.i.) plus 1.0 pound a.i. methyl parathion, had been replaced in part by the synthetic pyrethroid materials at 0.1 pound a.i. by 1978.

Infestations of cotton insect pests are highly variable. However, at the national level, the cost per acre of cotton insecticide material has remained remarkably constant. In four of the six surveys made in the years between 1966 and 1977, average material cost per treated acre has ranged between 20 and 25 dollars. Nevertheless, the Southeast and the Mid- south have been experiencing a trend to increasing material cost per acre while most of the Southern Plains (Texas and Oklahoma) have had decreasing cost.

30 F. T. COOKE, JR., AND D. W. PARVIN, JR.

INTRODUCTION

The cost of controlling insect pests of cotton constitutes an important part of the total cost of producing cotton in many areas of the United States. Because the kinds of insect pests and the severity of infestations are highly variable and difficult to predict, cotton producers and policy makers have difficulty forecasting the expected cost of insect control for a given year and over time. Therefore, there is a need to examine carefully the current and past cost of controlling cotton insects in order to have a basis for estimating the impacts of proposed future programs on insecticide use.

The primary purpose of this chapter is to provide information concerning the use of insecticides on cotton in different cotton producing regions and subregions of the United States. Such information will be useful in the evaluation of alternative beltwide cotton insect control strategies for cotton insects (Keller 1980).

OVERVIEW OF PESTICIDE USE

A perspective on pesticide use and the importance of pesticides (includes but is not limited to insecticides) is provided by an examination of the information on sales of pesticides in the world and in the United States for the past decade. Such data were obtained from confidential surveys of leading international market- ers as reported in Farm Chemicals (Anonymous 1975, 1977, 1979). In 1971, the pesticide market in the United States represented 40% of the world market, but in 1974 and 1978 the proportion stabilized at 33% (Table 1). Insecticide sales represented about 35% of

Table 1.—The world and U.S. pesticide markets, user's level J^/, selected years (constant dollars, 1979 = 100)

World 2/ United Stat es 1971 1974 1978 1971 1974 1978

Pesticide ■(millions dollars ;)

Herbicides 1,672 2,687 4,218 946 1,298 1,966 Insecticides 1,245 2,236 3,437 325 603 919 Fungicides 507 1,179 1,747 95 142 215 Soil fumigants 31 85 191 6 25 74 Defoliants and

desiccants 18 23 110 12 22 43 Other 3/ 59 94 137 27 36 30

Total 3,532 6,304 9,840 1,411 2,126 3,247

\J End use. 2^/ Includes U.S. figures. 3^/ Includes growth regulators, pheromones, attractants, and

viruses.

Source: Anonymous 1975, 1977, and 1979.

COST OF INSECTICIDES USED ON COTTON 31

pesticide sales in the world in 1971, 1974, and 1978, but in the United States, insecticide sales as a percentage of pesticide sales increased from 23 in 1971 to 28 in 1974 and 1978. Total pesticide sales increased from $1.4 billion in 1971 to nearly $3.3 billion in 1978. Herbicide sales increased about $1 billion and insecticide sales rose nearly $600 million increasing their total market share. The increased sales are, in part, a result of the use of more expensive insecticides.

Corn and cotton production provide the two largest single crop pesticide markets in the world and the United States (Table 2). At the world level, pesticide sales for cotton production exceeded those for corn production in 1971 and 1974. That relationship was reversed in 1978. In the United States, pesticide sales for corn production have consistently exceeded those for cotton production, but the figures reflect a strong, consistent upward trend for both.

Specifically, the world markets for cotton insecticides increased 122% (Table 3), and the U.S. market increased 145% during this period. The five largest single crop insecticide markets in the United States for 1971, 1974, and 1978 are listed in Table 4. In 1971 and 1974, the sales of cotton insecticides in the United States exceeded the sales of insecticides used for corn production. In 1978, expenditures for corn insecticides in the United States were approximately equal to expenditures for cotton insecticides. The acreage of corn produced in the United States has increased steadily over this period while cotton acreage has remained fairly constant.

Table 2.—Two largest world and U.S. single crop pesticide markets, user's level 1/, selected years (constant dollars 1979 = 100)

World y United States

1971 1974 1978 nillions

1971 1974 1978 Crop — — _ ~" I

Corn

Cotton

668

720

1,071

1,146

1,460

1,388

430

265

628 989

301 407

\J End use. Ij Includes U.S. figures.



Table 3.—World and U.S. cotton insecticide markets, user's level J^/, selected years (constant dollars 1979 = 100)

World l_l United States Year - - - - millions dollars -------

1971 455 96 1974 816 168 1978 1,012 235

\_l End use. Ij Includes U.S. figures.


Table 4.—Five largest U.S. single crop insecticide markets, user's level J^/, selected years (constant dollars 1979 = 100)

Crop

Cotton Corn Soybeans Alfalfa Tobacco

971 1974 1978 , . - millions dollars -

96 168 235 66 125 236

18 34 7 22 25 9 21 23

1_/ End use.


COTTON INSECTICIDE USE

The U.S. Department of Agriculture has completed four studies of farmer uses of pesticides on cotton and other crops. These surveys are available for the 1964, 1966, 1971, and 1976 crop years (Eichers et al. 1968, 1970, 1978; Andrilenas 1974). Also, the U.S. Department of Agriculture routinely publishes estimates of the cost of producing selected crops in the United States. These cotton cost of production estimates were supported by three surveys .(Starbird 1974, Krenz et al. 1976, U.S. Department of Agriculture 1979b), and the figures were used to develop the cost of insect control on cotton for 1969, 1972, and 1974 (Cooke and Parvin 1981b). In addition, a special cotton pesticide survey was conducted for the 1977 crop year (Lin et al. [in review]). Also, a 1961 survey was conducted in only the portions of the Cotton Belt that were heavily infested with boll weevils (Langsford 1964).


Finally, the so-called "normalized" study (Cooke and Parvin 1981a) was made only in the States infested with boll weevils (Cal- ifornia, Arizona, and New Mexico were excluded) and insect pressure, normal weather, and 1979 technology were assumed. Information was obtained by interviewing knowledgeable individuals in the boll weevil infested portion of the Cotton Belt. A few of these were agronomists and producers, but most respondents were Extension entomologists. Respondents tended to consider the last 5-10 years and conceptually averaged insect pressure and weather over that time. Basically, 1979 technology implied insecticides with 1979 labels.

Results of all of the specific studies are summarized in Table 5, Part I. Sample size, that is, number of farmers surveyed, ranged from 143 in 1976 to 2019 in 1977 to 4200 in 1969. The size of each of the study areas in terms of planted and harvested acres is reported in columns 3 and 4, and the percentage of acres treated is given in column 5. The 1961 study was conducted in areas where the boll weevil was considered to be a severe problem; thus, it would be inappropriate to expand these results to other areas of the Cotton Belt.

The beltwide estimates are reported in Table 5, Part II. Col- umns 12 and 13 are estimates of acres planted and harvested by year. Column 14 reports the number of applications per harvested acre. Column 15 lists acre treatments. From these last two columns, it can be seen that 1972 and 1974 were years of heavy insecticide use; 1969 was a light year.

POOLING THE SURVEYS TO APPROXIMATE EXPECTED VALUES

The usual method of estimating the extent of insecticide use and the cost is by conducting a survey. Over a period of years, as noted, ten surveys have been conducted (see column 1 of Table 5) that provided information on insecticide use and cost. However, several problems prohibit the simple averaging of the information to obtain estimates of the expected level of insecticide use and cost for the various regions and subregions of the Cotton Belt that are required to evaluate alternative beltwide cotton insect control strategies.

Generally, the purposes or objectives of the surveys were different. When one then tries to extract information from a survey that was not designed to provide such information, a large sample size is preferred. The sample size associated with a few of the surveys was too small to disaggregate the information into the required sub-State regions. Also, the regions and subregions selected for sampling in the various surveys were different.

In addition, costs over time must be compared in terms of constant dollars, but no valid index of prices paid by farmers for

34 . T. COOKE, JR., AND D. W. PARVIN, JR.

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^^ F. T. COOKE, JR, AND D. W. PARVIN, JR.

Table 6.—Index of prices paid by farmers

Production indexes Cost of production Cost of agricultural

Year (all commodities) chemicals

1961 271 1964 275 269 1965 277 271 1966 289 274 1967 290 277 1968 290 279 1969 302 275 1970 313 270 1971 328 274 1972 351 284 1973 424 292 1974 481 329 1975 528 443 1976 559 481 1977 579 434 1978 626 407 1979 711 495

Source: U.S. Department of Agriculture 1979a.

cotton insecticides is available. Of those that are available, the most helpful would seem to be the index of prices paid by farmers for agricultural chemicals (Table 6). However, this index declined for the periods 1968-71 and 1977-78, and the cost of cotton insecticides did not. Therefore, the index of prices paid by farmers for all production inputs, which reflects a consistent increase in the cost of all production costs to farmers for 1961-79 (Table 6), was used to adjust reported costs to 1979 constant dollars.

DISCUSSION OF SURVEYS

The 1961 Cotton Insecticide Survey

The 1961 cotton insecticide study (Langsford 1964) was conducted in areas where the boll weevil was known to be a severe problem. It would not be appropriate to expand the results of this survey to the rest of the Cotton Belt. However, the results are included because the sample size is relatively large and because the survey provides some information on approximately one-third of the cotton acreage in the United States.


The 1964, 1966, 1971, and 1976 National Pesticide Use Surveys

The national surveys of pesticide use of 1964 (Eichers et al. 1968), 1966 (Eichers et al. 1970), 1971 (Andrilenas 1974), and 1976 (Eichers et al. 1978) were made to arrive at an estimate of the total use of pesticides in the United States. The production regions used in these surveys (Figure 1) follow State lines and were extremely large. However, the cost of controlling cotton insects differs considerably from north to south in such large areas, especially in the Delta States and the Southern Plains Regions. Ad- ditionally, the number of cotton producers sampled was not adequate for providing regional estimates. Certainly the information is "too thin" to be disaggregated into State or sub-State regions.

The 1969, 1972, and 1974 Cotton Cost of Production Surveys

The cotton cost of production surveys of 1969 (Starbird 1974), 1972 (Krenz et al. 1976) and 1974 (U.S. Department of Agriculture 1979b) were designed to determine the annual cost of producing cotton. The production regions used in these surveys (Figure 2) were smaller than those used in the national pesticide use surveys and were not aligned with State lines, but Southeast Regions 1 and 2 and South Central Region 1 were still too large for our purposes, i.e., to obtain average costs of cotton insect control within regions, especially the Mississippi Delta Region, which includes the bootheel of Missouri; the Mississippi River Delta of Arkansas, Louisiana, and Mississippi; and the Red River Valley of Louisiana.

The 1977 Cotton Pesticide Use Survey

The 1977 cotton pesticide use survey was designed to assist with the evaluation of alternative cotton insect control strategies, commonly referred to as the boll weevil evaluation. The production regions used in this survey (Figure 3) involved still another group of geographical regions, whereby cotton producing regions were effectively separated according to pesticide use patterns, with the exception of Regions 1 and 3. (These regions are too large, and the insect control costs vary widely within these regions. Consequently, the estimated costs do not accurately reflect differences that exist within the regions.) Also, in this survey, Region 2 was not sampled, and minor cotton production regions (especially in Texas) were not included.

Normalized Estimates of Insecticide Use

The survey on normalized estimates of insecticide use (Cooke and Parvin 1981a), like the 1977 cotton pesticide use survey, was designed to assist with the evaluation of alternative cotton insect control strategies. Thus, the Cotton Belt was divided into six major production regions (Figure 4), and each of the six major

38 F. T. COOKE, JR, AND D. W. PARVIN, JR.

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Table 7.—Estimated harvested acres, number of harvested acre, selected years, by Delphi

1969 L972

Materials Materials Cotton 11 Har- cost Har- cost per produc- vested per acre vested acre

Delphi tion acres Number (1979 acres Number (1979 regior L sub- (x appli- constant (x appli- constant

1/ region 1,000) cations dollars) 1,000) cations dollars)

A SE-1 150 4.0 16.54 SE-2 492 7.0 19.27 540 13.0 43.30 SE-3 199 10.0 31.89 200 15.0 57.49

Total or average 841 7.2 21.77 740 13.5 47.13

B SE-7 530 4.0 11.02 713 5.0 12.73 SC-2 379 3.0 9.17 513 4.0 9.36

Total or average 909 3.6 10.25 1,226 4.6 11.32

C SE-4 296 4.0 14.22 365 5.0 19.43 SE-5 226 8.0 20.19 259 7.0 16.69 SE-6 148 6.0 20.02 SC-1 1,787 4.0 18.14 2,659 7.0 22.49

Total or average 2,457 4.5 17.97 3,283 6.8 21.69

D SC-3 750 2.0 6.30 744 2.0 6.15 SC-4 329 2.0 6.42 286 5.0 21.96 SC-5 290 6.0 18.33 299 9.0 37.11

Total or average 1,369 2.8 8.88 1,329 4.2 16.52

E SC-6 1,309 5.0 18.45 1,450 3.0 11.49 SC-7 1,920 1.0 4.51 2,357 2.0 10.62 W-6

or average 100

3,329 3.0 2.6

17.16 10.37 2.4 Total 3,807 10.95

F W-1 599 2.0 11.07 764 2.0 20.06 W-2 93 7.0 33.46 75 9.0 77.95 W-3 204 4.0 24.96 201 9.0 63.05 W-4 36 2.0 12.20 W-5 61 7.0 27.99 78 3.0 17.50

Total or average 993 3.2 17.10 1,118 3.8 31.49

j_/ See Figure 4. Ij See Figure 2. _3/ 5-year average, 1975-79.

Source: 1969, 1972, and 1974—Cooke and Parvin 1981b; 1977— Cooke and Parvin 1981a.

applications per treated acre, and materials cost per region and cotton production subregion.

1974 1977 Normalij sed

Materia Is Materials Materials

cost pe r cost pe !r < :ost per

acre acre acre

Har- (1979 Har- (1979 Har- (1979

vested Number con- vested Number con- vested con-

acres appli- stant acres appli" - stant acres 3/ Number stant

(x ca- dol- (x ca- dol- (x appli- dol-

1,000) tions lars) 1,000) tions lars) 1,000) cations lars)

50 6.5 38.32

460 14.0 51.58 228 18.9 64.08 229 12.7 66.38

191 14.0 67.77 206 12.5 39.86 105 13.6 71.10

651 14.0 56.35 434 15.9 52.58 384 12.5 64.02

791 7.0 13.94 292 0.9 2.69 512 6.2 23.73

444 5.0 16.95 818 2.2 6.83 659 2.0 5.57

1,235 6.3 15.02 1,110 1.8 5.74 1,171 3.7 13.51

350 8.0 19.95 229 5.5 18.08 115 5.5 17.03

236 8.0 22.84 207 12.5 39.86 174 11.5 54.13

207 12.5 39.86 88 7.9 24.42

2,401 7.0 24.54 1,692 8.5 24.77 1,826 8.9 41.98

2,987 7.2 23.87 2,335 8.9 26.79 2,203 9.0 40.94

680 4.0 9.09 560 3.7 7.80 429 2.2 2.40

205 4.0 19.98 685 6.7 20.90 194 5.5 17.03

316 10.0 5.6

43.32 19.96 5.4 15.01

273 896

5.3 3.8

20.17

1,201 1,245 10.98

1,440 5.0 13.14 1,797 0.6 2.26 1,511 1.4 3.61

2,379 2.0 5.18 3,496 0.3 .87 2,764 1.0 6.65

3.1 8.18 0.4 1.34 54

4,329 2.3 1.1

9.89

3,819 5,293 5.81

1,082 2.0 12.21 1,212 1.8 7.05

131 7.0 41.11 641 9.4 33.70 286 7.0 37.74

80 1.1 2.55

3.4 19.61 81

2,014 1.1 4.1

2.55 15.17 1,499

Cooke and Parvin 1981a; and Lin et al. [in review]; normalized-

^^ F. T. COOKE, JR, AND D. W. PARVIN, JR.

production regions was divided into several subregions with similar insect control practices so as to facilitate collection of estimates of insecticide use and cost from entomological experts within the subregions. The entomological experts were interviewed, the estimates were summarized, and the summaries were submitted to two to four rounds of review by the experts. This approach to collecting expert opinion is a modification of the Delphi method (Linstone and Turoff 1975), and the six regions (A-F in Figure 4) are referred to as Delphi regions. Region F was excluded from this study because boll weevils are not a threatening pest there. The experts in this inquiry consisted chiefly of one Extension entomologist per State in 11 weevil-infested States. A more comprehensive Delphi inquiry was conducted in 1980 and 1981 and reported elsewhere (Eco- nomic Research Service, U.S. Department of Agriculture, 1981).

INTERPRETATION OF SURVEY RESULTS

The number of insecticide applications used on cotton in any given year provides some insight as to the relative severity and duration of infestations of insect pests. It may also provide some insight into the effectiveness of insecticides against the target pests. A change in the number of treatments over time may reflect a change in insect management strategies or improved technology.

In Table 7, the normalized estimates are compared with the previously discussed estimates of insecticide use and costs for 1969, 1972, 1974, and 1977. Plainly, the number of insecticide applications per acre in Delphi Region A ranged from 7.2 in 1969 to 15.9 in 1977, but the estimated cost per acre ranged from $21.77 in 1969 to $56.35 in 1974. The normalized estimate of the number of insecticide applications (12.5) is thus within the range observed. However, the normalized material cost of $64.02 is greater than any value produced in any of the surveys. (This probably reflects an increasing availability and acceptance of the more expensive synthetic pyrethroid insecticides.) Region A had the highest per acre cost of insecticide materials of any of the regions, but between 1969 and 1977, cotton acreage decreased from 841,000 to 434,000 acres.

In Delphi Region B, the average number of insecticide applications was 1.8 per acre in 1977 and 6.3 in 1974. Average cost of insecticides ranged from $5.74 to $15.02 during these years. Thus the normalized estimates of 3.7 applications and $13.51 material cost are within the range obtained in the other surveys.

In Delphi Region C, the average number of insecticide treatments ranged from 4.5 in 1969 to 8.9 in 1977. The average cost for insecticides ranged from $17.97 in 1969 to $26.79 in 1977. The number of cotton acres declined from 3,282,000 in 1972 to 2,335,000 in 1977. The normalized estimates for the number of applications reflect this trend. However, the number of applications and the increased use of synthetic pyrethroid insecticides put the normalized estimate of material cost outside the range.


In Delphi Region D, the average number of insecticide treatments ranged from 2.8 to 5.6 between 1969 and 1974. Insecticide costs ranged from $8.88 per acre (1969) to $19.96 per acre (1974). Cotton acreage declined from 1,369,000 acres in 1969 to 1,201,000 acres in 1974. The normalized estimates of the number of applications and costs are consistent with these values.

In Delphi Region E, the number of insecticide applications ranged from 0.4 per acre (1977) to 3.1 per acre (1974). Per acre insecticide costs ranged from $1.34 to $10.95. Cotton acreage increased from 3,329,000 acres in 1969 to 5,293,000 in 1977. Region E had the lowest cost of insecticides of any of the regions.

Cost of Insecticides (Materials)

The cost of insecticides for the United States and for cotton producing States obtained from surveys made to determine the cost of producing cotton and from the Farm Enterprise Data System is reported in Tables 8 and 9, respectively. According to Table 8, insecticide costs have remained fairly constant from 1964 to 1980, increasing from $14.74 to $21.90 (1979 constant dollars). Accord- ing to Table 9, States with the highest insecticide cost per acre in the boll weevil infested part of the Cotton Belt were South Car- olina, Georgia, Alabama, and North Carolina. These States with the highest cost per acre are located in the southeastern United States. Louisiana, Mississippi, and Tennessee had the next highest insecticide cost. Texas and Oklahoma had the lowest insecticide cost of any of the boll weevil infested States.

Table 8.—U.S. cost of insecticide materials per harvested acre

1979 constant Year Dollars dollars

1964 5.69 14.74 1966 6.42 15.79 1969 6.79 15.96 1971 4.66 10.11 1972 7.35 14.92 1974 12.35 18.28 1976 15.83 20.10 1977 24.68 30.36 1978 21.49 24.50 1979 21.90 21.90 1980 25.31

Source: U.S. Department of Agriculture 1979b, Krenz et al. 1976, Starbird 1974.


Table 9.—Average insecticide material cost per harvested acre by States (1979 constant dollars)

State 1977 1978 1979

Alabama 82.82 72.00 Georgia 84.66 73.61 North Carolina 81.88 71.19 South Carolina 88.45 76.90 Arkansas 27.79 24.16 Louisiana 65.12 56.61 Mississippi 57.29 49.82 Missouri 19.56 17.01 Tennessee 40.53 35.24 New Mexico 4.59 3.99 Oklahoma 7.05 8.39 Texas 5.17 4.35 Arizona 139.06 120.91 California 44.96 39.09

64.42 65.86 63.70 68.81 21.61 50.65 44.57 15.22 31.53 3.57 7.37 3.80

108.18 34.98

Source: Krenz et al. 1976.

Cost of Applying Insecticides

The cost of applying insecticides estimated for Delphi regions 1-33 (Figure 4) is shown in Table 10. These costs ranged from $0.94 to $2.25 per acre.

Quantities of Insecticides Applied to Cotton

Relative quantities and per acre treatments of insecticides used on cotton are summarized in Tables 11, 12, and 13. It is clear from Table 11 that more insecticide is used in the Southeast and Delta States and that the decline in quantity used in the Southern Plains is substantial. Data on per acre treatments of specific insecticides are reported in Table 12. Methyl parathion, EPN, and toxaphene were the most extensively used materials. Data on pounds of specific insecticides used on cotton are reported in Table 13; for example, subsequent to cancellation of the registration of DDT on December 31, 1972, the use of methyl parathion and toxaphene increased sharply through 1974. However, by 1976 and 1977, the use of methyl parathion and toxaphene had declined, and increased usage of EPN, monocrotophos, and methorny1 was observed in 1977. Also, in 1977, an experimental use permit allowed use of new synthetic pyrethroid insecticides (permethrin and fenvalerate) for control of Heliothis spp. Subsequently, long-term normalized estimates indicated a major shift to the synthetic pyrethroid insecticides (permethrin, fenvalerate) for control of bollworms (Heliothis zea (Boddie)) and tobacco budworms (li. virescens (F.)). They also


Table 10.—Range in cost of one application per acre by Delphi subregion

Application cost per acre

Region 1/ (1979 constant dollars)

1 2 3 4 5 6 7 8 9

10 11 12 13 14 15 16 17 18

19 20 21 22 23 24 25 26 27

28 29 30 31 32 33 34 35

1 .50 1 .50 1 .25 1 .71

1. 50 ■ - 1. 58 1 .71 1 .71 1 .80 1 .80

37 - 1. 45 25 - 1. 74 ,37 - 2. 25 .37 - 2. 25 ,75 - 2. 00 .25 - 1. 50 .25 - 1. 50 .10 ~ 1. ,75 .25 - 1. ,50

.27 - 1, .33

.25 - 1. .31

.81 - 2, .00

.81 - 2, .00

.50 - 2, .00

.57 - 2 .25 2 .00 - 2 .25 1 .70 - 2 .00 2 .00 - 2 .25

0 .94 - 1 .50 1 .75 - 2 .00

2 i.25 2 '.00 2 L25 ¿ L25 2/ 2/

\J See Figure 4. 1) Application costs in Regions 34 and 35 were not reported sep-

arately. There aerial applicators charge for materials and application.

Source: Cooke and Parvin 1981a.


Table 11.—Quantities, by region, of insecticides used on cotton, 1964, 1966, 1971, and 1976

1964 1966 1971 1976 Region y 1,000 pounds active ingredients- - - -

Appalachian 4,999 3,302 3,610 4,092 Southeast l^.llk 22,603 27,259 20,581 Delta 2/ 23,948 21,004 29,361 32,653 Southern Plains 20,797 12,551 10,320 2,461 Mountain 2,253 4,357 1,868 3,337 Pacific 2,251 1,083 939 1,015 Total 78,022 64,900 73,357 64,139

XJ See Figure 1. y Includes Corn Belt States.

Source: Eichers et al. 1968, 1970, 1978; Andrilenas 1974.

Table 12.—Per acre treatments of insecticides, selected materials, 1964-77

1964 1966 1971 1976 1977 Insecticide _ - _ -^1 ,000 acres ) - - - -vi — — — —

Methyl parathion 5,420 3,577 6,384 6,166 22,303 EPN 9,459 Toxaphene 5,016 3,881 3,275 3,112 7,850 Methomyl 4,725 Monocrotophos 3,648 Dicrotophos 1,416 1,797 658 2,278 Endrin 1,194 403 lei 325 1,637 Permethrin 1,587 Parathion 751 860 682 1,496 1,210 Azinphosmethyl 1,131 Dimethoate 768 Fenvalerate 288 Chiordimeform 216 DDT 6,901

19,282 14,904 2,383 14,783

561 12,318 Subtotal \J 57,100

\J This subtotal includes only those insecticides listed and therefore represents something less than the total of all acre treatments.

Source: Eichers et al. 1968, 1970, and 1978; Andrilenas 1974; Lin et al. [in review].

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indicated that in the future, reduced amounts of methyl parathion, toxaphene, methomyl, and monocrotophos will be used for cotton insect control. For example, recommended dosages of the methyl parathion plus toxaphene combination commonly used for bolIworm-budworm control are 1.0 and 2.0 pounds active ingredients (a.i.), respectively, per acre per application, but the recommended dosages of the synthetic pyrethroid insecticides range from 0.1 to 0.2 pound a.i. per acre per application. The shift to the synthetic pyrethroid insecticides will therefore result in a significantly smaller total number of pounds of insecticide being applied to cotton.


LITERATURE CITED

Andrilenas, P. A. 1974. Farmers' use of pesticides in 1971—quantities. U.S. De-

partment of Agriculture, Economic Research Service, Agricul- tural Economic Report No. 252, 56 p.

Anonymous. 1975. World pesticide markets. Farm Chemicals 138:45-48.

1977. A look at world pesticide markets. Farm Chemicals 140: 38-43.

1979. A look at world pesticide markets. Farm Chemicals 142: 61-68.

Cooke, F. T., Jr., and D. W. Parvin, Jr. 1981a. The cost of controlling cotton insects in the boll weevil

infested States, Agricultural Economics Technical Report No. 28, Department of Agricultural Economics, Mississippi State University.

and D. W. Parvin, Jr. 1981b. Insecticides used to produce cotton in selected major production regions in the United States, 1969, 1972, and 1974. Economics and Statistics Service, U.S. Department of Agricul- ture, Economics and Statistics Staff Report No. AGESS810331, April 1981.

Eichers, T. R., P. A. Andrilenas, and T. W. Anderson. 1978. Farmers' use of pesticides in 1976. U.S. Department of Agriculture, Economics, Statistics, and Cooperative Service, Agricultural Economic Report No. 418, 58 p.

P. Andrilenas, H. Blake, R. Jenkins, and A. Fox. 1970. Quantities of pesticides used by farmers in 1966. U.S. Department of Agriculture, Economic Research Service, Agricul- tural Economic Report No. 179, 61 p.

P. Andrilenas, R. Jenkins, and A. Fox. 1968. Quantities of pesticides used by farmers in 1964. U.S. Department of Agriculture, Economic Research Servicie, Agricul- tural Economic Report No. 131, 37 p.

Keller, K. R. 1980. Status of the boll weevil eradication and optimum pest management trials. Tn Proceedings, 1980, Beltwide Cotton Production-Mechanization Conference (St. Louis, January 9-10, 1980), p. 29-34.


Krenz, R., C. Michael, G. Garst, D. Fawcett, and S. Rogers. 1976. Cost of producing food grains, feed grains, oil seeds, and

cotton, selected years. U.S. Department of Agriculture, Eco- nomic Research Service, Agricultural Economic Report No. 338,

40 p.

Langs ford, E. L. ^ 1964. Extent and cost of using chemicals in cotton production in

selected areas, 1961. U.S. Department of Agriculture, Economic Research Service, Farm Production Economics Division, ERS-155,

15 p.

Lin, Y. N., D. F. Caillavet, and D. W. Parvin, Jr. Estimation of insecticide, miticide, and nematicide applications in the Cotton Belt, 1977. Mississippi Agriculture and Forestry Experiment Station. [in review.]

Linstone, H. A., and M. Turoff, editors. 1975. The Delphi method: techniques and applications. Addison- Wesley Publishing Company, Reading, MA.

Starbird, I. R. 1974. Costs of producing upland cotton (selected years). U.S. Department of Agriculture, CS-265.

U.S. Department of Agriculture. 1979a. Agricultural Statistics 1979, p. 453-454.

1979b. Costs of producing selected crops in the United States selected years. Prepared for the Committee on Agriculture, Nutrition and Forestry, United States Senate.

1981. Economic Research Service. The Delphi: insecticide use and lint yields, beltwide boll weevil/cotton insect management programs, overall evaluation. Appendix E, ERS Staff Report No. AGESS810507.

53

Chapter 3

ECOLOGY OF COTTON INSECTS WITH SPECIAL REFERENCE TO THE BOLL WEEVIL

W. H. Cross Boll Weevil Research Laboratory Agricultural Research Service U.S. Department of Agriculture Mississippi State, MS 39762

ABSTRACT Study of the biology, behavior, and ecology of the boll weevil (Anthonomus grandis Boheman) reveals that this insect can easily adapt to new environments. However, there are critical weak points in its life cycle, and these provide opportunities for effective management of this pest.

For example, alternate host plants act as reservoirs for native cotton insect pests, but the boll weevil, as a relatively recent introduced pest, largely lacks alternate host plants in the United States.

In the Boll Weevil Eradication and Optimum Pest Management Trials, more than 50 miles of cotton rows were sampled in 1978-79 for infest- ing arthropods. These (more than 1 million) were identified by group and converted to per acre estimates to obtain a better understanding of the trophic structure of the cotton field arthropod community.

A case history of a Mississippi cotton field demonstrates how poor cotton insect management can increase pest problems and increase production costs.

INTRODUCTION

The cotton field is a dynamic community with a physical environment, a crop phenology, and a structured animal population that is much influenced by the presence of infield "weeds" and even more by the array of surrounding crops and native vegetation. These animal populations are also influenced by sequences of weather (varying annually) and by interplay among the species. This interplay of animal populations is often greatly simplified by using the categories "pests" and "beneficiáis."

54 W. H. CROSS

BOLL WEEVIL BIOLOGY, BEHAVIOR, AND ECOLOGY

The boll weevil (Anthonomus grandis Boheman) is a rather recent introduction from a tropical environment. (Only about 280 generations have developed in the United States.) Unlike native species, which tend to have many hosts, it survives in this country on cotton except for limited populations found on Cienfuegosia and Thespesia in southern Texas (Cross et al. 1975). Even in the Trop- ics, the boll weevil has a limited host range. For many years, cotton (Gossypium hirsutum L. and £. barbadense L.) was the only host known, but more recently, the weevil was found to reproduce on several other species of Gossypium and on several species in at least four other genera of the Malvaceae (Thespesia, Cienfuegosia, Hampea, and Hibiscus (one species)), especially those from the more southern parts of the range of the insect—Mexico, Central America, Colombia, and Venezuela (Cross et al. 1975). Thus, small populations are maintained in areas remote from cultivated cotton.

In fact, relatively few of the overwintering generation survive the winter in temperate climates. An average 10% is normal, and the rate is much lower after colder winters. Although many female boll weevils overwinter with viable sperm in their spermathecae and can thus lay fertile eggs without having to find a male in the spring, much cotton in fringe areas becomes infested only after reimmigration of adults (Figure 1). Thus, this pest at times maintains a tenuous existence in the United States.

Literature on the boll weevil has been summarized by Dunn (1964), Mitlin and Mitlin (1968), and Cross (1973). Basic studies of behavior of the boll weevil reported subsequently have been reported by Cross and Mitchell (1966), Lloyd et al. (1967), Cross et al. (1969), Hardee et al. (1969a, 1969b), Mitchell and Cross (1969, 1971), Walker and Bottrell (1970), and Roach et al. (1971).

The boll weevil is a typical snout beetle in the Curculioni- nae, the largest subfamily of the Curculionidae and one that includes many pests of crops and trees. The genus Anthonomus contains 113 known species in America north of Mexico (H. R. Burke personal communication). This phytophagous group demonstrates a high degree of host specificity and has a general preference for feeding and reproducing in flower buds.

General Annual Cycle

Boll weevils overwinter as adults in forest and hedgerow litter, usually near cotton fields. They return to cotton fields in the spring where they feed on the terminals of seedling plants and then feed on and reproduce in squares (flower buds). Later in the season, they attack and reproduce in bolls (fruit). Eggs are deposited singly at the bottom of punctures made with the slender rostrum of the female. The larvae feed for 7-14 days in either the squares (which abscise and normally fall to the ground 3-5 days

ECOLOGY OF COTTON INSECTS 55

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56 W. H. CROSS

after egg hatch) or the bolls and pupate; then after 3-5 days, the adults emerge through a hole cut to the outside. Variations in this cycle depend on average temperatures. Females of the new generation begin laying eggs after 3-4 days. As many as five generations may develop each season.

Emerging Overwintered Population

Although small numbers of overwintering boll weevils may move about during the warmer periods that occur throughout the winter, the maximum exodus from forest litter occurs from late April to early June. Thus, in areas where cotton is usually planted between May 1 and 15, weevils may be captured on sticky flight screens or on pheromone-baited traps several weeks before the cotton seedlings emerge. (Peak numbers may emerge following rains, especially after extended dry periods.) However, recent observations of native weevils marked with Zinc-65 and earlier observations of weevils caged above their hibernation sites with fruiting cotton plants indicate that these early emerging weevils lack interest in cotton for some period of time after they leave the litter. (Dissections of the early-season weevils disclose a considerable reserve of body fat and small gonads, indicating that they are still in diapause (W. H. Cross unpublished data).)

Although sampling of forest litter has revealed that at least small numbers of overwintering weevils are present every month of the year, most have emerged by early June. There is no evidence that these emerging adults feed on another plant before cotton is available. For example, when large numbers trapped May 1 as they entered a field that had just sprouted cotton seed were dissected, none contained any recognizable plant material in their alimentary tracts. Also, some of these weevils lived an average 11.0 days when they were placed in small cages in the field where nothing was available except small droplets of dew in the morning; some held similarly but with a wet cotton ball lived an average 13.6 days; and others caged with fruits and buds of a variety of native plants, including two species of wild Malvaceae, survived ca. 11 days (W. H. Cross unpublished data).

The total number of weevils emerging from hibernation varies greatly by location and year and depends on both the number entering hibernation the previous fall and the rate of survival. On the basis of sampling in forest litter in fall and spring, an average 5-10% survive. Mortality is greatest during winters with sharp freezes when no insulating snow is present, and especially during winters when freezes and intermittent warm periods occur. (in fact, such a sequence can eradicate a population locally.) Survi- val is greatest during mild winters: after such a winter, as many as several hundred weevils per acre of cotton may emerge in areas with a preponderance of small fields and correspondingly more forest edge. Males consistently represent 60-65% of an emerging


population, and there is some evidence that the first few weevils that emerge are usually males.

The most interesting and valuable studies of behavioral patterns in the boll weevil relate to their response to olfactory and visual stimuli. Repeated tests over several years suggest that emerging overwintered weevils (and weevils of other generations as well) cannot recognize cotton at distances greater than perhaps a few inches. However, a chemical arrestant has been isolated from cotton plants (with increasing concentration gradients towards terminals and buds) that elicits feeding by the weevil. Also, a distinct plant attractant has been isolated that is attractive to boll weevils when they are held in an olfactometer, but cages with plants are no more attractive to field weevils than cages without plants. Therefore, the first boll weevils seeking cotton in the early season apparently find it only through random movement.

There is likewise no attraction between the sexes or between individual weevils in the unfed emerging population. However, an isolated overwintered male weevil that finds and feeds on cotton squares for several days begins to emit a strong aggregating pheromone that attracts both sexes from proved distances of 100 feet and perhaps farther when wind conditions are optimum. Indeed, if male weevils feed on cotton terminals or on seedling cotton instead of cotton squares, they produce lesser amounts of the pheromone. Also, if they are fed an apple, banana, or other fruits in the laboratory, they elicit a limited response in an olfactometer, but evoke no response in field trapping tests.

The females attracted to the male boll weevil by the aggregating pheromone may or may not be stimulated to mate. However, in the laboratory, when females have been isolated and fed squares for several days, they usually respond to males and mate. In this instance (as also with weevils of other generations), the male does not recognize that a female is approaching until she is within less than 1 inch, but at this distance she seems to emit a short-range aphrodisiac that may excite him. If not, the female may stroke him with her antennae or walk over him one or more times until he responds and mates with her (Cross and Mitchell 1966). In a number of observations, mating of overwintered females lasted from 13 to 37 minutes (mean 27 minutes), and multiple matings were observed on the same and subsequent days (Mitchell and Cross 1971). Also, as noted, some overwintered females (as many as 60% or more) mate in the fall before hibernating and so, by retaining viable sperm in their spermathecae, can deposit fertile eggs without a spring mating though fecundity and fertility are reduced. Overwintered females were observed to excavate the puncture they had made for 1-24 minutes (mean 5.2 minutes) before turning 180°and inserting the ovipositor; they then took 0.2-3.2 minutes (mean 1.0 minute) to complete oviposit ion. They laid an average of 0.74 egg per hour during daylight, and none at night (Mitchell and Cross 1969).

58 W. H. CROSS

Overwintered weevils have been reported to live about 30 days after they enter cotton fields, but the period is difficult to determine precisely. When large numbers of weevils in forest litter, or just emerging from litter, were marked for identification, considerable numbers survived through July and August, and the males had decidedly greater longevity than females. For example, the last recapture of an overwintered, marked female occurred September 14; the last recapture of a similar male occurred October 13. How- ever, when a few of the overwintered weevils collected in late season were dissected, all were highly reproductive, and none showed evidence of diapause development in preparation for a second winter.

Emerging overwintered boll weevils may have to move considerable distances before finding cotton. For example, some marked weevils re-released in forest litter were recovered in pheromone- baited traps at distances of 1 and 1.7 miles from the release site, and 4.5% of 3380 marked weevils either missed or left nearby cotton and were recaptured in cotton that was 0.06 - 0.6 mile distant (W. H. Cross unpublished data.).

—1 and Subsequent Generations

As a general rule, F adult weevils begin emerging from squares when the flowers appear on the cotton plant (assuming that the overwintered weevils entered the field before or about the time the squares began to form). These adults walk from the fallen square to the cotton plant and immediately eat a hole in a leaf. (This is the only foliar feeding observed except when weevils are deprived of cotton for a number of hours.) A tenfold rate of population increase per generation has been considered a reasonable approximation of the normal field situation, but this rate has not been confirmed. The ratio of sexes is about 1:1, and parthenogen- esis probably does not occur. Both sexes of the F, generation are receptive to mating after about 3 days.

Once a moderately large population of weevils is present, the emission of pheromone may not be important to mating success because the newly emerged adults tend to congregate in flowers for early feeding. However, the pheromone emitted by males may produce limited aggregation or clumping since the number of males was higher than normal among 4250 weevils found together in cotton fruiting structures. With small populations, the pheromone is important in assuring mating and also in increasing the extent of range of the female since she flies most often in response to the male pheromone.

A virgin female weevil begins to oviposit after the third to fourth day. She may make a typical puncture in a square, apparently in preparation for the egg, and may insert her ovipositor within the puncture, but she always deposits these infertile eggs


on the outside of the square. Indeed, some of these eggs are deposited at random on the plant.

In cotton fields, boll weevils make occasional short flights that are not a response to pheromone. However, flights are rarely initiated at wind velocities above 3 miles per hour; and at 5 miles per hour or above, flying weevils tend to settle back onto the plants. Weevils generally begin flights by facing into the wind, but the flights are random in direction so far as wind direction or position of the sun is concerned. In flight, the front legs are held high above the head, a position that probably aids the weevil in its habit of landing on the underside of leaves.

In field tests in which 6-day-old or older virgin females were released downwind of pheromone-producing males, the responses to the pheromone were very positive. Typically, a female moved to the top of the plant and often to the edge of the leaf nearest to the emission, faced into the wind with rostrum and antennae raised, and perhaps lifted the elytra a few times. Individual flights were usually not more than 3 or 4 feet and often shorter so a female might make as many as 12 flights before reaching the male. However, once she reached the plant containing the male, flights were rare, and her search for him normally involved rapid crawling over the plant. Mating of current-season weevils was observed to last from 12 to 51 minutes (mean 28 minutes). Multiple matings were observed the same and subsequent days, and first oviposit ion after mating often occurred on a square near the mating site and within 4.8-52.0 minutes (mean 20.9 minutes) of the mating. However, the female seems not to oviposit in squares that are already infested unless most of the squares are infested. These current-season mated females ex- cavated the puncture for 0.8-17.2 minutes (mean 3.8 minutes) before turning 180** and inserting the ovipositor; they then took 0.2-3.2 minutes (mean 0.7 minute) to complete oviposit ion. They laid an average of 0.97 egg per hour. Thus, overall, the F. generation female (and subsequent females) were somewhat more efficient at oviposit ion than the overwintered females observed.

To find uninfested squares, newly mated females move from square to square, move onto an adjacent plant, or occasionally make short flights. Since multiple short flights of greater distances (10-30 feet) are almost always made to a male, the response to the male pheromone tends to increase the total area over which a female oviposits.

Late-Season Population

In late August, which is when the F. generation of boll weevils begins to appear, the behavioral patterns of the boll weevil change. By this time, fields in infested areas where insecticides have not been used probably have several thousand adults per acre. Also, at this time, the plants have ceased fruit production because

60 W. H. CROSS

of (1) a heavy feeding pressure by the large population of weevils, (2) the determinate nature of the cultivated varieties, and (3) possibly a deficiency of soil moisture and soil fertility. How- ever, many females are still actively producing eggs and are searching for uninfested squares or young bolls for oviposition sites. Therefore, large numbers of weevils migrate, apparently in search of uninfested cotton. As a result, in some cotton producing areas such as west Texas, isolated fields that do not have suitable adjacent litter or moisture for overwinter survival may become infested late in the season by weevils migrating as much as 50 miles, and migrating weevils have been captured in traps at considerable distances from cotton. Examination of 98, 309, and 1961 adult weevils collected on cotton in three fields newly infested by such migrating populations indicated that 63% were females (so more females than males may migrate) and that the migrating weevils were mature and mostly reproductive adults (W. H. Cross unpublished data).

Also, beginning in late August (on the average), a segment of the population of boll weevils begins to develop the physiological and morphological conditions of diapause. The percentage increases in September, but it then decreases in October because the older weevils have moved from the field to litter and new adults are continuing to emerge. (in the field, some percentage of older adults are highly reproductive as late as the first frost, probably a genetic mechanism for survival in the event of a change in climate.) This diapause condition in the boll weevil may be associated with boll feeding, scarcity of food, exposure of adults to cool night temperatures, or exposure of larvae and pupae to short days. The importance of these several factors seems to vary in different parts of the range of the weevil.

Weevils in firm diapause do not take part in long-range migration. Rather, they move relatively short distances to suitable hibernation sites. Also, many weevils not in firm diapause seek protection in litter with the onset of cool weather and may survive there through part of the winter though they all probably die, as do many in firm diapause, even when winter conditions are average. Both migratory and diapausing populations are extremely responsive to the male pheromone, even within forest environments.

Weevils involved in long-range dispersal, especially in the western parts of their range, are often transported passively by thermal currents (Fye 1968), but they do have some capability of sustained flight as indicated by flight mill studies of tethered weevils (W. H. Cross unpublished data). These males and females flew an average 1.32 and 1.43 miles, respectively, in the initial sustained flight and an average total of 2 and 2.2 miles to exhaustion. One female flew 11 miles before exhaustion. Average rate of flight was 180-200 feet per minute. Greater activity was observed at 29.5*^0 than at either 26.7°C or 32.3*^0. High-speed movies indicated the rate of wing beats at about 55 per second.


Late-season boll weevils and early-season weevils respond actively to pheromone-baited traps; midseason weevils respond much less. The greatest number of weevils respond when the traps are coated with daylight fluorescent paints that appear lemon yellow to our eyes but peak near the 525-nanometer (blue-green) range of the spectrum. Other regions of the spectrum are progressively less attractive; red is apparently not attractive.

THE COTTON FIELD ANIMAL COMMUNITY

Cotton fields are not, however, inhabited entirely, or even mainly, by boll weevils. A whole community of animals is present; thus, the ecology is dynamic. It changes because of or is changed by the interplay between species of animals searching for food as much as by the developing crop, the sequence of weather, and the presence of competing "weeds" and other vegetation.

Some idea of the makeup of the community can be obtained from Table 1. This table reflects some of the information obtained by two teams of entomologists \J during the cotton growing seasons of 1978 and 1979 on populations of arthropods in many of the cotton fields in North Carolina-Virginia and in Mississippi that were included in the Boll Weevil Eradication Trial and the Optimum Pest Management Trial. (The total collection is probably among the largest ever gathered from a single crop.) In these 2 years, 7066 D-Vac samples of 40-row feet per field, a total of 52.65 miles of cotton row (about 8.4 hectares), were taken at intervals designed to reflect all growth and development stages of cotton. All 1,037,067 arthropods collected in this sampling were segregated taxonomically by life stage and by trophic level by the two teams. See Chapter 12 of this handbook for a complete description of the sampling, for the technique employed in converting the counts of arthropods captured by D-Vac to a per area basis, and for the D-Vac-unit area ratios used to correct the numbers in Table 1.

The more than 1 million arthropods captured in the 2-year sampling are listed by major groups in Table 1 and show corrected number per acre and number per row-foot. These values represent the number of animals (arthropods) present and thus available to the diurnally operated D-Vac. Other animals known to inhabit cotton fields that were either poorly or not sampled by this method include those present on the cotton plants only nocturnally, those that occur below ground or on the soil surface, or those that are extremely active and so consistently escape the sampler. Among

\J Biological Evaluation Research Teams: one at the U.S. Department of Agriculture Boll Weevil Eradication Laboratory at Raleigh, NC—E. P. Lloyd, W. A. Dickerson, G. H. McKibben, T. J. Bradway, and D. C. Pierce; and one at the U.S. Department of Agri- culture Bioenvironmental Laboratory at Stoneville, MS—C. R. Parencia, J. W. Smith, W. P. Scott, and T. C. Lockley.

62 W. H. CROSS

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these are butterflies, larger grasshoppers (Melanoplus, Schisto- cerca, Dissosteira, Orchelimum, Conocephalus), Gryllidae, Carabi- dae, Collembola, Lycosidae, Odonata (Anax, lÊrythemis, Pantala), Annelida, amphibians (Bufo, Rana), reptiles, birds, and mammals (mice, shrews). In addition, the cotton growing seasons of both 1978 and 1979 followed colder than average winters, and the cotton fields sampled were usually included in the trial programs (about two-thirds of the fields were in the actual evaluation areas); consequently, pest populations were generally low, and beneficial populations were generally protected.

Other biases of the values are more specific. The family Chloropidae at more than two per row-foot includes several species of small gnats that were probably in the cotton foliage seeking a favorable physical environment and perhaps feeding on nectar. Whiteflies (Trialeurodes abutilonea), though present at almost the same density, did not cause significant damage. Leafhoppers (Cica- dellidae) tend to be more abundant on grasses than on cotton, so the large numbers (excluding a few genera such as Graphocephala) must indicate the presence of grass weeds in the cotton. The family Thripidae includes some banded-winged thrips (Aeolothrips) that are predaceous, but these are not identified separately. Similarly, the order Acariña includes a few predaceous Oribatidae, and the order Orthoptera includes a few Conocephalus and Oecanthus that are sometimes predators. Finally, Table 1 is oversimplified in that it does not take into account the effects of hyperpara- sit ism or prédation on predators. For example, a numerical summation (see footnote 1, Table 1) shows that lA + IB = 53.67% of the total, 2A + 2B = 15.01% of the total, and 3 = 28.22% of the total, so one might roughly assume that 15% of the secondary consumers (2A + 2B) are in fact tertiary consumers. Clearly, many direct field observations are required to measure the impact of secondary and tertiary consumers. Thus, many feeding relationships are in play within the community of the cotton field that are not readily apparent when a few pests and a few beneficial insects are sampled.

Nevertheless, those relationships that are important to the producer are readily apparent in Table 1. For example, the pests that a trained scout records in the eastern parts of the U.S. Cot- ton Belt are whiteflies, thrips, aphids, Lygus, fleahoppers (Pseudatomoscelis seriatus), Heliothis spp., clouded plant bugs (Neurocolpus nubilus), and boll weevils (Anthonomus grandis). Others may be listed but they are only occasionally economic pests (Little and Martin 1942, Young 1969). Principal beneficial insects that would be noted are indicated in Table 1—some Chalcidoidea and Braconidae (parasites) and a number of predators including Orius, ladybird beetles (Coccinellidae), spiders (Araneida), big-eyed bugs (Geocoris), and Nabidae. Others may play a role at times (Whitcomb and Bell 1964, Young 1969) and certainly have impact in composite.

Also, some pests are seasonal in importance. Thrips and aphids may appear on cotton plants throughout the season, but


thrips usually damage only young plants, and this is often true of aphids. Then there is the cotton leafworm (Alabama argillacea (Hübner)), which is not listed in Table 1. Formerly this immigrant from the Tropics was occasionally a devastating pest over wide areas, but in other years populations increased so late in the season that the insect simply helped producers defoliate the cotton in preparation for harvest. On the other hand, there are major pests such as Heliothis spp. and the boll weevil that develop several generations on cotton through the growing season. Plant bugs of several species, including Lygus spp. and, recently, Neurocolpus nubilus, also tend to have this characteristic.

A CASE HISTORY OF MISMANAGEMENT OF COTTON ECOLOGY

Experts have used the information on the biology, behavior, and ecology of the boll weevil and the composite picture of the cotton field community (summarized in Table 1) to devise techniques for managing pest populations in cotton. However, the justification for these techniques and their effects on the ecology of the cotton field can be understood most easily by presenting a case history of mismanagement. 2_/

The 23-acre cotton field in question is in northern Pontotoc County, MS, and was one of several small fields in the area farmed by a local grower. It was one of the several current practice fields for the Optimum Pest Management Trial (OPMT) in Panola Coun- ty, MS. Therefore, the arthropod population was sampled each season from 1977 to 1980. In addition, a team of entomologists V intensively sampled the field each 2 weeks in 1980. However, the results of the samplings were not conveyed to the grower in order to avoid influencing normal management in any way, thereby introducing bias into the check.

The peripheral area around the field had several good overwintering sites for boll weevils, and the winter of 1979 was mild enough to ensure good survival of overwintering weevils. In fact, four infield boll weevil traps placed on stakes around the field captured 31 weevils (7-8 per trap) in the 9-week period (April 23 to June 30) before the first puncture-sized squares were found in 1980. With optimum pest management, this number of captured weevils would have been the signal for close scouting to determine

2/ History largely prepared by Gordon L. Snodgrass. V W. H. Cross, G. L. Snodgrass, P. R. Miller, J. T. Robbins,

III, "et al.. Agricultural Research Service, U.S. Department of Agriculture, Boll Weevil Research Laboratory, Mississippi State, MS; and J. W. Smith and T. C. Lockley, U.S. Department of Agricul- ture, Bioenvironmental Laboratory, Stoneville, MS.

66 W. H. CROSS

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whether there was need for a pinhead square application of insecticide for boll weevils. (Capture of 4-5 per trap was used in the OPMT as the threshold for this application.) However, the grower did not use a cotton scout and made no application.

The overwintered weevils that entered the field infested 1.5- 3% of the squares; the F, generation emerged around the third week of July and infested 7-9% of the squares, and the F^ generation emerged around the first week of August and infested 51.5% of the squares. (Control measures are recommended when the rate exceeds 10%.) Meanwhile, a sizable population of beneficial arthropods was helping control the bollworm populations in the field (bollworms were first detected there July 17). On July 30, the grower made his first application of insecticide (1/2 pound methyl parathion plus 1/8 pound methomyl per acre); he then made three more applications (each 3 pound methyl parathion plus 3 pound toxaphene per acre) on August 8, 15, and 23. Plainly, at the time of the first application, the highest rate of square infestation had been reached. However, the grower probably sprayed because his neighbor sprayed, not because he realized the extent of the problem (the neighbor used a cotton scout). Also, the addition of methomyl to the material applied July 30 probably indicated that the grower did not know what his insect problems were (bollworms were not a problem in the field at that time). Finally, the timing of the last three applications was incorrect. They should have been 4 or 5 days apart instead of a week or more apart if they were to provide optimal boll weevil and bollworm control.

One obvious result of the series of events was a continuation of the boll weevil problem: boll weevils remained at an economically damaging level for the rest of the growing season. Another was the creation of a bollworm problem. One week after the first insecticide application, the bollworm population in the field reached an economically damaging level and remained there for the rest of the growing season.

The reason for the bollworm problem is clear from Figure 2, which reflects the combined populations of important beneficial arthropods (nabids, spiders, lacewings, ladybird beetles, Orius sp., and Geocoris sp.) present in the field during the 1978, 1979, and 1980 growing seasons. These levels were determined from D-Vac samples taken as part of the Current Insect Control practice comparison with the OPMT. In 1978 and 1979, when no insecticides were used in the field through August, the populations of beneficial arthropods peaked in July and August and began to decline during the last week of August. Thus, before the natural decline in the populations of beneficial arthropods that would probably have occurred around the last week of August 1980, the grower could have received the benefit of their presence to contain his bollworm problem. Instead, the four insecticide applications reduced these populations from 22,200 per acre on July 24 to 0 per acre on Auguát 26.

68 W. H. CROSS

Additional information on the effect of insecticides on the populations of beneficial arthropods in the field was obtained July 30-31 in two special surveys. On July 30, D-Vac samples were taken before the first application of insecticide, which was made that afternoon. A second set of D-Vac samples was taken during the morning of July 31. In addition, on July 31, the dead arthropods in 375 feet of row were picked up by the team and taken back to the laboratory for identification. From the D-Vac samples, the population which consisted of the same six groups of beneficial arthropods sampled earlier, was 20,234 per acre in the field before the first application and 8794 per acre after the application, a reduction of 56.5% in less than 24 hours. From the collection of dead arthropods on the ground in the field, the reduction was only to 5161 per acre, which was expected since it was difficult to find all the dead arthropods. However, the hand collection also showed that the insecticide had killed at least 586 boll weevils and 37 adult Heliothis spp. per acre, and both of these insects are poorly sampled by use of the D-Vac.

In sum, the producer's failure to use optimum pest management practices including a cotton scout led to additional insect problems in his field. Moreover, the use of insecticides to control the boll weevil was the key. If the boll weevil had been controlled by insecticide during the early part of the growing season, the need for insecticide treatments for boll weevil control would have been delayed until August. Better management of insect pests may or may not have increased yield of cotton lint, which was 479 pounds per acre in 1980, about average for the county. However, proper timing of one boll weevil treatment in the early fruiting period would almost certainly have resulted in less total expense for insecticide."

Once again it has been demonstrated that the boll weevil is the key pest because of inadequate natural biological controls. It therefore requires the early use of insecticide, which, in turn, kills predators of bollworm eggs and young larvae and so allows the pest population to explode. There may be exceptions. For example, in areas where large corn crops mature before the cotton crop, Heliothis spp. may shift so heavily to cotton that the predators cannot control them. However, the sequence described here has occurred over and over since the boll weevil first appeared in the United States. It is still occurring.


LITERATURE CITED

Cross, W. H. 1973. Biology, control, and eradication of the boll weevil. An- nual Review of Entomology 18:17-46.

D. D. Hardee, F. Nichols, H. C. Mitchell, E. B. Mitchell, P. M. Huddleston, and J. H. Tumlinson.

1969. Attraction of female boll weevils to traps baited with males or extracts of males. Journal of Economic Entomology 62: 154-161.

M. J. Lukefahr, P. A. Fryxell, and H. R. Burke. 1975. Host plants of the boll weevil. Environmental Entomology 4:19-26.

and H. C. Mitchell. 1966. Mating behavior of the female boll weevil. Journal of Ec-

onomic Entomology 59:1503-1507.

Dunn, H. A. 1964. Cotton boll weevil (Anthonomus grandis Boheman), abstracts

of research publications, 1943-60. U.S. Department of Agricul- ture, Miscellaneous Publication No. 985, 194 p.

Fye, R. E. 1968. Spread of the boll weevil by drainage water and air cur-

rents. Journal of Economic Entomology 61:18-24.

Hardee, D. D., W. H. Cross, and E. B. Mitchell. 1969a. Male boll weevils are more attractive than cotton plants

to boll weevils. Journal of Economic Entomology 62:165-169.

W. H. Cross, E. B. Mitchell, P. M. Huddleston, H. C. Mitchell, M. E. Merkl, and T. B. Davich.

1969b. Biological factors influencing responses of the female boll weevil to the male sex pheromone in field and large-cage tests. Journal of Economic Entomology 62:161-165.

Little, V. A., and D. F. Martin. 1942. Cotton insects of the United States. Minnesota Burgess Publishing Company, Minneapolis, 130 p.

Lloyd, E. P., F. C. Tingle, and R. T. Gast. 1967. Environmental stimuli inducing diapause in the boll wee-

vil. Journal of Economic Entomology 60:99-102.

Mitchell, H. C, and W. H. Cross. 1969. Oviposition by the boll weevil in the field. Journal of Economic Entomology 62:604-605.

^^ W. H. CROSS

Mitchell, H. C, and W. H. Cross. 1971. Mating of boll weevils in the field. Journal of Economic Entomology 64:773-774.

Mitlin, L. L., and N. Mitlin. 1968. Boll weevil, Anthonomus grandis Boh., abstracts of re-

search publications, 1961-65. U.S. Department of Agriculture, Miscellaneous Publication No. 1092, 32 p.

Roach, S. H., H. M. Taft, L. Ray, and A. R. Hopkins. 1971. Population dynamics of the boll weevil in an isolated cot-

ton field in South Carolina. Annals of the Entomological Sou- cie ty of America 64:394-399.

Walker, J. K., Jr., and D. G. Bottrell. 1970. Infestations of boll weevils in isolated plots of cotton

in Texas, 1960-69. Journal of Economic Entomology 63:1646- 1650.

Whitcomb, W. H., and K. Bell. 1964. Predaceous insects, spiders, and mites in Arkansas cotton

fields. Arkansas Agricultural Experiment Station, University of Arkansas, Bulletin No. 690, 84 p.

Young, D. F., Jr. 1969. Cotton insect control. Oxmoor House, Birmingham, AL,

185 p.

SECTION il SUPPRESSION COMPONENTS

73

Chapter 4

PLANT RESISTANCE AND MODIFIED COTTON CULTURE

L. N. Namken and M. D. Heilman Soil and Water Conservation Research Laboratory


J. N. Jenkins Crop Science and Engineering Research Laboratory

Agricultural Research Service U.S. Department of Agriculture Mississippi State, MS 39762

P. A. Miller National Program Staff Agricultural Research Service U.S. Department of Agriculture Beltsville, MD 20705

ABSTRACT The potential of genetic alterations plus improved pest management and cultural practices in cotton growing systems in the regions of the Cotton Belt where boll weevils (Anthonomus grandis Boheman) occur are evaluated. Studies involving use of frego bract, red plant color, and male sterility resistance traits are reviewed relative to overall cotton pest management practices and production efficiency. The advantages of rapid-fruiting cotton genotypes in short-season production systems are discussed, and data are presented to show that simultaneous improvement in rapid fruiting and fiber quality is possible. A short-season cotton production system developed for the south Texas environment is described.

INTRODUCTION

Research to develop cotton cultivars that have improved resistance to pest insects and modification of cotton production systems so as to manage these pests more effectively and efficiently are being emphasized across the Cotton Belt. In the portions infested with boll weevils (Anthonomus grandis Boheman), particular attention is being given to cultivars and production systems directed against boll weevils, tobacco budworms (Heliothis virescens

'^^ L. N. NAMKEN ET AL

(F.)), bollworms (Heliothis zea (Boddie)), and tarnished plant bugs (Lygus lineolaris (Palisot de Beauvois)). The range of environmental conditions in these areas and the diversity of insect problems these cotton growers face make it doubtful that any one cultivar or production system will suffice. Nevertheless, the probability that we can develop efficient systems capable of dealing with local or area problems has recently been greatly enhanced by (1) the availability and selection of more efficient genetic material, (2) the development of optimum pest management practices based on a better understanding of ways of minimizing boll weevil damage while suppressing other pests, (3) the development of more efficient cultural practices, and (4) the realization that it is through the integrated efforts of agronomists, plant breeders, entomologists, engineers, and economists that significant gains will be made.

Our primary objective here is to evaluate current advances in genetic alteration of the cotton plant, or those soon to be made available, and to consider their potential impact when they are coupled with improved pest management and cultural practices in cotton production systems in the regions of the Cotton Belt that are infested with boll weevils.

CURRENT COTTON CULTURE IN INFESTED AREAS

The average harvested acreage of cotton, the yield per acre, and the production of 480-pound bales for 1974-78 are summarized in Table 1. Similar data for 1970 and 1979 are shown in Table 2. These tables report data for four regions.

However, for the purposes of this discussion, which has to do with areas of the United States infested with boll weevils, the West Region has been dropped, and the other three regions have been rearranged as follows:

Southeast: Georgia, North Carolina, South Carolina Midsouth: Alabama, Arkansas, Louisiana, Mississippi,

Missouri, Tennessee Southwest: Oklahoma, Texas

Thus, Alabama is considered a part of the Midsouth Region (term replacing Delta), not a part of the Southeast Region. The West Re- gion is not involved since boll weevils do not occur there.

Southeast Region

Major cotton cultivars planted in the Southeast Region are listed in Table 3. The Coker, McNair, and Stoneville cultivars used in the Southeast Region are full-season or midseason cultivars with open-type bolls adapted to spindle-type harvesting. These cottons have relatively long (1 1/16-1 1/8 inch) fibers of high fiber tensile strength and relatively high micronaire (mature fiber) readings.

PLANT RESISTANCE AND MODIFIED COTTON CULTURE 75

Table 1.—Average acreage of cotton harvested, yield, and production by States, 1974-78

Yield Harvested per Production of acreage acre 480- -pound bales

Region State (1,000 acres) (pounds) (1 ,000 bales)

Southeast N. Carolina 78 432 69 S. Carolina 157 456 148 Georgia 219 405 191 Alabama 417 402 350

Delta Missouri 248 404 202 Arkansas 890 440 807 Tennessee 345 364 249 Mississippi 1,358 486 1,361 Louisiana 511 493 518

Southwest Oklahoma 456 298 289 Texas 5,113 323 3,502

West New Mexico 116 486 119 Arizona 444 1,046 960 California 1,215 957 2,352

Other States 1/ 10 481 10 United States 11,577 460 11,133

JL_/ Virginia, Florida, Illinois, Kentucky, Kansas, and Nevada.

Source: Economics, Statistics and Cooperative Service, U.S. Department of Agriculture. Cotton and Wool Situation, CWS-22, February 1980, p. 25.

Table 2.—Cotton production (percentage of total U.S. harvested acreage and production), 1970 and 1979

% of total harvested % of total acreage prodi

1970 iction

Region 1970 1979 1979

Southeast 12.3 4.8 11.5 4.3 Delta 30.1 18.6 37.5 20.7 Southwest 47.9 57.9 33.4 42.0 West 9.7 18.7 17.6 33.0

Source: Economics, Statistics and Cooperative Service, U.S. Department of Agriculture. Cotton and Wool Situation, CWS-22, February 1980, p. 24.

^^ L N. NAMKEN ETAL

Table 3.—Major cotton cultivars planted in the Southeast Region, 1979

Estimated cotton acreage (%) planted 1/

Cultivar North Carolina South Carolina Georgia

Coker 304 10 41 21 Coker 310 61 37 38 McNair 220 24 8 Stoneville 825 5

y Total acres planted: North Carolina, 50,000; South Carolina, 115,000; Georgia, 120,000.

Source: U.S. Department of Agriculture, Agricultural Market- ing Service, Cotton Division, Memphis, TN, September 1979.

Most cotton in this region is rain grown, though supplemental irrigation is applied in some areas. Chemical defoliants are generally used as a harvest aid, and a field can be harvested two or more times with a spindle-type, selective harvester. Both the boll weevil and the bollworm/budworm complex inflict substantial damage. Fusarium wilt (Fusarium oxysporum Schlecht. f_. vasinfectum [Atk.] Snyd. & Hans.) and root-knot nematodes (Meloidogyne incognita (Ko- foid & White) Chitwood) are prevalent, particularly on the more sandy, acid soils.

Midsouth Region

The major cultivars planted in this region are listed in Table 4. Stoneville and Deltapine types, which are full season or midseason in maturity, predominate. These cottons have open-type bolls and are adapted to spindle harvesting. Lint characteristics are similar to those of the southeast cultivars in that the fiber is relatively long, strong, and mature.

Some supplemental irrigation is used in the region, though most cotton in the region is rain grown. For the most part, the crop is spindle picked, and chemical defoliants are used to facilitate harvest. Plant bugs, the bollworm/budworm complex, and the boll weevil are important insect pests. Fusarium wilt, root-knot nematodes, and Verticillium wilt (Verticillium dahliae Kleb.) are prevalent. Boll rots (various organisms), particularly in the southern part of the region, often cause significant losses in yield.


Table 4.—Major cotton cultivars planted in the Midsouth Region, 1979

Estimated cotton acreage (%) pL anted 1/ Cultivar MO TN AR AL MS LA

Coker 310 15 Deltapine 16 8 10 8 11 Deltapine 55 15 9 10 7 18 21 Deltapine 61 11 10 23 15 20 29 Stoneville 213 58 48 52 27 40 27 Stoneville 825 7 10 6 6

1/ Total acres planted: Missouri, 170,000; Tennessee, 250,000; Arkansas, 700,000; Alabama, 335,000; Mississippi, 1,050,000; Louisiana, 480,000.

Source: U.S. Department of Agriculture, Agricultural Market- ing Service, Cotton Division, Memphis, TN, September 1979.

Southwest Region

The Southwest Region includes both the semiarid High Plains of Oklahoma and Texas (10-20 inches of annual precipitation) and the more humid areas (40-50 inches) of eastern Oklahoma and Texas. Cultivars and cultural practices, therefore, vary so greatly that the major cultivars planted in the region are listed in Table 5 by marketing service area (Figure 1). The major characteristics of these cultivars are compared with those of all cultivars grown in the three regions in Table 6.

The more arid western areas of Oklahoma and Texas, including the High Plains, Rolling Plains, and Blacklands, produce cotton for once-over stripper harvest so cultivars adapted to this type of harvest predominate. Seedling diseases (Rhizoctonia solani Kühn, Pythium spp., and Fusarium spp.), Verticillium wilt, and bacterial blight (Xanthomonas malvacearum [E.F. Sm.] Dows.) can cause major losses in these areas. The boll weevil is a problem, and the bollworm/budworm complex and the plant bug complex occasionally cause local problems.

Northeastern Texas, the river bottoms of central Texas, the Lower Rio Grande Valley, and the Coastal Bend areas have substantially more rainfall than the western areas, and growers spindle harvest a major portion of their crop. Stoneville, Deltapine, and McNair (open-boll cultivars) are therefore grown as are intermediate boll-type cottons adapted to both stripper- or spindle-type harvest. However, growers in the Coastal Bend area of Texas are shifting rapidly to short-season cultivars and are using once-over stripper harvest; and producers in the Lower Rio Grande Valley are also making some transition to short-season cottons that tend to

78 L N. NAMKEN ET AL

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have shorter lint, less tensile strength, and somewhat lower micronaire readings than the midseason or full-season cultivars. Most of the river bottoms and about half of the Lower Valley are irrigated. Growers may have serious problems with the bollworm/budworm complex as well as with the boll weevil. Root rot (Phyinatotrichum omnivorum [Shear] Duggar) may cause severe losses in local areas.

POTENTIAL OF RESISTANT COTTONS

Plants differ in their ability to produce under attack by pest insects, an ability that is commonly called resistance. Therefore, resistance of an experimental strain is usually measured by comparing the experimental strain with a cultivar known to be "susceptible." However, total resistance would be immunity, which would mean that a cultivar or strain is not attacked by a given pest under any condition, an exceedingly rare occurrence. Resistance is thus relative and encompasses any degree of favorable plant reaction less than immunity. Most often the level of resistance encountered in plant cultivars is moderate, that is, partial or intermediate. Practically, a resistant cultivar is resistant to a given pest when it produces a larger crop of satisfactory quality than other cultivars when all are challenged equally by that pest.

Usually, in cotton fields, there are several insects of importance. Therefore, strains that are resistant to one species of insect can be only one of the components of an integrated pest management program. One must consider the population of the pest to which the strain or cultivar is resistant and its response to other insects and to diseases in formulating an integrated program.

Frego Bract Resistance to Boll Weevils

The boll weevil is considered a key pest in areas where it occurs, so much effort has been expended in a search for resistance to this pest. One morphological trait of the cotton plant that has been investigated thoroughly is frego bract, a name applied to a rolled bract mutant found by a Mr. Frego in a field of Stoneville 2-B cotton near Manila, AR, in 1943 or 1944 (Waddle 1972). Frego is imparted by a single recessive gene designated _fg (Green 1955). Jones et al. (1964) recorded a 56% reduction in oviposition by boll weevils in field plots of frego cotton. Hunter et al. (1965) verified that the trait inhibited weevil feeding and oviposition when weevil populations were moderate to low. Resistance was also noted by Lincoln and Waddle (1965).

Investigating further, Jenkins et al. (1969) reported reduced oviposition by boll weevils in field plots planted to five frego strains compared with plots planted to a nonfrego control. How- ever, when weevils were confined in the laboratory on bracts of frego cottons, there was no reduction in oviposition. Mitchell et al. (1973) then found that overwintered and current season female

82 L. N. NAMKEN ET AL

weevils oviposited about 50% fewer eggs on frego cotton in field plots than on control cotton. Moreover, the marked weevils departed the frego cotton about twice as rapidly as they departed nonfrego cotton plots: 64% were recovered from squares in control plants and only 20% were recovered from frego buds. Also, weevils were frequently found on leaves and stems of frego cotton and more often on terminals than on squares, which were preferred locations in control plots. Thus, there was more plant-to-plant movement of females on frego cotton than on the control, which suggested several ways of using the frego character in an integrated control program. For example, pheromone traps might be more effective in plots of frego cotton.

Meanwhile Jenkins and Parrott (1971) planted 10-20 acres of frego cotton on four grower farms in an effort to estimate the cumulative effects of frego cotton and appropriate controls on populations of boll weevils exposed for three or four generations. They then compared oviposit ion (an indirect measure of population suppression) on the two types of cotton. Oviposition was 66, 71, 75, and 94% less in the four fields of frego cotton than in the control fields. Moreover, the lesser reductions each succeeding generation reflected smaller numbers of overwintering weevils present in the fields and different control measures used during the season. On two farms, no insecticides were necessary in the frego fields, but the cotton in the control fields had to have normal amounts.

Subsequently, the effects of frego cotton and reproduction- diapause control were studied by Jenkins et al. (1973) at 22 sites in Yalobusha County, MS. Populations of boll weevils in 4-acre fields of frego cotton that received or did not receive diapause control were suppressed 69 and 79%, respectively, compared with adjacent, similarly treated 4-acre control fields. Still more important, the beginning of weekly applications of insecticides for boll weevil control could be delayed 4 weeks in the frego cotton. Thus, growers who plant cotton cultivars that are resistant to boll weevils should be able to withhold applications of insecticides against boll weevils until populations of Heliothis spp. have peaked, thereby protecting the populations of beneficial insects that can contribute to control of the bo11worm/budworm complex. As other types of resistance to the boll weevil become available, they should be as useful as, or more useful than, the frego character in integrated pest management programs.

The interaction between insecticide and cotton cultivar was investigated in 12 fields planted to frego cotton (90 acres) and in 12 fields planted to nonfrego cotton (128 acres) in Copiah County, MS, in 1972 (Jenkins 1976). The populations of weevils in all fields averaged 42 per acre at time of pinhead square, the time when one application of azinphosmethyl (0.25 pound per acre) was made. Thereafter, fields were treated individually if more than 10% of the squares had damage due to weevil oviposition. In the fields of frego cotton, there were 50% fewer damaged squares than in the control fields and 46% fewer applications of insecticide.


Yields of cottons were essentially identical in all fields, 1.7 bales per acre.

More recently, reasons other than simple nonpreference have been advanced to explain the "resistance" of frego cotton to boll weevils. Parrott et al. (1973) recovered approximately seven times more insecticide from frego squares than from nonfrego squares, which should mean that insecticides applied to frego squares would give better control of boll weevils and other square feeding insects. Also, insecticides applied to frego cotton for control of Heliothis spp. were more effective (Schuster and Anderson 1976). McGovern and Cross (1976) found a higher rate of parasitism of boll weevil larvae by Bracon mellitor Say in frego cotton than in nonfrego cotton. They attributed the difference to the fact that frego has an exposed flower bud, which increases the efficiency of the parasite in its search for squares containing developing boll weevil larvae.

In view of the changes in behavior of boll weevils exposed to frego cotton, the effectiveness of the trait might well be enhanced by interplanting strips of nonfrego cotton with frego cotton. Wea- ver and Baker (1972), therefore, planted mixed strips of 40 rows of frego cotton and 8 rows of nonfrego cotton in a 10-acre field. Only 6 applications of insecticides had to be made to the frego cotton to control boll weevils; 14 were needed to protect the nonfrego cotton. Such an approach would increase the opportunities of boll weevils to express nonpreference, and so it has definite possibilities for pest management programs.

Other Potential Sources of Resistance

Red leaf (red stems and leaves) plant color has long been known as a nonpreferred cotton phenotype when boll weevils have a choice. For example, Isley (1928) reported that a red leaf strain had fewer damaged squares than a green leaf strain. Jones et al. (1978) discussed the potential of this and other plant resistance traits as management strategies and reported results obtained by several researchers in Georgia, Louisiana, and North Carolina. For example, when insecticides were applied only to strips of green, normal bract cotton planted in fields of red leaf cotton in Louisi- ana, in-season (July and August) control of boll weevils was obtained with 80% less insecticide. They also reported unpublished data of D. F. Clower, J. E. Jones, L. Williams, and J. R. Phillips who interplanted 88 rows of red leaf cotton with 8-row strips of a green, prolific-fruiting cotton. Again, good control of boll weevils was obtained until "cut out" by applying insecticides to only the 8-row strips of green cotton.

Weaver and Reddy (1977) studied the effects of frego, red stem, and male sterile cottons on activity of boll weevils. As a result, they suggested a system whereby 80-90% of a field is planted to frego bract, red leaf cotton and the remaining 10-20% to

84 L N. NAMKEN ETAL

green, male sterile, super okra leaf cotton, which the weevils should prefer. The male sterile cotton would act as a biological trap (reduced adult emergence); in addition, insecticides could be applied to the green strips. Also, in another experiment, they harvested significantly more frego cotton, red stem strain, than frego cotton, green strain (515 v. 370 pounds per acre), and found no significant difference in yields when no insecticides were used (979 V. 960 pounds per acre). These data show that even though frego bract does have boll weevil resistance, large populations of weevils can reduce yields of frego bract cotton significantly.

There has been a systematic search for other sources of boll weevil resistance in cotton. Buford et al. (1968) observed slight reductions in oviposition of weevils exposed to 26 of 252 cotton strains taken mostly from the regional collection. A strain of Gossypium barbadense L., Sea Island (Sl) Seaberry, was the most resistant. Jenkins et al. (1969) confirmed these reductions in small field-plot tests and also found that five frego, four red leaf, and several SI strains showed resistance. Day neutral selections from race stocks of Gossypium hirsutum L. T-25, T-80, and T-209 were reported by McCarty et al"! (1977) as carrying low levels of boll weevil resistance. Also, lines with genomes from Upland and cytoplasms from G^. arboreum L. , G_. herbaceum L. , and G^. anomalum Wawra ex Wawra & Peyr. reduced boll weevil oviposition about 15% (McCarty 1976), probably because these three lines have fewer anthers.

However, primitive races of G^. hirsutum are especially promising as a source of resistance that could be bred into cultivated cottons. In a study of boll weevil oviposition on 191 of such ac- cessions, 69 showed significantly less boll weevil oviposition than commerical cultivars (Jenkins et al. 1978). Most of these lines are photoperiodic in their flowering response, so Jenkins is presently converting them to day neutrality. Then the lines can be evaluated in field plots and other tests for resistance to boll weevil and other cotton insects.

Resistance to the Heliothis Complex

Breeding for resistance to boll weevil cannot be approached apart from proper consideration of other cotton insects. In areas infested by the boll weevil, this usually will involve Heliothis spp. and species of plant bugs.

Glabrous cotton plants are less preferred for oviposition, and nectariless plants that may be a poorer source of food (Lukefahr and Rhyne 1960, Lukefahr et al. 1965, 1971) have shown resistance ^^ Heliothis spp. Also, various types of larval antibiosis due to naturally occurring compounds have been reported (Lukefahr and Martin 1966, Oliver et al. 1967, Lukefahr and Houghtaling 1969). High terpenoid (commonly called high gossypol) is the most re- searched of these compounds, but tannins and related compounds have


recently been suggested as sources of resistance (Stipanovic et al. 1977, Waiss et al. 1977). Fourteen lines, mostly from the £. hirsutum race collection, reduced growth of larvae relative to growth on Deltapine 16 though no causal factor was identified (Parrott et al. 1978). These cottons are available as breeding materials.

On the other hand, frego bract, which is resistant to the boll weevil, is more susceptible to plant bugs, and cotton with a high content of gossypol has increased susceptibility to thrips (Thripi- dae) of various species.

Even glandless cottons show increased susceptibility to Helio- this spp. However, Meredith et al. (1979) identified nine glandless strains (apparently related) that were no more susceptible than Stoneville 7A glanded; and Oliver et al. (1970) found a wide range of oviposition and damage in glandless lines when 12 isogenic glandless and glanded lines were grown in field plots. Thus, significant resistance to Heliothis spp. is present in glandless cottons., but these lines are usually more susceptible to tarnished plant bugs. In contrast, Meredith et al. (1979) showed that when glandless was combined with nectariless, hirsutenèss, or rapid fruiting ability, susceptibility to plant bugs was reduced.

These problems may now be possible of solution. Methods of producing uniform infestations of Heliothis spp. on thousands of progeny rows (Hall et al. 1980, Jenkins et al. 1982) have recently been made available. These procedures should permit rapid evaluation of germplasm and should expedite the development of cottons that are resistant to Heliothis spp.

Resistance to Tarnished Plant Bugs

The nectariless cotton cultivars that are now available to growers have a relatively high degree of resistance to plant bugs. For example, Meredith et al. (1973) found that nectariless strains reduced populations of these pests about 60%; and their results were confirmed by Schuster et al. (1976), who also found reduced populations of fleahoppers (Pseudatomoscelis seriatus (Reuter)) on nectariless. This nonpreference may reflect the fact that almost 45% of the feeding time of tarnished plant bugs on cotton is spent on squares and that an additional 25% is spent at leaf nectaries (Latson et al. 1977).

However, additional sources of resistance to plant bugs are needed because the nectariless trait alone does not give adequate protection when populations of this insect are high, so research is continuing. Timok 811 (Jenkins et al. 1977) crosses involving 9.' hirsutum race stocks (Jenkins and Parrott 1976) and cottons from Bulgaria (Jenkins and Parrott 1976, Lambert et al. 1980) have been reported to show resistance, and these germplasm sources have been released for use by breeders. Pubescence too has been

86 L. N. NAMKEN ET AL

implicated in resistance (Meredith and Schuster 1979). The inheritance of plant bug resistance is simple enough so that progress can be expected to proceed at a fairly rapid rate (Meredith and Laster 1975, Jenkins et al. 1977).

Jones (1972), Waddle (1972), and Jenkins et al. (1973) reported increased susceptibility of frego cottons to tarnished plant bugs and other plant bugs. These workers thus concluded that even if a high degree of resistance to boll weevils was present in frego cottons, the increased sensitivity to fleahoppers and to tarnished plant bugs must be overcome before the trait could be potentially useful.

Also, glabrous cottons are more susceptible to tarnished plant bugs than are normal cultivars. Adding the nectariless trait to these cottons will increase their resistance to plant bugs, but they are still less resistant than normal cultivars. Bailey et al. (1980) concluded that frego or glabrous cottons, even after the addition of the nectariless character, will probably have formidable problems with plant bugs in the Mississippi Delta. Although breeders are attempting to find other sources of plant bug resistance that can be combined with nectariless, the sensitivity of frego and glabrous cottons to plant bugs remains a consideration.

RAPID FRUITING-EARLY MATURITY POTENTIAL

Rapid fruiting and early maturity have long been perceived by cotton breeders as traits that would help growers cope with pest insects, particularly the boll weevil (Parencia 1978). The importance of these characteristics was appreciated first when the boll weevil invaded the United States in the early 1900's. They became important again in the mid to late I960's and 1970*s when insect resistance to organophosphate insecticides was seen as a serious problem. Low input, short-season cotton management systems coupled with appropriate insect management practices are now recognized by plant breeders, agronomists, and entomologists as a promising method of noninsecticidal control. Rapid fruiting cotton genotypes could increase the probability that a crop would mature early enough to escape much of the heavy midseason to late-season insect pressures experienced in many cotton producing areas.

Cultivar Fruiting and Fiber Characteristics

One of the striking differences between the more recently released cotton cultivars and the older varieties selected in the Delta is the much faster flowering rate of the early maturing types, particularly during the early part of the bloom period (Walker and Niles 1971, Namken and Heilman 1973, Gerard and Reeves 1975, Namken et al. 1975, Wolfenbarger et al. 1979).


Namken et al. (1975) found that Tamcot SP-37 produced 1.7 times more blooms during the first 20 days of the bloom period than did Stoneville 213, a difference they attributed to the significantly shorter vertical and horizontal flowering intervals for Tamcot SP-37.

Additional data (L. N. Namken unpublished data) supporting earlier findings are shown in Figure 2A. By June 1, 1977, Tamcot SP-37 had produced nearly twice as many cumulative blooms per acre as Stoneville 213; and GH-11-9, an experimental strain selected from Tamcot SP-37, had produced 2.5 times more blooms per acre than Stoneville 213 and 1.3 times more blooms per acre than Tamcot SP- 37. Some of this accelerated production by GH-11-9 and Tamcot SP- 37 is explained by earlier first flowering (5-7 days earlier). However, regression of rate of fruiting against time showed increased rates of bloom. For example, when one eliminates the effect of earliness of first bloom, Tamcot SP-37 produced 1.4 times more blooms than Stoneville 213 during the first 20 days of bloom, and GH-11-9 produced 1.4 and 1.9 times more blooms than Tamcot SP- 37 and Stoneville 213, respectively. Yields of lint cotton followed the same trends. At 123 days from planting (July 8), yields were 513, 329, and 89 pounds of lint per acre for GH-11-9, Tamcot SP-37, and Stoneville 213, respectively. These yields represented 58, 53, and 14%, respectively, of the total yields for the three cottons.

Strain GH-11-9 was also compared with Tamcot SP-37, Stoneville 213, and Stoneville 825 in 1978 and 1979 at Weslaco, TX (L. N.

Namken unpublished data). The results from the four-row trials are presented in Table 7. Cotton yields were generally high in south Texas in 1978; yields in 1979 were relatively low, but some part of the low yield from the 1979 test field could be attributed to a moderate infestation of nematodes in the test field. Nevertheless,

Table 7.—Yields of lint cotton for three cotton genotypes in 1978 and 1979 variety tests at Weslaco, TX

Variety Lint cotton yields (pounds per acre) J^/

or 1978 2/ 1979 3/

strain 130 days Final 130 days Final

GH-11-9 1211 a 1398 a 458 a 761 a Tamcot SP-37 1090 b 1225 ab 204 b 398 b Stoneville 213 673 c 984 c 61 b 337 b

_!/ Means followed by the same letters are not significantly different at the 0.05% level according to Duncan's multiple range test.

2J Means of 4 replications. 3/ Means of 3 replications.


Cumulative Blooms/Ac (thousands)

300"

Cumulative Blooms/Ac (thousands)

300"

200

100

Figure 2.—Cumulative blooms from date of first bloom to June 1 for cotton strains and varieties GH-11-9, Tamcot SP-37 and Stoneville 213 in 1977 (A) and C23-8, GH-11-9, and Stoneville 213 in 1980 (B).


an important aspect of these findings was that the yields followed the same trends in both years; that is, each held the same rank in terms of portion of the total crop harvested at 130 days. Thus, there is potential for further increases in earliness and rapid fruiting.

Poor fiber quality, that is, short staple length, low micronaire readings, and low tensile strength, has been a problem with many short-season cotton cultivars, particularly in the Southwest Region where short-season production is more practiced. (in many areas, grower acceptance of the newer short-season cottons has been slow because buyers are reluctant to offer forward contracts for the lint of these cottons.) Thus, researchers have been encouraged to investigate the relationship between rapid fruiting and fiber quality.

At Weslaco, TX, (L. N. Namken unpublished data) in 1977, crosses were made between rapid fruiting selections and cottons with high lint quality. Seed from F progeny rows of selections that combined rapid fruiting with high lint quality were then com- posited and put into a replicated, two-row test in 1980. The experimental strain, GH-11-9, McNair 220 (a midseason cultivar), and Stoneville 213 (a full-season cultivar) were the checks. Earliness of the new strains was then checked by comparative testing. Re- sults (cumulative blooms from first bloom to June 1) for the experimental strain C23-8 and for GH-11-9 and Stoneville 213 are presented in Figure 2B. The trends are similar to those obtained in the 1977 comparisons (Figure 2A): strain C23-8 had an increased bloom rate compared with GH-11-9, which had the highest bloom rate in the 1977 test.

The next step was a comparison of the yields of lint and the fruiting characteristics of five rapid fruiting experimental strains and two checks, McNair 220 and Stoneville 213. The results are presented in Table 8. (One of the experimental strains, GH-11-9, has already been described.) The other four strains were F, selections from CAMD-E x Paymaster 4298 and Tamcot SP-37 x Pay- master 4298 crosses. The four F, strains and GH-11-9 had significantly earlier bloom, significantly more cumulative blooms by June 1, and significantly shorter vertical flowering intervals than either McNair 220 or Stoneville 213. However, the C23-8 strain also had significantly higher yields at 129 days from planting than any other entry in the test. Since this strain did not differ significantly from the other experimental strains in any of the earliness indexes (Table 8), the significantly increased yield at this time must be attributed to some other factor. (in this regard, we note that earliness indexes reflect potential, and yield data reflect how much of the potential a particular cotton reaches in a given environment.) Also, the C23-8 strain had significantly higher final yield than any entry except the C27-5 strain.


Table 8.—Fruiting characteristics and yields of lint cotton for five rapid fruiting strains and for McNair 220 and Stoneville 213, Weslaco, TX, 1980 1/, 2/

Lint cotton Cumulative yie lids

Variety Mean days Mean blooms (pounds per acre) or to first VFI 3/ per acre 129

strain bloom (days) by June 1 days Final

C23-8 68.5 a 2.01 a 254,700 a 753 a 1171 a

C27-5 69.5 a 1.98 a 248,200 a 558 b 1009 ab C27-1 68.5 a 1.98 a 264,000 a 596 b 984 b C26-6 69.5 a 1.81 a 256,300 a 564 b 988 b

GH-11-9 70.5 ab 1.99 a 224,300 a 557 b 921 b

McNair 220 72.0 b 2.52 b 141,300 b 470 b 946 b

Stoneville 213 72.5 b 2.51 b 109,700 b 288 c 888 b

Ij Means of 4 replications. 2/ Means followed by the same letters are not significantly dif-

ferent at the 0.05 probability level according to Duncan's multiple

range test. 3/ Vertical flowering interval.

The fiber properties of the same seven entries are summarized in Table 9. The GH-11-9 selection, which generally has a relatively low micronaire reading and has fiber strength similar to its

Table 9.—Properties of lint of five rapid fruiting strains and of McNair 220 and Stoneville 213, Weslaco, TX, 1980 1/, 2/

Micro- Strength Unifor-

Variety Lint Length naire (1/8-inch mity

or strain (%) (inches) reading gage) (m/uhm)

C23-8 33.9 be 1.09 e 4.8 ab 20.6 cd 82.9 be

C27-5 35.8 a 1.17 a 4.2 cd 20.8 bed 81.9 c C27-1 33.0 c 1.11 de 4.3 c 23.4 ab 82.0 c C26-6 34.6 ab 1.13 be 4.0 de 23.3 abc 84.4 ab

GH-11-9 34.7 ab 1.11 cde 3.9 e 19.2 d 83.1 be

McNair 220 34.8 ab 1.13 bed 4.6 b 25.0 a 85.7 a

Stoneville 213 34.3 ab 1.14 b 5.0 a 25.0 a 84.8 ab

Ij Means of 4 replications. 2j Means followed by the same letters are not significantly

different at the 0.05 probability level according to Duncan's multiple range test.


parent, Tamcot SP-37, was nevertheless within the acceptable range (3.9); however, it had the lowest micronaire reading of any entry in the test. Three of the four F, strains had significantly higher micronaire readings and two (C27-1 and C26-6) had significantly higher fiber tensile strength than GH-11-9. There were significant differences in fiber length among the entries, but all had fiber length in the acceptable range.

Thus, the results of the Weslaco tests indicate that simultaneous improvement of rapid fruiting and fiber quality of cotton is possible.

Impact of Rapid Fruiting on Boll Weevil Populations

Walker and Niles (1971) described the value of rapid fruiting cotton genotypes in the management of the boll weevil and to increased production efficiency. First, rapid fruiting increases the probability that an acceptable crop will be set before weevil infestations reach damaging levels. (This probability is increased if management practices are used to reduce populations of overwintered weevils that enter the fields at pinhead to one-third-grown square stages of plant development.) Second, earlier maturity allows for earlier stalk destruction which, in itself, reduces the number of overwintering weevils.

They therefore concluded that damaging infestations of weevils will not occur until after the second generation emerges if overwintered populations of female weevils are no higher than 20 per acre. (As few as 60 female weevils per acre would be a damaging first-generation infestation.) They also established that the time of emergence of the first and second generations is predictable; that is, the second generation will emerge approximately 45 days after the crop first reaches the one-third-grown square stage or about 30 days into the bloom period. Then they used the data for the rapid fruiting genotypes available at the time to develop a model that showed that rapid fruiting genotypes produce a majority of their cumulative blooms and set bolls in the 30-day period before the second generation of weevils emerge. Furthermore, the average age of bolls of the rapid fruiting genotypes is greater (lower percentage of bolls younger than 12 days) at this time than the average age of bolls of the long-season genotypes. (These had fewer bolls after 30 days of blooming, and a greater percentage of the total fruit was less than 12 days old.)

Studies by Walker et al. (1977) and Parker et al. (1980) have since indicated that bolls 12 days or older are not as susceptible to weevil damage as younger bolls. Thus, it is important to obtain a high percentage of 12-day-old or older bolls before the second generation of weevils emerge. Otherwise, acceptable yields cannot be obtained without intensive late-season control.

92 L N. NAMKEN ETAL

Further development of rapid fruiting cultivars may thus have a significant impact on the efficiency of future short-season cotton production systems. The following are some of the goals: (1) a higher percentage of total bolls set in the first 20-25 days of the bloom period, (2) reduction in the total number of insecticide applications needed, and (3) earlier harvest and stalk destruction to further suppress populations of overwintering boll weevils.

SHORT-SEASON COTTON MANAGEMENT SYSTEM

An integrated short-season cotton production system for south Texas was field tested in 1976, 1977, and 1978 (Heilman et al. 1977, 1979). In each year, 10- to 15-acre fields (seven in 1976, five in 1977, and four in 1978) were selected where a short-season production system could be compared with a conventional production system. Test sites had either medium- or fine-textured soils so the impact of soil, climate, and insect populations could be con- trasted. Short-season cultivars (Tamcot SP-37 and Tamcot CAMD-E), a midseason cultivar (McNair 220), and a full-season cultivar (Stoneville 213) were planted in late February or early March each year. Fields were listerbedded, preirrigated, or irrigated for seed germination and treated with a preplant herbicide. Nitrogen applications were approximately one-half (30 pounds per acre) the rate commonly used by south Texas cotton growers. A maximum of one postplant irrigation was used on the medium-textured soil and no more than two on the fine-textured soils; the timing and the number depended on visual evaluation of crop stress during the fruiting period.

In 1976 and 1977, grower fields of Stoneville 213 adjacent to each test site were used as checks for yield and production inputs (pesticides, irrigation, fertilizer). In 1978, yields and production inputs at the test sites were compared with means for growers of Stoneville 213 who were participating in the Integrated Pest Management Program of the Texas A&M University Extension Service.

With short-season cotton production, pest management is important because bolls on the bottom and in the middle of the plant must develop unharmed to achieve maximum production. Therefore, in these tests, 0.25 pound azinphosmethyl per acre was applied when approximately 25-50% of the plant population had first pinhead-size squares. A second application of azinphosmethyl (0.33 pound per acre) was made 7-10 days later, at or just before the first one- third-grown square was observed. The primary purpose of these early-season applications was to reduce the overwintering boll weevil population so damaging infestations would not be present until after the second generation emerged, which is about 30 days after first bloom in south Texas. The early applications also gave at least partial protection from plant bugs (particularly fleahoppers in south Texas) during this critical stage of plant development. (No additional insecticide was needed for fleahopper control at any of the test sites during the 3-year period.)

1976 4/18 1977 kll^ 1978 5/1 Mean


Table 10.—Average dates and time intervals between second application to control overwintering boll weevils and any subsequent application to control boll weevil or bollworm-budworm later in season (Heilman et al. 1979)

Date of— Days between 2nd overwintering Next required 2nd and 3rd

Year weevil application \J application Ij applications

6/15 58 6/15 50 6/10 40

49

1/ Second application of 0.33 pound of azinphosmethyl per acre applied at one-third-grown square stage of plant growth.

2/ Next required application applied when economic threshold reached for boll weevil or Heliothis spp. complex.

The average dates of applications of insecticides are shown in Table 10. By June 15, the latest date for the third application, second-generation boll weevils were just about to emerge so this first postbloom application was often applied for control of the Heliothis spp. complex rather than for control of boll weevils. However, at times, control of both insect pests was needed. The applications therefore controlled insect problems during the first 30-35 days of the bloom period. In addition, populations of beneficial insects monitored at the test sites following the two early- season applications were generally greater than those in the check fields where overwintered boll weevil control measures were not applied.

The yields of lint cotton from the rapid fruiting (short- season cottons) and the longer season cottons are compared in Table 11. Generally, the faster fruiting cottons had acceptable or

Table 11.—Average yields of lint cotton 1976-78 (Heilman et al. 1979)

Yield (pounds per acre) \J Variety 1976 1977 1978 Mean

Tamcot SP-37 698 b 570 a 673 be 647 ab McNair 220 812 a 663 a 919 a 798 a CAMD-E 652 a 671 a 803 ab 709 ab Stoneville 213 619 b 490 b 685 be 598 b Grower check 646 b 525 b 554 c 575 b

1/ Mean yields followed by the same letter within each column are noT significantly different at the 0.05 level according to Duncan's multiple range test.


Table 12.—Comparison of average production inputs for short-season cotton and grower check, 1976-78 (Heilman et al. 1979)

Short- season Grower

Production inputs cotton check

Seasonal insecticide applications 6 10 Irrigations (postplant) Medium-textured soil 1 2 Fine-textured soils 2 3

Fertilizer (pounds nitrogen per acre) 30 60

better than average yield levels. Then, since a large portion of the fruits were set during the 30-day period between first bloom and emergence of second-generation boll weevils, the grower had only to protect bolls that were already set and were more than 12 days old, which is much easier than protecting squares until they reach bloom and then protecting the young bolls.

The major production inputs for the short-season test fields and the grower check fields are summarized in Table 12.

CURRENT STATUS OF THE TECHNOLOGY

Plant Resistance

No glabrous, male sterile, red plant color, frego bract, or high gossypol cultivars are presently available for grower use; one nectariless variety, Stoneville 825, is. Although breeders have germplasm sources for each of these traits and for various combinations of these traits, cultivars that have the traits and that give acceptable agronomic performance over wide geographic areas have not been developed. For example, frego bract strains perform as well as normal bract strains in the absence of plant bugs; however, when plant bugs are present and uncontrolled, frego strains yield poorly. Breeders are thus attempting to combine frego with nectariless and other resistance to plant bugs in order to utilize the frego bract resistance to boll weevils.

Rapid Fruiting-Early Maturity

A number of rapid fruiting (short-season) cultivars are available to growers, but performance varies in different areas so individual State variety yield trials are the best guide to performance. The Tamcot, CAMD, Cascot, Lankart, Paymaster, and G&P short-season types were developed in Texas and are primarily adapted to the Southwest Region. Their performance in the Southeast and


Midsouth Regions has been highly erratic, an indication of a lack of adaptation to environmental conditions in these regions.

The primary advantage of the rapid fruiting genotypes is that they have proved to be very productive in high management level production systems (both cultural and pest management). The major problems include marginal lint quality and some evidence of a lack of drought tolerance in a number of the low rainfall dryland production areas of the Southwest.

Modified Cotton Production System

From data presented in this chapter and from the studies of Walker and Niles (1971), Walker et al. (1976), and Parker et al. (1980), an integrated cotton production system is an efficient way to grow cotton in many of the boll weevil infested areas of the Southwest Region. This system should combine: (1) rapid fruiting genotypes with a pest management program designed to minimize the damaging effects of the boll weevil, and (2) agronomic practices designed to hasten maturity so as to escape much of the late-season Heliothis spp. infestation. This type of production system would not necessarily be as effective in the other regions of the Cotton Belt where boll weevils occur. However, similar systems may be developed in the future. We need more efficient rapid fruiting genotypes adapted to these regions; and we need to incorporate more pest resistance into the rapid fruiting genotypes. We also need to develop improved agronomic practices including the use of bioregu- lators to control plant fruiting and vegetative growth. Finally, we need more information on insect dynamics so pest management practices can be improved.

96 L N. NAM KEN ETAL

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Hall, P. K., W. L. Parrott, J. N. Jenkins, and J. C. McCarty, Jr. 1980. Use of tobacco budworm, eggs and larvae for establishing

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Heilman, M. D., M. J. Lukefahr, L. N. Namken, and J. W. Norman. 1977. Field evaluation of a short season production system in Lower Rio Grande Valley of Texas. Iji Proceedings, Beltwide Cotton Production Research Conference, p. 80-83.

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J. C. McCarty, Jr., and W. L. Parrott. 1977. Inheritance of resistance to tarnished plant bugs in a

cross of Stoneville 213 by Timok 811. [Abstract] Ln Proceed- ings, Beltwide Cotton Production Research Conference, p. 97.

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J. B. Weaver, and M. F. Schuster. 1978. Host plant resistance to the boll weevil. In The Boll Weevil: Management Strategies. Southern Cooperative Series Bulletin No. 228, p. 50-73.

Jones, J. S., L. D. Newsom, and K. W. Tifton. 1964. Differences in boll weevil infestations among several bio-

types of upland cotton. Tn Proceedings, Beltwide Cotton Pro- duction Research Conference, p. 48-55.

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Latson, L. N., J. N. Jenkins, W. L. Parrott, and F. G. Maxwell. 1977. Behavior of the tarnished plant bug Lygus lineolaris on

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D. F. Martin, and J. R. Meyer. 1965. Plant resistance to five Lepidoptera attacking cotton. Journal of Economic Entomology 58:516-518.

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McCarty, J. C., Jr. 1976. Evaluation of species and primitive races of cotton for

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Meredith, W. R., Jr., B. W. Hanny, and J. C. Bailey. 1979. Genetic variability among glandless cottons for resistance

to two insects. Crop Science 19:651-653.


Meredith, W. R. , Jr., and M. L. Laster. 1975. Agronomic and genetic analyses of tarnished plant bug tol-

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plant bug. Crop Science 19:484-488.

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Namken, L. N., and M. D. Heilman. 1973. Determinate cotton cultivars for more efficient cotton

production on medium-textured soils in the Lower Rio Grande Valley of Texas. Agronomy Journal 65:953-956.

M. D. Heilman, and R. G. Brown. 1975. Flowering intervals, days to initial flower, and seedling

uniformity as factors for development of short-season cotton cultivars. ^ Proceedings, Beltwide Cotton Production Research Conference, p. 80-85.

Oliver, B. F., F. G. Maxwell, and J. N. Jenkins. 1967. Measuring aspects of antibiosis in cotton lines to the

bollworm. Journal of Economic Entomology 60:1459-1460.

F. G. Maxwell, and J. N. Jenkins. 1970. A comparison of the damage done by the bollworm to glanded

and glandless cottons. Journal of Economic Entomology 63:1328- 1329.

Parencia, C. R., Jr. 1978. One hundred twenty years of research on cotton insects in

the United State«. U.S. Department of Agriculture, Agriculture Handbook No. 515.

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Texas Agricultural Experiment Station, Bulletin No. B-1315, 45 p.

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tobacco budworm. Journal of Economic Entomology 71:310-311.

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Plant Resistance to Pests. American Chemical Society Symposium Series 62:197-214.

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Wolfenbarger, D. A., R. H. Dilday, and J. W. Davis. 1979. Fruiting requirements of short-season cottons to avoid damage by the boll weevil in the Lower Rio Grande Valley. In Proceedings, Beltwide Cotton Production Research Conference p. 88-90.

103

Chapter 5

ENTOMOPHAGOUS ARTHROPODS

J. R. Abies Cotton Insect Research Agricultural Research Service U.S. Department of Agriculture College Station, TX 77841

J. L. Goodenough and A. W. Hart stack Pest Control Equipment and Methods Research Agricultural Research Service U.S. Department of Agriculture College Station, TX 77843

R. L. Ridgway National Program Staff Agricultural Research Service U.S. Department of Agriculture Beltsville, MD 20705

ABSTRACT Entomophagous arthropods can be of great value in suppressing populations of cotton insects, especially Heliothis zea (Boddie) and jl. virescens (F.). Because of the particular importance of naturally occurring populations of predators in suppressing populations of these two important pests, this chapter fo- cuses on the efficacy of the complex of ca. 15 species of predators that regularly attack Heliothis spp. in cotton. Efficacy of these predators may be affected by: (1) density of predators and prey, (2) distribution of prey and area of the habitat searched, and (3) prey preferences and available alternative foods plus the disruptive influence of broad-spectrum insecticides and other factors as well.

MOTHZV-2, the Heliothis spp. population dynamics model, is useful in predicting the effect of various predator-prey ratios. These ratios can perhaps be used to make decisions regarding integrated pest management on a field- by-field basis. The model may also be useful in estimating the potential value of beneficial insects, particularly those that may be destroyied by insecticides, and in identifying species that could be used in augmentation programs.

104 J. R. ABLES ET AL

Insecticides applied to cotton to con-

trol codistributed pests such as the boll weevil (Anthonomus grandis Boheman), plant bugs (Lygus spp.), and the pink bollworm (Pec- tinophora gossypiella (Saunders)) release Heliothis spp. from natural control by killing the entomophagous arthropods. Pest management efforts should primarily be concentrated on selective methods of controlling these codistributed pests.

INTRODUCTION

Although ecologists often remark on the reduced diversity of plant and animal life in modern agroecosystems, such crop units as cotton production areas are, in fact, complex systems composed of numerous interacting entities. Thousands of species of arthropods thus may be present in a cotton field at one time or another; still only 60-70 species, ca. 2%, are potential phytophagous pests. Fur- thermore, only a few key species normally cause at least 80% of all cotton losses due to pest insects (Newsom and Brazzel 1968). The other phytophagous species rarely cause significant damage because their populations are suppressed by natural limiting factors including entomophagous arthropods, i.e., predaceous and parasitic insects, mites, and spiders.

The importance of entomophagous arthropods in regulating the species of phytophagous insects that damage cotton has been recognized for a long time (Gorham 1847, Riley 1873). However, a few of these pests, most notably the boll weevil (Anthonomus grandis Boheman), apparently are much less affected. For example, an intensive search revealed that over 50 species of parasites and predators, all except Ectatomma tuberculatum (Olivier) native to the

United States, attack the boll weevil (Pierce et al. 1912), but none has ever managed to give adequate control. This situation is consistent with the generally accepted theory of biological control whereby an introduced pest (such as the boll weevil), which is adapted to survive in a location to which it is not indigenous, will escape natural controls in the new location. Thus, efforts are now focused on the identification of exotic parasites and predators that might be introduced for control of the boll weevil, and studies in southern Mexico and other subtropical areas have revealed several potential parasites (Cross and Chesnut 1971, J. R. Cate unpublished data). Introduction and possible augmentation of hymenopteran parasites for this purpose have been considered for Bracon kirkpatricki (Wilkinson) (Cross et al. 1969) and for Cato- laccus grandis (Burks) (Johnson et al. 1973). Also, the red imported fire ant (Solenopsis invicta Buren), an introduced insect that is generally considered a pest, has recently proved capable of

ENTOMOPHAGOUS ARTHROPODS 105

providing some biological control of local populations of boll weevils (sterling 1978). However, there are many potential problems involved in establishment of introduced natural enemies in an annual crop such as cotton (Price 1981), so additional approaches should be considered. For example, Bracon mellitor Say, a native parasite, has at times been an effective suppressant (Bottrell 1976, J. R. Cate personal communication). Because relatively little is known of the biology or ecology of this parasite, further work based on those studies summarized and continued by Adams et al. (1969) could provide a way of using B^. mellitor in augmentative biological control of the boll weevil.

Likewise, naturally occurring populations of entomophagous arthropods seem to have less effect on cotton pests such as the introduced pink bollworm (Pectinophora gossypiella (Saunders)) and plant bugs. Thus, importation of natural enemies of these pests has recently been emphasized. However, in these cases, native natural enemies have not been studied in detail, and further work appears warranted to determine their true value.

On the other hand, several lepidopteran pests of cotton, armyworms (Spodoptera spp.), the cabbage looper (Trichoplusia ni (Hüb- ner)), the bollworm (Heliothis zea (Boddie)), and the tobacco budworm (li. virescens (F.)), are attacked by complexes of entomophagous arthropods that, if undisturbed by chemical insecticides, are frequently capable of suppressing populations of these pests to densities that cause no significant damage to cotton (van den Bosch et al. 1971, Ehler et al. 1973, van Steenwyk et al. 1976, McDaniel and Sterling 1979). These entomophagous complexes may be very diverse and extensive. For example, Whitcomb and Bell (1964) reported that over 600 predaceous species representing a total of 68 families of insects, spiders, and mites were found in cotton fields in Arkan- sas; and van den Bosch and Hagen (1966) provide a detailed list of ca. 60 species of parasites and predators of lepidopteran and other pests of cotton.

Natural populations of entomophagous arthropods are therefore of great value in suppressing certain phytophagous species in cotton. Furthermore, the use of entomophages through conservation, augmentation, and importation is increasingly seen as a viable approach to insect control; and the use of parasites is of considerable promise and importance. However, in the case of cotton insect management in multipest areas, the most immediate opportunities for substantial use of entomophages in the near term are most likely to be related to increased use of natural populations of predators for control of Heliothis spp. Therefore, in this chapter, we emphasize this particular interaction. Such a focus is further justified because Heliothis spp. may often account for most of the cotton yield lost because of damage by insects and mites. For example, in 1976 alone, 26 million pounds of insecticides were applied to cotton for control of Heliothis spp. (Liapis 1980).


POPULATIONS OF KEY PREDATORS OF HELIOTHIS SPP.

Among the numerous naturally occurring entomophagous arthropods, 15-20 species of the predaceous arthropods that occur in cotton are usually predominant, and evidence indicates that these are the most important predators of Heliothis spp. Some of these more common predators are listed in Table 1. The relative abundance and phenological occurrence of these and other predators in cotton are apparently governed by several interacting factors including geographical location and attendant climate and cultural practices, crop phenology, application of insecticides, and availability and type of prey. These factors are discussed in the following section.

Table 1.—Some common predators or groups of predators known to attack Heliothis spp. (Adapted from Ridgway and Lingren 1972)

Stage of Heliothis spp. primarily attacked

Egg Larvae (by instar) Predator 1-2 3 4-5

Hemiptera Lygaeidae (big-eyed bugs)

Geocoris punctipes (Say) x x Nabidae (damsel bugs)

Reduviolus americoferus (Carayon) x x x _R. alternatus (Parshley) x x x

Anthocoridae (minute pirate bugs) Orius insidiosus (Say) x x Orius tristicolor (White) x x

Neuroptera Chrysopidae (green lacewings)

Chrysopa carnea Stephens x x x Chrysopa oculata Say x x x Chrysopa rufilabris Burmeister x x x

Coleóptera Coccinellidae (lady beetles) Coleomegilla maculata (De Geer) x x Hippodamia convergens x x

Guerin-Meneville Scymnus spp. x x

Araneida (spiders) Araneidae (orb weavers) x x Oxyopidae (lynx spiders)

Oxyopes salticus Hentz x x Salticidae (jumping spiders) x x x x Thomisidae (crab spiders) x x


Geographical Location and Cultural Practices

The differences in predator populations among geographical areas certainly reflect differences in climate and probably differences in local cultural practices and phenotypic differences among varieties of cotton. Table 2 is presented to show the percentage relative abundance of four major predators in three diverse cotton growing areas of the United States. In California, the predaceous Hemiptera, Orius and Geocoris, are generally more abundant and spiders are less abundant than in the other locations. Also, Collops and Notoxus beetles tend to be more abundant in the arid Southwest and in eastern areas when rainfall is below normal (J. R. Abies unpublished data). Indeed, Gonzalez et al. (1977) reported that populations of all predators were much greater in California than in other locations.

Likewise, the abundance of predaceous arthropods appears to be affected by differences among cotton varieties. For example, Shepard et al. (1972) demonstrated that field populations of predators were more abundant on early maturing glabrous and Stoneville cottons than on a pilose variety, and Schuster et al. (1976) found that populations were 17-35% lower on nectariless cottons than on cottons with extrafloral nectaries. However, despite the numerous commercial varieties of cotton available to growers, ca. 80% of the total U.S. cotton acreage in 1979 was planted to ca. seven major varieties. Thus, regionwide acceptance of a limited number of specific varieties, though they do have different agronomic characteristics, may confound the factors responsible for regional differences in the species composition and abundance of predaceous arthropods.

Table 2.—Relative abundance of selected predators in cotton fields in different cotton growing areas of the United States

Cotton growing % re lat ive abundance area Orius Geocor is Coccinellidae Spiders

Texas Rio Grande Valley 1/ 13 11 20 30 Brazos River Bottoms 2/ 8 22 18 20

California Indio 3/ 35 43 6 Rosedale 3/ 21 47 3

Mississippi Delta 4/ 74 11 22 30 Blackbelt 4/ 22 35 7 28

\J Schuster and Boling 1974. 2/ J. R. Abies et al. unpubl'ished data. J/ Gonzalez et al. 1977. 4/ Pitre et al. 1978.

108 J.R. ABLESETAL

Cultural practices such as irrigation, cultivation, and application of insecticides can also be expected to influence the abundance of entomophagous arthropods in agricultural crops such as cotton (van den Bosch and Telford 1964).

Crop Phenology, Insecticides, and Prey Availability

The pest species that are the primary source of prey for predaceous arthropods change in relative abundance during the cotton growing season as the cotton crop itself progresses phenologically. Generally, thrips, aphids, boll weevils, and plant bugs are early- season pests and tend to be present from the plant seedling stage to initiation of plant fruiting; boll weevils, Heliothis spp., and spider mites are predominant midseason and late-season pests. Be- cause of this seasonal shift in pest species, types and rates of insecticides may tend to change during the season though most generally reduce populations of entomophagous arthropods directly by toxic effects or indirectly by depletion of the number of preferred prey. For example, the systemic insecticides that are normally applied at planting or shortly thereafter to control thrips and aphids were observed to severely reduce populations of entomophages (Ridgway et al. 1967). Also, a single application of an organophosphate insecticide against plant bugs and other early-season pests significantly reduced the number of entomophagous arthropods in two studies (Dinkins et al. 1970, Shepard and Sterling 1972). However, populations usually returned to near their original levels in ca. 14 days if no further applications were made. (Continued applications resulted in consistently low populations.) In sum, many conventional insecticides applied to early-season cotton are deleterious to populations of entomophagous arthropods, but the adverse effects vary with the rate, time, frequency, and method of application.

Several studies have suggested that populations of entomophagous arthropods usually decline during midseason and late season. Schuster and Boling (1974) attributed the decline to the end of a generation cycle, to a dispersal phase, or to prey reduction. Dinkins et al. (1970) suggested that late-season applications of insecticides were responsible. Smith and Stadelbacher (1978), after 3 consecutive years of study in untreated fields, concluded that peak populations of predators coincided with peak squaring of cotton and considered the seasonal decline of predators as natural. Yokayama (1978) provided further evidence that plant phenology and attendant changes in the nutritional value of the cotton plant may result in changes in populations of entomophages. Nevertheless, drift of insecticide from nearby treated fields, insecticidal depletion of entomophages in reservoir crops, and entrapment of im- migrating predators in treated cotton fields, especially in areas of extensive acreage that undergo treatments at 3- to 5-day intervals, likely contribute to the decline.


EFFICACY OF PREDATORS IN SUPPRESSION OF HELIOTHIS SPP.

Methods of Evaluating Efficacy

Determination of the effects of predators on a prey population is among the most challenging problems of population ecology studies. For example, destruction of a large part of the prey population may or may not affect net survival of prey because other factors may cause mortality in the population of the prey. How- ever, there is some degree of irreplaceable mortality due to predators, and its relationship to net prey mortality must be determined (Kiritani and Dempster 1973).

Two general methods, correlative (indirect) and experimental (direct), are widely used to assess the efficacy of predators. The correlative method mainly involves statistical methods of relating life table and density data of predators and prey to depict a cause-and-effeet relationship for the changes in density of the two populations (Stehr 1975). Proponents of this technique contend that predator efficiency can be evaluated without disturbing the ecosystem under study. If one uses both deterministic and stochas- tic processes, correlative methods allow rapid assessment. Fur- thermore, correlative methods appear more amenable to the eventual development and use of decision-making index charts and provide a convenient method of field testing or model validation. However, the methods are inferential, and the results may be misleading (Huffaker and Kennett 1969) because extrapolation beyond the bounds of existing data is usually required.

The experimental method often involves the use of paired comparison analysis of plots that have natural enemies with plots that lack natural enemies. Usually, the natural enemies are removed through exclusion techniques (chemicals, cages, hand removal), a process that can disrupt the system being studied. A useful, but onerous alternative method is direct observation of the frequency of prédation by a particular predator upon a specific prey (Whit- comb and Bell 1964).

Perhaps neither method of evaluation is adequate in itself for assessing the role of predators in the suppression of Heliothis spp. on cotton, though both have advantages. A complex of predators such as that associated with Heliothis spp. is easier to study by the correlative method because it can often be used to infer the impact of each predator species on the prey population. On the other hand, experimental methods can provide basic biological information that serves as a basis for developing functional models and can provide a means of obtaining data that may have been masked in a correlative method.

110 J. R. ABLESETAL

Experimental Data

Since the work of Quaintance and Brues (1905), there has been little question about the importance of predators of the Heliothis spp. complex in cotton, and researchers have repeatedly demonstrated that the more efficient predator species have a significant effect on populations of this pest. For example, Fletcher and Thomas (1943), in a 7-year study, demonstrated that arthropod predators consumed 15.3-32.9% of the eggs produced by the bollworm and in addition 12.6-59.6% of the first-instar larvae present. Bell and Whitcomb (1962) likewise reported 6-38% prédation of Heliothis spp. eggs in cotton, and Whitcomb (1967a, 1967b) reported that predators in cotton consumed 12-26% of Heliothis spp. eggs and 25-56% of their larvae. Lingren et al. (1968) found that the more effective predator species consumed 27-130 Heliothis spp. eggs per predator per day when confined with prey in petri dishes. They also reported a 76% reduction in tobacco budworms in field cages and a 96% reduction in Heliothis spp. larvae when Chrysopa carnea larvae were introduced at a rate of 420,000 per acre. Likewise, when Lopez et al. (1976) released C. carnea into field cages at a rate of 100,000 per acre, the population of tobacco budworms was reduced to 133 larvae per acre compared with 3491 per acre in the control cages. In California, naturally occurring predators destroyed 66-90% of the bollworm larvae present in field cages (van den Bosch et al. 1969) and 96% of bollworm eggs when predators were confined with prey on cotton terminals (Tejada 1971). Recently, McDaniel and Sterling (1979) used an improved radioactive labeling technique to determine that ca. 15 species of predators collectively preyed on 87-93% (seasonal average) of Heliothis spp. eggs, thereby preventing significant damage to cotton by the pest.

Despite the knowledge thus gained concerning the biology, ecology, and behavior of the species of predaceous arthropods associated with cotton, there remains a tendency to define their biological characteristics vaguely and to group them as beneficial insects. We are therefore concerned in this chapter to recognize and to define the differences among the more important species. Eight major predators or predator groups that attack Heliothis spp. have been selected as most important on the basis of several years of sampling of natural populations in central and south Texas. In addition, there is general agreement about their effectiveness as key predators, and our selections are quite similar to those selected for study in the Boll Weevil Eradication Trial in North Carolina and the Optimum Pest Management Trial in Mississippi. By using data on prey consumed per predator per day found in available literature or, when data were lacking, by using intuitive judgment, we developed a set of "normalized relative efficiency indices" for some of these groups (Table 3). The larger numbers indicate relatively higher efficiency (their use in computer modeling will be discussed in relation to decision making). The groups are by no means complete; that is, they do not include all predators, and other insects such as ants may be very important in certain areas of the


Cotton Belt. Furthermore, eventual recognition and quantitative evaluation at the species level are needed.

Plainly, the results of the various studies of predator efficiency that were used were quite variable because of differences in sampling techniques, methodology, and the temporal aspects of each study. Furthermore, conclusions were sometimes made without regard to densities of predators and their prey, variables that are basic to the dynamic interaction between predator and prey populations. Nevertheless, an understanding of these and other factors that determine the efficacy of predators in suppressing Heliothis spp. is essential to successful use of these natural controls in integrated pest management (IPM).

Table 3.—Relative efficiency indices for prédation on Heliothis spp. eggs and larvae by eight predator groups i/

Index for Index for egg prédation larval prédation

Predator factor factor

Scymnus 0.21 0.22 Other Coccinellidae 2/ 2.70 0.69 Other Coleóptera 3/ 0.23 0.086 Orius 0.31 0.40 Geocoris 0.92 2.30 Other Hemiptera 4/ 0.69 1.00 Chrysopa 2.50 2.90 Spiders 0.49 0.35

\J Original data (consumption of eggs or larvae per predator per day) were adjusted to reflect factors for each predator group relative to each other (i.e., a higher value represents a higher efficiency); due to normalization, the total for all factors is eight, which is the total number of predator groups.

2j Primarily the genera Hippodamia, Coleomegilla, and Cycloneda. V Primarily Collops spp., Notoxus spp., and small Carabidae. k_l Primarily Nabidae, Reduviidae, Pentatomidae (Asopinae), and

Miridae.

FACTORS AFFECTING PREDATOR EFFICACY

The extent to which predator populations can exploit populations of prey is determined mainly by the density of the predators and their ability to locate and consume prey. Thus, one must dis- tinguish between factors affecting predator abundance and those affecting predator efficiency (Hassell 1978). Earlier, we reviewed some of the factors that determine predator abundance. Some of them, for example, climate and actual predator abundance, also

^^^ J. R. ABLES ETAL

affect predator efficiency. In addition, predator efficiency is affected by (1) the interaction between prey density and predator density and their rates of increase, (2) the interaction between prey distribution and habitat area searched, and (3) the interaction between prey preferences and alternate foods.

Predator and Prey Density

One intuitively expects that a predator population will find and consume more prey as the population of the prey or the population of the predator increases. Thus, Solomon (1949) proposed the term "functional response" to describe the change in rate of préda- tion as prey density increases and the term "numerical response" to describe the changes in the density of predators as the density of prey changes. He further stated that a natural enemy must be density dependent and must take a greater percentage of the prey population as prey density increases if it is to control the prey population effectively.

The results of both empirical and theoretical studies suggest that most predaceous arthropods do not exhibit a really strong density-dependent functional response to prey populations. They generally show a decelerating increase in rate of prédation (to a limited maximum) as prey density increases. Such a response reflects the behavioral and physiological activities associated with prédation such as killing, eating, and digestion of prey; as these activities increase, the time spent in search of prey decreases. Also, the numerical response depends upon predator developmental response, rate of survival, and adult fecundity. Additionally, there is a lower threshold of prey consumption below which the predator cannot reproduce (Hassell 1978).

According to theory, the characteristic functional response of predaceous arthropods will lead to increasing or widely fluctuating densities of prey (Solomon 1949). Despite these apparently un- stable interactions, several factors may produce stable prey populations (Price 1975, Hassell 1978). For example, the predators that attack Heliothis spp. in cotton are generally polyphagous and feed on several types of prey that are distributed nonrandomly. Predators therefore might conceivably switch to the more abundant species of prey that may be disproportionately attacked by individual predators and the predator population as a whole. Such behavioral switching could have a short-term lag effect on pest populations to the point of producing stability.

After analyzing several years of data on populations of predaceous arthropods and Heliothis spp. eggs and larvae in cotton (j. R. Abies and A. W. Hartstack unpublished data), we are unable to discern any regular patterns of increase or decrease of predaceous species relative to the number of Heliothis spp. present. This failure to achieve close correlations is not surprising because the predator populations were generally sampled by the D-Vac


method, which has inherently great variability, and because of the predators' general lack of prey specificity. However, J. R. Abies (unpublished data) determined that increased numbers of predators result in lower numbers of Heliothis spp. larvae (Figure 1); and similar relationships have been demonstrated by comparing populations of Heliothis spp. in untreated cotton fields with populations in fields where predators were depleted by treatment with chemical insecticides (Ridgway 1969, van den Bosch et al. 1971, van Steenwyk et al. 1976).

No. Heliothis larvae (x 1000) 25

1 \ r 5 10 15 20 25 30 35 40

No. predators (x 1000)'

Figure 1.—The relationship between numbers of predators per acre and number of Heliothis spp. larvae per acre. Data points represent means for July (1979) in six cotton fields near College Station, TX (J. R, Abies unpublished data).

Prey Distribution and Habitat Searched

Most theoretical appraisals of the interaction between predators and prey assume a uniform distribution of prey in a uniform environment. However, Heliothis spp. eggs and larvae are not uniformly distributed among cotton plants nor does the environment remain uniform; for example, size of individual plants varies, and the plants grow. Usually, Heliothis spp. eggs are found on the upper one-third of the cotton plant, and larvae, except those recently hatched, usually feed within the relative shelter of fruiting parts (squares and bolls) of the plant. Thus, to locate Helio- this spp., predators must not only search a growing plant habitat but must also restrict their search to specific plant locations. Knipling (1979) accounted for the expanding search area in his simulation codeveloping models by assuming that the cotton plant increases by a factor of 1.0 every 10 days. Donahoe and Pitre (1977)


documented this inverse relationship when they demonstrated that Reduviolus roseipennis (Reuter) captured fewer first-instar bollworm larvae as plant age and size increased. They also identified the underside of leaves of the upper one-third of the plant as the major area of search by this predator.

Prey Preferences and Alternate Foods

Although the predators found in cotton may show distinct preference for particular types of prey, they are generally polyphagous in their habits. For example, Abies (1978) determined that an assassin bug (Zelus renardii Kolenati) was most adapted to the capture of flying insects but fed on various forms of at least 15 species of arthropods, 32% of which were potential cotton pests; 12% of the total diet consisted of Heliothis spp. larvae.

If a predator can feed on several prey types, then preferences or selection of prey may shift in accordance with the relative abundance of the various available types of prey (Price 1975). In fact, Abies et al. (1978) noted that prédation on tobacco budworm eggs by five species of predators was reduced in the presence of aphids. Also, many predators feed on extrafloral nectaries of the cotton plant, and the time spent feeding on such plant materials may limit time spent feeding on prey (J. R. Abies unpublished data).

When Heliothis spp. is the selected prey, different predator species and different ages of the same predator species may often show an apparent preference for prey at different stages of development. For example, Lawrence and Watson (1979) showed that first- instar Geocoris punctipes nymphs fed almost exclusively on tobacco budworm eggs; older nymphs and adults fed on eggs and larvae (primarily first-instar). Likewise, many predators in cotton such as Orius and Geocoris are relatively small and are able to feed only on eggs and small larvae; asopine pentatomids and vespid wasps feed primarily on larger larvae.

MODELING POPULATIONS OF ENTOMOPHAGOUS ARTHROPODS AND HELIOTHIS SPP. FOR IPM DECISION MAKING

Two general types of modeling of predator-prey systems, complex (component) and simple, are presently used. Published models of the complex type include those of Watt (1959) and of Holling (1966), both of which model the searching, attacking, digesting, and resting time of each species of predator. Development of complex models for use in cotton would sometimes require that each of the pest species, each stage of the predator, and each stage of the prey be modeled. Also, accurate estimates of host crop phenology (leaf area, height of plant, distribution of fruit as to location as well as age) would be needed. We feel that these models are far more complex than is probably necessary; however, resulting


information could be a tremendous help in developing or testing simpler models.

Simple predator-prey models have been reported by Knipling and McGuire (1968), Knipling (1979), and Hartstack et al. (1976). In these cases, the hypotheses are such that many factors considered by the complex models are simplified; also, no attempt is made to measure minute details on each predator or prey. This more sim- plistic approach is taken, at least in part, because of the enor- mous task of measuring the host population accurately and the even more difficult task of monitoring the predator populations.

The simple model proposed by Knipling and McGuire (1968) for Trichogramma, an egg parasite of Heliothis spp., and later adapted and suggested for general use in cotton models by Hartstack et al. (1975) in the dynamic Heliothis spp. model MOTHZV-2 is,

M = 1 - EXP (-0.693)(P^)

(N) (S)"" where,

M = Probability of mortality of Heliothis spp. eggs or larvae P = Number of effective predators N = Number of effective predators required to cause a 50% mor-

tality of prey S = Relative search area (1 = first square to 6 = mature

plant)

The daily rate of prédation of larvae is reduced as the larvae increase in size with age as follows:

M = (M) EXP -0.42 (A) 0.657

where A = age of larvae in days.

To improve the effectiveness and versatility of this basic model, the life histories for Heliothis spp. and each predator group were divided into different age distribution classes, and relative prédation efficiency indices were assigned to each predator species or group. The end result was a flexible predator-prey subroutine to the Heliothis spp. population dynamics model MOTHZV-2. We revised the relative efficiency indices according to latest available literature of eggs removed per predator per day (Table 3). When we then applied the MOTHZV-2 model—with modifications described by Hartstack and Witz (Chapter 14 this handbook)—to data from 19 cotton fields, we were able to predict the survival of large Heliothis spp. larvae with reasonable accuracy (Figure 2). We have also used MOTHZV-2 to determine the conceptual effects of different densities of total predators on the survival of Heliothis spp. and on subsequent plant damage and potential trends in yield. The predicted means for these parameters when we multiplied actual data on populations of Heliothis spp. from eight fields in the presence of actual populations of predators by factors of 0, 1, 2,


Actual no. large Heliothis larvae

15,000 "

1 1 1 2500 7500 12,500 Predicted no. large Heliothis larvae

Figure 2.—Comparison of MOTHZV-2 computer-simulated population and actual field populations of large Heliothis spp. larvae in 19 south Texas cotton fields. Data are maximum number per acre of either predicted (x-axis) or actual (y-axis) populations before July 12, 1973.

and 4 are shown in Table 4. As the predator population was increased, the number of Heliothis spp. larvae and plant damage decreased, and the total production of bolls increased significantly enough to suggest the potential of considerably higher crop yield. Note that while we use the general phrase "number of effective predators" (P in previous equation and in Figure 3), our inputs include specific data on abundance and relative efficiency for each of the predators listed, in Table 3.

Hartstack et al. (1975) suggested that MOTHZV-2 might be used to include entomophages in deciding whether an insecticide should be applied. Practitioners of integrated pest management in cotton recognize the value of conserving entomophagous arthropods but presently do not have well-defined guidelines for including the presence and potential impact of entomophages in their decision- making process. A trichotomous decision chart was therefore developed. A recently modified version is presented in Figure 3. If the data on effective natural predators (the sum of field estimates times the relative efficiency values shown in Table 3, x-axis) and the number of Heliothis spp. eggs (y-axis) plot to the right of the decision line, the predator population is predicted as large enough to prevent the Heliothis spp. population


Table 4,—Predicted mean maximum (X) number of large Heliothis spp. larvae and total bolls and percentage of square and boll damage in the presence of four levels of naturally occurring predators in cotton 1/

X maximum X maximum

X number number number X maximum X maximum predators large larvae bolls % damaged % damaged per acre per acre 2/ per acre squares 3/ bolls

0 14,381 41,706 27.9 21.9 9,566 4/ 3,132 84,842 5.4 5.1 19,133 1,384 107,032 2.2 1.6 38,264 556 115,257 1.2 0.4

\J Means were predicted by MOTHZV-2 model based on one to three samples per week taken in eight fields in Frio County, TX, during mid-May to mid-July 1973.

Ij Assumed threshold: 2500 large larvae per acre. _3/ Peak square production occurred in early July. 4/ Actual mean.

from exceeding an assumed threshold (action level) of 2500 large larvae per acre (Adkisson et al. 1964, Ridgway 1969, Hartstack et al. 1978). If the populations plot to the left side of the decision line, predator populations are predicted as too small to adequately suppress the Heliothis spp. populations, and the need for corrective action is assumed. If populations plot at the approximate center of the chart, the impact of predators is unpredictable, and populations should be monitored daily until a decision can be made.

A close look at the quantitative relationships apparent in Figure 3 suggests that a ratio of at least two effective predators per one Heliothis spp. egg will usually eliminate the need for corrective action; as the ratio decreases below this level, some type of action may be required. However, time of initiation of action should also depend on the choice of action selected. For example, action directed against the larval population resulting from eggs that have escaped prédation should not be taken until small larvae are actually found and until the recommended plant damage thresholds are reached. (Small larvae are also susceptible to prédation so the predators that attack them may still prevent economic losses to the crop.) Actions directed against larvae may be of several kinds (chemical or microbial insecticide or the augmentative release of a larval parasite or predator), and the effective time of use may vary. On the other hand, if action is to be applied against the egg stage (chemical ovicides or the augmentative release of an egg parasite or predator), the action must be made on the basis of the natural ratios of predators to eggs.


Action No No. Of Heiiothis Required Undecided Action eggs (x 1000)

100

75

50 «s I \ 1 1 \ 1 1

0 10 20 30 40 50 60 70 No. of effective natural predators (x 1000)

Figure 3.—A decision-making chart showing the number of naturally occurring predators and Heiiothis spp. eggs per acre of cotton. A required corrective action is expected when the number of large Heiiothis spp. larvae reaches or exceeds 2500 per acre.

Although results of our field studies and of those of McDaniel and Sterling (1979) indicate that our predicted results for specific ratios of predators to Heiiothis spp. are reasonably accurate, there is need for continued improvement of the predator-prey subroutine to provide greater precision and flexibility in the application of MOTHZV-2 to IPM assessments in highly variable field situations. Hartstack and Witz (Chapter 14 in this handbook) detail the improvements that are needed.

APPROACHES TO THE USE OF ENTOMOPHAGOUS ARTHROPODS IN IPM IN COTTON

Most of this chapter has been concerned with the impact of predators on populations of Heiiothis spp. in cotton. The role or value of these entomophages in IPM programs has been best demonstrated by those studies in which predators were eliminated by insecticides. This elimination has frequently been followed by a resurgence of key pests and by severe outbreaks of secondary pests. Furthermore, the increased use of insecticides that is then necessary to deal with the resulting catastrophic populations of pests has probably been a major reason for the development of insecticide resistance in such pests as the tobacco budworm, boll weevil,


spider mites, and lygus bugs (Newsom and Brazzel 1968, van den Bosch et al. 1971, Reynolds et al. 1975).

For example, in California, van den Bosch et al. (1971) demonstrated that three applications of azodrin reduced the populations of predators so severely that populations of bollworms and boll damage were greater in treated fields than in untreated fields. Also, van Steenwyk et al. (1976) reported that predator numbers were higher and bollworm populations lower in California fields treated with insecticides one to three times for pink bollworms than in fields treated six to seven times (eight to nine treatments apparently suppressed both pests). Although Heliothis spp. have been controlled by entomophagous arthropods in the absence of broad-spectrum insecticides, management programs for Heliothis are complicated by the fact that Heliothis spp. in cotton are often codistributed with such other pests as the boll weevil, pink bollworm, and plant bugs. When insecticides must be applied against these codistributed pests, the end result is often an outbreak of Heliothis spp. and/or other lepidopteran pests. Therefore, IPM recommendations and supporting research should be focused simultaneously on control of the codistributed pests and conservation of the entomophages that control Heliothis spp. The advantage of any such cotton IPM strategy was demonstrated by Pimentel et al. (1980) who estimated that 40% of all insecticide costs in cotton result from the loss of natural enemies; the total added cost was estimated to be more than $119 million. An additional added cost due to increased resistance of pests to insecticides was estimated to be ca. $36 million.

Conservation

Conservation of entomophagous arthropods in cotton is simply the avoidance or reduction of activities that are deleterious to these natural enemies of pest insects. Perhaps the most important method of conservation is the use of selective control strategies such as host plant resistance, selective insecticides, or judicious use of certain broad-spectrum insecticides. A successful IPM program for cotton would likely include all of these methods as well as others that are ecologically sound. For example, Ridgway et al. (1977) suggest that a cotton insect management program designed for optimum use of entomophages would consist of "(1) the production of an early crop through selection of varieties and other management practices, (2) the use of resistant or tolerant varieties where available, and (3) a method of controlling injurious plant bugs and boll weevils that will have the minimum effects on natural enemies." These strategies should also be supported by precise decision-making procedures.

120 J. R. ABLESETAL

Augmentation

Although naturally occurring entomophagous arthropods often suppress pest populations adequately, ecological restrictions may prevent numbers from increasing to an effective level. In such cases, one solution is augmentation, the deliberate increase of the populations or their beneficial effects by the release of laboratory-reared species, the provision of supplemental hosts or other foods, the use of behavioral chemicals, or any combination of these methods (Abies and Ridgway 1981). In an appraisal of augmentative programs in the United States, Abies and Ridgway (1981) noted that the technical knowledge about the use of most entomophagous arthropods in ecological pest control is not adequate to allow the determination of when and where augmentation (or alternatives) should be used. However, the technology is most advanced for the egg parasites Trichogramma spp., the predator Chrysopa carnea, and other species that have been studied for use in cotton. Indeed, the benefits to be derived from augmentation are likely to be highest when the approach is used in the type of situation common in cotton fields where insecticides must be used to control pests such as pink bollworm, Heliothis spp., and boll weevils.

Importation

Importation, the classical approach to biological control, involves foreign exploration for and introduction of natural enemies of insect pests that are not native to the United States and that are therefore not suppressed adequately by the native entomophagous arthropods. Because this is true for the boll weevil, the pink bollworm, and perhaps other pests such as lygus bugs, foreign exploration for natural enemies of these pests is in process. Scien- tists at Texas A&M University are exploring areas of southern Mex- ico in attempts to screen potential natural enemies of the boll weevil. Also, scientists at the University of California, River- side, have for several years explored a variety of geographical regions and have introduced several promising species of parasites of the pink bollworm. In addition, a Federal and State cooperative program has recently been developed for the exploration and introduction of natural enemies of plant bugs that attack cotton. Con- tinued research and education in these different approaches will be necessary to implement the various forms of biological control in cotton.

ACKNOWLEDGMENTS

Outputs from the MOTHZV model were based on data collected by R. E. Kinzer, S. L. Jones, and D. Kizer to whom we are grateful. We thank D. W. McCommas, Jr., for preparation of the figures.


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Bell, K. 0., Jr., and W. H. Whitcomb. 1962. Efficiency of egg predators of the bollworm. Arkansas Farm Research 11:9.

Bottrell, D. G. 1976. Biological control agents of the boll weevil. In Boll Weevil Suppression, Management, and Elimination Technology. U.S. Department of Agriculture, ARS-S-71, p. 22-25.

Cross, W. H., W. L. McGovern, and H. C. Mitchell. 1969. Biology of Bracon kirkpatricki and field releases of the

parasite for control of the boll weevil. Journal of Economic Entomology 62:448-454.

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Dinkins, R. L., J. R. Brazzel,. and C. A. Wilson. 1970. Seasonal incidence of major predaceous arthropods in Mis-

sissippi cotton fields. Journal of Economic Entomology 63:814- 817.

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Donahoe, M. C, and H. N. Pitre. 1977. Reduviolus roseipennis behavior and effectiveness in re-

ducing numbers of Heliothis zea on cotton. Environmental Ento- mology 6:872-876.

Ehler, L. E., K. G. Eveleens, and R. van den Bosch. 1973. An evaluation of some natural enemies of cabbage looper on

cotton in California. Environmental Entomology 2:1009-1015.

Fletcher, R. K., and F. L. Thomas. 1943. Natural control of eggs and first instar larvae of Helio-

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Gonzalez, D., D. A. Ramsey, T. F. Leigh, B. S. Ekbom, and R. van den Bosch.

1977. A comparison of vacuum and whole-plant methods for sampling predaceous arthropods on cotton. Environmental Entomology 6:750-760.

Gorham, D. P. 1847. The cotton worm. DeBow's Commercial Review 3:535.

Hartstack, A. W., Jr., R. L. Ridgway, and S. L. Jones. 1978. Damage to cotton by the bollworm and tobacco budworm. Journal of Economic Entomology 71:239-243.

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1976. MOTHZV-2: a computer simulation of the Heliothis zea and Heliothis virescens population dynamics. Users manual. U.S. Department of Agriculture, ARS-S-127.

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(MOTHZV-1) in pest management decision making. Proceedings, 1973 Beltwide Cotton Production Research Conference, Phoenix, AZ, January 9-10, 1973, p. 118-122.

Hassell, M. P. 1978. The dynamics of arthropod predator-prey systems. In Monograph in Population Research Biology No. 13. PrinceTon University Press, Princeton, NJ, 237 p.

Holling, C. S. 1966. The functional response of invertebrate predators to prey

density. Memoirs Entomological Society of Canada. No. 48, 86 p.

Huffaker, C. B., and CE. Kennett. 1969. Some aspects of assessing efficiency of natural enemies. Canadian Entomologist 101:425-447.


Johnson, W. L., W. H. Cross, W. L. McGovern, and H. C. Mitchell. 1973. Biology of Heterolaccus grandis in a laboratory culture

and its potential as an introduced parasite of the boll weevil in the United States. Environmental Entomology 2:112-118.

Kiritani, K., and J. P. Dempster. 1973. Quantitative evaluations of natural enemy effectiveness. Journal of Applied Ecology 10:323-330.

Knipling, E. F. 1979. The basic principles of insect population suppression and management. U.S. Department of Agriculture, Handbook No. 512, 659 p.

and J. U. McGuire, Jr. 1968. Population models to appraise the limitations and potenti-

alities of Trichogramma in managing host insect populations. U.S. Department of Agriculture, Technical Bulletin No. 1386, 44 p.

Lawrence, R. K., and T. F. Watson. 1979. Predator-prey relationship of Geocoris punctipes and Heli-

othis virescens. Environmental Entomology 8:245-248.

Liapis, P. S. 1980. Controlling Heliothis spp. on cotton through the release

of Trichogramma pretiosum and applications of Bacillus thuringiensis: An economic assessment. U.S. Department of Agricul- ture Economics, Statistics, and Cooperative Services, Natural Resources Branch, Staff Report, 36 p.

Lingren, P. D., R. L. Ridgway, and S. L. Jones. 1968. Consumption by several common arthropod predators of eggs

and larvae of two species of Heliothis that attack cotton. An- nals of the Entomological Society of America 61:613-618.

Lopez, J. D., Jr., R. L. Ridgway, and R. E. Pinnell. 1976. Comparative efficacy of four insect predators of the bollworm and tobacco budworm. Environmental Entomology 5:1160- 1164.

McDaniel, S. G., and W. L. Sterling. 1979. Predator determination and efficiency on Heliothis vires-

cens eggs in cotton using P. Environmental Entomology 8: TÖ83-1087.

Newsom, L. D., and J. R. Brazzel. 1968. Pests and their control. In. Advances in Production and Utilization of Quality Cotton: Principles and Practices, p. 367-405. F. C. Elliot, M. Hoover, and W. K. Porter, editors. Iowa State Universit,y Press, Ames.

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Pierce, W. D., R. A. Cushman, and C. E. Hood. 1912. The insect enemies of the cotton boll weevil. U.S. De-

partment of Agriculture, Bureau of Entomology Bulletin No. 100, 99 p.

Pimentel, D. , D. Andow, D. Gallahan, I. Schreiner, T. E. Thompson, R. Dyson-Hudson, S. N. Jacobson, M. A. Irish, S. F. Kroop, A. M. Moss, M. Shepard, and B. G. Vinzant.

1980. Pesticides; environmental and social costs. In Pest Control: Cultural and Environmental Aspects, p. 99-158. D. Pimentel and J. H. Perkins, editors. American Association for Advancement of Science Selected Symposium No. 43. Westview Press, Boulder, CO.

Pitre, H. N., T. L. Hillhouse, M. C. Donahoe, and H. C. Kinard. 1978. Beneficial arthropods on soybeans and cotton in different

ecosystems in Mississippi. Mississippi Agricultural and Fores- try Experiment Station, Technical Bulletin No. 90, 9 p.

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reau of Entomology Bulletin No. 50, 155 p.

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Pest Management, p. 379-443. R. L. Metcalf and W. Luckman, editors. Wiley and Sons, New York.

Ridgway, R. L. 1969. Control of the bollworm and tobacco budwoirm through con-

servation and augmentation of predaceous insects. In Proceed- ings, Tall Timbers Conference of Ecological Animal Control by Habitat Management, p. 127-144.

E. G. King, and J. L. Carrillo. 1977. Augmentation of natural enemies for control of plant pests

in the Western Hemisphere. In Biological Control by Augmenta- tion of Natural Enemies, p. 379-416. R. L. Ridgway and S. B. Vinson, editors. Plenum Press, New York.

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Ridgway, R. L., P. D. Lingren, C. B. Cowan, Jr., and J. W. Davis. 1967. Populations of arthropod predators and Heliothis spp. af-

ter applications of systemic insecticides to cotton. Journal of Economic Entomology 60:1012-1016.

Riley, C. V. 1873. Fifth annual report of the noxious, beneficial and other

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gous insects in cotton in the Lower Rio Grande Valley of Texas. Texas Agricultural Experiment Station, Miscellaneous Publica- tion No. 1133, 31 p.

M. J. Lukefahr, and F. G. Maxwell, 1976. Impact of nectariless cotton on plant bugs and natural

enemies. Journal of Economic Entomology 69:400-402.

Shepard, M., and W. L. Sterling. 1972. Effects of early season applications of insecticides on beneficial insects and spiders in cotton. Texas Agricultural Experiment Station, Miscellaneous Publication No. 1045, 14 p.

W. L. Sterling, and J. K. Walker, Jr. 1972. Abundance of beneficial arthropods on cotton genotypes. Environmental Entomology 1:117-121.

Smith, J. W., and E. A. Stadelbacher. 1978. Predatory arthropods: seasonal rise and decline of popu-

lations in cotton fields in the Mississippi Delta. Environmen- tal Entomology 7:367-371.

Solomon, M. E. 1949. The natural control of animal populations. Journal of Animal Ecology 18:1-35.

Stehr, F. W. 1975. Parasitoids and predators in pest management. In, Intro- duction to Insect Pest Management, p. 147-188. R. L. Metcalf and W. Luckman, editors. Wiley and Sons, New York.

Sterling, W. L. 1978. Fortuitous biological suppression of the boll weevil by

the red imported fire ant. Environmental Entomology 7:564-568.

126 j. R. ABLESETAL

Tejada, L. O. 1971. Evaluation of the effectiveness of some general predators

at different predator-prey densities, with special reference to their attack on Heliothis zea (Boddie). Ph.D. dissertation. University of California, Riverside.

van den Bosch, R., and K. S. Hagen. 1966. Predaceous and parasitic arthropods in California cotton

fields. California Agricultural Experiment Station, Bulletin No. 820, 32 p.

T. F. Leigh, L. A. Falcon, V. M. Stern, D. Gonzalez, and K. S. Hagen.

1971. The developing program of integrated control of cotton pests in California. In Biological Control, p. 377-394. C. B. Huffaker, editor. Plenum Press, New York.

T. F. Leigh, D. Gonzalez, and R. E. Stinner. 1969. Cage studies on predators of the bollworm in cotton. Journal of Economic Entomology 62:1486-1489.

and A. D. Telford. 1964. Environmental modification and biological control. In Biological Control of Insect Pests and Weeds, p. 459-488. P. DeBach, editor. Chapman and Hall, London.

van Steenwyk, R. A., N. C. Toscano, G. R. Ballmer, K. Kido, and W. T. Reynolds.

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Whitcomb, W. H. 1967a. Field studies on predators of the second instar bollworm, Heliothis zea (Boddie) (Lepidoptera: Noctuidae). Journal of the Georgia Entomological Society 2:113-118.

1967b. Bollworm predators in northeast Arkansas. Arkansas Farm Research 16:2.

and K. 0. Bell, Jr. 1964. Predaceous insects, spiders, and mites of Arkansas cotton

fields. Arkansas Agricultural Experiment Station, Bulletin No. 690, 84 p.


Yokayama, V. Y. 1978. Relation of seasonal changes in extrafloral nectar and fo-

liar protein and arthropod populations in cotton. Environmen- tal Entomology 7:799-802.

129

Chapter 6

MICROBIAL AGENTS

M. R. Bell Western Cotton Insects Laboratory Agricultural Research Service U.S. Department of Agriculture Phoenix, AZ 85040

ABSTRACT Although applications of protozoan and fungal pathogens will produce infection in boll weevils (Anthonomous grandis Boheman) in the field, the pathogens act too slowly to protect the plants. At present, the only microbial agents used on cotton are the Heliothis nuclear polyhedrosis virus and Bacillus thuringiensis Berliner, both of which can suppress moderate to low populations or even control some large populations of the bollworm (Helio- this zea (Boddie)) and the tobacco budworm (Heliothis virescens (F.)). However, proper timing, application techniques, and special formulations are necessary. Because these microbial agents are highly selective (compared with chemical insecticides), they are particularly useful for control of Heliothis spp. when broad-spectrum insecticides are not needed to control other insects such as the boll weevil.

INTRODUCTION

The early studies of diseases of insects were concerned almost entirely with diseases of such useful species as the silkworm (Bombyx mori (L.)) and the honey bee (Apis mellifera L.). Then as these studies slowly spread to include diseases of other insects, the discipline of insect pathology evolved, and scientists began to think of using pathogenic micro-organisms to control pest insects. Insect pathology is therefore relatively young as a separate discipline of entomology. Indeed, the first international conference was held in Prague in 1958. Since that time, the growing number of scientists working specifically in this area of research has produced a rapid increase in information about insect diseases, but diseases of pest species continue ta be the most studied.

Some degree of success has been achieved in the use of insect pathogens (now termed microbial insecticides) in management of pest

""^^ M. R. BELL

insects in crops, but they are presently used much less for this purpose than are chemical insecticides. The simple fact is that the potential for microbial control envisioned in the 1950*s and I960's has not been realized, not because that potential was un- real but because new methods necessary for effective use have not been developed as rapidly as anticipated. For example, at present, only two insect pathogens are registered for use on cotton in the United States, the nuclear polyhedrosis virus (NPV) from Heli- this zea (Boddie) and the bacterium Bacillus thuringiensis Ber- liner, variety HD-1 (B ._t. ). Both have been exempted by the Envi- ronmental Protection Agency from the requirement of a tolerance for residues, and treated fields may be reentered immediately after application.

Another difficulty with microbial insecticides has been lack of consistent economic control, which sometimes stems from lack of knowledge of the user. For example, a user such as a cotton producer is probably skilled in the application of chemical insecticides and knows what to expect from them. However, entirely new problems can arise when pathogens are used in pest management systems, and both the limitations of the pathogens and their potential must be understood. Some of these problems may be specific to one insect pest on one crop; others may be inherent in the pathogen itself. Nevertheless, laboratory and field studies conducted with a variety of microbial agents against several major cotton insect pests indicate that such problems can be solved.

The purpose of this chapter is to review the major characteristics of pathogens that are being used or are being studied for use in controlling cotton insects in the United States and to report the results of field trials. Hopefully, it will give those persons already familiar with cotton insect pest management a better understanding of the potential of microbial control.

GENERAL CHARACTERISTICS OF PATHOGENS IN COTTON INSECT MANAGEMENT

A pest control advisor who recommends the use of pathogens for control of insects, like those who recommend the use of chemical insecticides, must have an understanding of the terms used to describe pathogens and disease processes and must be familiar with the specific characteristics of the microbial. Steinhaus and Mar- tignoni (1970) present short definitions of terms used in invertebrate pathology (e.g., pathogen, disease, infection, incubation period, epizootic). Following are brief descriptions of the microbial agents most often considered for use against cotton insects.

Viruses

More than 700 species of insects and mites have been reported to harbor viruses (David 1975), but viruses in a genus termed

MICROBIAL AGENTS 131

"Baculovirus" are considered to have the greatest potential for control of insects in agriculture. Baculoviruses (identified in more than 300 species of insects) are of two types, the nuclear polyhedrosis viruses (NPV*s) and the granulosis viruses (GV's). Both have infectious units ("virions") that are composed of deoxyribonu- cleic acid and are enclosed in a capsid and surrounded by an enve- lope. In addition, NPV*s form polyhedral inclusion bodies (PIB's) in the nuclei of infected cells (Figure 1), and these polyhedra are composed of several virions embedded in a proteinaceous matrix. The only virus so far registered for agricultural use on row crops in the United States is the NPV from Heliothis zea. It is produced by Sandoz, Inc., under the trade name Elcar.

All presently known insect viruses must be ingested by the insect pest if they are to be effective. In the case of an NPV, which generally infects only larvae, the protein matrix dissolves in the gut and releases the virions, which then move into other tissues of the host. Within 24 hours, the nuclei of cells in certain tissues of the larvae may contain polyhedra, but external appearance and behavior may not be noticeably changed. Indeed, during the succeeding incubation period, the larvae may continue to feed on the plant and to grow, though this may be affected by such factors as the quantity of active virus consumed, the size of the larvae, the temperature, and the food supply. Among the first symptoms of nucleopolyhedrosis (the disease caused by NPV) are sluggishness and decreased feeding. Then the larvae soon cease feeding and die within about 3 days, depending on the susceptibility of the host. The time from ingestion of a lethal dose of NPV to death for lepidopteran larvae on field cotton ranges from about 3 to 15 days. Other pathological characteristics of insect viruses are detailed by Steinhaus (1963), Smith (1967, 1977), and David (1975).

Plainly, the incubation period of an NPV and the fact that the material must be ingested should be recognized when an NPV is considered for control of cotton insects. In addition, NPV*s may be destroyed by ultraviolet radiation, pH, and plant defenses (Bullock 1967, Young and Yearian 1974, Jacques 1977), problems that can be partly overcome by using protective materials to increase the field persistence of the virus (ignoffo and Batzer 1971, Bull et al. 1976). Also, the stored virus may be destroyed or its activity reduced by exposure to high temperatures (McLeod et al. 1977). Finally, timing of an application of NPV is critical if larvae are to be infected as soon as possible after hatch and before they can do serious plant damage.

On the other hand, NPV*s are usually selective and host specific (i.e., the Heliothis NPV infects only Heliothis spp.), which can be a disadvantage or an asset; for example, an application against a pest insect would not affect beneficial insects, but it also would not affect any other pest species present. Finally, none of the baculoviruses has been found to be hazardous to man or other mammals, and they can be produced in the quantities needed

132 M. R. BELL

■5.1) -^ • '' *'i-^. ^w^

f4 ^^

« ^

v; :• §àt; (A) Cell nucleus containing immature polyhedra of a nuclear polyhedrosis virus

•7v \

V-..:

4

(B) Mature polyhedra of a nuclear polyhedrosis virus

(C) Virions of a nuclear polyhedrosis virus

Figure 1.—Tissue infected with a nuclear polyhedrosis virus. Original electron microphotography by F. D. Stewart, U.S. Department of Agriculture, Animal and Plant Health Inspection Service, Phoenix, AZ.


at an economically competitive price (Shieh and Bohmfalk 1980). For further information on problems and benefits, the reader is referred to in-depth reviews of the subject (Cameron 1963, Stairs 1971, Ignoffo 1974, Falcon 1976).

Bacteria

Entomogenous bacteria may be either sporeformers (bacteria that produce persistent endospores) or nonsporeformers. At present, only the sporeformers are being seriously investigated for control of cotton insect pests. However, nonspore-forming pathogens are found in cotton insects. For example, the bacterium Serrâtia marcescens Bizi o sometimes causes mortality of a wide range of insect hosts including the boll weevil (Anthonomus grandis Boheman) (McLaughlin and Keller 1964). It is particularly associated with insects when they are being reared in the laboratory or are otherwise subjected to stress (Angus 1974).

By far the most promising bacterium available for microbial control of cotton insects is B^._^. The strain used at present (the HD-1 isolate) produces a proteinaceous parasporal crystal inclusion that is toxic to lepidopteran larvae but has little or no effect on other animals. Soon after the parasporal crystals are ingested, the gut cells of larvae of susceptible species are affected in such a way as to inhibit feeding by the larvae. In fact, treatment with B._t^. normally results in less feeding by the larval pest during the incubation period than treatment with an NPV or a GV, a matter of considerable importance when minimum damage to foliage is of concern.

Also, sublethal doses of B^._^. provide some control of larvae of at least some cotton insect pests. They may recover from the dose, but they feed less than untreated larvae and grow slowly for some time after exposure (Dulmage et al. 1978; M. R. Bell unpublished data). In addition, with this extended larval development period, they may be exposed to adverse environmental factors that may produce a control effect.

Bacteria, like viruses, must be ingested by an insect pest before they can have any effect. Therefore, oviposition site, feeding habits of the larvae, and methods of application are important. Also, bacteria are usually adversely affected by the environment, and repeated applications may be necessary to maintain plant protection. Finally, bacteria, especially those presently registered for use, are (like the viruses) considered environmentally safe. However, B^._t. has two major advantages over NPV ' s as a microbial agent. It has a wider host range, and large volumes can be readily produced by using fermentation equipment. This wide host range of the HD-1 isolate (it affects most Lepidoptera but is selective enough to be safe) gives it a large market. For this reason, the HD-1 isolate is marketed by several companies under various trade names (e.g., Dipel, Thuricide, Bactur). Many

134 M. R. BELL

publications are available that deal with various aspects of B.t. as a microbial insecticide (Heimpel and Angus 1963, Heimpel iTóT, Dulmage 1970, Burgerjon and Martouret 1971, Cooksey 1971, Falcon 1971b).

Fungi

Fungi differ from the bacteria, viruses, and protozoa that are being considered for control of agricultural pests in that ingestion is not usually necessary for infection: the organisms can penetrate through the surface of the integument. Success of this mode of invasion, however, seems to depend on certain environmental conditions and on the physiological condition of the host cuticle. These conditions vary with different hosts and fungi. Temperature, humidity, and light are among the factors known to affect disease incidence.

Once cotton insects have been infected by a fungus, the general pathology of the disease (mycosis) is as follows: the infective unit, usually the protected resting stage or spore, germinates on the cuticle, and the germ tube penetrates to the hemocoel. With most entomogenous fungi, fragments of the mycelium, so-called hy- phal bodies, then multiply in the body cavity. Thus, by the time of the death of the host, the host body is filled with mycelium and may become firm. At this point, the resting stages of the fungus may then be formed, usually as spores on conidiophores that have erupted from the insect body, which causes the body to take on a fuzzy appearance.

People working in cotton insect control have seen epizootics of fungal diseases that dramatically reduced the insect population. As a result, there is considerable interest in fungi as control agents. However, no fungi are presently registered for use on cotton in the United States. In general, the fungi have the advantage of a relatively wide host range and external invasion, and they can be produced by using culture methods. On the other hand, this wide host range may encompass beneficial insects, the necessary environmental conditions are sometimes limiting, and the incubation period may be long.

Nevertheless, the fungi have potential as microbial agents on cotton, especially in areas of normally high humidity such as the southeastern part of the Cotton Belt. More research is needed to obtain the knowledge required for decision making. In-depth descriptions of mycoses and reports on the use of fungi in microbial control are available (Madelin 1966, Roberts and Yendol 1971, Bell 1974, McCoy 1974, Ferron 1978).

Protozoa

Few protozoan pathogens of insects have been field tested as microbial control agents of crop pests, perhaps because the

MICROBIAL AGENTS I35

incubation period is so long that crop damage usually is not controlled (McLaughlin 1971). This is because few protozoa are highly virulent. Instead they tend to cause slow, debilitative symptoms that do not lead to the rapid control needed for most crops. This is a disadvantage when the concern is protection of a crop but could be an advantage when spread and persistence of the disease are more important factors.

In general, the protozoan pathogens that are being studied as microbial agents are applied in the resistant stage (spores or cysts). Once this stage has been ingested by the host, the invasive stage emerges in the gut, penetrates the gut wall, and begins to multiply in the host tissue. Most protozoan pathogens can only be produced in insect hosts, so it may sometimes be difficult to produce large quantities. However, some are transmitted from generation to generation within the egg, which enhances persistence of the disease in the population. Because the life cycles and types of protozoan pathogens are diverse, the reader is referred to more detailed reviews and descriptions for further information (Tañada 1959, Weiser 1963, McLaughlin 1971).

General Considerations

From the previous brief discussions, certain characteristics are obviously common to most pathogens that are used or are under study as microbial agents for control of cotton insects. Since control usually cannot occur until the pathogen is consumed, the techniques used to apply the pathogen are often very important. For example, even with fungi, which can penetrate the integument, the pathogen must contact the host. Therefore, a technique is needed that places the pathogen close to the target pest. However, there are also considerations such as the persistence of the mi- crobe, the formulation used (e.g., baits, stickers, protectants), and the possibility that rapid plant growth may dilute the microbial. The user must consider the biology of the host insect and the symptomatology of the disease, particularly as it affects the activity of the insect pest during the incubation period (e.g., where and how much feeding will occur). Finally, the methods used to evaluate the effects of microbial treatments should take into account the expected impact of an epizootic of the disease under study.

REVIEW OF MICROBIAL CONTROL OF COTTON INSECT PESTS

Boll Weevil

Few pathogens have been found in field populations of boll weevils, and none is registered for use at this time. Even though McLaughlin et al. (1966) isolated a variety of bacteria and fungi from dead, field-collected weevils, none of those tested proved to

136 M. R. BELL

be pathogenic. The researchers did, however, note that the microbial flora might have caused mortality of otherwise stressed weevils. Also, Serratia marcescens caused an epizootic in caged weevils that could only be controlled by feeding the weevils antibiotics (McLaughlin and Keller 1964). (The mechanism of pathogenicity of this bacterium was described (Slatten and Carson 1967).) Further, boll weevils were found to be susceptible to infection by the nonoccluded Chilo irridescent virus (McLaughlin et al. 1972), the fungus Beauveria bassiana (Balsamo) Vuillemin (McLaughlin 1962), and the fungi Metarrhizium anisopliae (Metschnikoff) Sorokin and Nomuraea rileyi (Farlow) Samson (R. E. McLaughlin and M. R. Bell unpublished data). Although all these infect boll weevils in the field, results of tests have been inconclusive as to their possible use in control systems.

More extensive trials were conducted in 1965-67 with two protozoan pathogens, both isolated from colonies where boll weevils were being mass reared (Gast 1966). One protozoan was Mattesia grandis McLaughlin (McLaughlin 1965), and the other was Glugea gast i McLaughlin (McLaughlin 1969). Both protozoa also infect the bollworm, the tobacco budworm (H_. virescens (F.)), and the pink bollworm (Pectinophora gossypiella (Saunders)) (ignoffo and Garcia 1965). In all cage tests and field trials, the protozoa were applied to cotton in a bait formulation based on cottonseed oil that enhanced feeding activity of weevils (Daum et al. 1967). An oil- soluble dye added to mark weevils that fed on the bait formulation aided in evaluating the effectiveness of treatments. The percentage of weevils marked by the dye and the incidence of the protozoan diseases were high early and late in the growing season but relatively low throughout the period of rapid development of the cotton during the middle of the season (McLaughlin 1967, McLaughlin et al. 1968, 1969). For example, about 80% of the marked weevils were infected by G_. gasti in late June to mid-July, but only 11-25% were infected from mid-July through August. Later in the season, the weevils again responded, and as many as 70% were diseased. Also, over 60% of the weevils collected from winter trash around the field were diseased, and winter mortality of diapausing weevils was higher in the test area.

Thus the research showed that epizootics could be induced in a weevil population with a bait formulation though the protozoan pathogens acted too slowly to protect the crop.

Pink Bollworm

At present, no pathogens are recommended for use in controlling the pink bollworm. However, results of some field tests have been promising. Ignoffo (1962a, 1962b) found that pink bollworm larvae were susceptible to injections of _B.^. spores, determined the lethal dose, and showed that field conditions would probably be such that the bacterium could be used for control of pink bollworms. Subsequently, in field-cage studies, about 40% of


mature larvae were killed by incorporating ^»t_, into soil (ignoffo and Graham 1967); however, the rates necessary to achieve this reduction were not economically feasible. Also, in other field-cage studies, Bullock and Dulmage (1969) obtained significant control (only 10% of the bolls had larval mines) when jB.t^. was sprayed on cotton subsequently infested with pink bollworms; in the untreated control, 80% of the bolls had larval mines. However, the results were not reproducible in subsequent experiments. Graves and Watson (1970) also reported poor control with a commercial preparation of

Bacillus thuringiensis thus has promise for control of the pink bollworm because isolates are highly virulent. However, consistent results have not been obtained because no effective method of usage has been developed. As with other pathogens and other hosts, the major problem is getting the target larvae to ingest the pathogen, but the difficulty is especially great with the pink bollworm. Green bolls are a favored site for oviposition for pink bollworm females, and a high percentage of eggs on bolls are placed under the calyx (Brazzel and Martin 1957). However, larvae from eggs hatched on the bolls enter the bolls within minutes after hatching, and even larvae from eggs oviposited on other parts of the plant enter fruit within about 40 minutes (McLaughlin 1972). This short exposure to the external environment means that larvae have little time to consume an effective dose of pathogen.

The matter of time for ingestion is also a problem with viral pathogens. The NPV isolated from the alfalfa looper (Autographa californica (Speyer)) the so-called ACNPV, also infects pink bollworm larvae (Vail et al. 1972) as well as several other lepidopteran pests of cotton (Vail et al. 1970, Vail and Jay 1973). How- ever, in field tests involving weekly applications of ACNPV, only 1% of 3500 larvae examined (Vail et al. 1978) were infected, presumably because the larvae did not ingest the pathogen.

An attempt was therefore made to increase the ingestion of virus by first-instar pink bollworm larvae by incorporating the pathogen in a feeding stimulant (Bell and Kanavel 1975). When this formulation was applied to greenhouse plants, 60.7% of larvae from eggs placed randomly on the plants were infected; when plants were treated with virus in water alone, only 28.7% of the larvae were infected. Also, in a subsequent field test, application of ACNPV plus bait (the feeding stimulant) reduced the number of pink bollworm larvae in bolls 69% compared with the controls, and the percentage of damaged bolls decreased (Table 1) (Bell and Kanavel 1977). In fact, the feeding adjuvant alone reduced the numbers of pink bollworm larvae in bolls 43%, apparently because the feeding behavior of newly hatched larvae was altered. The virus alone had no effect. Although this degree of control was not deemed practical because of the quantity and cost of materials, the results indicated than an early-season application of such a formulation might be useful as a suppression method.

138 M. R. BELL

Table 1.—Effect of nuclear polyhedrosis virus from Autographa californica in water or in bait on pink bollworm damage to cotton, 1975 1,2/

No. pink bollworms per %

Treatment 3/ 50 bolls damaged bolls

Untreated control 37.3 a 37.6 a 2.97X10^^ PIB*s per ha w/o bait 34.6 a 33.0 ab 935 liters bait per ha w/o virus 21.8 ab 24.0 be 2.97X10 PIB's per ha in 935 liters

bait 11.6 b 14.1 c

\J Average of four replications per treatment during the 1975 growing season.

1_/ Values within column followed by the same letter are not significantly different at the 5% level as determined by LSD.

_3/ FIB = polyhedral inclusion body.

Other pathogens infect the pink bollworm and can be considered potential control agents. For example, the protozoa earlier identified as a boll weevil pathogen also infected pink bollworms (no field tests were conducted) (ignoffo and Garcia 1965). Also, a cytoplasmic polyhedrosis virus found in a laboratory culture of pink bollworms (ignoffo and Adams 1966) produced chronic, débili- tât ive effects on the insect. At present, this pathogen is not considered a promising candidate as a microbial agent for control of pink bollworms because of the quantity of virus required to produce mortality and problems associated with production (Bell and Henneberry 1980).

Cotton Bollworm and Tobacco Budworm

Most of the research effort involving microbial control of cotton insects in the United States has had to do with the bollworm and tobacco budworm. Both B^.^. and the NPV from H. zea (so- called B£CU]JOVÍ£US h£]^^^ are registered for use against these pests, and the ACNPV, though not yet registered, has shown promise against tobacco budworms.

However, the level of control of Heliothis spp. on cotton produced by multiple applications of the Heliothis NPV has been erratic. In some tests, the control obtained has been comparable to that obtained with chemical insecticides. For example, Ignoffo et al. (1965) reported yields of 560 kilograms and 715 kilograms of seed-cotton per 0.4 hectare from plots treated with 6x10 and 6x10 PIB's per 0.4 hectare, respectively, in 25.4 liters of spray per 0.4 hectare; yields from untreated plots were 294 kilograms per 0.4 hectare. Also, Allen et al. (1967) found that in small plots.


applications of 1.2x10 PIB's per 0.4 hectare were as effective as the insecticide standard (toxaphene-DDT). In large plots, applications of the virus plus the naturally occurring predator-parasite complex gave satisfactory control (Allen et al. 1966). Shieh and Bohmfalk (1980) also found that yields of seed cotton increased 10-40% over yields from check plots when multiple treatments of Elcar were applied to cotton against relatively low populations of Heliothis spp. However, other researchers have obtained marginal to no control with Heliothis NPV used alone in field tests (McGarr and Ignoffo 1966, McGarr 1968, Pfrimmer 1979).

Generally, the control of Heliothis spp. obtained with B^.^. variety HD-1 has been more consistent than that obtained with the Heliothis NPV. Control comparable to that obtained with a chemical insecticide was reported by McGarr et al. (1970), but the quantity of formulation necessary was too great for applications to be economically feasible. Others report that application of 3.6-7.3x10 International Units (lU) per 0.4 hectare will suppress a larval population and result in increased yield (Pfrimmer et al. 1971, Bull et al. 1979, Pfrimmer 1979). However, the level of control obtained was usually not comparable to that obtained with chemical insecticides. On the other hand. Bull et al. (1979) found that B._t.and the Heliothis NPV gave comparable control of moderate popu- Tations of larvae when applied at their respective recommended rates.

Several attempts have been made to increase the effectiveness of the Heliothis NPV and B.t_. against Heliothis spp. One possibility that was explored because of the known rapid inactivation of NPV on cotton (Yearian and Young 1974, Young and Yearian 1974, Ig- noffo et al. 1976b) was spray formulations that would improve the persistence of the pathogens on field cotton. In fact, formulations that protected the polyhedra from sunlight did increase the field persistence of NPV (Bull et al. 1976) but did not significantly increase efficacy. Apparently what was needed was an adjuvant that included a gustatory stimulant, a sunlight protectant, and an evaporation retardant (ignoffo et al. 1976a), but the most important of these additions would be a gustatory stimulant capable of increasing foliar feeding of the larvae since that is of major importance for the consistent effectiveness of microbial treatments. A number of the materials that elicit feeding responses in Heliothis spp. have been identified and tested for use (Montoya et al. 1966, McLaughlin et al. 1971, Patti and Garner 1974, Bell and Kanavel 1978). In most instances, the addition of these materials to NPV or B.t. sprays has increased the effectiveness of the microbials.

Two gustatory-type spray adjuvants are presently marketed for commercial use with NPV or B^._t. on cotton. One is Gustol, developed and manufactured by Sandoz, Inc. The other is COAX, manufactured by Traders Oil Mill Co. Both increase foliar feeding of Heliothis spp. larvae and thus increase effectiveness of the microbials. Both also increase the persistence of NPV on cotton. In ten field tests, applications of Heliothis NPV and Gustol to

140 M. R. BELL

early-season cotton resulted in 3.4% of the squares being damaged and 2.8% of the bolls; 6.2% of the squares and 5.2% of the bolls were damaged when the NPV was applied without the adjuvant (L, Russo, Sandoz, Inc., personal communication). Likewise, in full- season trials (average, three tests), yields of seed cotton were 505, 622, and 723 kilograms per 0.4 hectare for untreated fields, fields treated with virus alone, and fields treated with virus plus Gustol, respectively.

Much the same thing has happened when adjuvants have been added to ACNPV. Field tests conducted on late-planted cotton in Arizona indicated that applications of a mixture of ACNPV plus B^._t. plus COAX gave acceptable control of a moderate to heavy infestation of Heliothis spp. (93-98% H. virescens) (Bell and Romine 1980). Only <10% of the squares treated with the mixture were damaged; 30-60+% were damaged in untreated cotton. Moreover, yield was greatly increased (Table 2).

Thus the mixture of B^.£. and virus appeared to give more effi- cacious control than the other treatments even though these two pathogens were antagonistic in laboratory tests (M. R. Bell unpublished data). Possibly the sublethal effect of JB._t. (reducing growth rate) described by Dulmage et al. (1978) was involved. The larvae, though alive, remained small for some time and may have been killed by the virus before they recovered from the JB._t.

Microbials have also been mixed with chemical insecticides to improve the level of control of Heliothis spp. in cotton (Pieters et al.1978, Luttrell et al. 1979, Yearian et al. 1980). However, results reported to date have indicated that little was gained by mixing NPV or ^.t_. with these materials.

In summary, procedures that tend to increase the probability that Heliothis spp. larvae will ingest an active microbial at the proper time have been relatively effective in increasing the level of control. These procedures include the use of a feeding-stimulant adjuvant, optimum dosages, spray methods that result in maximum deposits on the target area, and proper timing of the application so it affects larvae of the right age (Falcon 1971a, Chapman and Ignoffo 1972, Stacey et al. 1977a, 1977b). Another possibility that has not been much investigated is the effect of growth and fruiting pattern of the cotton on damage. Falcon (1974) discussed the possible effect of the presence of squares and small bolls on cotton during the latter part of the season. Such fruit would not normally mature and be harvested, but could provide feeding sites for young Heliothis spp. larvae during the incubation period of the viral pathogen. This feeding damage apparently would not reduce yield, and the preference of the larvae for the small bolls during that period would presumably protect the more mature, harvestable bolls.


Table 2.—Yield of late-planted (June 26) cotton treated with microbials for control of Heliothis spp. , Phoenix, AZ, 1978 l_l

_____

seed cotton Treatment Rate per ha 2/ (kg/ha)

Test 1 Bacillus thuringiensis (B^._t. ) 560 g 1427 a

+ACNPV V 7.41x10 FIB 4/ +adjuvant 3.36 kg

ACNPV 7.41x10^^ PIB 1066 b +adjuvant 3.36 kg

ACNPV alone 7.41x10^^ PIB 744 c

Untreated control 322 d

Test 2 B.£. 560 g 1108 a +adjuvant * 3.36 kg

B.£. alone 560 g 837 b

Untreated control 328 c

1/ Average of four replicates; 15 row-meters handpicked per replicate. Means within columns not followed by the same letter are significantly different at the 5% level of confidence (Duncan's multiple range test—analysis of variance of Latin square).

2^/ All treatments were applied in a total volume of 93.5 liters water per hectare.

_3/ ACNPV = nuclear polyhedrosis virus of the alfalfa looper. 4/ PIB = polyhedral inclusion body.

Other Cotton Insects

The NPV's of the cabbage looper (Trichoplusia ni (Hübner)) and the beet armyworm (Spodoptera exigua (Hübner)) occur naturally in populations of larvae in cotton and are important in the regulation of their respective hosts. When densities of larvae are high,the natural epizootics that usually follow greatly reduce the populations. The feeding behavior of these two species favors ingestion and rapid spread of the viral diseases; thus when augmentation is necessary, these viruses can be applied with standard equipment and without elaborate preparations (Falcon 1971a). However, control of

142 M. R. BELL

these species is seldom needed because cotton can tolerate considerable damage to the foliage at the time populations are normally high. The viruses could nevertheless be important in an area pest management program when reduction of a population on cotton might prevent excessive damage to fall crops.

The cotton leafperforator (Bucculatrix thurberiella Busck) is considered a sporadic pest of cotton in the western United States. Although this insect is a leaf miner during most of its larval stage and thus is not exposed to microbial applications during that time, Vail et al. (1977) obtained partial control with multiple applications of the ACNPV. Further, multiple applications of B^._t^. at normal recommended rates (0.227-0.454 kg per ha) resulted in an acceptable level of control (M. R. Bell unpublished data). Such methods probably would not be used to control this pest, but treatments directed against other pest insects could reduce populations of cotton leafperforators.

CONCLUSION

Although often ignored, pathogens act continuously to limit populations of some cotton pests such as the cabbage looper. Their usefulness in regulating populations of Heliothis spp. in cotton has also been demonstrated. In addition, insect pathogens may interfere with development or reproduction of pest insects and can increase their susceptibility to predators, parasites, or chemical insecticides.

Many efforts are being made to increase the effectiveness and use of microbial agents in management of cotton insects. These include but are not limited to: (1) identifying new, more virulent pathogens or new strains of known pathogens; (2) improving spray formulations; (3) developing new methods of applying or dissemina- ting pathogens; and (4) determining plant-insect-pathogen interactions. The development of these more effective methods or materials, plus the fact that users are more knowledgeable about the factors involved in the use of microbials, should result in more consistent control of cotton insect pests.


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and Bioengineering XXII:1357-1375.

Slatten, B. H., and A. D. Carson. 1967. Mechanism of pathogenicity of Serratia marcescens. I. Virulence for the adult boll weevil. Journal of Invertebrate Pathology 9:78-81.

Smith, K. M. 1967. Insect virology. Academic Press, London, 256 p.

1977. Virus-insect relationships. Longman, New York, 287 p.

Stacey, A. L., W. C. Yearian, and S. Y. Young, III. 1977a. Evaluation of Baculovirus heliothis with feeding stimu-

lants for control of Heliothis larvae on cotton. Journal of Economic Entomology 70:779-784.

S. Y. Young, III, and W. G. Yearian. 1977b. ^Effect of larval age and mortality level on damage to

cotton by Heliothis zea infected with Baculovirus heliothis. Journal of Economic Entomology 70:383-386.

^^^ M. R. BELL

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crobial Control of Insects and Mites, p. 97-124. H. D."Yurges and N. W. Hussey, editors. Academic Press, New York.

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demic Press, New York.

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Vail, P. v., T. J. Henneberry, L. A. Bariola, R. L. Wilson, F. D. Wilson, D. L. Kittock, and H. F. Arle.

1978. Evaluation of several control techniques as potential components of an integrated system for pink bollworm suppression in the Southwest. U.S. Department of Agriculture, Production Research Report No. 172, 18 p.

T. J. Henneberry, and M. R. Bell. 1977. Cotton leafperforator: effect of a nuclear polyhedrosis

virus on field populations. Journal of Economic Entomology 70: 727-728.

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153

Chapter 7

BOLL WEEVIL STERILITY

J. E. Wright and E. J. Villavaso Boll Weevil Research Laboratory Agricultural Research Service U.S. Department of Agriculture Mississippi State, MS 39762

ABSTRACT Early sterilization of boll weevils (Anthonomus grandis Boheman) with gamma irradiation was not satisfactory because the treatment caused high mortality and did not completely sterilize the males and females. Chemosteri- lants were therefore evaluated, and the weevils used in the Pilot Boll Weevil Eradication Exper- iment in southern Mississippi in the early 1970's were treated with these materials. How- ever, chemosterilization was effective only for male boll weevils, so errors in separating the sexes resulted in the release of some fertile females. Also the effects of the chemosterilants on all males were not permanent; some recovered fertility before death. Research produced other candidate sterilization procedures such as irradiation of pupae with fractionated doses of irradiation, fumigation of adults, and gamma irradiation plus immersion in solutions of chemosterilants. Finally, a new method was devised that sterilized both sexes. Newly emerged adults are fed for 5 days on a thin layer (slab) of adult diet containing 100 ppm of diflubenzuron; and on the 6th day both sexes are exposed to 10,000 rad of gamma irradiation in a nitrogen atm.osphere from a cesium-137 source. Male and female boll weevils treated by this method are 99.99% sterile and are dead within 14 days after irradiation. Thus, no regeneration of reproductive tissues occurs.

Tests of the field competitiveness of the sterilized weevils show that they are about 25% as competitive as untreated weevils from days 0 through 4 after release; then competitiveness rapidly decreases.

154 j. E. WRIGHT AND E. VILLA VASO

Boll weevils sterilized by the new method were released in the Boll Weevil Eradication Trial in North Carolina and Virginia in 1979.

There was no evidence of reproduction by native or released weevils in the evaluation area following the release of more than 11 million sterile insects.

The development and successful use of sterile boll weevils is described, and the ramifications for further implementation are discussed.

INTRODUCTION

Since Knipling (1955) proposed that insect control or eradication could be achieved by the introduction of sterile male insects into a natural population, scientists have sought a satisfactory method of sterilizing the boll weevil (Anthonomus grandis Boheman). Davich and Lindquist (1962) reported that gamma irradiation was not satisfactory because sterilization was not permanent and the dose required to produce the temporary sterility was the lethal dose. Davich et al. (1965) also calculated that the sterilized males lost about 80% vigor and were only about 20% as competitive for native females as the native (unirradiated) male weevils.

Meanwhile certain chemicals were reported to be effective sterilizing agents (Knipling 1960, Lindquist 1961), and LaBrecque (1961) reported that three alkylating agents (aphoxide, apholate, and aphomide) caused a high degree of sterility in house flies (Musca domestica L.). Haynes (1963) subsequently found that one of these, apholate, reduced subsequent hatch of eggs when male boll weevils were dipped in a 2% aqueous solution. Hedin et al. (1964) then reported that male boll weevils were sterilized when apholate was incorporated into the diet or applied as a foliar spray to cotton plants to which they were exposed. On the other hand, Lind- quist et al. (1964) reported failure of a small-scale eradication test against the boll weevil when apholate was used as the sterilant.

Davich et al. (1965) speculated that the reason for their failure to achieve eradication in a small-scale test was that sexual competitiveness was reduced in the males. Also, Borkovec (1962) reported that apholate and other chemosterilants had an effect on insects similar to that of gamma irradiation; i.e., in- duction of a dominant lethal effect (Knipling 1964).

Next, fractionated doses of gamma irradiation were tried as a method of sterilizing the boll weevil (Flint et al. 1966), but the lethal effects were such that this procedure was not considered

BOLL WEEVIL STERILITY 155

further at that time. Thermal neutrons, fast neutrons, and micro- waves were investigated by several scientists. Some sterility was induced but mortality was high (Klassen et al. 1969). Bartlett et al. (1968) reported that in laboratory studies, male boll weevils sterilized by gamma irradiation were relatively competitive for 4-5 days and might be able to suppress a native population during that time. Davich (1976) tested this idea in Texas in 1968 on 65 acres of cotton and achieved a reduction in the size of the native population. However, when Davich et al. (1967) attempted to eradicate a natural field population of weevils in a partly isolated area in Baldwin County, AL, by releasing males sterilized by dipping them twice in a 2% apholate solution (24-hour intervals), eradication was not achieved because of (1) lack of isolation, (2) initially high populations, (3) sterility of males ranging from 88 to 100% and averaging ca. 95%, (4) males that survived and regained fertility, and (5) necessity of sexing males by hand to remove females that were not sterilized by the treatment. (The 2% error in separating the sexes resulted in the release of some fertile females.)

A chemosterilant, busulfan, was reported to sterilize male boll weevils without causing appreciable damage to vigor or mating ability (Klassen et al. 1968, Klassen and Earle 1970). The three major disadvantages of busulfan identified at the time were: (1) it was not an adequate female sterilant; (2) there was only a small margin of safety in the dosage requirements (again the sterilizing dose and the lethal dose were approximately the same); and (3) to obtain sterilized males, the males had to consume a sterilizing dose of the treated adult diet. Haynes et al. (1973) showed that a combination of hempa and busulfan was superior to busulfan alone. Lloyd et al. (1976) reported that feeding an adult diet containing busulfan or busulfan and hempa produced an average 93% sterility (from laboratory and field assays, the range was from 70.6 to 99.6%) in male boll weevils released during the Pilot Boll Weevil Eradication Experiment (PBWEE) though 30.3 ± 2.3 yg of busulfan had to be ingested to obtain this level of sterility. Even so, weevils were obviously not completely sterile, and those that survived regained fertility. In fact, in 1973, the final year of the PBWEE (Lloyd et al. 1976), males were sterilized by feeding a 0.09% concentration of busulfan in the adult diet. During the PBWEE, fertile eggs and larvae were detected in two fields in the most isolated part of the eradication zone. Since these eggs were believed to be the progeny of released females, procedures were changed. A combination of 0.09% busulfan and 0.4% hempa was fed in the adult diet to increase the sterility induced in both males and females. The resulting level of sterility initially appeared to range from 94 to 100%. Knipling (1976) in the report of the Technical Guid- ance Committee for the Pilot Boll Weevil Eradication Experiment therefore indicated a need for (1) improved mass-rearing procedures to assure the capability of producing adequate numbers of high quality boll weevils for sterilization and release, (2) an improved technique to assure maximum and consistently high levels of sterilization with a minimum detrimental effect on the vigor

156 j. E. WRIGHT AND E. VILLAVASO

and mating competitiveness of the males, and (3) new methods for sterilizing both sexes of the boll weevil. Subsequently, major research efforts were made to improve rearing procedures and to develop a new sterilization procedure.

DEVELOPMENT OF.NEW METHODS OF STERILIZATION

Since the results of the PBWEE had indicated that a new method of sterilizing both sexes of the boll weevil was needed, several were developed and tested.

In 1975, D. Birkenmeyer and D. Childress (unpublished data) investigated the effect of fractionated doses on adult boll weevils. Haynes and Mitchell (1977) and Haynes et al. (1977) found that fractionated doses of irradiation applied to pupae or newly emerged adult boll weevils (total dose of 6-8 krads) resulted in 98-100% sterility.

Gassner et al. (1974), Terry et al. (1974, 1977), and Earle and Leopold (1975) described procedures for application of chemosterilants to boll weevils based on fumigation in vacuum. McHaffey and Borkovec (1976) tested a reduced-pressure dipping method for the materials. Also, Borkovec and McHaffey (1977) chemosterilized adult boll weevils by fumigation (both sexes) at atmospheric pressure with alkylating aziridinyl phosphine sulfides and oxides. The chemosterilant, bisazir, was investigated by Borkovec et al. (1978) and McCoy and Wright (1979) and was found to sterilize about 99% of treated males. However, mortality was similar to that produced by sterilizing doses of radiation.

Either fumigation or irradiation of aged adults was therefore satisfactory for sterilizing male boll weevils, but the females would oviposit fertile eggs until the lethal effects of the treatments were expressed. The insect growth regulator, diflubenzuron, and its analog penfluron had been shown to prevent hatch of eggs from exposed female insects (Moore and Taft 1975, Wright and Spates 1976, Borkovec et al. 1978). Wright et al. (1979) dipped adult weevils in an acetone solution of diflubenzuron, which rendered the females infertile after the adults were irradiated (mode of action described in detail subsequently). However, Earle et al. (1979a) reported that the flight ability of irradiated male boll weevils treated with diflubenzuron in acetone was apparently impaired by the acetone. Also, Haynes et al. (1981) repo>-ted that the acetone decreased flight activity.

Fractionated irradiation treatment of young adult weevils was compared with acute irradiation of aged boll weevils by Haynes et al. (1979), who reported that mortality was less when weevils were treated 6 days after emergence. Earle et al. (1978) showed that acute irradiation of adults was at least as effective a procedure as fractionated irradiation of pupae. Subsequently, Haynes et al. (1978) evaluated the possibility of sterilizing large numbers of


weevils by exposing the pupal and early adult stages to fractionated doses of irradiation while they were still in the larval medium. This procedure was eventually eliminated from consideration because of the complexity of the problems involved in handling, irradiation, and transportation.

Wright et al. (1979) then examined the effects of aging the adults before exposing them to sterilizing procedures and compared the mating ability, sterility, and survival of weevils treated by irradiation or fumigation. They determined that more males were available to mate after the irradiation treatment because fumigated males had significantly higher mortality at 7 days posttreatment. Next, Wright et al. (1980a) compared the three most promising techniques for sterilization of the boll weevil: (1) irradiation in a nitrogen atmosphere plus dipping 6-day-old adults in a 0.1% diflubenzuron solution; (2) irradiation of pupae with fractionated doses; and (3) fumigation of adults with bisazir plus dipping 6- day-old adults in penfluron. The results indicated that technique (1) was the best experimentally. Both sexes of weevils were sterilized when diflubenzuron was administered in the adult diet in combination with irradiation or fumigation, though a dose of 500 ppm of diflubenzuron appeared to reduce sperm transfer and the antibiotics caused reduced production of pheromone by the males. In contrast, males fumigated for 90 minutes in bisazir and then dipped in an acetone solution containing 1.35% penfluron (Borkovec et al. 1978) were 23% as competitive as normal males.

When adult boll weevils were held for 5 days after emergence on diet containing 100 ppm diflubenzuron and then exposed on the 6th day to 10 krad of gamma irradiation from a cesium-137 source in a nitrogen atmosphere, both males and females were sterile (Wright et al. 1980b). There was no indication that this lower level of diflubenzuron affected sperm transfer or mating behavior. Moore et al. (1978) fed males 500 ppm of diflubenzuron in adult diet for 3 days or dipped males in a 0.6% acetone solution and observed no adverse effects on sperm transfer. Earle et al. (1978) reported that diflubenzuron reduced matings as much as 40-50% when adults were dipped in 0.01-0.1% acetone solutions, though such dipping did not affect the mating performance (Earle et al. 1979a).

Villavaso et al. (1977) stated that an acetone solution of diflubenzuron applied to 4-day-old males following irradiation did not affect insemination of females by males.

In summation, the holding of both sexes of weevils on a slab of adult diet for 6 days so they could age before irradiation allowed mating to occur, but the addition of the diflubenzuron to the diet meant that this material was incorporated within the eggs of the females so the eggs did not hatch (Ivie and Wright 1978, Bull and Ivie 1980). The 10 krad of gamma irradiation that was then administered caused all the insects to die within 12-15 days posttreatment. The mortality occurred early enough to prevent recovery of fertility by the released adults.

"•58 j. E. WRIGHT AND E. VILLA VASO

This latest method of sterilizing boll weevils was now tested against 1,350,000 mass-reared weevils. When the eggs (1,701,140) produced by these treated adults were collected and evaluated for fertility (treated x treated crosses), the sterility factor was 99.999% (Wright and Roberson, 1981). Moreover, the 0.001% fertility was believed to result from contamination by colony adults since the experiments were done in the mass-rearing facility where isolation was incomplete. The same procedure for sterilizing weevils was field tested in an isolated cotton planting in Florida (Mitchell et al. 1980). The more than 600,000 sterile boll weevils released there did not establish a population in the field.

COMPETITIVENESS OF STERILIZED WEEVILS

The detrimental effects of irradiation on the vigor of male boll weevils has been well-documented (Davich and Lindquist 1962, Flint et al. 1966). The impact of this reduced vigor on the competitiveness of treated males was equally evident. For example, Davich et al. (1965) reported that the mating competitiveness of irradiated males in a field-cage test was 20% that of normal males.

Chemosterilization too results in reduced vigor. Villavaso and Earle (1976) showed that males sterilized by feeding on a diet containing 0.08% busulfan for 6 days mated with only one-half as many females as did normal males in field tests. Also, Haynes et al. (1975), in laboratory tests, found that the mating competitiveness of males sterilized by feeding on diet containing 0.08% busulfan plus 0.4% hempa for 6 days was 25-33% that of normal males.

In 1977, Villavaso et al. (1979) devised field tests to determine estimates of the competitiveness of sterile male boll weevils. Sterile and fertile males and fertile virgin females were released into isolated, weevil-free plots of cotton. After 7 days, squares with oviposition punctures were collected and incubated in the laboratory, and percentage egg hatch was determined. This experimentally determined value for percentage egg hatch in the field was then used along with the values for percentage egg hatch obtained from crosses between sterile males and normal females and normal males and normal females in estimating competitiveness by the formula of Fried (1971) in which no assumptions were made concerning the factors involved in the degree of competitiveness achieved as:

where

(——TT-) (-77) X 100 = % competitiveness Ee-Hs S ^

Ha = % egg hatch of N^î x N9 Hs = % egg hatch of S^ x N9 Ee = experimentally determined egg hatch from the

field N = the number of normal males used S = the number of sterile males used


Males sterilized by the pupal fractionation treatment of Haynes et al. (1977) were 23% as competitive as normal males. How- ever, males allowed to remain on the surface of the larval diet for 3-4 days after emergence were 36% as competitive as normal males when they were then sterilized by 7 krad of gamma irradiation followed by a 5-second dip in a 0.02% solution of diflubenzuron in acetone (R. A. Leopold, D. T. North, personal communication, Earle et al. 1978).

Males given 10 krad of gamma irradiation in a nitrogen atmosphere and then dipped in an acetone solution containing 0.1% diflubenzuron were 17% as competitive as normal males; the competitiveness of males treated by the pupal fractionation treatment was 12% (Villavaso et al. 1980). The nitrogen was used because it anes- thetized the weevils so they were easier to handle. Furthermore, Earle et al. (1979b) showed that male mating capability was approximately the same whether the males were given 10 krad in nitrogen or 8 krad in air.

RELEASE OF STERILE MALES IN BOLL WEEVIL ERADICATION TRIAL

The procedure adopted in preparing the sterile boll weevils for release during 1979 in the Boll Weevil Eradication Trial (BWET) was as follows: 13-14 days after the eggs were implanted in the artificial medium, the newly emerged adults were collected into 30- X 40-centimeter, nylon marquisette bags (about 6000 per bag) that were placed on top of diet slabs (32 x 42 x 1 centimeters). These slabs had been treated by mixing antibiotics (streptomycin (0.01%), neomycin sulfate (0.01%), and polpet (0.03%) with sand and grits (Grit-o-Cobs 0-60) and spreading the mixture thinly over the surface of the slabs to prevent bacterial contamination. The second day, the bags were lifted, and slabs were turned over. New slabs were provided the third and the fifth days. The sixth day, the adults were chilled in a walk-in refrigerator (ca. 4°C) and placed in a seed separator for removal of dead adults. Then they were exposed to the 10 krad of irradiation, packaged, and shipped to North Carolina by commercial air carrier for release.

In all, 11 million adults were mass reared, sterilized, and released in the BWET in 1979. No evidence of reproduction attributable to the released sterile boll weevils was found. Adults were exposed to a single dose of 10 krad of gamma irradiation in a cesium-137 source (3107 ± 5% curie). The doses were monitored by Fricke dosimetry and thermoluminescent dosimeters (Fricke and Hart 1966). The nitrogen atmosphere was used during irradiation to lower oxygen tension and according to Earle et al. (1979b) should have enhanced the competitiveness of the males.

^^^ J. E. WRIGHT AND E. VILLA VASO

SELECTION OF ARTIFICIAL DIET FOR MASS REARING

Vanderzant and Davich (1958) developed the first artificial diets for the boll weevil. Other diets were developed by several researchers including Earle et al. (1966), Sterling et al. (1965), Gast and Davich (1966), and Lindig and Malone (1973). However, most of the diets were designed for use with small laboratory colonies, and there were some questions concerning their suitability for mass production of boll weevils, including (1) cost, (2) the limited supply of specialized ingredients, and (3) possible incom- patibility with mechanized equipment.

Three experimental diets appeared to fit all parameters necessary for mass rearing boll weevils. One was a modification of a diet devised by Gast and Davich (1966) (Gast diet), one was a diet devised by Lindig and Malone (1973) (HG), and one was the cottonseed flour diet (CSF) of R. F. Moore (unpublished information). The composition of these three diets is indicated in Table 1.

Because of the large numbers of adults required for sterile insect releases, these three diets were evaluated by feeding each to 3 million adult weevils per week. Eggs were mechanically extracted from the diet pellets (Griffin and Lindig 1977), surface sterilized with 10% formalin solution (Sikorowski et al. 1977), and implanted in congealed larval test diets by spraying. (Concur- rently, small-scale tests were also conducted.) Data for the large-scale test (Table 2) showed that significantly more adults were produced from each tray of Gast diet (382.9) than from trays of the HG diet (326.2) or the CSF diet (198). No differences were detected in the small-scale tests. In the large-scale test, the average numbers of days necessary to obtain 80% of the total adult emergence from the Gast, CSF, and HG diets were 4.7, 4.6, and 4.2, respectively. The averages for the small-scale test were 4.3, 4.3, and 3.8 days, respectively. Adults emerging from the HG diet were slightly larger (12.8 mg) than adults emerging from the CSF (12.6) or Gast (12.1) diets. (Also, the weights of adults fed on these three diets for 15 days were 15.8, 16.9, and 17.1 mg, respectively.) In the concurrent small-scale tests, females exposed to the HG diet laid a significantly higher average number of eggs per female per day for 12 days (13.2) than females exposed to the CSF diet (11.7) or the Gast diet (12.3), but the average dropped to ca. 5.5 eggs per female per day when the females were handled according to mass-production procedures. Thus mechanical extraction and the handling of eggs in mass greatly reduced the number of eggs recovered.

The Gast diet produced more adults at the least cost (Table 2), but the HG diet consistently had a higher percentage of eggs hatching. Otherwise, there were few differences among the diets in ease of handling in the large-volume mechanized procedures (flash-sterilizing units, tray forming and filling, or diet preparations) except that the dry ingredients used in the CSF diet were extremely dusty. This constituted a potential hazard, and more


Table 1.—Composition of 3 artificial diets for mass rearing of the boll weevil

Gast CSF 1/ HG \_l

Adult and Adult Larval Adult Larval larval

Ingredients diet diet diet diet diets

Agar (grams) 80 78.6 80.4 88.5 80 Sugar (grams 65 74 178.9 179 60

Wesson salt (grams) 10.5 12 13.2 13.1 10.5

Cholesterol (grams) 2.75 3.4 2.24 2.21 1.0 Vitamin mix (ml) 10.8 12 2.0 1.0 10.0

Ascorbic acid (grams ) 2.5 2.75 7.16 7.08 5.0

Potassium 5.4 6.0 2.2 8.7 5.4

sórbate (grams) Methyl paraben

(grams) 3.5 3.8 3.35 6.64 3.5 Cottonseed 265.0 310.75 meal (grams)

Cottonseed flour (grams) 223.6 221.3

Underflow (grams) 200 Cottonseed 100 101.75 meats (grams)

Promine D (grams) 100 116.5 100

Casein (grams) 150

Wheat germ (grams) 100

Corn cob grits (grams) 56 Choline chloride

(grams) 4.47 4.43

Tocopherol (grams) 0.72 0.71

Zinc acetate (grams) 0.044 0.044

Cobalt chloride (grams) 0.022 0.022

Sodium molybdate (grams) 0.022 0.022

Wheat germ oil (ml) 13.42 13.12

Methenamine (grams) 0.75 2/0.75

Biotin solution 0.6 0.6 0.6

(0.1%)(ml) B,^ solution 0.6 0.6 ^t0.01%)(ml)

HCL 6 N (ml) 4 4 Formaldehyde (ml) Water (ml) 3800 3800

1.12 1.15 3800 3800

0.6

4

3800

1/ CSF = cottonseed flour; HG = diet devised by Lindig and Malone (l'973).

2/ Adults only.

162 j. E. WRIGHT AND E. VILLA VASO

Table 2.—Production of adult boll weevils from test diets, mass-production procedures

Mean Mean cost Mean num~ weight of diet ber of of Mean % Mean % needed to adults emerging of 100 of traps produce

emerging weevils eggs yield- contami- 1000 adults 3/ Diet 1/ per tray 2/ (mg) ing adults nated (dollars)

Gast 382.9 a 12.1 15.4 2.1 0.21 CSF 198.0 c 12.6 8.1 1.4 0.58 HG 326.2 b 12.8 12.9 1.2 0.31

j_/ CSF = cottonseed flour; HG = diet devised by Lindig and Malone (1973).

Ij Means followed by different letters are significantly different at the 5% level of probability as determined by Duncan's new multiple range test.

_3/ Includes cost of tray and cover.

labor and equipment were needed for the dry-mixing stage of the CSF diet. The Gast diet was selected as the mass-rearing diet, and all insects used in the BWET were reared on this diet.

GENETICS OF STRAIN

Bartlett (1967) selected a strain of boll weevils with an ebony characteristic; i.e., it is identifiable by ebony color of the entire body of the adult. The trait is semidominant and requires selection and backcrossing to maintain. The genotypes and progeny phenotypes resulting from possible crosses are listed in Table 3. Jenkins et al. (1972) introduced a pearl-eyed ebony characteristic into the maintenance colony in 1969, but the pearl- eyed characteristic was removed from the colony in 1970-71 because behavioral characteristics indicated that the pearl-eyed mutant was not adapted for use in the field.

An ebony colony that was to provide identifiable weevils for the sterile releases in the BWET was set up in 1971 by collecting native specimens from North Carolina and crossing them with the laboratory ebony colony. By 1977, the ebony characteristic in the colony was only about 50%; thus, in October 1978, ebony adults were selected from pupal cells and a selected, isolated colony was begun for the ebony body characteristic. In 1979, when the adult boll weevils were sterilized and released in the BWET, 99% had the ebony trait.


Table 3.—Genotypes and progeny phenotypes resulting from crosses of ebony (e) and wild-type body (+)

Genotype Phenotype

e/e e/+ +/+ e/e X e/e e/e X e/+ e/+ X e/+ e/e X + /+ e/+ X +/+ + /+ X + /+

Ebony - black Bronze - (lOR 3/4 Munsell Notation) Wild-type (lOR 4/8 Munsell Notation) All ebony 1 ebony: 1 bronze 1 ebony: 2 bronze: 1 wild-type All bronze 1 bronze: 1 wild-type All wild-type

ADULT MARKING WITH CALCO OIL RED

Calco oil red N1700 dye was first used to mark the boll weevil by Gast and Landin (1966) who incorporated 1000 ppm within the larval diet. The result was that the oil was found within the fat bodies of the emerging adults. Although the dye had no adverse effects when small numbers of weevils were reared, Wilkinson et al. (1972) reported that it did produce significant differences in the pupal weight, adult longevity, and egg production of three lepidopteran species. Since the dye might therefore affect the quality of mass-reared adult weevils, we analyzed its effects on the sterility, mortality, and pheromone production of mass-reared weevils. For this test, the dye, 550 ppm, was dissolved in ca. 100 ml of corn oil or wheat germ oil and added to standard larval diet (Lin- dig 1979) that had been flash-sterilized according to the proce-

dures of Griffin et al. (1974). Normal mass-rearing procedures (Roberson and Wright 1982) were used in forming trays, dispensing diet, and implanting eggs. Trays of control diet (no dye) were prepared and planted the same day for comparison. Weight of emerging adults, oviposit ion, and hatch data were determined according to the procedure described by Lindig (1979); that is, the usual wax-coated adult diet pellets were fed to both marked and unmarked adults for the oviposition and hatch tests. The adults were then held on diet slabs for 6 days and exposed to 10 krad. The procedures used to determine the sterility, egg hatch, and mating ability of both types of weevils were those described by Wright et al. (1979). Pheromone production was quantitated by the method of McKibben et al. (1976). Frass collected daily for days 1-4 and 5-8 was combined for extraction and analysis. Also, acetylcholines- terase and B^carboxylesterase enzyme activities in the 5-day-old dyed and control insects were determined according to the methods of Ellman et al. (1961) and Chambers (1973), respectively.

164 J. E. WRIGHT AND E. VILLA VASO

Table 4.—Effects of incorporating red dye in larval diet of boll weevils

No. % mor- Adults eggs Weight (mg) tality

per per % of emerg- at 14 tray day hatch ing adults days

Diet (±X SD) (±X SD) (±X SP) (±X SP) (±X SP)

Standard 646.1±148.1 8.6±1.4 72.6±4.2 13.2±0.4 8.5±4.9 Standard

+ dye 597.1±110.3 9.5±1.1 74.7±3.6 13.0±0.2 8.3

The results showed no significant differences between the dyed weevils and the control weevils (Lindig et al. 1980) (Table 4).

The Calco oil red dye provided a positive marking of all adults. They could easily be identified in the field or elsewhere by visual examination of the thin dorsal coverings of the abdomen under the elytra. Also, moribund adults could be identified by grinding them in a small amount of acetone and observing the red- dish color. Still more importantly, the eggs produced by the sterilized released females were dyed and therefore distinguishable from the eggs oviposited by native females in cotton squares. All sterile adults released in the BWET had been fed the calco oil red dye.

IRRAPIATION SOURCE

The cobalt-60 irradiation source at the Boll Weevil Research Laboratory, which had an output of 356 krad per minute, was used in the first efforts to sterilize the boll weevil by irradiation. However, this source had limited chamber space in which to place insects. A cesium-137 source was purchased subsequently so fractionated doses of irradiation could be applied to boll weevil pupae (Flint et al. 1966, Haynes et al. 1977). This cesium-137 source has a relatively low rad output—120 rad per minute—but its chamber capacity is large enough to accommodate ca. 125,000-150,000 adults. On the other hand, it took ca. 90 minutes in the cesium source to administer 10 krad and only ca. 15 minutes in the cobalt source. Thus the difference in the energy levels of radiation to which the adult boll weevils were exposed and the time required to reach the necessary dose of 10 krad could have an effect on the longevity and sterility of the treated weevils. The sensitivity of male and female boll weevils to lethal effects of gamma irradiation in the two chambers was evaluated by exposing 2-, 3-, and 6-day-old adults (sexes held separately after treatment) to 0, 1250, 1570, 2480, 3140, 4970, and 6800 rads. There were no significant differences in the biological effects of the cesium and cobalt sources at the levels tested (Abdul Matin et al. 1980).

EVALUATION OF THE STERILE BOLL WEEVILS RELEASED IN THE BOLL WEEVIL ERADICATION TRIAL IN 1979

Mortality of sterile weevils held in the rearing laboratory was 50% at 4.6 days, 70% at 5.4 days, and 99% at 8.4 days. Mortal- ity of sterile weevils caged in the field was 50% at 5.8 days, 70% at 7.2 days, and 99% at 11.7 days. However, in the Florida test, mortality of sterile weevils held in the laboratory (50, 70, and 87% after 4.1, 5.2, and 9.1 days, respectively) was similar to that of weevils held in the field (50, 70, and 99% at 7.4, 8.7, and 13.2 days, respectively). Mortality was always directly correlated with the effects of the irradiation on the destruction of the midgut epithelial cells. Irradiation treatment also produced a decline in vigor the 7th day (Nilakhe and Earle 1976, Earle et al. 1978).

Sperm transfer by treated males taken at random from each of the 29 shipments to North Carolina averaged 46.6% compared with 58% for the controls. This was satisfactory since irradiated boll weevils produce no sperm 5 days after treatment (Nilakhe and Earle 1976), and released sterile males had the ability to transfer sperm the day they were released in the cotton field. Normal male boll weevils usually attain peak mating activity after they are 4 days old (Cross 1973).

According to McKibben et al. (1976) and Gueldner and Wiygul (1978), male boll weevils produce little pheromone (<20 nanograms per male) until they are more than 5 days old. McGovern et al. (1975) reported that exposure to 10 krad of gamma irradiation did not affect pheromone production by the males until about the sixth day after treatment; then production was only about one-third that of the controls. Earle et al. (1978) reported similar results. This decrease in pheromone was one of the reasons adult weevils were aged before release; the released steriles should be capable of pheromone production the day of release. McGovern et al. (1975) and Villavaso et al. (1979) showed that males produced pheromone on days 0-3 after emergence if they were fed fresh cotton squares.) The sterile male boll weevils released during the BWET averaged 290 nanograms pheromone per day when they were held in the laboratory; similar unsterilized males averaged only 221 nanograms per male per day (Wright and Thomas 1981).

The ebony marker and the presence of calco oil red dye within the adult boll weevils made it easy to identify the sterile weevils released in the BWET. Only 1.2% of the released weevils were bronze and only one wild-type weevil was observed among those sampled. Projection of these figures indicates that ca. 450 wild-type and 158,818 bronze weevils were present among the 13,050,000 sterile weevils shipped to North Carolina.

The flight behavior of adult weevils released in the BWET was tested to determine their locomotor activity because earlier, when diflubenzuron was applied in an acetone dip, movement was severely curtailed (19% flight v. 39% for controls) (Haynes et al. 1981).

166 J. E. WRIGHT AND E. VILLAVASO

The data for the sampled weevils showed that an average 28% of the sterile insects and 49% of the controls (untreated) were capable of flight. M. C. Ganyard (personal communication) of Animal and Plant Health Inspection Service reported that 76,000 of the released sterile insects were captured in traps at distances of >400 meters from their release points.

The High Pressure Liquid Chromâtography analysis of diflubenzuron in the treated boll weevils at day 6 showed that an average 182 and 221 nanograms were present in the released males and females, respectively. Additional analysis of eggs laid by these weevils indicated that ca. 8.5 ppm diflubenzuron was present in the eggs. Both findings are important. In the first place, the incor- poration of diflubenzuron in the adult diet makes it possible to sterilize both sexes of boll weevils (Wright et al. 1980b, Wright and Roberson 1981) since diflubenzuron inhibits the synthesis of chitin and interferes with larval development in eggs of treated females as long as the material is present within the females. Ir- radiation then prevents further oogénesis after the initial eggs containing diflubenzuron are oviposited, which occurs within 4 days after treatment in the laboratory (Wright and Roberson 1981). In the second place, as Bull and Ivie (1980) noted in a study on the fate and activity of diflubenzuron in the boll weevil, 1.0 ppm diflubenzuron must be present in the egg to inhibit hatch.

The sterile boll weevils released in the BWET in the North Carolina-Virginia area in 1979 had been sterilized by acute irradiation plus diflubenzuron treatment. The method was selected because of its simplicity and because of the potential health hazard associated with the fumigation treatment. Also, the diflubenzuron was fed (100 ppm for 5 days before irradiation) to newly emerged weevils (Wright et al. 1980b) because of the adverse effects of acetone on flight ability discovered in 1978 (Earle and Simmons 1979). Samples of weevils released in the BWET were observed to be 12% as competitive as normal males (Villavaso 1981).

In 1980 and 1981 other weevils treated with the same method were evaluated for competitiveness in Louisiana: treated weevils averaged 7 and 12%, respectively, over the 7-day posttreatment period (Villavaso unpublished data). The sterile weevils were 23% as competitive as untreated weevils for days 0-4 and 14% as competitive for days 0-5 after release. In addition, mortality and mating studies of laboratory-held and caged males showed that the sterile males were most effective for the first 4 days (Villa- vaso 1981) (Table 5). The combined competitiveness data would support the release of steriles for better effectiveness at intervals of 5 days rather than every 7 days.

The relative effectiveness of released sterile boll weevils with different ratings for competitiveness is difficult to demonstrate in the field, especially when native populations are very low and eradication is the goal. However, theoretical

Table 5.—Competitiveness of sterile males treated with acute irradiation plus diflubenzuron 1/

Untreated Treated male females ScJ:S9:N<?

Year strain released ratio

1977 Ebony No 1:0:1 1978 Ebony No 3:0:1 1979 Ebony or

native Yes 5:5:1 1980 Ebony Yes 5:5:1 1981 Ebony Yes 5:5:1

No, untreated virgin females % released per competi- plot tiveness

300 300

300 300 150

36 17 20 6 7

12

\J In 1977 and 1978, adults were dipped in an acetone solution of 0.02% diflubenzuron; in 1979 and 1980, adults were fed 100 ppm diflubenzuron in the diet for 5 days.

possibilities of mating between sterile males and native females can be determined mathematically as shown in Table 6.

Therefore, in a situation where one native male and one native female are present in a 4-hectare field and releases of sterile insects are made (assuming 22% competitiveness), there would be an effective sterile to native male ratio of 110:1 or ca. 1 chance in 110 of a native x native mating. If one assumes 6% competitiveness, there would be a 30:1 effective sterile to native male ratio or ca. 3.4 chances in 100 of a native x native mating. However, in such a situation, if native x native matings of overwintered weevils did occur, the progeny (F^ generation) could be detected by using infield traps installed at the rate of one trap per 0.4 hectare (Lloyd et al. 1980). Such reproducing clumps, once detected, could then be eliminated by other suppression methods.

Table 6.—Number of probable matings when 50 sterile males are released per week, competitiveness is 22 or 6%, and emergence of overwintered weevils over a 10-day period is uniform

Assumed % Ratio of No. of No. of field competi- - sterile probable probable

No. native tiveness of to native fertile fertile matings/ ^ and 9/ released males matings over 8000 hectares

400 hectares males over 10 days ; 10 days (extrapolated)

10^, 109 22 1100:1 0.005 0.1 6 300:1 0.024 0.48

100^, 1009 22 110:1 0.05 1.0 6 30:1 0.24 4.8

168 J. E. WRIGHT AND E. VILLA VASO

When sterile boll weevils are to be used in efforts to eradicate, they should be used against an emerged overwintered population that has been reduced to a low level by other suppression technology. Once most of the overwintered weevils have emerged, releases of sterile weevils could be terminated, and a pheromone trapping system (Chapter 8 in this handbook) could be installed to detect reproducing clumps.

Releases of sterile boll weevils could also be considered for pest management since we now have reliable insect rearing and improved sterilizing procedures. Additional research is needed to determ.ine how such releases can be used as a component of existing pest management program-s for cotton.

REQUIREMENT FOR USING STERILE INSECTS

The analyses of the PBWEE by Whitten and Foster (1975), Eden et al. (1973), the National Academy of Sciences (1975), and Perkins (1980) all included remarks to the effect that technical shortcomings in the degree of sterility and behavioral competitiveness of the released sterilized weevils had seriously limited that eradication experiment. Knipling (1979) listed the conditions he felt had to be met before the sterile male technique could be used in an eradication attempt. These were:

(1) Mass rearing of quality insects. (2) Method of sterilizing that produces males that are suf-

ficiently competitive. (3) Quantitation of natural populations of insects to deter-

mine numbers of sterile insects that should be released. (4) Distribution of released insects at the most opportune

time so that they will be spatially competitive with the natural populations for mating.

(5) Information available concerning the normal population dynamics at the time of release.

(6) Information concerning the degree of infiltration of weevils from areas outside the test area and its impact upon the technology being used.

(7) Prior analysis of costs, effectiveness, and ecological effects of this autocidal method as opposed to other available methods.

(8) Information concerning the effects of released insects on crops, health, and man.

These requirements are formidable and indicate that sterile releases or other autocidal techniques cannot provide a practical way to deal with most pest problems. At the same time, the technique does have potential in managing some important pests, especially when the method is integrated with other suppression methods.


Knipling (1979) has pointed out that sterile insects may be useful in four situations:

(1) For suppression or elimination of low-level natural populations.

(2) For elimination of incipient populations in a new area. (3) For prevention of the establishment of a new population

in a given area. (4) For pest management programs.

The sterile boll weevil should now be considered a candidate for these situations.

The effort to induce sterility in male and female boll weevils has extended over more than two decades. The search was for a treatment that (1) would not destroy the regenerative cells of the midgut so digestive enzjrmes would be produced; (2) would destroy all spermatogonia and oogonia so sterility would be permanent; and (3) would induce dominant lethal mutations in all gametes. The sterilization method developed and utilized sterilizes both sexes and yields a male that is about 23% competitive during the first 5 days or so after release. The effects of the irradiation are then manifested, competitiveness decreases, and the boll weevils die within 14 days.


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179

Chapter 8

PHEROMONES FOR SURVEY, DETECTION, AND CONTROL

E. P. Lloyd and G. H. McKibben Boll Weevil Eradication Research Agricultural Research Service U.S. Department of Agriculture Raleigh, NC 27607

J. E. Leggett Cotton Production Research Laboratory Agricultural Research Service U.S. Department of Agriculture Florence, SC 29503

A. W. Hartstack Pest Control Equipment and Methods

Research Agricultural Research Service U.S. Department of Agriculture College Station, TX 77843

ABSTRACT Since 1968, pheromones of the boll weevil (Anthonomus grandis Boheman), bollworm (Heliothis zea (Boddie)), and tobacco budworm (Heliothis virescens (F.)) have been isolated, identified, synthesized, formulated, and released in the field with effective dispensing systems. The pheromone of the boll weevil is most effective when the four components (grandlure) are prepared in polyethylene glycol and the mixture is impregnated at the desired dosage into polyester-wrapped cigarette filters. Traps have evolved from sticky wing traps painted green to inverted 1-liter plastic soda cups painted fluorescent saturn yellow and fitted with a capture device on the top of the cups.

In field tests with grandlure-baited traps specially designed for use inside cotton fields, nearly all of the responding weevils were unmated females. Subsequent tests in which pheromone traps were combined with closely spaced applications of insecticide showed that the combination effectively prevented reproduction by emerged overwintered boll weevils. Results of field experiments indicated a 94% probability

180 E. P. LLOYD ET AL

of detecting the F progeny of a single overwintered female weevil and a 100% probability of detecting the F« progeny when infield traps were spaced 64 m apart.

INTRODUCTION

The need to control the boll weevil (Anthonomus grandis Bohe- man) and other cotton insects, particularly the bollworm (Heliothis zea (Boddie)) and the tobacco budworm (il. virescens (F.)), has resulted in the development of highly effective insecticides that are applied during the fruiting period of the cotton plant to protect the developing crop from damaging pests. Cooke and Parvin (1982) estimated that the cost of the insecticides (does not include application costs) used on cotton was $235 million in 1978. Parencia et al. (1982) stated that estimated losses in yield due to the boll weevil from 1903 to 1950 averaged 10%. The National Cotton Council put the estimated costs of insecticide and application directed against boll weevils at $260 million annually for 1970-72 and noted that losses in yield in the southeastern United States were set at 11-23%.

The use of pheromones to suppress populations of pest insects or as part of an integrated management or eradication system may allow us to reduce our reliance upon insecticides while reducing costs and insect losses since pheromones evoke natural responses in insects. However, the pheromone must be used in such a way that it will elicit the desired response. Also, usage must be synchronized with development of the natural population and must be appropriate to the actual size of the population. In this chapter, we report on the efforts made to use pheromones to control Heliothis spp. and boll weevils in cotton.

PHEROMONES OF HELIOTHIS ZEA AND H. VIRESCENS

In 1962-63 in tests conducted at Oxford, NC (Gentry et al. 1964), to determine the sex attractant of the tobacco budworm, virgin females at least 4 days old were observed to attract males. Berger et al. (1965) subsequently found that extracts of adult female _H. zea and _H. virescens elicited responses by males when conditions were carefully controlled. Mitchell et al. (1974), in later small-scale field tests with traps, found that extracts of calling Jl. virescens were attractive to males.

Roelofs et al. (1974) and Tumlinson et al. (1975) reported the isolation and identification of two components of the H. virescens pheromone, (_Z)-11-hexadecenal (Z^-11-HDAL) and (Z^)-9-teTradecenal (_Z-9-TDAL), better known as virelure (Hendricks et al. 1977). The ratio of the two components in extracts of live females was 16 parts ^-11-HDAL to 1 part ^-9-TDAL. Klun et al. (1979, 1980a, 1980b) concluded that H. zea females produce a mixture of (Z)-ll-

PHEROMONES FOR SURVEY, DETECTION, CONTROL 181

HDAL, (Z^)-9-hexadecenal, (_Z)-7-hexadecenal, and hexadecenal. Con- currentTy, Klun et al. (1980a, 1980b) concluded that the sex pheromone of H. virescens contained these same four components plus Z-11-HDAL, tetradecenal, and Z^-9-TDAL. These recent identifi- "cations of the sex pheromones of H. zea and H. virescens may be useful in suppression programs. Additional research will be required to determine their usefulness and the approach required for effective population suppression.

Dispensing System for Heliothis spp. Pheromone

Hendricks and Tumlinson (1974), working with the two components of H. virescens pheromone identified earlier, concluded that an ether e^xtract from the crude extract from females or 500 mg of the 16:1 ratio of the two synthesized components (virelure) in hex- ane were attractive to males for only 3-4 hours. They also concluded that higher doses (50 mg) of virelure dispensed from filter paper were not attractive for more than 6 hours during a single night and were completely unattractive by the second night.

Subsequently, Hendricks et al. (1977) found that mixing the two components of virelure with adhesive and laminating the mixture between two layers of vinyl polymer plastic sheets (formulated by Herculite Protective Fabrics Corporation, New York, NY 10010) prolonged attractiveness to the point that 1.3- x 2.5-cm segments (dispensers) containing 20 mg of virelure were attractive at least 7 days and had minimum loss of attractiveness for 21 days. Also, Sparks et al. (1979a, 1979b) reported that in field tests the four-component H. zea pheromone and the seven-component H. virescens pheromone were highly attractive to males when they were dispensed from cigarette filters; however, these baits were attractive for only a few hours. They also reported that the formulation of the seven-component H. virescens pheromone was approximately three times as attractive as virelure when evaporated from cigarette filters.

On the other hand, Hartstac^ et al. (1980) found that laminated plastic dispensers (3.3 cm ) containing 20 mg of the seven- component pheromone were no more attractive than similar dispensers (6.7 cm ) containing virelure and that both were ca. 60-70% as effective as five virgin females. The laminated plastic baits were effective attractants for at least 14 days in the field.^ They also found that rubber septa containing 20 mg of virelure (Flint et al. 1979) were as attractive as the laminated plastic dispensers; however, rubber septa containing the seven components were significantly less attractive. (The reason for the difference in attractiveness of the seven-component H. virescens pheromone dispensed from cigarette filters and from laminated plastic dispensers is not known, but it probably involves the rate of dissipation of the various chemicals from the laminated plastic dispenser.) In addition, the four-component Ö. zea pheromone (10 mg formulated in laminated plastic; 6.7 cm ) and rubber septa (20 mg of pheromone)

"•02 E. P. LLOYD ET AL

dispensers were both significantly less attractive than virgin females (ca. 35 and 20%, respectively). The attractiveness of both these dispensers was increased when the amount of pheromone was reduced to 2.5 mg per dispenser. The laminated plastic baits were effective for at least 14 days.

Lopez et al. (1981) found that when they reduced the dosage of pheromone to 2.5 mg per bait (6.5 cm ) and used a thinner plastic, the four-component E. zea pheromone in a laminated plastic dispenser was very effective for at least 11-14 days.

Development of Heliothis spp. Pheromone Traps

For many years, major efforts have been made to develop and use traps to monitor or control populations of Heliothis spp. As the pheromones became available, the effort has taken another turn, partly because of the inconvenience of providing the electric power required by grid traps (Hollingsworth et al. 1963). One of the resulting pheromone traps, the pie plate or sticky trap (Snow and Copeland 1969), consists of two opposed 27.5-cm plastic plates joined centrally to maintain a 2.5-cm, 360** opening in a 4-cm-diameter x 6-cm-high cylinder shaped from 8- x 8-mesh hardware cloth. The upper surface of the lower plate is coated with Stikem. This trap is inexpensive and portable but relatively inefficient. A more efficient trap, the wind vane trap (Sparks et al. 1979a), was developed to catch male moths alive. It is made of plywood, sheet metal, and hardware cloth, and it turns so the entrance is always downwind, which means there is an opening for moths flying upwind toward the bait. Once through the opening, moths fly up and are trapped in a cage at the top of the trap. This trap, though efficient, is expensive to build and requires wind at all times for proper orientation.

The cone (or TP) trap with a pheromone source as bait that was designed and developed by Hartstack et al. (1979) has proved to be very efficient in capturing adult male Heliothis spp. Both the 50- 25 and 75-50 versions are similarly constructed of galvanized wire (hardware cloth, 8x8 mesh) and consist of two inverted wire cones, one inside the other. The outer cone has a base diameter and height of 50 or 75 cm, and the inner cone has the same diameter but a much flatter slope and no top. Thus, moths enter through the openings (50 and 25 cm for the 75-50 and 50-25 traps, respectively). The large trap will capture ca. 1.62 times as many moths as the 50-25 trap.

The performance of Heliothis spp. pheromone traps changes with time, primarily because of changes in the density of the population, which alters the competitiveness of the traps vis-a-vis native females. In the spring and early summer, recovery of released marked moths was as high as 9.15%; at that time, nightly catches of ca. 10 moths per trap indicate field popujations estimated at one

PHEROMONES FOR SURVEY. DETECTION, CONTROL 183

moth per ha. In August, recovery was only 1.83% (Hartstack and Witz 1981).

Use of Pheromone for Control of Heliothis spp.

Methods of using pheromones to control populations of Helio- this spp. consist primarily of disruption and mass trapping. Some tests of disruption in small-scale field plots have shown reduction! in pheromone trap catches (Mitchell et al. 1975), and these may or may not reflect reductions in mating and thus some degree of control. No control has yet been demonstrated in large-scale field tests. Possible causes for this failure are migration of moths in- to fields from outside and short life of the pheromone formulations. Within the next few years, researchers should develop much better formulations, and control by disruption may be possible.

No mass trapping experiments with Heliothis spp. pheromone traps have been conducted to date. However, now that efficient traps are available, this concept should be tested where populations are low. For exampl.e, mass trapping in large areas in the spring when overwintering moths are emerging could reduce spring populations significantly. The resulting suppression could delay the onset of serious Heliothis spp. pressure and might mean that the crop would escape damaging infestations in August.

PHEROMONE OF THE BOLL WEEVIL

Seasonal Response of the Boll Weevil to Its Pheromone

Croso and Mitchell (1966) reported that male boll weevils feeding on cotton plants attracted female boll weevils at distances of 9.1 m or more. Hardee et al. (1969) observed that in the spring, traps baited with live males were more attractive to both sexes of overwintered boll weevils than weevil-free cotton plants. Mitchell and Hardee (1974) then reported that when pheromone-baited traps were placed in the field during the fruiting period of the cotton plant, nearly all of the field-generation weevils captured during July and early August were unmated females. However, Mit- chell et al. (1976) subsequently found that before squaring, more males than females were captured in traps; during midseason (July and August), many more female weevils were captured (280 to 24 males); and during September, as the crop matured, substantial numbers of males were captured. Therefore, during emergence of the weevil population from overwintering in the spring before squaring, the boll weevil pheromone functions as an aggregating pheromone. Then, during the fruiting period of the cotton plant, it functions almost entirely as a sex pheromone. Finally, in the fall when weevil populations are often large, feeding and oviposition sites are limited in some fields, and weevils move from one field to another, the boll weevil pheromone again serves as an aggregating pheromone.


Isolation, Identification, and Synthesis of the Boll Weevil Pheromone

Keller et al. (1964) reported that a substance that was attractive to female boll weevils in the laboratory could be collected by drawing air over males, passing the air through activated charcoal, and extracting the charcoal with chloroform. Hedin (1976) found that extractions of males with dichloromethane produced a substance that was consistently attractive to females. The substance was even more attractive when it was steam distilled and solvent extracted. Tumlinson et al. (1969) found that when the frass of males (and later that of mixed sexes) was steam distilled, it too was highly attractive to males. Tumlinson et al. (1971) isolated, identified, and synthesized four terpenoid compounds ((+)-cis-2-isopropenyl-l-methlcyclobutaneethanol; (Z^)-3,3-dimethyl-

A-"^' cyclohexaneethanol; (Z^^-3,3-dimethyl-A cyclohexaneacetalde-

hyde; and (£)-3,3-dimethyl-A '^ cyclohexaneacetaldehyde) as the components of the pheromone of live male boll weevils. The synthesis and structural assignments of the four compounds are also reported by Tumlinson et al. (1971).

Later when McKibben et al. (1977) steam distilled frass of female boll weevils, they obtained an extract that was more attractive to males than to females in the laboratory; and when these extracts were purified by thin-layer chromatography, they were only attractive to males. The active components appeared to be alcohols and hydrocarbons. However, females were estimated to produce only 0.01 as much pheromone as the males, which explains the failure of earlier workers to find this pheromone.

Dispensing Systems for the Boll Weevil Pheromone

As noted, the pheromone produced by male boll weevils is a mixture of the two terpenoid alcohols and two aldehydes that were isolated, identified, and synthesized by Tumlinson et al. (1969). However, when the mixture of the synthesized components, grandlure, was dispensed in field tests by applying solutions to chromatography supports such as firebrick, these release systems were attractive for only a few hours. McKibben et al. (1971) therefore screened a number of polymers as controlled-release additives and found polyethylene glycol the most effective in controlling the release of grandlure. Where grandlure was added to polyethylene glycol heated to ca. 40°C and then poured into empty gelatin cap- sules, the response of test weevils increased as the concentration of grandlure was increased. Hardee et al. (1972) then found that a formulation of grandlure containing glycerol, water, and methanol dispensed first from cotton dental rolls and then from cigarette filters was 80% as attractive for just under 7 days as live, caged males fed on cotton squares.

In 1972, a commercial gel formulation of grandlure was prepared by Zoecon Corporation (Hardee et al. 1974) and was used in


the Pilot Boll Weevil Eradication Experiment (PBWEE) then underway in southern Mississippi. Also, McKibben (1976) developed a cottonseed oil base gel formulation of grandlure that was tested in the PBWEE. These dispensers were improvements over the cigarette filter dispenser because they released grandlure for almost 2 weeks. However, Bull et al. (1973) were able to slow the rate of release of grandlure from the cigarette filter dispenser by placing it in an open glass vial (filter-in-vial system) that functioned as a physical barrier.

Bull (1976) later described a physical barrier formulation devised by A. Higgins, F. Boyd, and D. Whittam of the Animal and Plant Health Inspection Service, U.S. Department of Agriculture. A special paper cartridge was used instead of the glass vial to reduce costs and facilitate aerial distribution. Also, McKibben (1972, 1974) devised and improved a device that made it possible for one operator to inject grandlure into 3000 cigarette filters in 1 hour. A laminated plastic dispensing system for grandlure developed by Health-Chem Corporation was described by Hardee et al. (1975). Four thicknesses of these three-layer vinyl polymer lami- nates (ca. 0.5, 1.0, 1.5, and 2 mm thick) were placed in a clearing within a wooded area where no cotton was grown within 8 km, and laboratory-reared female boll weevils were released. The thicker dispensers appeared to retain grandlure longest in the field, but all were effective dispensers.

Because the polyethylene glycol filter-in-vial system was inexpensive and easily formulated, more than one million of these dispensers were used from 1973 to 1977. Dosage of grandlure per dispenser was 3 mg when effectiveness was needed for 1 week, 8 mg for 2 weeks, and 24 mg for 4 weeks. In Leggett traps, these grandlure dispensers were placed on top of the inverted floral liner (various formulations were placed at several locations on the „ Leggett traps); in infield traps, they were placed in the 5-cm plastic capture box on the top. However, the capture box slowed the rate of release of the grandlure because it constituted an additional barrier and the rate of release from an unprotected filter was too rapid. McKibben et al. (1980) therefore conducted analytical studies of several impervious coverings for the cigarette filter to optimize the rate of release of grandlure. As a result, a commercially available polyester-wrapped cigarette filter became available in early 1978. In field tests conducted at five locations, McKibben et al. (1980) found that a filter of this type placed inside the capture box was the most attractive of all grandlure dispenser systems tested. It was used as the standard dispenser for the Boll Weevil Eradication and Optimum Pest Management Trials in 1978 and 1979.

Development of Boll Weevil Pheromone Traps

The first field tests with traps baited with male boll weevils were conducted by Cross et al. (1969) in Mexico and Florida and


near Mississippi State, MS. Of the 12 types of traps tested, a solid wing trap and an oblique funnel trap appeared most efficient when live males fed on fresh cotton squares were used as bait. However, the wing traps were coated with Stikem; weevils entering the oblique funnel traps were simply captured in a box that was not coated with an adhesive. Therefore, a Stikem-coated plywood wing trap painted dark green and baited with males fed on cotton squares or artificial diet was used in most field tests. Then in 1968, Cross et al. (1971) reported that white or bright-yellow traps were more attractive to boll weevils than the darker green traps. As a result, metal wing traps, 30 cm wide x 25.4 cm high, painted canary yellow but similar in construction to the plywood wing trap, were used in most 1969 field tests. Later, in 1968, Cross et al. (1976), in detailed studies with traps painted various colors, found that wing traps painted a fluorescent yellow (solar yellow) were the most attractive. Also, in 1970, Cross et al. (1971) devised a Stikem-coated wing trap made from plastic-impregnated, 2.1-liter paper cartons that were painted with a daylight fluorescent saturn yellow paint. These traps were 19 cm wide x 25.5 cm high and were constructed by trimming two unformed cartons and sta- pling them together so that they formed a wing trap when unfolded. Subsequently, Leggett and Cross (1971) developed the so-called Leg- gett trap, a nonsticky trap constructed from a floral liner 29.21 cm high. It was painted daylight fluorescent yellow and capped with a screen cone (held just off the inverted liner with glass beads or other spacers) that had a small hole in the apex, which opened into a 5-cm plastic box. The completed trap was mounted on a stake ca. 1.22 m above the ground. A small cube of Vapona No- Pest strip placed in the box killed captured weevils. When Leggett et al. (1975) compared the Leggett trap with seven other designs, the Leggett trap captured significantly more weevils than the other traps. It also caught as many weevils when the screen cone and capture box were placed on top of the inverted floral liner (Leg- gett trap) as when the floral liner was coated with Stikem (Whittam trap).

Mitchell and Hardee (1974) designed an infield (Mitchell) trap that was similar to the Leggett trap but had a smaller base for use inside cotton fields. This trap was constructed of a 1-liter soda cup (inverted), painted saturn yellow, and topped with a screen cone that was fastened to the cup with brass fasteners. A 5-mm hole in the apex of the cone opened into a 5-cm plastic box. Ten or twelve triangular-shaped openings cut in the top of the cup allowed weevils to pass from the cup upward into the capture device. Dickerson et al. (1981) modified the Mitchell trap to reduce cost and facilitate mass production. The modified Mitchell trap appeared to be ca. 1.4 times more efficient than the original Mit- chell trap in capturing weevils.


Male-Baited Traps Around Cotton Fields for Suppression of Overwintered Boll Weevils

Because of the discovery that the male boll weevil emits a pheromone, many researchers made an effort to use male boll weevils to capture a sizable proportion of the overwintered population as it emerged in the spring. For example, Hardee et al. (1971), in an area with a very low population of native boll weevils, compared the following six treatments: (1) one wing trap per 0.4 ha, around the field; (2) one wing trap per 0.4 ha, in the field; (3) one-half wing trap per 0.4 ha, in the field and one-half wing trap per 0.4 ha, around the field; (4) one wing trap per 0.4 ha, around the field plus untreated trap plots of cotton; (5) one wing trap per 0.4 ha, around the cotton field, plus aldicarb-treated trap plots of cotton; and (6) one wing trap per 0.4 ha, around the field in three tiers. The wings of these traps were constructed of sheet metal, painted canary yellow, coated with Stikem, and mounted on reject hoe han- dles. The traps were baited with laboratory-reared boll weevils (weevils in transit from Mississippi State, MS, to the Crosbyton, TX, area were fed on artificial diet) that were provided with artificial diet, seedling plants, squares, or bolls as available. During the spring trapping period, from May until August 22, the traps captured an average 0.64 weevils per trap from field populations estimated at 0.08 to 0.21 weevils per 0.4 ha. Although all treatments therefore suppressed the boll weevil population by 62.6-100%, the small size of the populations made it difficult to ascertain the most effective treatment.

Boyd et al. (1973), in a large-scale trapping experiment conducted on 30,000 ha of cotton in the Rolling Plains area of west Texas in 1969, evaluated the effectiveness of Stikem-coated wing traps painted canary yellow, baited with male weevils, and placed around all of the cotton fields. Approximately 26,000 traps captured 10,159 weevils between April 23 and July 23, and at least one weevil was captured in 14.7% of the traps. The fact that about 85% of the traps captured no weevils indicated that the location of individual traps was very important. In addition, 85% of captured weevils were trapped between May 28 and June 25. As in the test reported by Hardee et al. (1971), the degree of suppression of the overwintered boll weevil population achieved was difficult to assess since the population was generally low and the area was very large, but infestations did develop in 19.2% of the fields by August 27.

Lloyd et al. (1972a), in an areawide trapping experiment, installed approximately one trap per 0.4 ha around 1600 ha of cotton in Monroe County, MS, in the spring of 1969 following a voluntary


grower-sponsored reproduction-diapause control program conducted during the fall of 1968. Again, Stikem-coated wing traps painted canary yellow and baited with males were placed around the cotton fields in April. Traps were baited beginning on April 29 and were supplied with fresh males twice a week through August 22 except for 3 weeks when they were baited only once a week.

Because the reproduction-diapause control program was voluntary and implemented by individual growers, effectiveness varied. The result was sizable boll weevil populations in some parts of the test area. These larger populations reduced the effectiveness of the trapping program, but they also provided an opportunity to assess the efficiency of the traps against populations of varying sizes. The results are shown in Table 1. Clearly, as the population increased, trap efficiency decreased.

As a part of the same experiment, trap densities of one, two, four, and eight traps per 0.4 ha were compared. Although the number of weevils captured per trap did not differ, the total numbers of weevils trapped per 0.4 ha by one, two, four, and eight traps per 0.4 ha differed greatly, 7.16, 9.37, 17.73, and 34.60, respectively, and more weevils were observed in fields with more ty^ps. Thus more traps apparently attracted more weevils into the vicinity of the fields because more weevils were captured on the traps and more weevils were observed in the fields with the greatest numbers of traps. The most efficient arrangement in this experiment was two traps per 0.4 ha.

Roach and Ray (1972), in field experiments conducted in 1970 at the Pee Dee Experiment Station near Florence, SC, and Socastee, SC, used 10 traps per 0.2-ha cotton field (20 traps per 0.4 ha) to capture emerging overwintered boll weevils. These trap densities appeared to suppress the native overwintered population and prevented damage until the F^ field generation emerged in early

August.

Results of these large-scale field experiments with male- baited sticky traps placed around cotton fields therefore indicated that efficiency was inversely related to density of overwintered boll weevils. Traps suppressed low populations, but large populations were not affected.

Pheromone-Baited Traps in Crops for Suppression of Overwintered Boll Weevils

Mally (1901) observed that in a given area, those cotton fields planted first were the first to be infested by the boll weevil and suggested that a few rows of an early-maturing variety should be planted so emerging weevils would gather there and be trapped. Hunter (1912) did not believe that weevils emerged early enough from overwintering quarters so that a trap plot would concentrate appreciable numbers. Much later, Isley (1950) reported

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that in Arkansas, trap plots 3-30 rows wide did concentrate overwintered boll weevils where they could be destroyed more easily with insecticides; his suggestion resulted in "spot dusting" by small cotton producers on upland or hill soils.

After Cross and Mitchell (1966) discovered the response of female boll weevils to the male pheromone, interest was renewed in attracting and concentrating overwintered boll weevils into trap crops where they could be killed without treating the entire field. The resulting reduction in insecticide usage became important when Ridgway et al. (1968) found that the systemic insecticide, aldicarb, though it was highly effective in suppressing populations of overwintered boll weevils, did produce outbreaks of bollworms and tobacco budworms.

Bradley (1967) found that in Louisiana, overwintered boll weevils could be expected to congregate in early planted border strips provided that the difference in planting dates was sufficient to give a height advantage to the trap crop. Lloyd et al. (1972b), in a large-scale field experiment conducted in 1970 in Grenada County, MS, compared weevil populations in untreated fields and in fields treated with (1) traps only (sticky wing traps baited with males placed around cotton fields at the rate of one trap per 0.4 hectare); (2) traps plus aldicarb-treated strips of cotton (male- baited traps installed at the same rate but concentrated on two sides of the field adjacent to strips treated with aldicarb); (3) bait males (sterile males restricted by gluing wing covers together) placed 7.6 m apart on rows adjacent to two sides of fields; and (4) restricted sterile males placed 7.6 m apart on the second of four untreated rows adjacent to aldicarb-treated strips on two sides of the fields.

The boll weevil population in the test area was low as a result of a diapause control program in the fall of 1969 and a severe winter. The effectiveness of the treatments was therefore appraised by noting the dates on which fields exposed to each treatment needed insecticidal control for boll weevils.

Average number of days after July 21 before

Treatment application of insecticide J_/

Males only 16.42 a Untreated 19.28 a Traps only 23.28 ab Traps + strips 27.14 b Males + strips 30.00 b

\J Numbers followed by the same letter are not significantly different at the 5% level according to Duncan's multiple range test.


Scott et al. (1974) also evaluated the use of trap crops in fields (1) planted 2 weeks early to an early fruiting variety, Qua- paw, treated with aldicarb, and then baited with grandlure; (2) planted as in (1) but on the normal planting date and treated with aldicarb; and (3) planted on normal planting date, without grandlure. Trap crops, with and without grandlure, proved to be much more attractive than the normal plantings until the normal planting began squaring, an indication that the early response of the boll weevil was to early fruiting as well as to the grandlure. However, after squaring began in the normal planting, trap crops with grandlure were more attractive than those without grandlure.

Rummel et al. (1976), in 3 years of field tests on the Rol- ling Plains of Texas, failed to obtain consistent suppression of boll weevils with trap crops; however, they found that in Glascock County, TX, early planted, aldicarb-treated trap crops effectively suppressed populations of overwintered weevils and prevented the development of damaging infestations. Gilliland et al. (1976), in southern Mississippi, also found trap crops to be an effective means of concentrating and suppressing emerging boll weevil populations if the trap crops were planted earlier than the main crops and if pheromone bait stations were used.

The use of trap crops has not had wide acceptance in the Cot- ton Belt because the northern parts have cool weather early in the season and growers in the warmer parts have such heavy demands on their time during the period when trap crops should be planted. However, in many sections, early planting of a trap crop of early fruiting varieties and subsequent baiting of traps with grandlure will attract a very high percentage of emerged overwintered weevils until squaring begins in normal plantings. Trap crops therefore represent a means of suppressing early-season boll weevils by treating or trapping only a small percentage of the crop. They should be considered one of several tools for improved management of cotton insects.

Infield Traps and Insecticides for Boll Weevil Suppression

Knipling (1979), on the basis of simulation models, advanced the following hypothesis: the total suppressive action of two methods of control that differ in efficiency when insect populations are high or low may be substantially greater than the sum of the action of each method used alone. This would occur if at least one of the methods potentiates the action of the other method and if the efficiency of the first method is enhanced when the pest population is low. Also, some suppressive techniques may be mu- tually potentiating, resulting in an even greater increase in efficiency. An example of the potentiating effect cited by Knipling would be the concurrent use of infield traps and the application of insecticides for boll weevil suppression. The insecticide


applications should achieve essentially the same degree of kill regardless of the density of the boll weevil population; however, the efficiency of a given number of pheromone traps should increase as the boll weevil population is reduced.

We therefore have examined the total effect of calculating the degree of suppression that might be expected from insecticide applications alone, use of infield traps alone, and concurrent use of the two methods against a low level overwintered boll weevil population. The results are presented in Table 2.

The application of insecticides makes two important contributions to total suppression. The assumed kill of 90% of the boll weevils reduces the number that can reproduce. It also reduces tenfold the number of males that will be competing with the traps for the attraction of the surviving females that are seeking mates. Therefore, the ratio of traps to competing males will increase from 10:1 when traps only are used to 100:1 when insecticides are also applied. Efficiency of trap capture should thus increase from 91 to 99%. If these methods of suppression were used independently and acted independently and if each achieved 90% control, regardless of pest density, the suppression achieved by using the two concurrently would be only 99%. Theoretically, this degree of suppression would allow one successful mating and some potential progeny. In fact, the increasing effect of the traps as the population increases would seem to mean that no matings would be expected at the density assumed. The practical implications of such a high degree of suppression during a single generation are therefore reflected by the relative number of progeny of survivors that can be expected when the techniques are used alone and when they are used concurrently. We thus have an example of the possibilities when the boll weevil pheromone is appropriately integrated with other suppressive measures.

The theoretical findings were subsequently tested in the field. Mitchell et al. (1976) combined twice weekly applications of azinphosmethyl (0.11 kg per 0.4 ha) from appearance of pinhead squares (June 13) until July 6 with 10 infield traps per 0.4 ha. Results are shown in Table 3.

Thus 10 infield traps per 0.4 ha plus twice weekly treatment with insecticide prevented reproduction during the treatment period (Phase II). In fact, infiltration of some mated females from other cotton growing areas cannot be precluded though the experiment was conducted in an area some 40 km from other cotton. (W. A. Dicker- son, personal communication, captured a marked boll weevil 104.6 km from the release point.) Therefore, complete elimination of reproduction could not be achieved. The results obtained during Phase II, however, clearly indicate that concurrent application of insecticides and the operation of infield traps could be used against any isolated persisting infestations or new infestations should a beltwide eradication program be undertaken.

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Table 3.—Capture of boll weevils in infield traps (10 per 0.4 ha) on 43.2 ha of cotton near Havana, AR, 1974

Number of boll weevils captured

Date Males Females Total

Phase I 1 [no insecticide treatments) 171 103 274 336 205 541 364 277 641 114 156 270 158 217 375

1143 958 2101

*hase II (twice weekly insecticide treatments) 45 58 103 2 9 11

1/5 0

1/7 3

1/12 3

1 53

0 77

1 131

Phase III (no 1 insecticide treatments) 0 50 50 1 1

52 102

53 103

Phase IV (no i insecticide treatments) 1 83 84

10 37 47 2 13 15

10 45 55 87 353 440 92 364 456

132 239 371

May 21 May 27 June 3 June 10 June 13

Total

June 17 June 21 June 26 July 2 July 9

Total

July 12-19 July 23-31

Total

August 2-8 August 13 y August 19-23 August 26 September 4 September 10 September 17

Total 334 1134 1468

\J Sex of one weevil not determined. 2_/ An application of monocrotophos + azinphosmethyl (0.45 + 0.11

kg per 0.4 ha) applied for control of bollworms and boll weevils on August 14.

Infield Traps for Detection and Suppression

Detection of boll weevils when populations are low is essential to any evaluation of containment and eradication programs. However, visual examination of a large number of plants for live insects or damage is laborious and costly and is also a relatively insensitive procedure when populations are low, particularly when progeny of reproducing females are closely clumped. Infield traps


baited with grandlure appeared to be a more sensitive method of detection. A field test was therefore conducted by Leggett et al. (1981) to determine the sensitivity of different densities of traps for the detection of the F, progeny that would be expected from a single overwintered female weevil reproducing naturally in a cotton field. A clump of 20 infested squares was placed in special weevil-free fields. In fields with one trap per 0.4 ha, the trap catches allowed detection of four of seven of the reproducing clumps in the F, generation; in fields with four traps per 0.4 ha, the trap catches allowed detection of seven of seven of the clumps.

In the initial special field tests of Leggett et al. (1981), one and four traps per 0.4 ha were spaced 64 m and 32 m apart, respectively, but the number of traps per hectare equaled the number of hectares times the desired trap density. In order to more fully understand the influence of trap densities and spacing on the probability of detecting and controlling small isolated reproducing clumps of boll weevils, Lloyd et al. (1980) conducted a series of field experiments in 1979 in a noncotton area (Surry County, NC) that was more than 129 km from the nearest commercial cotton plantings. By using this site and creating known infestations, they eliminated competition from unknown competing males. From July 9 for 9 days, overwintered female weevils were allowed to deposit eggs in cotton squares at the Agricultural Research Service, Cotton Production Research Laboratory, U.S. Department of Agriculture, Florence, SC. The squares were then held on moist sand in an out- door insectary to simulate natural conditions as closely as possible. Ca. 10-12 days later, the squares were transported to Surry County by automobile and placed near the center of 24 cotton plots (average 1.28 ha) laid out so they were 3.2 or more km apart. Sites for the squares were selected on the basis of the usual pattern for such clumps of progeny. Treatments were as follows: 20 infested squares per clump with traps 64, 45, 36, and 32 m apart; and 10 infested squares per clump with traps 45 and 32 m apart. The resulting captures of emerged F, generation weevils are summarized in Table 4.

Knipling and McGuire (1966) and Knipling (1976, 1979) advanced the theory that the degree of control of insects obtained with pheromone-baited traps in a given area is governed by the relative attractiveness of the pheromone (competitive attraction) produced by calling insects present in the area. They set up theoretical models to estimate the potential value of traps for detection and for control. These simulation models and assumed parameters have proved useful in experimental design and interpretation of data obtained in these investigations.

The more important variables that govern efficiency of traps used for detection and control of boll weevils include: (1) the attractiveness of the pheromone emanating from the traps v. the attractiveness of the pheromone disseminated by the males; (2) the number of traps and the distribution of traps v. the number and


Table 4.—Summary of capture of F and F^ generation boll weevils with infield traps in test fields, Surry County, NC, 1979

Average number captured Distance (m) F F

^ "^2 ^^1. between tri ips

.4 ha)

20

emerging

(traps per 0. Males Females Total weevils from squares

infested squares per clump 64 (1.9) 2.0 17.5 77.0

45 (3.6) 0.2 3.0 15.2 78.0

36 (4.2) 1.0 5.5 9.5 73.0

32 (5.7) 10

0.7 6.7 5.7 infested squares per clump

63.0

45 (3.0) 0.2 2.7 5.0 77.0

32 (6.6) 0.5 3.0 2.0 76.0

distribution of the pheromone-producing males and the mate-seeking females; (3) the area within which a trap and competing males can elicit a response from mate-seeking females; and (4) the actual efficiency of the traps in capturing responding females (and males in the case of overwintered populations). Then if all traps in a field are as attractive as males and are equally near to mate- seeking females, we can calculate the proportion of the available females that will be captured by assuming that all females responding to the traps will be captured. When these calculations are related to actual capture, we can obtain clues to the type of action and the effectiveness of different densities of infield traps in relation to the distribution pattern of sexually active boll weevils. For example, the distribution of a given number of boll weevils entering a cotton field from hibernation will probably differ greatly from the distribution of the same number of F^ progeny emerging in a restricted area from one or more egg-laying females. Also, if traps are uniformly distributed in a cotton field, overwintered males and females will probably not aggregate because of the confusion (interference) produced by the synthetic pheromone emitted by the traps. On the other hand, F males emerging in a restricted area (clumps) would be expected to be more attractive than the synthetic pheromone to the emerging females in these clumps because the traps will usually be farther away than the emerging aggregated males.

To determine the theoretical capture rates for traps on the basis of the assumption that when traps and male boll weevils are uniformly distributed, traps are fully competitive in all respects with males for the attraction of mate-seeking females, we made the calculations presented in Table 5. Such estimates can then be compared with actual capture rates at given trap spacings and densities to arrive at the relative effectiveness of traps and males in attracting females. Critical comparison of the data should then help in identifying and evaluating factors governing the action and


Table 5.—Daily probability of capturing emerging F female boll weevils on 0.4 ha if males and traps are equally attractive l_l

Probability of capturing F, femal es with indicated distance (m) between tr aps 2/

Day of 64 45 36 32

emergence 1/ (1.95) (3.59) (4.23) (5.67)

1 0.66 0.78 0.81 0.85

2 0.49 0.64 0.68 0.74

3 0.39 0.55 0.59 0.65

4 0.33 0.47 0.51 0.58

5 0.28 0.42 0.46 0.53

6 0.25 0.38 0.42 0.48

7 0.22 0.34 0.38 0.44

8 0.19 0.31 0.35 0.41

Total 2.81 3.89 4.20 4.68

1/ Assumed one female and one male emerging each day. ~2_l Number traps per 0.4 ha in parentheses.

effectiveness of pheromone' traps for the detection and control of small populations.

A brief description of the method of calculations based on the equal competitiveness assumption may be helpful. The data for days 1 and 2 and the density of 1.95 traps per 0.4 ha will be cited as examples. On day 1, the numerical ratio of traps to one competing male is 1.95:1 for the attraction of one mate-seeking female. The probability of female capture would be 0.66, and the probability of the female mating, therefore, would be 0.34. On day 2, the traps would be in competition with two males for the attraction of the one female seeking a mate on that day. The ratio of traps to males would be 1.95:2, and the probability of capturing the female would be 0.49.

Thus by the time of the emergence of the approximately eight males and eight females in each field, the traps will be more competitive than the males in capturing females. Theoretically, the 4.23 traps per 0.4 ha, spaced 36 m apart, should capture 4.2 females per replicate. In fact, actual capture was 5.5 females per replicate. Also, the 5.67 traps per 0.4 ha, spaced 32 m apart, should capture 4.68 females per replicate; they actually captured 6.75. Plainly, the higher density of traps and the proximity of the traps to the clumps of F, progeny resulted in a concentration of pheromone that competed effectively with the pheromone produced by the males. Most females were eventually drawn to the traps rather than to the competing males.

These results are of great practical significance since they suggest that such trapping may be highly effective in suppressing

198 E. P. LLOYD ET AL.

and managing low populations of boll weevils. Not only is the ratio of traps to competing males a major factor in efficiency but so also is the greater volume of pheromone due to the shorter distance from the traps to females. For example, distribution appears to be so important that the system will likely be even more effective against scattered individual overwintered boll weevils as they enter cotton fields than it is against females emerging in the clumps. If that hypothesis is correct, this system of suppression deserves high research priority, specifically in regard to reduced cost of traps and pheromone, prolongation of effectiveness of pheromone, and increased efficiency of actual capture.

In the test by Lloyd et al. (1980), infield traps spaced 64 m apart detected four of four clumps. However, the traps were so arranged that the entire field was covered with a reasonably uniform array. (The first trap was installed approximately 4.6 m from one field corner, and the rest of the traps were 64 m apart.) The data indicate that 94% of the time, the F progeny of a single-mated overwintered female will be detected with such a spatial arrangement. As Table 4 shows, all arrangements detected F^ generation weevils. These results therefore support the conclusions reached by Leggett et al. (1981) that infield traps provide a highly sensitive method of detecting the existence of boll weevil infestations resulting from a single reproducing female in a cotton field of any size.

In addition, significant suppression of the F generation was achieved when traps were spaced 36 and 32 m apart. This reduction is reflected by the rate of capture of F« females at all trap densities (Table 4). If reproduction had been normal, the average F^ populations should have been similar in the four replicates of each trap spacing and density, and capture of F^ females should have been low at the lowest trap density and high at the highest trap density.

We estimate that 80% or more of the F. females were captured when traps were spaced 36 m apart and probably more than 90% of the F. females were captured when traps were 32 m apart. These results indicate the potential value of grandlure for both detection and control. They also suggest that high density trapping can be used to manage populations of boll weevils that originate from low overwintered populations.


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1972a. Evaluation of male-baited traps for control of boll weevils following a reproduction-diapause program in Monroe County, Mississippi. Journal of Economic Entomology 65:552- 555.


Lloyd, E. P., W. P. Scott, K. K. Shaunak, F. C. Tingle, and T. B. Davich.

1972b. A modified trapping system for suppressing low-density populations of overwintered boll weevils. Journal of Economic Entomology 65:1144-1147.

Lopez, J. D., Jr., T. N. Shaver, and A. W. Hartstack, Jr. 1981. Evaluation of dispensers for the pheromone of Heliothis

zea. Southwestern Entomology 6(2): 117-122.

McKibben, G. H. 1972. A device for injecting grandlure into cigarette filters. Journal of Economic Entomology 65:1509-1510.

1974. An improved device for dispensing pheromone solutions. Journal of Economic Entomology 67:558.

1976. Composition for attracting the cotton boll weevil. U.S. Patent 3,803,303.

D. D. Hardee, T. B. Davich, R. C. Gueldner, and P. A. Hedin.

1971. Slow-release formulations of grandlure, the synthetic pheromone of the boll weevil. Journal of Economic Entomology 64:317-319.

P. A. Hedin, W. L. McGovern, N. M. Wilson, and E. B. Mitchell.

1977. A sex pheromone for male boll weevils from females. Journal of Chemical Ecology 3:331-335.

W. L. Johnson, R. Edwards, E. Kotter, J. F. Kearney, T. B. Davich, E. P. Lloyd, and M. C. Ganyard.

1980. A polyester-wrapped cigarette filter for dispensing grandlure. Journal of Economic Entomology 73:250-251.

Mally, F. W. 1901. The Mexican cotton-boll weevil. U.S. Department of Agri-

culture, Farmers' Bulletin No. 130, p. 11-12.

Mitchell, E. B., and D. D. Hardee. 1974. Infield traps: a new concept in survey and suppression

of low populations of boll weevils. Journal of Economic Ento- mology 67:506-508.

E. P. Lloyd, D. D. Hardee, W. H. Cross, and T. B. Davich.

1976. Infield traps and insecticides for suppression and elimination of populations of boll weevils. Journal of Economic Entomology 69:83-88.


Mitchell, E. R., J. H. Tumlinson, W. W. Copeland, R. W. Hines, and M. M. Brennan.

1974. Tobacco budworm: production, collection, and use of natural pheromone in field traps. Environmental Entomology 3:711- 713.

M. Jacobson, and A. H. Baumhover. 1975. Heliothis spp.: disruption of pheromonal communication with (Z^)-9-tetradecen--l-ol formate. Environmental Entom.ology 4:577-5"79.

Parencia, C. R., T. F. Pfrimmer, and A. R. Hopkins. 1982. Insecticides for control of cotton insects. U.S. Depart- ment of Agriculture, Agriculture Handbook. [in press.]

Ridgway, R. L., S. L. Jones, J. R. Coppedge, and D. A. Lindquist. 1968. Systemic activity of 2-methyl-2-(methylthio)propionalde- hyde 0^-(methylcarbamoyl)oxime (UC-21149) in the cotton plant with special reference to the boll weevil. Journal of Economic Entomology 61:1705-1712.

Roach, S. H., and L. Ray. 1972. Boll weevils captured at Socastee, South Carolina, in

1970, in wing traps placed around fields with and without growing cotton. Journal of Economic Entomology 65:599-560.

Roelofs, W. L., A. S. Hill, R. T. Carde, and T. C. Baker. 1974. Two sex pheromone components of the tobacco budworm moth, Heliothis virescens. Life Science 14:1555-1562.

Rummel, D. R., R. C. Mclntyre, and C. W. Neeb. 1976. Suppression of boll weevils with grandlure-baited trap

crops. In Detection and Management of the Boll Weevil With Pheromone. Texas Agricultural Experiment Station, Research Monograph No. 8, p. 53-61.

Scott, W. P., E. P. Lloyd, J. 0. Bryson, and T. B. Davich. 1974. Trap plots for suppression of low density overwintered

populations of boll weevils. Journal of Economic Entomology 67:281-283.

Snow, J. W., and W. W. Copeland. 1969. Fall armyworms: use of virgin female traps to detect males and to determine seasonal distribution. U.S. Department of Agriculture, Production Research Report No. 110.

Sparks, A. N., J. E. Carpenter, J. A. Klun, and B. G. Mullinix. 1979a. Field responses of male Heliothis zea (Boddie) to pheromonal stimuli and trap design. Journal of the Georgia Entomo- logical Society 14:319-325.


Sparks, A. N., J. R. Raulston, P. D. Lingren, J. E. Carpenter, J.

A. Klun, and B. G. Mullinix. 1979b. Field response of male Heliothis virescens (F.) to pheromonal stimuli and traps. Bulletin of the Entomological Society of America 25:268-274.

Tumlinson, J. H., D. D. Hardee, R. C. Gueldner, A. C. Thompson, P. A. Hedin, and J. P. Minyard.

1969. Sex pheromones produced by the male boll weevil: isolation, identification, and synthesis. Science 166:1010-1012.

R. C. Gueldner, D. D. Hardee, A. C. Thompson, P. A. Hedin, and J. P. Minyard.

1971. Identification and synthesis of the four compounds com- prising the boll weevil sex attractant. Journal of Organic Chemistry 36:2616-2621.

D. E. Hendricks, E. R. Mitchell, R. E. Doolittle, and M. M. Brennan.

1975. Isolation, identification, and synthesis of the sex pheromone of the tobacco budworm. Journal of Chemical Ecology 1:203-214.

207

Chapter 9

INSECT GROWTH REGULATORS WITH EMPHASIS ON THE USE OF BENZOYLPHENYL UREAS

D. L. Bull and J. R. Abies Cotton Insects Research Agricultural Research Service U.S. Department of Agriculture College Station, TX 77841

E. P. Lloyd Boll Weevil Eradication Research Agricultural Research Service U.S. Department of Agriculture Raleigh, NC 27607

ABSTRACT Insect growth regulators (iGR's) are highly selective chemical pesticides that interfere in different ways with the normal development of certain life stages of treated arthropods. Although many IGR's have been evaluated in laboratory and field experiments as alternatives to the conventional broad- spectrum insecticides currently used to control phytophagous pests of cotton, only a few substituted benzoylphenyl ureas have shown sufficient promise for practical use. Of these, only diflubenzuron has been approved by the Environmental Protection Agency for use on cotton. This IGR is effective against the boll weevil (Anthonomus grandis Boheman) and appears to have little adverse effect on populations of beneficial species or other important pests associated with cotton.

The results of extensive field experimentation suggest that diflubenzuron may be used to suppress low-to-moderate populations of the boll weevil. However, the chemical must be applied with an emulsifiable crop oil if it is to be adequately effective; applications must begin at the immediate onset of fruiting, that is, before overwintered boll weevils have a chance to initiate oviposition; and applications must be repeated at 5- to 7-day intervals to reinforce coverage of boll weevils present in fields and to insure contact with insects that will continue to emerge from hibernation quarters well into the fruiting cycle.

208 D. L BULL ET AL

The most effective use of diflubenzuron or a related product against boll weevils will probably be as a component of an integrated pest management system wherein community-wide applications of the IGR will complement other suppression strategies such as the early and complete postharvest destruction of stalks, fall applications of pesticides to reduce the overwintering generation of boll weevils, the planting of early maturing varieties of cotton, and, if necessary, the judicious and strategic use of conventional pesticides to reduce the numbers of overwintered weevils that emerge in early spring or the numbers that remain in fields after the applications of the IGR have been terminated.

INTRODUCTION

Many of the phytophagous pests found in cotton fields must be controlled if producers are to avoid unacceptable economic loss. However, the use of conventional insecticides against the so-called "primary" pests has tended to precipitate new problems. Primary pest species in cotton include the pink bollworm (Pectinophora gossypiella (Saunders)) and a lygus bug (Lygus hesperus Knight) in the western United States; the boll weevil (Anthonomus grandis Boheman) and the cotton fleahopper (Pseudatomoscelis seriatus (Reuter)) in the Southwest; and the boll weevil and the tarnished plant bug (Ly- gus lineolaris (Palisot de Beauvois)) in the Midsouth (Anonymous 1975TT These species are normally managed by using broad-spectrum insecticides. As a result, natural populations of entomophagous parasites and predators that normally hold populations of "secondary" pests in check may be reduced to the extent that these pests too attain primary status. When this occurs, the producer may either suffer substantial crop loss or become locked into a costly, sometimes futile, season-long need to apply insecticides.

Presently, the most important of the secondary pests in cotton are the tobacco budworm (Heliothis virescens (F.)) and the bollworm (R, zee (Boddie)). In fact, these species now have the status of major pests across much of the Cotton Belt (Bottrell and Adkisson 1977). According to recent estimates (Anonymous 1980), they account for as much as 35% of all losses attributable to insect damage to cotton. The problem is particularly severe in areas where populations of the tobacco budworm have developed resistance to organophosphorus insecticides and can be controlled only by using more costly materials.

Other potentially important secondary pests that may be released from the control of their natural enemies by pesticides to the point that they inflict economic damage, though usually on a more limited scale, include the cabbage looper (Trichoplusia ni

INSECT GROWTH REGULATORS 209

(Hubner)), the saltmarsh caterpillar (Estigmene aerea (Drury)), the cotton leafperforator, (Bucculatrix thurberiella Busck), the beet armyworm (Spodoptera exigua (Hübner)), and different species of spider mites.

In view of the problem with Heliothis spp. and the potential for new problems of the same kind, efforts are underway to find selective materials and methods that could be alternatives to broad- spectrum insecticides in the management of cotton pests. Some of these methods are discussed elsewhere in this handbook. We are concerned here with the potential of chemicals that manifest their activity through disruption of normal insect growth.

BENZOYLPHENYL UREAS AS INSECT GROWTH REGULATORS

A broad array of synthetic chemicals are included among the insect growth regulators (lGR*s) that are considered the third generation of pesticides. The chemicals that make up this group, though diverse, have two characteristics in common. They manifest biological activity by interfering in different ways with the normal development or functions of specific life stages of treated insects; and those that are approved or are being considered for use in pest control appear to be somewhat less detrimental to the environment and to nontarget organisms than most conventional chemical pesticides. Indeed, certain IGR's seem to offer the advantage of interspecific selectivity among some insect biocenoses to the extent that they favor natural enemies. The literature is replete with scientific reports and reviews of research on IGR's; for general reviews, the reader is referred to Menn and Beroza (1972) and Staal (1975).

Of the IGR's that have been evaluated for use in managing insect pests of cotton, only certain substituted benzoylphenyl ureas have shown sufficient promise for practical use. Currently, three of these materials (Figure 1) are being investigated intensively: ( 1 ) di f lubenzuron (N^-[ t (4-chlorophenyl)amino] carbonyl]-2 ,6-difluorobenzamide; Dimilin, TH 6040); (2) penfluron (2,6-difluro- N_-[[[4-(trifluoromethyl)phenyl]amino]carbonyl]benzamide; AI3- 63223); and (3) BAY SIR 8514 (2-chloro-N-[[[4-(trifluoromethoxy) - phenyl]amino]carbonyl]benzamide).

Diflubenzuron was introduced by Philips-Duphar B. V., Amster- dam, Holland, and developed in the United States by Thompson- Hayward Chemical Co., Kansas City, KS. Of the three benzoylphenyl ureas specified, only diflubenzuron is approved by the U.S. Envi- ronmental Protection Agency for commercial use in this country. It has conditional registration for use on cotton against the boll weevil and on forests for control of the gypsy moth (L3miantria dispar (L.) ).

Penfluron was originally synthesized by Philips-Duphar B. V. (Wellinga et al. 1973). Subsequently, Oliver et al. (1977)

210 D. L BULL ET AL

.0' '■^r"^

Ri

DIflubenzuron -CI 2,6-F2 Penfluron -CF3 2,6-F2 BAY SIR 8514 -OCF3 2-CI

Figure 1.—Structures of some benzoylphenyl urea compounds tested for use in cotton pest management.

synthesized penfluron and reported that it was considerably more active than diflubenzuron in inhibiting the hatch of boll weevil eggs. Because of this improved activity, penfluron may replace diflubenzuron as the chemical component of the combined treatment (irradiation and chemical) used to produce nonreproductive boll weevils for release in eradication experiments and programs. Pen- fluron is also being investigated for possible use as a foliar spray. In other studies (Chang 1979, Chang and Borkovec 1980), penfluron was more than twice as potent as diflubenzuron in inhibiting the hatch of eggs of the house fly (Musca domestica L.).

BAY SIR 8514 was introduced by Bayer A. G., Leverkusen, Ger- many (Zoebelein et al. 1980) and is being developed in the United States by Mobay Chemical Corp., Kansas City, KS. This IGR has been reported to be more effective than diflubenzuron against the house fly (Chang 1979), the fall armyworm (Spodoptera frugiperda (J. E. Smith)) (Zoebelein et al. 1980), and a black fly (Simulium vittatum Zetterstedt) (Lacey and Mulla 1978). Preliminary results of field and laboratory tests at Florence, SC, by R. F. Moore and A. R. Hopkins (private communication) indicate that BAY SIR 8514 is as active as diflubenzuron against the boll weevil. These investigators also observed that crop oil need not be added to BAY SIR 8514 to obtain effective insecticidal activity. (Diflubenzuron is essentially inactive without oil.)

DIFLUBENZURON

The preponderance of information concerning the use of the benzoylphenyl ureas in cotton pest management has been developed for diflubenzuron. Laboratory tests have shown that diflubenzuron is active against the pink bollworm when certain larval stadia are fed treated diet (Flint and Smith 1977), but it apparently is not effective against this pest in the field (Flint et al. 1978). Also, diflubenzuron has been generally ineffective in field tests


against Heliothis spp. (Taft and Hopkins 1975, House et al. 1978, Nemec 1978, Bull et al. 1979); the tarnished plant bug; the cotton fleahopper; the carmine spider mite (Tetranychus cinnabarinus (Boisduval)); and the cotton aphid (Aphis gossypii Glover) (Taft and Hopkins 1975, Nemec 1978). On the other hand, tests in field cages (Flint et al. 1977, 1978) indicate that diflubenzuron may provide good control of the cotton leafperforator, though information on practical control is apparently lacking. In addition, in both field and laboratory tests, diflubenzuron has been highly effective against the boll weevil. Thus, after it had been established that diflubenzuron affected reproduction in the boll weevil (preliminary unpublished observations reviewed by Taft 1978), Moore and Taft (1975) conducted the first documented study and demonstrated conclusively that diflubenzuron inhibited the hatch of boll weevil eggs in the laboratory. On the basis of observations associated with subsequent intensive investigations of the effect of diflubenzuron on the boll weevil, we can conclude that the boll weevil is the only major cotton pest that is significantly affected by field applications of diflubenzuron.

Mode of Action of Diflubenzuron in the Boll Weevil

The biological activity of diflubenzuron against invertebrates is attributed to destructive physiological events that are trig- gered when the chemical disrupts the synthesis of chitin, an essential structural component of insect cuticle (Mulder and Gijswijt 1973, Post et al. 1974, Verloop and Ferrell 1977, Hajjar and Casida 1979). Apparently, when adults of some species contact diflubenzuron or are fed the material, the eggs oviposited subsequently do not hatch. This result has been observed in the boll weevil (Moore and Taft 1975) and in several other species such as Spodoptera littoralis (Boisduval) (Ascher and Nemny 1974); the house fly (Gross- curt 1976); stable flies (Stomoxys calcitrans (L.)) and horn flies (Haemotobia irritans (L.)) (Wright and Harris 1976, Wright and Spates 1976); and several species of weevils that attack citrus (Schroeder et al. 1976, Lovestrand and Beavers 1980). The effect is caused by the ovicidal action of the IGR rather than by sterilization of the treated adult (Grosscurt 1976, Verloop and Ferrell 1977, Ivie and Wright 1978). Typically, embryonic development in an egg from a treated female appears normal until the expected time for eclosión. Grosscurt (1976, 1978) concluded that affected em- bryos of the house fly and the Colorado potato beetle (Leptinotarsa decemlineata (Say)) developed into larvae that were unable to leave the egg. He attributed this failure to the effect of diflubenzuron in disrupting the formation of chitin in the larval cuticle and the resulting incapacitation of muscular function. Moore et al. (1978) made similar observations in their study of the boll weevil; they also found that larvae that were able to emerge from the eggs of treated females were usually moribund.

Ample evidence is available to prove that the primary action of diflubenzuron against the boll weevil is manifested in the adult

212 D. L BULL ET AL

females and that the chemical is effective when it is ingested or when it is administered as a contact treatment. There is also evidence that it is the secretion of unmetabolized diflubenzuron in the eggs of treated female boll weevils that apparently accounts for the ovicidal effects (Bull and Ivie 1980). The same is true for the house fly and the stable fly (ivie and Wright 1978, Chang and Borkovec 1980). Moreover, the females probably must be exposed to the chemical directly to obtain maximum results. Moore et al. (1978) concluded that treated males probably could not transfer sufficient diflubenzuron during copulation to cause a substantial inhibition of egg hatch. Though holding topically treated males continuously with females in very small cages did produce some inhibition, such an indirect exposure of females to diflubenzuron seems unlikely to be of significant importance in the field.

14 In studies of the fate of C-labeled diflubenzuron after

topical application to adult virgin female boll weevils, Bull and Ivie (1980) demonstrated that the chemical was absorbed very slowly and that large amounts did not accumulate internally. For example, at 8 days posttreatment, ca. 64% of the applied diflubenzuron was unabsorbed, and internal radioactive material never exceeded 4% during the experimental period. Also, only ca. 3% of the applied diflubenzuron was metabolized by hydrolysis and conjugation reactions. Still and Leopold (1978) found no evidence that diflubenzuron was metabolized in boll weevils treated by immersion or injection or by feeding on treated cotton squares. On the other hand, Chang and Stokes (1979) reported that boll weevils metabolized and excreted as much as 19% of an injected dose of diflubenzuron in the form of water-soluble conjugates.

14 Bull and Ivie (1980) studied the secretion and fate of C-

labeled diflubenzuron in eggs after a single topical application (1 |ig per insect) to adult female boll weevils (Figure 2). At 4 days,posttreatment, eggs of treated females contained ca. 2.24 ppm of C-labeled diflubenzuron equivalents, but the amount declined progressively to ca. 0.4 ppm at 26 days posttreatment. This dimi- nution of secreted radiocarbon occurred despite the fact that diflubenzuron was quite persistent on the treated females. Periodic analyses of the eggs revealed that all the radiocarbon in the eggs was unchanged diflubenzuron.

Daily observations of subsamples of the eggs from the treated females showed that hatch was inhibited in ca. 80% of the eggs through 10 days posttreatment. Thereafter, recovery was fairly rapid; and by 22 days posttreatment, 80-90% of the eggs hatched (Figure 2). At the 50% hatch level, which occurred at ca. 16 days posttreatment, the diflubenzuron content of eggs was ca. 0.6 ppm. Chang and Borkovec (1980) found a similar relationship between IGR secretion ( C-labeled diflubenzuron and penfluron) in eggs and hatch of house fly eggs. The study by Bull and Ivie (1980) thus supports and helps explain previous observations in the laboratory by McLaughlin (1976) and Moore et al. (1978), who found that the


PPM in eggs Untreated Percent hatch

O o ^O 100

I 1 \ 1 1 \ 4 8 12 16 20 24

Days Post Treatment

14 Figure 2.—Secretion of C-labeled diflubenzuron into eggs and

hatch of eggs after treatment of virgin adult female boll weevils who were then paired with untreated males. Dose of 1 jLig per insect. (Adapted from Bull and Ivie 1980.)

effects of single oral or topical doses of diflubenzuron on boll weevils are transitory. As a result of an apparent interruption in the transport of the IGR to the site of secretion and its posttreatment clearance from that site in the insect, fertility is regained fairly rapidly, and retreatment is needed for continued suppression of egg hatch.

Environmental Fate of Diflubenzuron

Information about the posttreatment fate of a pesticide is essential to its safe, effective use. In addition, such information is useful in establishing use rates, in evaluating the persistence

214 D. L BULL ET AL

of posttreatment biological activity, and in assessing the potential for detrimental effects of residues on nontarget organisms.

Available evidence (Bull and Ivie 1978, Mansager et al. 1979) indicates that whatever the method of foliar application of diflubenzuron, little of the material (ca. 5% of the dose) is absorbed by the cotton plant and that residues of the IGR are quite persistent on foliar surfaces. In a ffgld study. Bull and Ivie (1978) found that ca. 90% of a dose of C-labeled diflubenzuron remained on treated leaf surfaces at 14 days posttreatment. In both the aforementioned studies, analyses revealed that unchanged diflubenzuron accounted for > 98% of the unabsorbed and absorbed material that was recovered. All evidence indicates that the chemical is highly resistant to decomposition, either by photodegradation on foliar surfaces or by metabolism within the leaves of cotton. Sim- ilar results documenting the persistence of foliar residues and stability on plant material were reported by Verloop and Ferrell (1977) after application of diflubenzuron to soybeans, cabbage, corn, and apples.

In season-long studies of small plots of cotton treated at J^day intervals with multiple (six and ten) spray applications of C-labeled diflubenzuron (70 g active ingredient (Al) in 9.35

liters crop oil and 93.5 litçjs water per ha). Bull and Ivie (1978) found less than 0.01 ppm of C-labeled diflubenzuron equivalents in mature seed from cotton plants treated six times and only ca. 0.02 ppm in those from plants treated ten times. However, radioactive residues were rather high in some other parts of the plants, particularly in foliage (ca. 40-125 ppm) present during treatments.

Since diflubenzuron is quite persistent on cotton, it would probably be lost from treated foliage as a result of wind abrasion or rainwashing or because of the fall of senescent leaves. The recommended schedule of a maximum of six applications of diflubenzuron, with no more than 421 g AI per ha applied to a field during a season, should establish good coverage of plant foliage without producing hazardous residues in seed.

Soil can be contaminated with diflubenzuron directly by runoff of sprays or indirectly by contact with treated plant materials. In laboratory studies of soil treated directly with diflubenzuron, Metcalf et al. (1975) found that the material degraded very slowly, but Verloop and Ferrell (1977) and Mansager et al. (1979) reported rapid degradation (similar treatments but different soils). The differences can probably be attributed to the particle size of the diflubenzuron that was used in the studies since Ver- loop and Ferrell (1977) have demonstrated that the half-life of 10-ym particles in soil is 8-16 weeks, whereas that of 2-ym particles is 0.5-1 week. Particles in some of the earlier studies averaged ca. 10 ym; those in later (and current) preparations average ca. 2-5 ym. Bull and Ivie (1978) found that diflubenzuron was somewhat stable when it was applied to soil indirectly. For example, when treated cotton plants were shredded after harvest and cultivated


into the soil, residues of diflubenzuron did not begin to decline appreciably until the middle of the following summer, ca. 9 months later. During the 9 months, much of the residual material (ca. 80%) associated with the soil could be recovered by solvent extraction, and the content was predominately (> 95%) diflubenzuron. Also, in laboratory tests (Bull and Shaver 1980) and field tests (Bull and Ivie 1978), diflubenzuron did not leach appreciably in different types of soil, and residues were concentrated near the surface (0-7.5 cm). Thus, the eventual decline of the postharvest residues in the field was probably caused by increased accessibility of the molecule to different mechanisms of degradation in soil as a result of the progressive decay of the plant material with which it was initially associated. Fortunately, there is evidence (Bull and Ivie 1978) that crops (wheat, beans, collards, radish, native grass, and weeds) grown in rotation in fields previously planted to cotton that had been treated with the recommended dosage of diflubenzuron did not take up significant levels of residues.

Veech (1977, 1978a) has shown that application of diflubenzuron to cottonseed can provide protection from attack by the root- knot nematode (Meloidogyne incognita Kofoid & White), apparently by reducing the numbers of egg masses produced and by inhibiting the hatch of eggs through interference with the synthesis of chitin (which, in this organism, is found only within the egg shell). However, Veech (1978b) concluded that the levels of residues (maximum of 0.1-0.3 ppm) that accumulate in soil when diflubenzuron is used for boll weevil control (Bull and Ivie 1978) probably would not provide practical control of several species of free-living nematodes.

Effects of Diflubenzuron on Natural Enemies

Because diflubenzuron appears to have little or no effect on other pest insects that often occur concurrently with the boll weevil, something other than an IGR may be needed to suppress major pests such as the Heliothis spp. That alternative may well be conservation of the many natural enemies that prey on Heliothis spp. eggs and larvae and thus frequently retain these pests below economic injury levels (Whitcomb and Bell 1964, Ridgway and Lingren 1972, McDaniel and Sterling 1979).

Abies et al. (1977), Wilkinson et al. (1978), and House et al. (1980) tested diflubenzuron in the laboratory for harmful effects to several species of entomophagous arthropods. Spray applications (7.7 ppm AI) to pairs of adult convergent lady beetles (Hippodamia convergens Guerin-Meneville) reduced egg hatch and prevented larval development, but these harmful effects gradually subsided after treatments were terminated (Abies et al. 1977). Keever et al. (1977) reported similar effects on reproduction of H. convergens adults collected from diflubenzuron-treated (140 g AI per ha, 9-10 applications) cotton fields' and held in the laboratory. Wilkinson et al. (1978) reported that topical applications (concentrations

216 D. L BULL ET AL

of _< 10,000 ppm) of the IGR had no apparent adverse physical effects on adult convergent lady beetles. Studies of the effects of diflubenzuron on the common green lacewing (Chrysopa carnea Stephens) indicated that egg hatch was inhibited when the adults were treated topically and that larval and pupal mortality were increased when larvae were fed topically treated prey (Abies et al. 1977). Wilkinson et al. (1978) also found that topical applications of diflubenzuron to C^ carnea larvae significantly increased the mortality of pupae that developed from the treated larvae.

Laboratory tests showed that sprays of aqueous suspensions of diflubenzuron had no apparent effect on Geocoris punctipes (Say), Apanteles marginiventris (Cresson), and Trichogramma pretiosum Riley (Abies et al. 1977, Wilkinson et al. 1978). However, when applications of aqueous suspensions of diflubenzuron in oil for control of boll weevil were combined with inundative releases of Trichogramma for control of Heliothis spp. in the field. House et al. (1980) observed that the IGR treatments seemed to cause a transient reduction in the levels of parasitism of Heliothis spp. eggs by the parasites (5-44% decrease within 2-3 days postapplica- tion). These authors then conducted laboratory tests to study these effects and found (Table 1) that sprays of aqueous suspensions of diflubenzuron alone had no adverse effect on parasitism of Heliothis eggs, but the mixture of diflubenzuron and oil (Savol) and the oil alone significantly reduced the levels of parasitism when host eggs were treated before exposure to the parasites; there was no adverse effect when eggs were treated after they were parasitized (Table 1). House et al. (1980) also demonstrated that treatments of host eggs with corn, soybean, and cottonseed oils had similar adverse effects on the subsequent levels of parasitism by Trichogramma.

Despite the relative consistency in results of the cited laboratory studies, extrapolation to actual field conditions is not advised. Some of the topical applications probably produced greater direct exposure to the chemical. Also, many of the concentrations used were much higher than those that would be applied to cotton in the field. The effects of field applications of diflubenzuron on predaceous arthropods in cotton were studied in North Carolina by Keever et al. (1977) and in Texas by Abies et al. (1977) and Rummel et al. (1979). Keever et al. (1977) reported that diflubenzuron (140 g AI in 3.8 liters of crop oil per ha, 9-10 applications) caused a significant reduction in populations of G. punc- ^ipes and a reduction in the hatch of _H. convergens eggsT other predaceous species apparently were unaffected. Turnipseed et al. (1974) observed that populations of Geocoris spp. and Nabis spp. were reduced when diflubenzuron (281 or 562 g AI per ha) was applied twice to soybean foliage; however, they could not determine whether the reduction was caused by the IGR, by a shortage of prey, or by a combination of these factors.

Studies by Abies et al. (1977, 1980b) in central Texas indicated that diflubenzuron had little or no impact on predaceous

Table 1.—Effect of different treatments on parasitism of tobacco budworm eggs by Trichogramma Ij

Test 1 2j 1' Test 2 h Al % % adult % % adult

No. para- emer- No. para- emer- Treatment eggs sitism gence eggs sitism gence

Untreated 629 60 a 95 a 685 72.7 a 95 a Diflubenzuron

+H 0 Savol + H^O Diflubenzuron

696 51 a 89 a 732 75.9 a 98 a 720 15 b 91 a 707 71.1 96 a

+ Savol + H^O 552 19 b 92 a 640 72.1 a 93 a

IJ Data taken from House et al. (1980). 2/ Eggs treated and then exposed to parasites. T/ Means followed by same letters are not significantly different

(P < 0.05) according to Duncan's multiple range test. Figures for % adult emergence are for eggs that were considered to have been parasitized. Data represent averages of eight or more replicates.

4/ Eggs exposed to parasites and then treated.

arthropods when sprays were applied six times at 5-day intervals at rates of 35, 70, or 140 g AI in 4.5 liters of crop oil plus 13.6 liters of water per ha. Predator populations were slightly higher in the untreated plots, but the plots receiving the highest dose of diflubenzuron had a greater abundance of predators than any of the other treated plots. (Of course, the observed differences may have been influenced by factors other than the IGR; for example, by plant phenology and prey abundance.) On the other hand, application of insecticide (methyl parathion plus toxaphene plus chlordimeform) severely reduced the numbers of predators (Abies et al. 1977). Also Rummel et al. (1979), in a similar study in west Texas, demonstrated that seasonal means for populations of predators were higher in the plots treated with diflubenzuron (rate of 140 g AI per ha) than in plots receiving lower rates or in the untreated control; meanwhile, applications of azinphosmethyl (336 g AI per ha) caused a major reduction in predators.

Thus, the available information suggests that diflubenzuron, and especially the emulsifiable crop oils with which the IGR is formulated, may have a detrimental impact on some of the entomophagous species associated with cotton. However, these effects are relatively slight and seem to diminish after treatments are terminated. It is clear that diflubenzuron is much more selective than most conventional insecticides. If the material is used in accordance with current recommendations (six applications at a rate of

218 D. L BULL ET AL

70 g per ha), many entomophagous arthropod species will be conserved.

Effects of Diflubenzuron on Field Populations of the Boll Weevil

Most of the available information obtained by applying diflubenzuron against the boll weevil in field tests is summarized in Table 2, Almost all field testing has been done with a 25% wettable powder (WP) formulation of diflubenzuron that has been milled to provide a mean particle size of 2-5 um.

Taft and Hopkins (1975) provided the first documentation of the effects of diflubenzuron against field populations of the boll weevil. Mixtures of the IGR with invert sugar-molasses baits caused dramatic reductions in weevil reproduction: adult emergence from egg-punctured squares was only ca. 2% in diflubenzuron-treated plots but was 89% in plots treated with conventional insecticides. Although this test involved relatively excessive amounts of diflubenzuron (14 applications of 280-560 g AI per ha), the research represented a significant first step in the development of the product. Lloyd et al. (1977) subsequently evaluated formulations of diflubenzuron in the greenhouse and determined that mixtures of the IGR with certain oils, especially suspensions in raw cottonseed oil, were as effective as the invert sugar-molasses bait and potentially more convenient for practical application. Significantly, they also observed that simple mixtures of diflubenzuron and water were ineffective. When sprays of a suspension of diflubenzuron (280 g AI per ha, 16 applications) in raw cottonseed oil were then applied in the field, boll weevil reproduction was suppressed to the extent that no filial generations were detected until August 20, near the end of the season. (The late-season development of populations was attributed to incomplete control by diflubenzuron rather than to immigration of untreated boll weevils because the test site was somewhat isolated from potential sources of infestation.)

Ganyard et al. (1977) conducted an extensive study in which 141, 282, or 564 g AI per ha of diflubenzuron formulated in raw cottonseed oil were applied to small plots (0.07-0.09 ha) of cotton planted in an isolated, noncotton growing area of North Carolina. Test plots were infested artificially by releasing known populations of overwintered weevils. All rates of the IGR (total of 12 applications throughout the season) provided > 99% suppression of reproduction. Meanwhile, boll weevils in the untreated (control) plots increased dramatically: as many as ca. 90,000 per ha were found; but only five insects were found in all treated plots. On the basis of these studies and those of others, Ganyard et al. (1977) concluded that diflubenzuron would have to be used regularly for prolonged periods to maintain suppression of boll weevil reproduction because of the tendency of the insects to recover fertility after treatments were terminated.

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Because neither the invert sugar-molasses bait nor the raw cottonseed oil formulations were practical for large-scale research or commercial use, special field tests were conducted in Mexico during the spring of 1976 (in advance of the growing season in the United States) to assess the efficacy of mixtures of diflubenzuron with different commercial crop oils (Johnson et al. 1978). Results demonstrated that combinations of the IGR with Savol or Sun Oil 7N were as effective as mixtures with raw cottonseed oil: all suppressed boll weevil reproduction to some extent. Since that time, most field experimentation has been done with suspensions of diflubenzuron and emulsifiable crop oil in water; in fact, the current registration label specifies that applications should include Dimoil at the rate of 4.68-9.35 liters per ha with at least two parts of water for each part of oil.

A large-scale test of the effects of diflubenzuron on cotton insects was conducted in 1976 (Ganyard et al. 1978) in Chowan County, NC, which is isolated by 40 km from other commercial cotton fields. The IGR was applied 9-10 times at a rate of 140 g per ha to the 76 fields (total of 262 ha) located in the county. Repro- duction by native boll weevils was reduced 90% while comparable initial populations (in fields 40 km west of the treated area) that were treated with conventional chemicals increased 12-fold (Ganyard et al. 1978). In addition, populations of Heliothis spp. in the fields treated with diflubenzuron were controlled during most of the growing season by natural enemies (Keever et al. 1977). (Chlordimeform had to be applied six times to these fields during August when population pressure was intense, but no broad-spectrum insecticides were used.) The study by Ganyard et al. (1978) thus established that: (1) areawide applications of diflubenzuron could effectively suppress boll weevils if treatments were initiated at the onset of fruiting and overwintered populations were low to moderate; (2) repetitive weekly applications had an accumulative effect; (3) most of the egg-punctured squares contained eggs that failed to hatch or newly eclosed larvae that died as a result of diflubenzuron treatments; they did not abort, but continued to develop normally; and (4) the crop seemed to mature earlier in fields treated with diflubenzuron than in fields treated with conventional insecticides. This last point has been noted by others (Harris 1980), but the cause has not yet been established. Possibly there is improved setting of the bottom crop of bolls as a result of effective pest suppression, an avoidance of the lateness associated with the use of organophosphorus insecticides, or a physiological response by the plant. In any case, the effect would be advanta- geous if it is indeed real and consistent.

The studies of the field efficacy of diflubenzuron conducted in Texas differed from those conducted in the eastern region of the Cotton Belt in that all took place in areas where there was no isolation of treated fields from the potential influx of boll weevils from untreated areas. Also, in most of the tests made in Texas, the rates of diflubenzuron were more in line with those specified in the current registration. For example. House et al. (1978)


compared three rates of diflubenzuron (35, 70, and 140 g per ha, seven applications). They reported definite suppression of reproduction by all treatments and a differential response to the different concentrations. The results of 2 years of testing in central Texas (Abies et al. 1980a, House et al. 1980) indicated that the effect of the diflubenzuron was greatest against the F, generation. They observed increases in the reproductive potential of the ensuing generations even though diflubenzuron was still being applied. This effect was attributed to an influx of untreated boll weevils from adjacent fields, a conclusion in agreement with the conclusions of Ganyard et al. (1978) concerning the importance of areawide applications in achieving maximum impact on indigenous populations.

Preliminary results of large-scale replicated tests comparing the efficacy of aqueous suspensions of diflubenzuron (70 g AI per ha, six applications) with and without Dimoil (4.67 liters per ha) indicate that the IGR is somewhat less effective (ca. twofold) against the boll weevil when the oil is omitted (Table 2) (D. L. Bull unpublished information, 1980). Although both mixtures suppressed insect reproduction significantly from that in untreated fields or in fields treated with conventional insecticides, fewer adults emerged and more egg-punctured squares remained on the plant when diflubenzuron was applied in oil. This is the first field demonstration of diminished activity of diflubenzuron in the absence of oil; and it substantiates the findings of Lloyd et al. (1977) in their greenhouse studies. Other results substantiate the report by Ganyard et al. (1978) of an apparent earliness in maturation of bolls in treated fields. For example, when open bolls were counted August 7, 1980, 74% were open in fields treated with IGR/ oil/water combinations, 46% were open in fields treated with IGR/ water mixtures, 14% were open in the check fields, and 17% were open in fields treated with standard insecticides.

In a study of the integrated control of codistributed populations of boll weevils and Heliothis spp., Bull et al. (1979) demonstrated that treatment with diflubenzuron (70 g per ha, seven to nine applications) was compatible with augmentative releases of the egg parasite Trichogramma pretiosum and with applications of microbial pesticides. The biological methods effectively reduced heavy populations of Heliothis spp. (ca. mean of 140,000 eggs and 40,000 larvae per ha in the control) to levels below the economic damage threshold, and the IGR had no obvious adverse effects on the performance of the parasites. Even though the applications of diflubenzuron were apparently initiated after overwintered boll weevils had entered the fields and begun ovipositing, the survival of the pest in egg-punctured squares was reduced substantially (seasonal mean of 22% adult emergence compared with 66% in untreated check). There was a distinct increase in the emergence of adults from egg-punctured squares when applications of the IGR were terminated: within ca. 3 weeks, the levels of reproduction in plots previously treated with diflubenzuron were similar to those in the check.

224 D. L BULL ET AL

probably because of the combined effects of recovery of fertility by treated insects and immigration of untreated insects.

Field tests of diflubenzuron in the cotton production area of the Texas Rolling Plains were made against extremely high populations of overwintered boll weevils (> 8000 adults per ha) in 1976 (Rummel et al. 1979), and again in 1977 against somewhat lower populations (Rummel 1980). In 1976, the test fields were sprayed with malathion in an attempt to reduce the immense populations of overwintered boll weevils to a manageable level; then applications of diflubenzuron (35, 70, and 140 g per ha, eight applications) were begun at the time when squares were in the pinhead stage. Even under these conditions, which were not at all optimum for the use of the IGR, treatments reduced reproduction to about half that in the untreated check. Yields of plots treated with the higher rates of diflubenzuron were significantly greater than those of the check and statistically equivalent to those of plots treated with azinphosmethyl. Results of unreplicated tests in 1977 (Rummel 1980) on larger fields demonstrated that diflubenzuron was very effective against the lighter populations of boll weevils. All three rates (52.5, 70, and 140 g per ha; four applications) provided distinct levels of suppression compared with those in the untreated check, and there was a definite differential response to the different rates. The results obtained by Rummel (1980), like those in the earlier tests obtained by House et al. (1978) in Texas, thus suggest that a rate of 35 g of diflubenzuron per ha is insufficient to control this pest.

Large-scale evaluations in the Upper Gulf Coast area of Texas (Cole 1980) demonstrated that three or five applications of diflubenzuron (70 g per ha) suppressed reproduction by light populations of the boll weevil to about half that observed in fields that were untreated or were treated with azinphosmethyl (Cole 1980). Cole (1980) also observed that survival of immature stages in egg- punctured squares in IGR-treated fields increased rapidly when treatments were terminated; recovery of reproductive potential began about 1-2 weeks after the last application of the season.

In contrast to all the studies described thus far, tests in the Lower Rio Grande Valley of Texas over a 2-year period (1976-77) failed to demonstrate any differences in either the seasonal survival of boll weevils in egg-punctured squares or in yields in plots untreated or treated with diflubenzuron at rates ranging from 35 to 140 g per ha (Harding and Wolfenbarger 1980). Since the test area had a history of heavy populations of boll weevils, immigration from adjacent untreated areas may have been so extensive that the effects of the IGR were negated. There was no apparent suppression of predator populations by the diflubenzuron.


Potential for Use of Diflubenzuron in Pest Management

The evidence indicates that under certain conditions, diflubenzuron (and most likely other benzoylphenyl ureas with comparable activity) can provide effective and selective control of the boll weevil. It is clear that the overwintered population of boll weevils is the key to effective use of diflubenzuron in a suppression program. Early-season scouting is critical because IGR treatments must begin before the overwintered generation has a chance to begin reproductive activity and become established in the field. Fortu- nately, in this country, commercial cotton is the only important host for the boll weevil; thus, distribution of the insect during the feeding/reproductive phase is reasonably predictable. The first application of diflubenzuron must be made at the time dominant plants in a potentially vulnerable field of cotton are producing the primordial squares. Treatment should then be continued at no more than 7-day intervals because treated females tend to regain fertility after 7-10 days and because the spring emergence of overwintered boll weevils from hibernation can continue for several weeks after fruiting begins (White and Rummel 1978). This need for repeated treatment might appear unusual since diflubenzuron is known to be quite persistent on foliar surfaces. However, this persistence may not have a major influence on efficacy because it is also well established that field populations of boll weevils tend to recover the reproductive function rapidly when treatments stop. Thus, for maximum efficacy, it may be necessary for the insects to have direct contact with the sprays or with recently sprayed surfaces.

If the eggs deposited in squares by IGR-treated females do not hatch, or if newly eclosed larvae die without feeding, most of the squares will continue to develop normally and will not abort (assuming that growing conditions are favorable for plant development). This retention of superficially damaged squares is, of course, an advantage, but it complicates the assessment of current damage levels and estimates of impending populations (Ganyard et al. 1978). Traditional guidelines used in making control decisions are usually based on the results of examinations of cotton fields for the presence of adult boll weevils or for damaged fruit. As a typical example, the Texas Agricultural Experiment Station and Ex- tension Service recommend that, in fields where potentially damaging populations of overwintered boll weevils are found before the onset of fruiting and must be controlled, conventional insecticides should be applied beginning when squares are in the matchhead stage. The treatment is then repeated 3-5 days later if needed. Subsequently, decisions concerning the need for additional treatments are based upon the results of weekly examinations of 100 squares (at least one-third grown) selected at random from

226 D. L BULL ET AL.

representative areas in a field and from different parts of the plant. If boll weevil damage of the fruit reaches 15-25% during the time of squaring up to peak bloom, treatments with conventional insecticides should be initiated and repeated at 5-day (or less under heavy pressure) intervals for as long as necessary.

Obviously, such guidelines are not valid for IGR's. Decisions about launching this type of treatment will probably be based on such criteria as (1) the previous history of boll weevil activity in the area of concern, (2) the anticipated survival of the overwintering generation, and (3) estimates of the actual survival and potential for infestation by emerging overwintered weevils based upon early-season monitoring of populations with pheromone traps or visual observations. Although all the technology needed to make such assessments is not yet in place, continued research will probably lead to the development of mathematical models that will facilitate decisions having to do with control strategies in cotton pest management, including the use of IGR*s.

Presently, there is no question but that diflubenzuron must be applied with a crop oil to be effective against boll weevils. Should continued research establish that other benzoylphenyl ureas (penfluron, BAY SIR 8514) with greater innate biological activity can be effective without oil, then the advantages that would accrue are obvious. The added cost of application and the apparent adverse action of the oil on certain nontarget organisms would be eliminated. However, we need yet to determine whether the benzoylphenyl ureas that seem to be more active than diflubenzuron against the boll weevil also have a more adverse effect on beneficial species.

Plainly, diflubenzuron is most effective when it can be used against low-to-moderate populations of boll weevils in large production areas where immigration of untreated insects is minimized or eliminated. Piecemeal use may well have only limited potential in commercial cotton production. However, IGR*s should serve well as components of a supervised integrated pest management (IPM) program.

An IPM program for suppressing the boll weevil while making maximum use of the natural enemies of codistributed pests such as Heliothis spp. might include: (1) destruction of cotton stalks as soon as possible after harvest to deprive the overwintering generation of food, thus reducing the numbers that successfully enter diapause; (2) applications of insecticide in the fall to reduce the number of overwintering weevils; (3) the use of an early maturing variety of cotton, planted on schedule, to shorten the period of crop vulnerability to insect attack; (4) six applications of IGR (7-day intervals), beginning at the time of onset of fruiting, to suppress reproduction by overwintered insects and reduce the potential for development of damaging populations in ensuing generations; and (5) selective application of microbial pesticides or


other biological methods to enhance natural control of lepidopteran

pests.

Obviously, there are obstacles to the consistent, successful implementation of such an IPM program. For example, if populations of plant bugs must be controlled with insecticides early in the season, the natural control provided by parasites and predators will be disrupted, and problems with Heliothis spp. could increase. Also, the applications of an IGR might not adequately suppress the boll weevils. In this case, conventional controls could be needed to avoid unacceptable crop damage, and this need might develop at the time when the potential for creating a Heliothis spp. problem was greatest. Finally, populations of natural enemies might be insufficient to suppress infestations of Heliothis spp. Then augmentative biological control methods or perhaps conventional insecticides might be needed to manage these pests.

JUVENILE HORMONE MIMICS

The IGR class of pesticides includes a large number of chemicals that are categorized as juvenile hormone (JH) mimics (Menn and Beroza 1972). These chemicals, though they have widely different structures, have a common mode of action: they evoke a response in treated insects that mimics that induced by the natural JH (Staal 1975). Application of a JH mimic at the appropriate time can severely disrupt normal growth and development; the affected insect either dies or becomes incapacitated. There was much early enthusiasm for the potential of JH mimics in the management of cotton pests, but none has yet shown sufficient potential for practical use.

The period of maximum vulnerability of lepidopteran species to JH treatment is during the last larval instar and early pupal stages (Staal 1975). Cawich et al. (1974) conducted laboratory tests of one of the more promising JH mimics (Stauffer Chemical Co., R-20458 (£)-3-[5-(4-ethylphenoxy)-3-methyl-3-pentenyl]-2,2-di- methyloxirane) against the pink bollworm and found that relatively high doses of the chemical could induce both morphogenetic effects and termination of diapause. However, the cryptic feeding/developmental behavior of this species and the apparent lack of unusual sensitivity to JH applications are such that these chemicals do not appear to have significant potential for use in controlling the pest. Similarly, a large number of candidate JH mimics have been tested unsuccessfully against the tobacco budworm (Guerra 1970, Benskin and Vinson 1973, Guerra et al. 1973). Certain of the chemicals induced typical JH responses such as supernumerary instars, extended larval development, and failure to pupate, but the doses required were excessive, and none of the chemicals offered sufficient promise for practical use. Although laboratory tests (Ben- skin and Vinson 1973) indicated that the extended development of tobacco budworm larvae also extended the feeding period and


resulted in oversized individuals, there is no evidence that such larvae would survive in the field or would cause increased crop damage. Because Heliothis spp. spend much of their larval development period feeding within the fruit of cotton and then burrow into the soil to pupate, they, like pink bollworm, offer an uncertain target for treatments with JH mimics, even if the chemicals have sufficient biological activity.

As a group, weevils are also considered relatively insensitive to JH mimics (Staal 1975). In the boll weevil, maximum vulnerability to JH treatment occurs during late prepupal and early pupal development (Whitten and Bull 1978). Although this pest is relatively sensitive to certain JH mimics (Hedin et al. 1972, Jacobson et al. 1972, Whitten and Bull 1978, Moore 1980), the immature stages develop within the cotton fruit and are usually protected during that time from any type of chemical treatment.

Bull et al. (1973) evaluated a large number of JH mimics representing a broad array of structural types for activity against such cotton pests as the tarnished plant bug, the cotton aphid, and the carmine spider mite, and also against some important predators of cotton pests including the common green lacewing, the big-eyed bug, and the convergent lady beetle. Their studies demonstrated that: (1) none of the JH mimics was effective against spider mites and only one chemical (hydroprene) had promising activity against aphids; (2) several JH mimics were active against the tarnished plant bug, but only at relatively high doses; and (3) the compounds that were effective against pests also had a deleterious effect on the three species of predators that were tested. They concluded that none of the JH mimics they evaluated were promising for practical use in the field.

The evidence thus suggests that at present the available JH mimics hold little promise for use in controlling major pests of cotton. Those that have biological activity must be used at concentrations that are too high for practical use. Moreover, the JH mimics have not demonstrated the unique selectivity associated with the aforementioned benzoylphenyl ureas; for example, JH mimics that are active against plant bugs have an equally adverse effect on beneficial hemipterans and other predators associated with cotton. The role of these compounds in pest management may well be limited to use in ecosystems where the target is well defined and readily accessible.


LITERATURE CITED

Abies, J. R., V. S. House, S. L. Jones, and D. L. Bull. 1980a. Effectiveness of diflubenzuron on boll weevils in central

Texas River Bottoms area. Southwestern Entomologist 5(Supple- ment Number 1):15-21.

S. L. Jones, and M. J. Bee. 1977. Effect of diflubenzuron on beneficial arthropods associa-

ted with cotton. Southwestern Entomologist 2:66-72.

S. L. Jones, V. S. House, and D. L. Bull. 1980b. Effect of diflubenzuron on entomophagous arthropods asso-

ciated with cotton. Southwestern Entomologist 5(Supplement Number 1):31-35.

Anonymous. 1975. Cotton pest control. In Pest Control: An Assessment of

Present and Alternative Technologies, Volume 3. National Acad- emy of Sciences, Washington, DC, 139 p..

1980. Annual Report, 33rd Cotton Insect Research and Control Conference, St. Louis, MO.

Ascher, K. R. S., and N. E. Nemny. 1974. The ovicidal effect of PH 60-40 (l-(4-chlorophenyl)-3-

(2,6-difluorobenzoyl)-urea) in Spodoptera littoralis Boisd. Phytoparasitica 2:131-133.

Benskin, J., and S. B. Vinson. 1973. Factors affecting juvenile hormone analogue activity in

the tobacco budworm. Journal of Economic Entomology 66:15- 20.

Bottrell, D. G., and P. L. Adkisson. 1977. Cotton insect pest management. Annual Review of Entomol-

ogy 22:451-481.

Bull, D. L., V. S. House, J. R. Abies, and R. K. Morrison. 1979. Selective methods for managing insect pests of cotton. Journal of Economic Entomology 72:841-846.

and G. W. Ivie. 1978. Fate of diflubenzuron in cotton, soil, and rotational

crops. Journal of Agricultural and Food Chemistry 26:515- 520.

and G. W. Ivie. 1980. Activity and fate of diflubenzuron and certain derivatives

in the boll weevil. Pesticide Biochemistry and Physiology 13:41-52.


Bull, D. L., R. L. Ridgway, W. E. Buxkemper, M. Schwarz, T. P. McGovern, and R. Sarmiento.

1973. Effects of juvenile hormone analogues on certain injurious and beneficial arthropods associated with cotton. Journal of Economic Entomology 66:623-626.

and T. N. Shaver. 1980. Fate of potassium 3,4-dichloro-5-isothiazolecarboxylate in

soil. Journal of Agricultural and Food Chemistry 28:982-985.

Cawich, A., L. A. Crowder, and T. F. Watson. 1974. Effects of a juvenile hormone mimic on the pink bollworm. Journal of Economic Entomology 67:173-176.

Chang, S. C. 1979. Laboratory evaluation of diflubenzuron, penfluron, and

BAY-SIR-8514 as female sterilants against the house fly. Journal of Economic Entomology 72:479-481.

and A. B. Borkovec. 1980. Effects of diflubenzuron and penfluron on viability of house fly eggs. Journal of Economic Entomology 73:285-287.

and J. B. Stokes. ,, 14^

1979. Conjugation: the major metabolic pathway of C-diflubenzuron in the boll weevil. Journal of Economic Entomology 72:15-19.

Cole, C. L. 1980. Effectiveness of diflubenzuron in the upper Gulf Coast of

Texas. Southwestern Entomologist 5(Supplement Number l):22-26.

Flint, H. M., and R. L. Smith. 1977. Laboratory evaluation of TH-6040 against the pink boll-

worm. Journal of Economic Entomology 70:51-53.

R. L. Smith, D. Forey, and B. Horn. 1977. Diflubenzuron: evaluation for control of the pink bollworm, cabbage looper, and cotton leafperforator in a field cage test. Journal of Economic Entomology 70:237-239.

R. L. Smith, J. M. Noble, D. Shaw, A. B. Demilo, and F. Khalil.

1978. Laboratory tests of diflubenzuron and four analogues against the pink bollworm and a field cage test with diflubenzuron and EL-494 for control of the pink bollworm and cotton leafperforator. Journal of Economic Entomology 71:616-619.

Ganyard, M. C, J. R. Bradley, J. F. Boyd, and J. R. Brazzel. 1977. Field evaluation of diflubenzuron (Dimilin) for control

of boll weevil reproduction. Journal of Economic Entomology 70:347-350.


Ganyard, M. C, J. R. Bradley, and J. R. Brazzel. 1978. Wide-area test of diflubenzuron for control of an indige-

nous boll weevil population. Journal of Economic Entomology. 71:785-788.

Grosscurt, A. C. 1976. Ovicidal effects of diflubenzuron on the housefly (Musca domestica). Mededelingen Rijksfaculteit Landbouwwetenschappen, Gent 41:949-963.

1978. Diflubenzuron: some aspects of its ovicidal and larvici- dal mode of action and an evaluation of its practical possibilities. Pesticide Science 9:373-386.

Guerra, A. A. 1970. Effect of biologically active substances in the diet on

development and reproduction of Heliothis spp. Journal of Eco- nomic Entomology 63:1518-1521.

D. A. Wolfenbarger, and R. D. Garcia. 1973. Activity of juvenile hormone analogs against the tobacco

budworm. Journal of Economic Entomology 66:833-835.

Hajjar, N. P., and J. E. Casida. 1979. Structure-activity relationships of benzoylphenyl ureas

as toxicants and chitin synthesis inhibitors in Oncopeltus fasciatus. Pesticide Biochemistry and Physiology 11:33-45.

Harding, J. A., and D. A. Wolfenbarger. 1980. Evaluation of diflubenzuron for boll weevil control in the Lower Rio Grande Valley of Texas. Southwestern Entomologist 5(Supplement Number l):27-30.

Harris, W. 1980. Dimilin status, cotton boll weevil. Ln Proceedings, 1980 Beltwide Cotton Production Mechanization Conference, St. Louis, MO, p. 78.

Hedin, P. A., L. R. Miles, A. C. Thompson, and R. C. Gueldner. 1972. Constituents of the boll weevil. V. Factors inhibiting

larval development. Journal of Economic Entomology 65:1232- 1235.

House, V. S., J. R. Abies, S. L. Jones, and D. L. Bull. 1978. Diflubenzuron for control of the boll weevil in unisolated

cotton fields. Journal of Economic Entomology 71:797-800.

J. R. Abies, R. K. Morrison, and D. L. Bull. 1980. Effect of diflubenzuron formulations on the egg parasite Trichogramma pretiosum. Southwestern Entomologist 5:133-138.

232 D. L BULL ET AL

Ivie, G. W., and J. E. Wright. 1978. Fate of diflubenzuron in the stable fly and house fly. Journal of Agricultural and Food Chemistry 26:90-94.

Jacobson, M., M. Beroza, D. L. Bull, H. R. Bullock, W. F. Chamberlain, T. P. McGovern, R. E. Redfern, R. Sarmiento, M. Schwarz, P. E. Sonnet, N. Wakabayashi, R. M. Waters, and J. E. Wright.

1972. Juvenile hormone activity of a variety of structural types against several insect species. Ln Insect Juvenile Hormones, p. 249-302. J. J. Menn and M. Beroza, editors. Academic Press, New York and London.

Johnson, W. L., D. L. Moody, E. P. Lloyd, and H. M. Taft. 1978. Boll weevil: egg hatch inhibition with four formulations

of diflubenzuron. Journal of Economic Entomology 71:179- 180.

Keever, D. W., J. R. Bradley, Jr., and M. C. Ganyard. 1977. Effects of diflubenzuron (Dimilin) on selected beneficial

arthropods in cotton fields. Environmental Entomology 6:732- 736.

Lacey, L. A., and M. S. Mulla. 1978. Biological activity of diflubenzuron and three new IGR's

against Simulium vittatum (Diptera: Simulidae). Mosquito News 38:377-381.

Lloyd, E. P., R, H. Wood, and E. B. Mitchell. 1977. Boll weevil: suppression with TH-6040 applied in cotton-

seed oil as a foliar spray. Journal of Economic Entomology 70:442-444.

Lovestrand, S. A., and J. B. Beavers. 1980. Effect of diflubenzuron on four species of weevils attack-

ing citrus in Florida. Florida Entomologist 63:112-115.

McDaniel, S. G., and W. L. Sterling. 1979. Predator determination and efficiency on Heliothis vires-

cens eggs in cotton using P. Environmental Entomology~Ti 1083-1087.

McLaughlin, R. E. 1976. Response of the boll weevil to TH-6040 administered by

feeding. Journal of Economic Entomology 69:317-318.

Mansager, E. R., G<i¿G. Still, and D. S. Frear. 1979. Fate of [ C]diflubenzuron on cotton and in soil. Pest-

icide Biochemistry and Physiology 12:172-182.

Menn, J. J., and M. Beroza. 1972. Insect juvenile hormones. Academic Press, New York and London, 341 p.


Metcalf, R« L., Lu Po-yung, and S. Bowlus.

1975. Degradation and environmental fate of l-(2,6-difluorobenzoyl)-3-(4-chlorophenyl)urea. Journal of Agricultural and Food Chemistry 23:359-364.

Moore, R. F. 1980.^ Boll weevils: effect of insect growth regulators and juvenile hormone analogues on adult development. Journal of the Georgia Entomological Society 15:227-231.

A. Leopold, and H. M. Taft. 1978. Boll weevils: mechanism of transfer of diflubenzuron from male to female. Journal of Economic Entomology 71:587-590.

and H. M. Taft. 1975. Boll weevils: chemosterilization of both sexes with bu-

sulfan plus Thompson-Hayward TH-6040. Journal of Economic En- tomology 68:96-98.

Mulder, R., and M. J. Gijswijt. 1973. The laboratory evaluation of two promising new insecti-

cides which interfere with cuticle deposition. Pesticide Science 4:737-745.

Nemec, S.

1978. How a consultant looks at Dimilin. Ln Dimilin: Break- through in Pest Control, p. 19-20. Agri-Fieldman and Consult- ant, Willoughby, OH.

Oliver, J. E., A. B. Demilo, R. T. Brown, and D. G. McHaffey. 1977. AI-63223: a highly effective boll weevil sterilant. Journal of Economic Entomology 70:286-288.

Post, L. C, B. J. DeJong, and W. R. Vincent. 1974. l-(2,6-disubstituted benzoyl)-3-phenylurea insecticides:

inhibitors of chitin synthesis. Pesticide Biochemistry and Physiology 4:473-483.

Ridgway, R. L., and P. D. Lingren. 1972. Predacious and parasitic arthropods as regulators of Heliothis populations. Ln Distribution, Abundance, and Control °^ Heliothis Species in Cotton and Other Host Plants. Southern Cooperative Service Bulletin No. 169, p. 48-56.

Rummel, D. R. 1980. Effectiveness of diflubenzuron on boll weevils in the Tex-

as rolling plains. Southwestern Entomologist 5(Supplement Num- ber 1):8-14.

G. R. Pruitt, J. R. White, and L. J. Wade. 1979. Comparative effectiveness of diflubenzuron and azinphosmethyl for control of boll weevils. Southwestern Entomologist 4:315-320.

234 D. L BULL ET AL

Schroeder, W. J., J. B. Beavers, R. A. Sutton, and A. G. Selhime. 1976. Ovicidal effect of TH-6040 in Diaprepes abbreviatus on

citrus in Florida. Journal of Economic Entomology 69:780-782.

Staal, G. B. 1975. Insect growth regulators with juvenile hormone activity. Annual Review of Entomology 20:417-460.

Still, G. G., and R. A. Leopold. 1978. The elimination of (N-[[(4-chlorophenyl)amino]carbonyl]-

2,6-difluorobenzamide) by the boll weevil. Pesticide Biochem- istry and Physiology 9:304-312.

Taft, H. M. 1978. Early tests with Dimilin on the boll weevil. In Dimilin: Breakthrough in Pest Control, p. 10-11. Agri-Fieldman and Con- sultant, Willoughby, OH.

and A. R. Hopkins. 1975. Boll weevils: field populations controlled by sterilizing

emerging overwintered females with a TH-6040 sprayable bait. Journal of Economic Entomology 68:551-554.

Turnipseed, S. G., E. A. Heinrichs, R» F. P. da Silva, and J. W. Todd.

1974. Response of soybean insects to foliar applications of a chit in synthesis inhibitor TH-6040. Journal of Economic Ento- mology 67:760-762.

Veech, J. A. 1977. A possible new approach to the chemical control of nema-

todes. Journal of Nematology 9:184-185.

1978a. The effect of diflubenzuron on egg formation by the root- knot nematode. Journal of Nematology 10:208-209.

1978b. The effect of diflubenzuron on the reproduction of free- living nematodes. Nematologica 24:312-320.

Verloop, A., and C. D. Ferrell. 1977. Benzoylphenyl ureas—a new group of larvicides interfering with Chitin synthesis. In. Pesticide Chemistry in the 20th Cen- tury, p. 237-270. J. Plimmer, editor. ACS Symposium Series Number 37, American Chemical Society, Washington, DC.

Wellinga, K., R. Mulder, and J. J. Van Daalen. 1973. Synthesis and laboratory evaluation of l-(2,6-disubsti-

tuted benzoyl)-3-phenylureas, a new class of insecticides. II. Influence of the acyl moiety on insecticidal activity. Journal of Agricultural and Food Chemistry 21:993-998.


Whitcomb, W. H., and K. Bell. 1964. Predaceous insects, spiders, and mites of Arkansas cotton

fields. Arkansas Agricultural Experiment Station, Bulletin No. 690, 83 p.

White, J. R., and D. R. Rummel. 1978. Emergence profile of overwintered boll weevils and entry

into cotton. Environmental Entomology 7:7-14.

Whitten, C. J., and D. L. Bull. 1978. In vivo effect of a juvenile hormone analogue on the non-

spec i"fTc""iest erase s of the boll weevil. Southwestern Entomolo- gist 3:226-231.

Wilkinson, J. D., K. D. Biever, C. M. Ignoffo, W. J. Pons, R. K. Morrison, and R. S. Seay.

1978. Evaluation of diflubenzuron formulations on selected parasitoids and predators. Journal of the Georgia Entomological Society 13:227-236.

Wright, J. E., and R. L. Harris. 1976. Ovicidal action of Thompson-Hayward TH-6040 in the stable

fly and horn fly after surface contact by adults. Journal of Economic Entomology 69:728-730.

Wright, J. E., and G. E. Spates. 1976. Reproductive inhibition activity of the insect growth regulator TH-6040 against the stable fly and the house fly: effects on hatchability. Journal of Economic Entomology 69: 365-368.

Zoebelein, G., I. Hammann, and W. Sirrenberg. 1980. BAY SIR 8514, A new chitin synthetase inhibitor. Zeitschrift fuer Angewandte Entomologie 89:289-297.

237

Chapter 10

INSECTICIDES FOR CONTROL OF COTTON INSECTS

C. R. Parencia, Jr. and T. R. Pfrimmer Bioenvironmental Insect Control Laboratory Agricultural Research Service U.S. Department of Agriculture Stoneville, MS 38776

A. R. Hopkins Cotton Production Research Agricultural Research Service U.S. Department of Agriculture Florence, SC 29502

ABSTRACT Dust formulations of inorganic insecticides such as arsenicals, sulfur, and cryolite were applied by airplane in the 1920's to control cotton insects. When the organochlorine and organophosphorus insecticides became available in the mid 1940's and late 1940's, they could be formulated as emulsifiable concentrates that could be applied as emulsion sprays with low-pressure, low-volume spray equipment. A high percentage of the cotton acreage is presently treated by making aerial applications of insecticide sprays. However, many of the insect pests of cotton have developed or are developing resistance to insecticides. Therefore, researchers are searching for alternate methods of control. Use of these new methods to manage insect populations is reducing the number of insecticide applications needed to achieve control of target insects.

INTRODUCTION

Problems with cotton insects in the United States did not begin in 1892 with the introduction of the boll weevil (Anthonomus grandis Boheman) (Townsend 1895). The early colonists who cultivated cotton had problems with other insects; and T. Glover, the first Government entomologist, mentions cotton insects in his first and second reports (Glover 1854, 1855). In those days, the cotton Leafworm (Alabama argillacea (Hübner)) and the bollworm (Heliothis sea (Boddie)) were the most important pests of cotton (Comstock L879, Riley 1885), and there are many references to other insects affecting cotton in the early entomological publications.

238 C. R. PARENCIA, JR., ET AL

Then the boll weevil entered Texas and at once became the most important pest of cotton in the rain belt portion of the Cotton Belt. Today the boll weevil is present from the eastern two-thirds of Texas and Oklahoma to the Carolinas, and it often causes extensive losses to cotton producers.

Dependable methods of controlling the boll weevil were not available until insecticides were developed in the 1920*s. How- ever, once they became available, large quantities of insecticides have been applied annually by growers to the point that estimated costs (insecticides plus application) now range from $250 million to $300 million a year. Indeed, even in 1976, the National Cotton Council of America put the price at $260 million annually for the period 1970-72, and by 1976, an estimated 64.1 million pounds of insecticide were being applied for control of cotton insects (Eichers et al. 1978). As a result, strains of boll weevil have developed that are resistant to the organochlorine insecticides used initially, which leaves the organophosphorus insecticides as the major class available for control. Meanwhile, the Heliothis spp. complex, which is present across the Cotton Belt, has become resistant to both organochlorine and organophosphorus insecticides.

In fact, cotton insect problems are interrelated and are complex. The boll weevil is the key pest in the rain belt, Lygus spp. in the Midsouth and far West, the cotton fleahopper (Pseudatomos- celis seriatus (Reuter)) in the Southwest, and the pink bollworm (Pectinophora gossypiella (Saunders)) in the far West. The Helio- this spp. complex now is a serious problem beltwide, in part because natural populations of beneficial arthropods that provide control have been killed with insecticides applied for control of the other insect pests.

COTTON CROP LOSSES TO INSECTS

Any discussion of insecticides for control of cotton insects must include some details concerning grower losses. For a fuller discussion of the topic, please refer to Chapter 13 of this handbook.

Estimates of annual loss of cotton due to the boll weevil and to other insects for the period 1909-54 were prepared by the Bureau of Agricultural Economics and are shown here in Tables 1 and 2, respectively (taken from file of C. R. Parencia, Jr.).

The U.S. Department of Agriculture estimated that from 1942 to 1951 in States where the boll weevil occurs, 10.1% of the projected yield was lost because of boll weevils. The loss due to other cotton insects ranged from 1.6 to 8.9%. In States where the boll weevil does not occur, estimated losses to insects ranged from 2.9 to 10.1% (Anon3anous 1954). Also, the U.S. Department of Agricul- ture put the losses in cotton yield due to insects for the period

INSECTICIDES FOR CONTROL OF COTTON INSECTS 239

1951-60 at 19% and attributed 8% to the boll weevil (Anonymous 1965). More recently, the National Cotton Council estimated the annual average loss in yield to the boll weevil as 7.4% for the period 1970-72 (National Cotton Council 1973), and the Cotton Foun- dation put all insect losses to the cotton crop for 1974-76 at 6.6% annually (DeBord 1977). Even today with all the sophisticated control measures that are available, the loss in yield to insects for the Cotton Belt for 1979 was put by the annual Conference on Cotton Insect Research and Control (Anonymous 1980) at 8.8% with 1.4% attributed to the boll weevil. (This group will develop figures annually hereafter.)

INORGANIC INSECTICIDES

The development of materials capable of controlling the boll weevil is of considerable historical interest. In the early part of the century, before the advent of calcium arsenate, Paris green and lead arsenate were the principal insecticides used to control outbreaks of the cotton leafworm. (The Paris green sulfur mixture became popular in the far West for control of hemipteran insects in the 1920*s.) Since Paris green was so effective against the cotton leafworm, it was tested against the boll weevil in 1896 but found to be ineffective. Also, a wettable powder of lead arsenate formulated as a spray was effective in controlling the bollworm and the cotton leafworm but was not effective against the boll weevil. Even when this material was formulated as a dust, control of boll weevils was erratic, so lead arsenate was not recommended by the Bureau of Entomology nor used extensively by growers. Sulfur, too, was sometimes used for control of the cotton fleahopper, and cryolite was used for control of the bollworm on cotton though it was not as effective in preventing damage as it was on such crops as lima beans.

The first significant breakthrough in chemical control came when Coad (1918) found that calcium arsenate was effective in field tests against the boll weevil, and machines that could be used for applying the dust were developed. The next step was the application of calcium arsenate dust from airplanes, a procedure suggested by the success the Ohio Agricultural Experiment Station achieved with aerial applications of lead arsenate for control of the catal- pa sphinx (Ceratomia caltalpae (Boisduval)) in 1921. The first aerial applications against cotton insects were made to control the cotton leafworm in 1922. This method of application rapidly became widespread, and commercial companies soon maintained fleets of airplanes for use in controlling the boll weevil and the cotton leafworm. Thereafter, for many years, that is, until 1945, arsenicals and sulfur were the principal insecticides used for control of cotton insects (Parencia 1978).

Although a mixture of calcium arsenate and Paris green was more effective against bollworms than calcium arsenate alone (Parencia 1978), calcium arsenate was the main weapon against the

240 C. R. PARENCIA, JR., ETAL.

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boll weevil, bollworm, and cotton leafworm. However, when this material was used, there tended to be injurious infestations of the cotton aphid (Aphis gossypii Glover). For this reason, nicotine, the only available aphicide, was sometimes mixed with calcium arsenate or formulated in hydrated lime. Also, mixtures of sulfur and calcium arsenate were widely used for control of combination infestations of boll weevils and cotton fleahoppers. Sulfur suppressed populations of cotton aphids, but sulfur used in combination with arsenicals did not always prevent injurious infestations.

ORGANIC INSECTICIDES

The development of organochlorine insecticides in the mid- 1940' s brought about the first major change in insecticides used on cotton since the development of calcium arsenate (Ewing and Paren- cia 1948). Federal and State research workers concerned with cotton insects made haste to explore the possibilities of these new materials. Their general effectiveness then produced wide acceptance by growers. As a result, by the late 1940's, considerably more cotton acreage was being treated with insecticides than ever before, and organochlorine compounds had largely replaced calcium arsenate though for a while it continued to be used to some extent in certain areas. Much of this changeover was based on research accomplished at U.S. Department of Agriculture research laboratories and at many State agricultural experiment stations.

Among the new materials, BHC, aldrin, dieldrin, chlordane, and heptachlor were effective against boll weevils but were ineffective against bollworms, and mixtures of these materials with DDT gave effective control of combination infestations of these two important pests. Toxaphene and endrin were effective against both pests. Subsequently, organophosphorous compounds such as parathion, methyl parathion, azinphosmethyl, demeton, and EPN and the carbamate, carbaryl, were developed, and these provided a broader range of chemical weapons with which to combat cotton insects.

INSECTICIDES APPLIED AS DUSTS

In the mid-1940's when the organochlorine insecticides were being introduced, the only equipment available for applications was that developed for application of calcium arsenate dust; thus, for several years, the new materials were applied only as dusts. There were, however, two major problems. One was the fact that weather conditions were critical. Dusts had to be applied during late afternoons, at night, or in early morning when the air was calm, or nearly so, to insure plant coverage and prevent excessive drift. In many areas, such conditions lasted only a short time and often did not occur at all so the acreage that could be treated in a day was limited. The second was the fact that use of the organochlorine insecticides often resulted in the buildup of populations of such secondary pests as spider mites (Tetranychus spp.), though


this particular difficulty was solved by including at least 40% sulfur in the dust formulations.

Entomologists at the Waco, TX, Cotton Insects Laboratory therefore took a new look at "presquare" control of boll weevils with the idea of developing a method of controlling early-season injurious insects such as thrips, cotton aphids, overwintered boll weevils, and cotton fleahoppers. Community-wide experiments in early-season cotton insect control with dust formulations of organochlorine insecticides conducted in Wharton County, TX, in 1948, proved conclusively that an early-season control program was profitable for that area and would simplify the farmer's control problem (Ewing and Parencia 1949a). However, the critical weather conditions necessary for application continued to limit the effectiveness of such control programs.

INSECTICIDES APPLIED AS SPRAYS

In 1948, the new organochlorine insecticides were found to be effective when they were formulated as emulsifiable concentrates and applied as emulsion sprays in low-pressure, low-volume (2 to 10 gallons per acre) spray equipment. Again, community-wide, early- season insect control experiments with ground machine sprays were conducted in central Texas. The results obtained in 1949 and 1950 were outstanding, and the problems experienced with dusts were considerably reduced (Ewing and Parencia 1949b and 1950). Moreover, the successes laid the groundwork for the concepts of total insect population suppression and integrated control that came to the forefront in the United States in the 1970's.

Spray applications of insecticides for control of late-season insect pests also were readily accepted by growers because of their several advantages over like application of dusts. For example, they fit well into a daytime farm operation, and weather conditions are less critical than with dusts. Today a high percentage of cotton acreage is treated with sprays applied by aircraft.

Meanwhile, however, problems of cotton producers with the spider mite had become somewhat more serious because sulfur could not be included in sprays of organochlorine insecticides. This difficulty was solved when organophosphorous insecticides such as parathion, methyl parathion, and demeton became available as sprays.

Finally, in the 1960's, techniques were developed for applying technical materials as ultra-low volume sprays (0.5 gallon or less of total spray per acre) (Cleveland et al. 1966). Research results showed that most materials were at least equally effective when they were applied in this way as they were when the same dose was applied as low-volume (conventional) sprays. Only malathion, azinphosmethyl, endosulfan, methyl parathion, and a mixture of malathion plus methyl parathion are presently approved for ultra-low volume aerial applications to control certain cotton insects.


SYSTEMIC INSECTICIDES

Systemic insecticides such as phorate and disulfoton (developed in the mid-1950's) can be applied to cottonseed and will protect seedling plants for several weeks from such pests as thrips, the cotton aphid, and spider mites (Parencia et al. 1957). This method of control, however, has not been widely accepted because the insecticides are expensive, do not give protection as long as desired early in the season, often reduce plant emergence, and may delay fruiting. Also, granular formulations of systemic insecticides can be applied in the seed furrow at planting and as side-dressings to established plants. For example, aldicarb (developed in the 1960's) applied in the seed furrow at planting will kill overwintered boll weevils and control cotton fleahoppers for 8 weeks after planting. It will also kill boll weevils developing in cotton squares when it is applied to plants as a side-dressing at the time they are in the early squaring stage (Hopkins and Taft 1965); however, it is not used in this manner because the applications often result in increased subsequent infestations of the bollworm.

RESISTANCE TO INSECTICIDES

In Louisiana, the boll weevil developed resistance to the organochlorine insecticides in the mid 1950's (Roussel et al. 1957); in Arkansas and Mississippi and in other States where boll weevils occur, resistance developed somewhat later. Fortunately, an organophosphorous compound, methyl parathion, was effective and available. Also, azinphosmethyl and malathion had been tested and were soon available though they were more expensive, which limited their early use. Once azinphosmethyl was marketed competitively, it came to be considered the most effective "weevilcide" available. In addition, the carbamate, carbaryl, was soon available, but it never gained full grower acceptance because it could be formulated only as a dust or a wettable powder and so was more difficult to apply than an emulsifiable concentrate. A mixture of toxaphene and DDT, though both are organochlorines, continued to be effective against resistant boll weevils. However, DDT was banned for use on cotton by the Environmental Protection Agency on December 31, 1972.

In sum, since 1947 when organic chemicals began to be widely used on cotton, 25 species of insects and spider mites that attack cotton have developed resistance to organochlorine insecticides, and there is reason to suspect several more species are now resistant. Moreover, at least one resistant species occurs locally in most cotton producing States from California to North Carolina. In addition, four species of spider mites, the fall armyworm (Spodoptera frugiperda (J. E. Smith)), the bandedwing whitefly (Trialeurodes abut ilonea (Haldeman)), the bollworm, and the tobacco budworm (Heliothis virescens (F.)) are known to be resistant to organophosphorus compounds (Anonymous 1980).


Development of resistance to both the organochlorine and organophosphorus insecticides in the tobacco budworm and bollworm was an especially serious matter since very few effective insecticides were available (Lukefahr 1970). At first, the then recently developed insecticides methomyl and chlordimeform were of some help in control of these resistant pests. However, methomyl proved to be phytotoxic and cannot be used in a regular schedule of applications. Also, chlordimeform, which came into widespread use as an ovicide applied in combination with larvicides, was withdrawn from the market in 1976. (it became available again in 1978 on a limited trial basis but only as a restricted closed system aerial application material, which eliminates exposure of loaders and pilots. It has been available under this restriction since that time.) Then the synthetic pyrethroids, permethrin and fenvalerate, were developed. These eased the problem of bollworm tobacco/budworm resistance (Hopkins et al. 1977), and the materials also suppress moderate infestations of boll weevils. Still other pyrethroids are presently being evaluated, but most researchers feel that the Heli- othis spp. complex may well develop resistance to these materials depending on the intensity of their use. A new organophosphorus compound, sulprofos, is available, but it is not effective against boll weevils.

REPRODUCTION-DIAPAUSE CONTROL

Cotton entomologists have long been aware that naturally occurring predators and parasites can sometimes keep infestations of the bollworm complex at subeconomic levels. They are also aware that insecticides applied for the control of pest insects such as the boll weevil, the bollworm complex, cotton fleahoppers, and plant bugs kill these beneficial insects. The difficulty is that in-season application of insecticides is necessary to protect the crop until it matures and is no longer attractive (Parencia 1978). The problem was brought into focus when the bollworm complex became increasingly difficult to control because it had developed resistance to previously available effective insecticides.

Because of this, in the late 1940*s, Ewing and Parencia (1949a, 1949b, and 1950) developed a system of providing early- season control of cotton insects that would meet the peculiar needs of the Texas Blacklands (Lincoln and Parencia 1977). Community- wide participation was stressed. Emphasis was placed on control of thrips and cotton fleahoppers, pests that delay early-season growth and fruiting, and on reduction of the population of overwintered boll weevils. In addition, applications of insecticides were terminated at least 30 days before the date when bollworms normally became a problem so as to allow populations of beneficial arthropods time to recover and contribute to the control of this pest. This was achieved by scheduling applications for entire communities encompassing several thousands of acres of cotton, thereby over- coming the deficiencies of the conventional scouting system in


which one scout could adequately cover less than 2000 acres of cotton (Lincoln and Parencia 1977). Late-season treatments for control of boll weevils and the bollworm complex often were not needed. The system worked well in the Texas Blacklands, but in the Midsouth and Southeast, it was not as effective where better hibernation sites were available to the boll weevils. In other areas, overwintered boll weevils emerged later, and the infestation of the first generation of the bollworm complex was greater than in Texas. Thus, there was often need for additional crop protection when the scheduled treatment period was over (communication with T. R. Pfrimmer and A. R. Hopkins).

Later, Brazzel and Newsom (1959) found that boll weevils must enter a physiological condition called diapause if they were to survive adverse environmental periods. (Diapause in the boll weevil is characterized by cessation of gametogenesis and atrophy of gonads, increase in fat content, decrease in water content, and decrease in respiratory rate.) Brazzel and Hightower (1960) reported that in central Texas weevils with the diapause condition were first observed from late July through August in populations from selected fields. Lloyd and Merkl (1961) reported that in some fields in Mississippi such weevils were first observed as early as August 11; and in other fields, they were first observed as late as September 8. Subsequent studies by Lloyd et al. (1964) showed initial entry of a segment of the weevil population into diapause was coincident with cessation of flowering by cotton plants in individual fields, but in laboratory studies, Lloyd et al. (1967) associated initiation of diapause with boll feeding by adult weevils, limited numbers of squares available to adult weevils, low night temperatures, exposure of immature stages to a short photophase, and larval feeding on bolls. In the field, these workers observed two periods of entry of the boll weevil into diapause. The first occurred in August or September (under Mississippi conditions) when fields ceased flowering and only bolls remained for food. The second period occurred during October when night temperatures decreased and only squares were available for food.

During 1959, a large-scale boll weevil diapause control experiment (Brazzel et al. 1961) was conducted in the Big Bend area of Texas to determine whether weevils could be killed before they attained firm diapause. Four applications of methyl parathion were made at a rate of 0.5 pound per acre from September 30 to November 8 on a 525-acre isolated cotton planting. As a result, during the next crop season, only one of the ten treated fields had populations of boll weevils that reached damaging levels before insecticide treatments were required for bollworm-budworm control. How- ever, when a similar test was made in Mississippi (Lloyd et al. 1964), insecticide treatments spaced a week or more apart in Sep- tember permitted sufficient deposition of boll weevil eggs so there were sizable boll weevi1 ,populations in mid- to late October when cooler temperatures reduced the effectiveness of insecticide treatments. Nevertheless, fall populations of boll weevils were significantly reduced.


Knipling (1963) suggested improved timing of insecticide treatments against the last reproducing generation (treatments spaced close together) so as to limit egg deposition. Harris et al. (1966) determined that boll weevil eggs laid after ca. Septem- ber 25 at Mississippi State, MS, would not develop into adult weevils before the first killing frost. Tingle and Lloyd (1969) observed that newly emerged adult weevils had to feed 2 to 4 weeks to attain firm diapause at temperatures simulating those of late Octo- ber. Lloyd et al. (1966), in field tests conducted in 1963-64, applied six insecticide treatments at 5-day intervals against the last reproducing generation of boll weevils during September and one insecticide treatment in October against weevils that had survived or emerged following the September treatments. The results of this so-called "reproduction-diapause" program was to severely limit reproduction by the last reproducing generation of weevils in the late summer and to kill surviving and late emerging weevils from late September until frost if treatments were applied at 10- to 14-day intervals during this period. Adkisson et al. (1966) and Fye (1968) subsequently demonstrated that in Texas boll weevil populations could be suppressed 98% or more in the fall by applying ca. seven reproduction-diapause control treatments.

Reproduction-diapause control was used in 1972 in the Pilot Boll Weevil Eradication Experiment (13 insecticide treatments) in southern Mississippi. (This number was required because of the long growing season and the large boll weevil populations in that area.) Pheromone trap catches in the spring of 1973 indicated that few boll weevils survived (99% or better suppression) in the eradication and first buffer areas (Parencia 1978).

Also, reproduction-diapause control applications were made in Year 1 (1978) of the Boll Weevil Eradication Trial (BWET) in both the evaluation and buffer areas. In Years 2 (1979) and 3 (1980), none were applied in the evaluation area. However, in Year 2, sterile boll weevils were released on all the evaluation acreage, and diflubenzuron was applied on 11% of this acreage. The evaluation area was judged free of native boll weevils at the end of the Trial (Cross et al. 1981). Likewise, in the Optimum Pest Manage- ment Trial (OPMT), four applications of methyl parathion were scheduled each year for control of diapausing boll weevils. The first application was applied 10 days after the grower made his last in-season application. The second was applied 10 days later and the last two at 15-day intervals. Trap captures in 1979 and 1980 in Panola County where this Trial was conducted were 74 and 94%, respectively, below captures in the control area (Pontotoc County) where diapause control was not used (Anonymous 1981).

In discussing the suppression of diapausing boll weevils as a pest management component, Rummel and Frisbie (1978) state that "The high level of organization and cooperation required is the greatest disadvantage in application of this control technique. However, it has been demonstrated in several areas that the necessary organization and cooperation can be achieved and an effective


management program accomplished." The consensus is that, especially in the heavily infested areas of the Cotton Belt, regulatory procedures will have to be adopted by the producers for a reproduction-diapause control program to be effective.

AN APPRAISAL OF COTTON INSECT CONTROL WITH INSECTICIDES

Knipling (1979) discusses the merits and limitations of chemical insecticides in suppressing insect populations. The merits are: (1) chemical insecticides are effective in controlling thousands of species that affect plants, animals, man, structures, and stored products; (2) insect control by chemicals is positive and rapid; (3) a single insecticide or a combination of two or more insecticides can often be used to control several pest species on a given crop at the same time; (4) an individual property owner can take unilateral action as needed to protect his interests when pest problems arise; (5) suitable materials, formulations, and equipment are readily available for immediate use; and (6) one or more of the chemical insecticides already available can be evaluated quickly for use against new pest species.

He lists the following limitations: (1) broad-spectrum action of many insecticides creates hazards or risks of hazards to man and to nontarget organisms in the environment; (2) broad-spectrum insecticides decimate the populations of natural biological agents that are so important in maintaining a balance between beneficial and harmful or potentially harmful pest species; (3) use of insecticides to suppress pests only when and where economic thresholds are reached does not provide any permanent solution to the pest problem and may still permit substantial losses; (4) continued dependence on insecticides for control, that is, year after year, is costly on a long-term basis; and (5) the ability of insects to develop insecticide-resistant strains limits the period a given material can be used.

It is therefore interesting to consider the actual impact of insecticides on cotton yield over the years. Three Agricultural Research Service laboratories—Florence, SC, in the Southeast; Tal- lulah, LA, in the South; and Waco, TX, in the Southwest—kept annual records of yields from treated and untreated plots for periods of 31, 37, and 32 years, respectively (Parencia 1978). The records, though they reflect crop losses to insects in these areas when insecticides were not applied, must be accepted for what they are. For example, the use of the "best" insecticides does not prevent all insect damage. Also, a certain amount of damage can be tolerated before use of an insecticide is economically reasonable because cotton plants can suffer some fruit loss or foliage damage before yield is reduced. Finally, more than one insect was usually monitored in the various tests, and no attempt was made to show how much of the loss in yield was attributable to a particular insect. Insects involved at all locations were boll weevils, bollworms, cotton aphids, and spider mites. In addition, lygus bugs were


involved at Tallulah and the cotton fleahopper, tobacco budworm, and thrips were involved at Waco.

Despite these limitations (and the obvious fact that insect infestations and weather conditions vary from year to year), records of this type made over a period of years are more meaningful than records for selected years. It is thus important that at Florence the average increase in yield in treated over untreated plots for the 31-year period 1928-58, was 40.6% (5.3% in 1942 to 217.9% in 1950); at Tallulah, for the 37-year period 1920-56, it was 31.2% (1.1% in 1924 to 112.8% in 1950); and at Waco, for the 32-year period 1939-70, it was 54.3% (9.9% in 1939 to 426.0% in 1961).

Obviously there has been considerable improvement in cotton insect control at the three locations since 1945 and the advent of the organochlorine, organophosphorus, and carbamate insecticides and the phasing out of inorganic insecticides. Table 3 summarizes improvement in insect control since the new insecticides have been used.

Table 3.—Increase in cotton yield over time

Study period

% increase in yield in treated over untreated plots

Location Average Before 1945 After 1945

Tallulah, LA Florence, SC Waco, TX

1920-56 1928-58 1939-70

31.2 40.6 54.3

26.4 23.6 34.0

41.3 53.9 77.6

Insecticides and miticides now used for control of cotton insects and spider mites are listed in Tables 4 and 5, respectively.

252 C. R. PARENCIA, JR., ETAL

Table 4.—Recommended dosages (pounds per acre technical of major Insecticides Boll Bollworm or Cotton Cotton

(pounds) weevil tobacco budworm aphid fleahopper

Acephate Ij Aldicarb 2/ 0. Azinphosmethyl 4^/0.1 Bacillus

0.75-1.0 6-1.0 2-0.5

0.3-0.5 0.6-1.0 0.25 1.0-0.25

thuringiensis 0.5-1.0 Baculovirus heliothis 5/ 0.12-0.25

Carbaryl 1.0-2.0 0. .25-1.4 Carbophenothion Chlor dime form jô/ 0.12-0.5

0.5-1.0

Chlorpyrifos Demeton

0.5-1.0 0.25-0.38

Dicrotophos 0.1-0.25 0. .1-0.25 Dimethoate 0.1-0.25 0. .1-0.25 Disulfoton 7/ 0.6-1.0 Endosulfan EPN 0.25-0.5 0.75-1.25 EPN + methyl

parathion 8/ 0.25+0.25 0.5-1.0+0.5-1, .0 Ethion 0.5 Fenvalerate 0.1-0.2 Malathion kj 0.5-1.0 0.5-1.25 0, .7-1.25 Methamidophos 0.5-1.0 Methomyl Methyl

parathion 4/ 0.25-0.5

0.45-0.67

1.0-2.0 0.25-0.5 0, .12-0.5 Monocrotophos 9^/ 0.6-1.0 0.6-1.0 Oxydeme t onme thy1 Parathion 0.25-1.0 1.0

0.25-0.38 0.2-0.5

Permethrin 0.1-0.2 0.1-0.2 Phenamiphos 3/ Phorate Ij 0.5-1.5 Sulprofos 0.75-1.0 Toxaphene Toxaphene + methyl

parathion 8/

2.0-4.0

1.0-2.0+

2.0-4.0

2.0-3.0+1.0-1 .5 0. .5-2.0 0.25-0.5

Trichlorfon 0. .25-1.0

J_/ For control of insects of lesser importance see Anonymous pound per hundredweight of cottonseed for thrips control. _3/ malathion, and methyl parathion may be applied ultra-low volume 0.5-0.75 pound per acre, respectively. _5/ 36-72 larval equiva- system. Jj In-furrow granule treatment or as seed treatment at and 1.3-1.5 pounds per hundredweight for phorate. 8^/ Chlor- for bollworm/tobacco budworm control. 9/ Monocrotophos may be of cottonseed for thrips control.


material) of the principal insecticides used for the control cotton insects 1/

Cotton Cotton leaf- Lygus bugs and Pink leafworm perforator other mirids bollworm Thrips

1.0 0.1-0.5 2.0 0.6-1.0 0.3-0.5

0.25-0.38 0.125-0.25 0.5-1.0 0.08-0.2

0.5-2.0 1.0-2.0 1.5-2.5 0.5-0.8

0.5

0.1-0.2 0.1-0.25 0.1-0.25 0.1-0.25

0.6-1.0 0.3-0.75

0.25+0.25-0.25+0.25

0.1 0.4-1.25 0.7-1.2 0.25-1.3

0.45-0.67

0.12-0.25

1.0

0.25-0.5 0.12-0.5 0.12-0.5 0.1-0.25 0.6-1.0 0.1-0.2

0.1-0.2 1.6-3.3 0.5-1.5

2.0-4.0 1.0-4.0 1.0-2.0

0.5-1.5

(1980). Ij Acephate may be applied as seed treatment at 0.5 In-furrow granule treatment at planting, kj Azinphosmethyl, as technical material at 0.125-0.25 pound, 0.5-1.2 pounds, and lents per acre. 6^/ Restricted to aerial application in a closed 0.25-0.5 pound per hundredweight of cottonseed for disulfoton dime form, methomyl, or chlorpyrifos may be added to the mixture applied as seed treatment at 0.25-1.25 pounds per hundredweight


Table 5.—Dosages (pounds per acre technical material) of miti-

Mítícíde Carmine Desert McGregor Pacific

Aldicarb J^/ 0.6-1.0 0.6-1.0 0.6-1.0

Carbophenothion 0.25-0.75

Chlorpyrifos 0.25-1.0

Demeton 0.38 0.38 0.38 0.38

Dicofol 1.0-1.5 0.8-1.6 0.8-1.0

Dicrotophos 0.25-0.5 0.25-0.5 0.25-0.5

Disulfoton Ij 0.5-1.0 0.5-1.0

Ethion 0.25-1.5 0.25-0.75 0.25-1.0

Methidathion 1.0 1.0 1.0 1.0

Methyl parathion 0.6

Monocrotophos 0.5-1.0 0.5-1.0 0.5-1.0 0.5-1.0

Oxydemetonmethyl 0.25-0.5 0.25-0.5 0.25-0.5 0.25-0.5

Parathion 0.25-0.5 0.1-0.2

Phorate _3/ 0.5-1.5 0.5-1.5

Propargite 1.25 0.8-1.6

Sulfur 25-35

\J In-furrow granule treatment at planting. Ij In-furrow granule treatment at planting or 0.5 pound per _3/ In-furrow granule treatment at planting or 1.3-1.5


cides for the control of species of spider mites (Tetranychus)

T. ludeni Schoene Strawberry Tumid Two s pot ted Zacher

0.6-1.0 0.6-1.0

0.25-0.5 0.375

0.25-1.0

0.25-0.75

0.25-1.0

0.38 0.38

0.8-1.6

0.25-0.5

0.5-1.0

0. .38 0.38

0.8-1.6

0.25-0.5

0.5-1.0

0.38

0.25-1.0 0.25-1.0 0.25-1.5

1.0 1.0 0.5-1.0

0.6 0. .6 0.6

0.5-1.0 0.5-1.0 0. .5-1 -.0 0.5-1.0 0.5-1.0

0.25-0.5 0.25-0.5 0. ,25- ■0.5 - 0.25-0.5

0. .25- -0.5 0.125-1.0 0.2

0.5-1.5 0.5-1.5

0.8-1.6 0.8-1.6

25-35 20-50

hundredweight of planting seed. pounds per hundredweight of planting seed.


INSECTICIDES IN AN INSECT PEST MANAGEMENT SYSTEM

Insecticides used for control of cotton insects beltwide in recent years will be discussed in other chapters of this handbook. However, methyl parathion and azinphosmethyl were chosen for control of diapausing boll weevils in the OPMT and BWET, respectively. This choice was made, and the schedule of applications was drawn up (see Table 6), by the participating producers in areas that were involved in the OPMT and, after 1978, in the BWET. They were in accordance with the choices and the schedules suggested in the Cotton Insect Control Guides for the respective States.

Table 6.—Insecticide use during the growing season in Optimum Pest Management Trial (OPMT) and Current Insect Control (CIC) areas, Boll Weevil Eradication Trial (BWET), and buffer areas 1977-80

Average no. insecticide applications for— Bollworm/

Lygus tobacco Boll ^^^^ Thrips bugs budworm weevil

OPMT 0.2 3.9 0 0.3 1.9 0 0.6 1.6 0 0.5 2.4 0.1

CIC 0 1.6 0 0 1.9 0 0 0.6 0 0 0.3 0.6

BWE 0 7.7 0.4 0 3.7 6.2 0 2.1 0.4 0 1.2 0

Buffer 0 0 0 0 11.3 0.7 0 7.8 5.1 0 4.4 3.9

1977 1/ 1978 1979 2/ 1980

1977 1978

i/

1979 2/ 1980

1977 1/ 1978 1979 1980

1977 1/ 1978 1979 1980

1, .5 0. .4 0. .6 0, .5

0. .3 0, .1 0. ,1 0. ,03

0 0 0 0

0 0 0 0

j_/ Prototype operation before Trials began. l_l Applications for boll weevil included in those for bollworm/

tobacco budworm.


Nevertheless, total reliance on insecticides is no longer acceptable (and was not the pattern in these Trials) because of adverse effects of insecticides on the environment and on nontarget species. At the same time, the development of alternatives, though it is receiving much emphasis, is proving difficult and costly. Insecticides will therefore continue to be important in the control of cotton insects. This is why there is concern because comparatively few promising candidate materials have recently been made available for testing.

In fact, the cost of developing and registering a compound also is expensive and continues to increase. Industry is thus taking a hard look at compounds after initial screening to see whether their continued development is justified. As a result, few new compounds are being made available for testing programs, and only a small number of these are carried on to registration and ultimate use by growers. The resulting lack of new effective compounds is especially serious in regard to control of the Heliothis spp. complex that has developed resistance to the comparatively few available effective insecticides. Possibly some of the alternative tactics for insect control can be used in conjunction with insecticides in insect pest management systems that will reduce the crises produced because so few effective insecticides are available. Also, management systems that incorporate nonchemical tactics and strategies may reduce the number of insecticide applications needed to achieve control of cotton insects.


LITERATURE CITED

Adkisson, P. L., D. R. Rummel, W. L. Sterling, and W. L. Owen, Jr. 1966. Diapause boll weevil control: a comparison of two meth-

ods. Texas Agricultural Experiment Station B-1054, lip.

Anonymous. 1954. Losses in agriculture. U.S. Department of Agriculture, ARS-20-1, 190 p.

1965. Losses in agriculture. U.S. Department of Agriculture, Agriculture Handbook No. 291, 120 p.

1980. 33rd annual conference report on cotton insect research and control. U.S. Department of Agriculture, Science and Edu- cation Administration, 77 p.

1981. Final Report, Optimum Pest Management Trial, Panola Coun- ty, MS. Cooperative Extension Service, Mississippi State Uni- versity, 35 p.

Brazzel, J. R., Jr., and L. D. Newsom. 1959. Diapause in Anthonomus grandis Boheman. Journal of Eco- nomic Entomology 52:603-611.

and B. G. Hightower. 1960. A seasonal study of diapause, reproductive activity, and

seasonal tolerance to insecticides in the boll weevil. Journal of Economic Entomology 53:41-46.

T. B. Davich, and L. D. Harris. 1961. A new approach to boll weevil control. Journal of Econom-

ic Entomology 54:723-730.

Cleveland, T. C., W. P. Scott, T. B. Davich, and C. R. Parencia, Jr.

1966. Control of the boll weevil on cotton with ultra-low volume (undiluted) technical malathion. Journal of Economic Entomol- ogy 59:973-976.

Coad, B. R. 1918. Recent experimental work on poisoning cotton boll weevils.

U.S. Department of Agriculture, Bulletin No. 731, 15 p.

Comstock, J. H. 1879. Report on cotton insects. U.S. Department of Agriculture,

315 p.


Cross, W. H., et al. 1981. Final Report, Biological Evaluation, Beltwide Boll Weevil

Cotton Insect Management Programs. Attachment C.

DeBord, D. V. 1977. Cotton insect and weed loss analysis. The Cotton Founda-

tion, 121 p. Memphis, TN.

Eichers, T. R., P. A. Andrilenas, and T. W. Anderson. 1978. Farmer's use of pesticides in 1976. U.S. Department of Agriculture, Agricultural Economic Report No. 418, 58 p.

Ewing, K. P., and C. R. Parencia, Jr. 1948. Control of boll weevil and cotton aphid with dusts con-

taining chlorinated camphene, benzene hexachloride or other new insecticides. Journal of Economic Entomology 41:558-563.

and C. R. Parencia, Jr. 1949a. Experiments in early-season application of insecticides

for cotton insect control in Wharton County, Texas during 1948. U.S. Department of Agriculture, Bureau of Entomology and Plant Quarantine E-772, 6 p.

and C. R. Parencia, Jr. 1949b. Early-season applications of insecticides for cotton in-

sect control. U.S. Department of Agriculture, Bureau of Ento- mology and Plant Quarantine E-792, 9 p.

and C. R. Parencia, Jr. 1950. Early-season applications of insecticides on a community- wide basis for cotton insect control in 1950. U.S. Department of Agriculture, Bureau of Entomology and Plant Quarantine E- 810, 8 p.

Fye, R. E. , C. L. Cole, F. C. Tingle, A. Stoner, D. F. Martin, and L. F. Curl.

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Harris, F. A., E. P. Lloyd, and D. N. Baker. 1966. Effects of the fall environment on the boll weevil in

northeast Mississippi. Journal of Economic Entomology 59: 1327-1330.


Hopkins, A. R., and H. M. Taft. 1965. Control of certain cotton pests with a new systemic insec-

ticide, UC-21149. Journal of Economic Entomology 58:746-749.

H. M. Taft, and W. James. 1977. Tobacco budworm, bollworm, and boll weevil: effectiveness

of newly developed experimental insecticides on cotton in the southeast. Journal of Economic Entomology 70:723-726.

Knipling, E. F. 1963. An appraisal of the relative merits of insecticidal con-

trol directed at reproducing and diapausing boll weevils in efforts to develop eradication procedures. Entomology Research Division, ARS, USDA. (Mimeographed, 22 p.)

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Lincoln, C, and C. R. Parencia, Jr. 1977. Insect pest management in perspective. Bulletin of Ento- mological Society of America 23:9-14.

Lloyd, E. P., and M. E. Merkl. 1961. Seasonal occurrence of diapause in the boll weevil in Mis-

sissippi. Journal of Economic Entomology 54:1214-1218.

M. L. Laster, and M. E. Merkl. 1964. A field study of diapause, diapause control, and popula-

tion dynamics of the boll weevil. Journal of Economic Ento- mology 57:433-438.

F. C. Tingle, J. R. McCoy, and T. B. Davich. 1966. The reproduction-diapause approach to population control

of the boll weevil. Journal of Economic Entomology 59:813-816.

F. C. Tingle, and R. T. Gast. 1967. Environmental stimuli inducing diapause in the boll wee-


Lukefahr, M. J. 1970. The tobacco budworm situation in the Lower Rio Grande Val-

ley and Northern Mexico. In Proceedings, Annual Texas Confer- ence on Insects, Plant Diseases, Weed and Brush Control, Texas A&M University, p. 140-145.

National Cotton Council. 1973. Boll weevil losses: value and location of losses caused

by the boll weevil. National Cotton Council Report, 52 p.


Parencia, C. R., Jr. 1978. One hundred twenty years of research on cotton insects in

the United States. U.S. Department of Agriculture, Agriculture Handbook No. 515, 75 p.

J. W. Davis, and C. B. Cowan, Jr. 1957. Control of early-season cotton insects with insecticides

employed as seed treatments. Journal of Economic Entomology 50:31-36.

Riley, C. V. 1885. Fourth Report of the U.S. Entomological Commission, being

a revised edition of Bulletin No. 3 and the final report on the cotton worm together with a chapter on the bollworm, 399 p.

Roussel, J. S., R. V. Bielarski, and D. F. Clower. 1957. The status of chlorinated hydrocarbon resistance in the boll weevil in Louisiana. Louisiana Agricultural Experiment Station, Department of Entomology Special Release No. 1.

Rummel, D. R., and R. E. Frisbie. 1978. Suppression of potentially overwintering boll weevils as a

pest management practice. The boll weevil: management strategies. Southern Cooperative Series Bulletin No. 228, p. 39-49.

Tingle, F. C, and E. P. Lloyd. 1969. Influence of temperature and diet on the attainment of

firm diapause in the boll weevil. Journal of Economic Entomol- ogy 62:596-599.

Townsend, C. H. T. 1895. Mexican cotton-boll weevil in Texas. Insect Life 7:295-

309.

SECTION III SUPPORT COMPONENTS

265

Chapter 11

MASS REARING BOLL WEEVILS

J. G. Griffin Boll Weevil Research Laboratory Agricultural Research Service U.S. Department of Agriculture Mississippi State, MS 39762

P. P. Sikorowski Department of Entomology Mississippi State University Mississippi State, MS 39762

0. H. Lindig Boll Weevil Research Laboratory Agricultural Research Service U.S. Department of Agriculture Mississippi State, MS 39762

ABSTRACT Because large numbers of sterile boll weevils (Anthonomus grandis Boheman) were to be used as a component of weevil eradication programs, rearing and equipment development research was conducted for all phases of weevil production in a laboratory. This resulted in new and improved weevil rearing technology and adoption of certain sanitary practices. Since most of the production operations were mechanized, the manual labor needed for rearing was reduced by 85% or more. Also, mechanization meant more aseptic operation. In addition, sanitation practices were developed that practically eliminated the microbial contamination that was so harmful to weevil rearing. The newly developed rearing technology was tested in mass production trials to evaluate its capability of rearing large numbers (5-6 million per week) of high quality weevils. The first test disclosed that minor changes were needed. After these changes were made, a second test and a production trial proved that high quality weevils can be reared economically.

^^^ J. G. GRIFFIN ET AL

INTRODUCTION

The first of the developments that eventually made it possible to mass rear boll weevils (Anthonomus grandis Boheman) in a laboratory was the formulation of a suitable artificial diet (Van- derzant and Davich 1958). This basic diet has since been modified CEarle et al. 1959, Vanderzant and Davich 1961, Gast and Davich 1966, Lmdig and Malone 1973), most recently by Lindig et al (1979), to make it better adapted for the insect, less expen¡ive, and more compatible with the equipment and procedures used for mass rearing.

The second of the developments was the progress made in designing mechanical equipment that could be used to rear larger numbers of weevils at lower cost (Gast 1961, 1965; Gast and Vardell iVbj;. Initially, use of the new equipment somewhat decreased the percentage of adults obtained from a given number of eggs, though

^QIA^^"^^^^ ^^^^ ^^^ weevil decreased much more (Gast and Davich 1966). Finally, by the midseventies to late seventies, the production of weevils was no longer limited by labor-intensive techniques.

The third development was the beginning of progress in controlling the diseases and microbial contamination encountered during the first efforts to accomplish laboratory rearing of weevils (Gast 1966).

As this progress was being made, the need arose to produce millions of sterile weevils per week for weevil eradication programs. Improved or new mass rearing technology would be required if these insects were to be mass reared economically and in the desired quantities. Therefore, a new research and production facility was constructed, and efforts were increased to achieve these goals.

FACILITY

The^new structure is known as the Robert T. Gast Rearing Lab- oratory (commonly the Gast rearing facility) and is located on the campus of Mississippi State University. It was designed to accommodate the rearing technology available at that time and was completed and equipped by June 1972. McLaughlin (1970), Griffin et al. (1971), and Griffin and Lindig (1978) have described the laboratory in detail.

The facility was used during the summers of 1972 and 1973 to produce and sexually sterilize the weevils used in the sterile male release component of the Pilot Boll Weevil Eradication Experiment in south Mississippi and adjoining areas of Alabama and Louisiana. Production during these years was unsatisfactory because of problems with contamination and because of the large amount of labor required. However, the information gained was valuable because it

MASS REARING BOLL WEEVILS 267

indicated that rearing procedures and equipment would have to be improved to achieve a successful mass rearing operation.

During the next few years, major efforts were made to design adequate rearing equipment and procedures. Thus by 1976, semiautomatic or automatic equipment had been developed to handle many of the rearing chores that had previously been handled manually, which meant that sanitary conditions were easier to achieve. In addition, labor requirements were reduced tremendously without reducing the percentage yield of weevils.

Therefore, in the summer of 1976, a 6-week mass trial was conducted at the Gast rearing facility to determine the production capability of the newly developed and modified rearing equipment and procedures. The goal was to produce 5 million weevils per week, and it was achieved, but the need for further changes in the operation became apparent. As a result, additional changes were made as follows: (1) High-Efficiency Particulate Air (HEPA) filters were installed over outlets of the air conditioning supply in the egg planting and larval development rooms; (2) adult weevils were moved into rooms that were farther away from the egg planting and larval development areas; (3) the larval development area was expanded from one room to two adjoining rooms so there could be more space and thus better air circulation around the carts that held the trays of diet and the eggs and larval stages; (4) a cabi- net was installed for fumigating the plastic and Tyvek used in constructing rearing trays; (5) antimicrobial agents were added to the sand used to cover the diet and eggs in the rearing trays (Sikorow- ski et al. 1980); and (6) the storage and processing operations relating to the diet were moved to a separate building to reduce the flow of microbes produced by these operations into the rearing areas. Most of these changes were made to provide better sanitation within the rearing facility because this had proved to be critical to control of microbial contamination during production.

Another 6-week production trial was conducted during the summer of 1977. Once again the goal of 5 million weevils per week was attained, and this time there were fewer problems and less contamination. However, the need for other modifications was apparent so the following changes were made: (1) a rackveyor was developed (Griffin 1979b) for stacking, holding, and conveying the rearing trays; it replaced the cart system (Griffin et al. 1979); (2) corncob grit was mixed with the sand used to cover the diet and eggs in the rearing trays (S. Malone unpublished data); (3) a chamber was constructed for fumigating the rackveyors; (4) a high temperature (hot) chamber was constructed to kill the weevils remaining in rearing trays that were to be discarded and the adults in the egg producing colony that had become too old; (5) the sugar-starch planting solution (Griffin et al. 1979) was replaced with a solution of Furcelleran (Bentonite 44/A) (S. Malone unpublished data); (6) emergence cubicles were developed and installed to replace the emergence boxes (Griffin and Roberson 1980); (7) the electrically operated mixers used in the egg harvesting operation were replaced

26Ö J. G. GRIFFIN ETAL

with pneumatically operated ones for better control of the mixing speed; (8) "escape" holes for emerging weevils were burned in the rearing trays so it would not be necessary to manually peel off the covering; and (9) new quality control and contamination monitoring operations were added. These changes saved labor, improved sanitation, reduced the numbers of live insects discarded to the outside environment, and helped in identifying some of the sources of contamination.

The equipment and techniques developed as a result of the 1976 and 1977 production trials were used to rear the weevils used in the North Carolina-Virginia Boll Weevil Eradication Trial program during the summer of 1979.

Thus by 1979, the Gast rearing facility included the following production areas: (1) diet sterilization, (2) pellet making, (3) oviposition, (4) egg harvesting and cleaning, (5) egg and planting solution sterilization, (6) sand and corncob grit (granular materials) preparation, (7) egg planting, (8) larval development (2 adjoining rooms), (9) emergence, (10) general supply storage, (11) storage for dry ingredients of diet, and (12) dry ingredient processing areas. However, areas 11 and 12 are located in a separate building away from the mass rearing facility. The oviposition, larval development, and emergence rooms have specially controlled environments; the other areas have environments designed for human comfort.

Nevertheless, during production in 1979, several deficiencies in the facility became apparent. These will need to be improved, if possible, and should be avoided in designing future mass rearing facilities. For example, areas of the seamless floor covering peeled from the concrete base, which makes the floor surface rough and harder to clean and sanitize. Quarry tile of better quality or a better method of applying the seamless covering material is needed. Also, some of the interior partition walls covered with gypsum board have deteriorated as a result of exposure to cleaning and sanitizing materials and procedures and, in some instances, because they were damaged when equipment was moved. Wall materials must be durable and easy to keep clean and must withstand the cleaning and sanitizing materials and application procedures. On the other hand, masonry (cinder) blocks or clay tile painted with epoxy enamel have given good service. Then drains were not provided in the floors, and these are needed for better washing and cleaning of the floors and walls. In addition, although the light fixtures are recessed and have covers, adult weevils still can enter the fixtures. When they die there, they cause an unsanitary condition that can be eliminated only by frequent cleaning of the fixtures. Fixtures with better sealed enclosures that are properly installed should help eliminate this problem.

Moisture condenses on the inside surfaces of the exterior win- dows and walls, especially in the rooms that have special environmental controls, when outside temperatures are low. This excess


moisture creates unsanitary conditions. The fewest and smallest possible insulated window units should be used, and the walls should be insulated to reduce or eliminate this problem. There is 3**-6**C differential in air temperature between the floors and ceilings in the rooms with environmental control. Proper type and location of the outlets that supply and return the conditioned air should eliminate or reduce the temperature differentials. Also, the use of insulation in the ceilings, walls, and floors would be helpful. Control of the environment is a separate problem that is particularly important in the areas where the culture is maintained; e.g., the development, emergence, and oviposition rooms. Therefore, the equipment must be of the proper type and must be adequate and reliable. Backup equipment for the heating, cooling, and air moving operations must be available.

Finally, proper sanitation is the first concern in arranging work areas or rooms in a facility. Work and materials must flow from the cleanest to the less clean areas. Traffic must be restricted in all areas, but it must be even more restricted in the clean rooms; e.g., the egg planting, pellet making, and larval development rooms. (At the Gast facility, access between separate areas is by covered outside walks, but a central corridor would be satisfactory.) Also, dressing and shower accommodations and clean uniforms must be provided for workers entering these clean rooms, and their use must be mandatory.

DIETS

Ingredients and Proportions

Two diet formulations are presently used for mass rearing boll weevils; one is used for rearing larvae and the other is used with adults, both for feeding and as oviposition sites. The dry ingredients and proportions for both diets are given in Table 1. Other diet formulations have been tested recently (Lindig et al. 1979), but the ones shown are presently used as the standards. Ingredi- ents are normally obtained in quantities to last through a summer rearing season or a program. If necessary, the materials are stored in cool, dry, and easily accessible quarters that are as resistant to rodents and damaging insects as possible. Records are maintained on sources and dates of acquisition, and any changes of material are noted.

Processing

The ingredients of the vitamin mix used in both diets (Table 1) are mixed on-the-job in batches (Table 2) and blended to a homogenous mixture in a twin shell blender.

Batches of the dry mix for both regular diets are prepared in advance by weighing out the ingredients in the quantities indicated

2'^° J. G. GRIFFIN ET AL.

in Table 1. Before the cottonseed meal is used, it is sifted to remove the large particles of cottonseed hulls and other large foreign particles that are not beneficial or desirable in the diet and may cause pumping problems in the flash sterilizer. The sifting is done with a vibratory separator equipped with a 32-mesh screen (Griffin et al. 1979).

The correct quantities of sifted cottonseed meal, sugar, potassium sórbate, cholesterol, and cottonseed meats are weighed out, thoroughly mixed in a blender, and milled in a hammer mill with

Table 1.—Ingredients and quantity of each used to make one batch of the dry ingredients for the two boll weevil diets

Quantity (grams) Ingredient Adult diet Larval diet

Cottonseed meal (sifted) 28,500 31,800 Agar 8,400 8,280 Sugar 6,850 7,800 Promine D 10,800 12,280 Corncob grits (60 mesh) 6,000 1/ Cholesterol 300 360 Wesson salt 1,125 1,260 Vitamin mix 2/ 1,170 1,260 Potassium sórbate 585 630 Tegosept 375 400 Ascorbic acid 270 290 Methenamine 60 1/ Cottonseed meats 10,800 10,724

j_/ Not used. 2/ See Table 2,

Table 2.—Ingredients and quantity of each used in batch of vitamin mix

Ingredient Quantity (grams)

Niacinamide 20 Ca Pantothenate 20 Riboflavin 10 Thiamine HCl 5 Pyridoxine HCl 5 Folie acid 5 Inositol 40 Sugar 6160


0.6-mm screen openings. (The ingredients milled with the cottonseed meats absorb the oil from the meats, which would otherwise clog the mill screen.) The milled mixture and the other ingredients are mixed in a blender until homogenous. Then the completed batch is sifted on the separator used to sift the cottonseed meal so as to remove lint and hull particles from the cottonseed meats and any other large particles or foreign material introduced in un- milled ingredients. Finally, the dry mix is placed in containers that are properly labeled and stored in the diet sterilizing room. During a production program, dry mixes are prepared 5 days per week so as to reduce storage time.

Processing of the dry mix produces considerable amounts of dust, which contains and supports microbes. The room used for this operation is therefore ventilated to keep the dust at acceptable levels (for the operator) and to prevent it from accumulating in the storage room(s). Because of the dust and the microbes, the storage and processing rooms are located in a separate building away from the main rearing facility.

Sterilizing

The diets used in mass rearing boll weevils are thermally sterilized by using a flash sterilizer (Cherry-Burell NO-Bac. Uni- therm IV) (Griffin et al. 1974, 1979) (Figure 1) in a separate room of the main rearing facility.

The diet is prepared for sterilizing by weighing out or measuring by volume each of the ingredients listed in Table 3. Then

Table 3.—Ingredients and quantity of each used in preparing 45.4 kg (water quantity) of the two boll weevil diets

Quantity Ingredient Larval diet Adult diet

Dry mix, kg (see Table 1) 8.5 8.6 Water, kg B,„ vitamins (0.01%), ml

45.4 45.4 9 12

Biotin (0.01%), ml 9 9 HCl, ml 40 40

these materials are placed in the product tank of the sterilizer and mixed to a homogenous mixture with a propeller-type mixer. The mixture is next pumped through the sterilizer, where it is heated to ca. 141 **C and then held at this temperature for a minimum of 30 seconds. Heated mixture to be used for larval and adult diets is cooled to ca. 40.5**C or 52*C, respectively, and then transferred through stainless-steel tubes to the points of use, the

272 J. G. GRIFFIN ETAL.

pellet machine in the case of the adult diet or the egg planting machine in the case of the larval diet (see sections on pellet making and egg planting). The sterilizers have heat exchangers made of coiled tubing inside a pressure-tight metal jacket and use steam for heating and regular tap water for cooling. The heating and cooling temperatures are automatically controlled with two proportional temperature controllers and motor-operated valves. Each sterilizer is rated at 170 liters per hour capacity, a size compatible with the capacity of the equipment the units are serv- ing. The sterilizer units are cleaned and sanitized after each use (Sikorowski 1975).

Figure 1.—Sterilizer and auxiliary equipment used to sterilize the diets.

EGG PRODUCTION

Source of Weevils

Boll weevils used in the Boll Weevil Eradication Trial were obtained by crossing weevils collected in the fields of North Caro- lina with an ebony strain (Bartlett 1967) that has been maintained at the Boll Weevil Research Laboratory for several years. This


crossing, and careful selection for ebony characteristics, produces weevils that are easily identified when they are released in the field for eradication or for research work. Calco Red dye can also be incorporated into the larval diet to produce a marker (Gast and Landin 1966, Lindig et al. 1980).

Adults used for egg production, that is, the brood colony, are selected from those collected the first day of emergence from

the rearing trays.

Pellet Making

The pellets of adult diet that serve as both food and oviposition sites for adult weevils in the brood colony are prepared in a pellet-making machine and then placed in a waxing machine where they are coated with a mixture of 40% beeswax and 60% paraffin (Griffin and Lindig 1974) (Figure 2) to prevent or reduce desiccation. (Also, the females prefer this cover for oviposit ion.) The procedure is as follows: Sterile diet is pumped from the sterilizer to the pellet machine through stainless-steel tubes. It then flows through automatically operated control valves into the forming tubes, ca. 8-mm i.d., of the heat exchanger. The cold water flowing around these tubes causes the diet to solidify. As the resulting gelled rod is discharged from the tubes, a rotating drum with wires spaced around the circumference cuts it into ca.^U-mm sections. These sections fall into the vat of warm, ca. 68*'C, wax of the waxing machine. Then an inclined wire belt lifts the pellets out of the wax and discharges them over the edge so they fall into a catching container. As they fall, a blast of air from a fan causes the wax coat to harden. The finished pellets are ca. 9.5 (diameter) x 13 (long) mm. They are stored in sanitized covered

plastic pans until used.

The pellet making should be done in a separate clean-air room with an independent air conditioning system to hold microbial contamination of the diet to a minimum. The wax mixture used to coat the pellets is sterilized by boiling in a steam kettle and then held at the desired temperature in a wax warmer tank (Griffin et al. 1979). It is transferred from the tank to the vat as needed.

The equipment and space are cleaned and sanitized each day after operation (Sikorowski 1975).

274 J. G. GRIFFIN ETAL

Figure 2.—Pellet making equipment used for making and wax coating the food pellets.

Management of Oviposition Equipment and Procedures

The oviposition room, a separate room of the rearing facility with an independent air conditioning system, houses the adult weevils used for egg production. These weevils are held in stainless-steel cages (Griffin and Lindig 1979) that are ca. 46 (width) X 99 (length) x 5 (height) cm and consist of a base, a removable lid, and a feed basket. The bottom of the base is covered with 5.5-mesh (wires per cm) wire cloth for light entrance, air ex- change, and debris discharge. The feed basket has 2.5-cm side walls, and the bottom is covered with 1.6-mesh wire cloth to facilitate separation of the weevils from the diet pellets at feeding time. The cages of weevils are supported and moved about in the room by a conveyor unit (Figure 3).

When a cage is to be stocked with weevils, ca. 2250 diet pellets, measured by volume, are spread evenly over the bottom of the feed basket of a clean, sanitized cage. Newly collected adults (9000, mixed sex, measured by weight) selected from the group eclosing the first day of emergence after implanting are scattered over the diet pellets. Examination has shown that the sex ratio of these newly emerged weevils is ca. 1:1.


Figure 3.—Oviposition cage, shaker, and conveyor for mass rearing boll weevils.

Once each day, the conveyor is used to move the oviposition cages to the feeding table. There they are lifted from the conveyor, and old pellets are removed and replaced with fresh pellets. Then the conveyor moves the cages away from the feeding table as needed. Fresh pellets are provided at a rate of ca. four weevils per pellet.

The old pellets are later carried to the egg harvesting area for the harvesting operation.

Also, each day, new cages of young adults, the number needed to maintain the colony at the desired level, are prepared and placed in the oviposition room. Likewise, each day, cages containing 14-day-old weevils (weevils are kept in the brood colony for egg production for 14 days) are removed and destroyed by placing them in a paper bag and holding them at ca. 66°C for over 20 hours.

Environment

The oviposition room is maintained at 31°±1°C and 50%±5% relative humidity and in total darkness except during feeding and cleanup, usually a matter of 3-4 hours per day. Uniform air movement, ca. 30 m per minute, around the cages is necessary to maintain the pellets at a moisture level that will give maximum egg

276 J. G. GRIFFIN ET AL.

production. Air velocity greater than ca. 50 m per minute around the cages will dry out the pellets, thereby reducing egg production.

EGG HARVEST AND PREPARATION

Harvest

After the females deposit their eggs at various depths in the diet pellets (beneath the wax coat), the eggs are harvested from the pellets mechanically (Griffin and Lindig 1977, Griffin et al. 1979) as follows:

Pellets collected from the oviposition cages during the adult feeding operation are dumped into the hopper of an electrically operated lift, transferred into a vibratory feeder hopper ((1) in Figure 4), and then sprayed with tap water as they are fed into wax crimping rollers (2). The rollers crack the wax coat, and the

Figure 4.—Equipment for harvesting the eggs from pellets.


water, diet particles, and wax coating are discharged from the rollers into one compartment of a two-compartment separation tank (3) where the mixture is agitated by an air-operated, propeller- type mixer. When one compartment is filled, the flow of water and broken pellets is directed into the other compartment, and the mixer in the first compartment is stopped. Wax particles then rise, and diet particles and eggs sink. The wax is skimmed off, washed, drained, placed in a steam kettle, and boiled to remove the remaining moisture and to sanitize it for re-use. The diet-eggs-water mixture is pumped (4) to disintegrators (choppers) (5) where the diet particles are further reduced in size so the eggs can float free. Then the mixture is discharged into the liquid-solid separator (6). One deck of the separator (top) consists of 10-mesh screening; the other (bottom) of 19-mesh screening. The larger particles of diet from the mixture remain on the top deck, and the eggs and smaller particles are deposited on the lower deck and then discharged into a basket covered with 20-mesh hardware cloth. The water and large particles of diet are deposited into and flushed down a trough into the waste disposal system.

Cleaning

The initial separation of the eggs from fine diet particles is done in saturated sodium chloride solution (brine) and a 57-liter separatory tank. First, the basket of eggs and fine particles is placed in brine in the tank, stirred thoroughly, and let set for ca. 5 minutes. Since the eggs float and the diet particles sink, the floating eggs can be skimmed from the surface. (The brine and diet particles are drained from the tank to make the tank ready for a new batch.) The final cleaning of eggs is accomplished by placing the eggs in a 1000-ml separatory funnel and rinsing them with fresh brine. Then the clean eggs are rinsed in fresh water to remove the brine and placed in graduated cylinders for measurement and transfer to the sterilizing area.

The egg harvesting and cleaning operation produces a moist unsanitary environment; therefore, these operations are performed in a separate, well-ventilated room. All equipment is cleaned daily after use, and a constant supply of brine is maintained in two 303-liter plastic tanks.

Surface Sterilizing

After the cleaning, the eggs are surface sterilized in a solution of formalin and water to kill any microbes that could contaminate the diet during the rearing period (Sikorowski et al. 1977). A bottle, ca. 3.8 liter, containing 2000 ml fresh water (filtered by a millipore filter with 0.3 micron pore size) and 500 ml of 37% formalin solution can accommodate 200 ml of eggs. This bottle with the eggs and the solution is shaken on a laboratory


shaker for 20 minutes and then rinsed twice in filtered water by shaking on the shaker for 10 minutes.

Planting Solution

A sterile planting solution, prepared by mixing 2000 ml water and 10 g Furcelleran (S. Malone unpublished data), is placed in a regular planting bottle and shaken to dissolve the Furcelleran. The Furcelleran produces the necessary viscosity to hold the eggs in suspension. The bottle and contents are then sterilized in an autoclave and stored in a clean area at 21°C. Just before planting, solution and eggs, 7:1 ratio, are placed in a sterile planting bottle and mixed under a laminar flow clean air hood. The bot- tles of suspended eggs are then held in the clean hood until the actual egg planting operation.

REARING

Egg Planting

In 1973, plastic trays replaced the petri dishes used at the Gast rearing facility to mass rear boll weevils (Griffin 1978, Griffin et al. 1979, Harrell et al. 1977). As a result, major changes in equipment and methods were necessary. The rearing trays now used are formed from roll stock of ca. 17-mil-thick, high- impact polystyrene and are covered and sealed with a film of Tyvek lidding material, also from roll stock.

The egg planting operation is performed semiautomatically with an in-line form-fill-seal machine (FFSM). Auxiliary equipment consisting of a diet filler, diet cooler, egg planter, and granular material filler is located along the line between the forming and sealing heads of the FFSM (Griffin et al. 1979, Harrell and Griffin 1981) (Figure 5). The trays, 15 (width) x 28 (length) x 1.9 (depth) cm, are formed sequentially in a continuous ribbon and moved intermittently along the processing line by the FFSM.

The semiliquid filler machine accumulates the sterile larval diet from the sterilizer and meters and dispenses ca. 185 ml into each tray cavity. After the tray is filled, it passes through the diet cooler (Griffin 1979a) where the diet is solidified by cooling. Next, the trays move to the planter (Griffin 1979c), which meters and uniformly disperses 4 ml of the egg suspension (ca. 2100 eggs) on the surface of the diet. Then the granular material filler machine meters and dispenses ca. 48 ml of granular material (described later this section) into each tray. Now the tray is moved to the sealing head where it is covered and sealed with Tyvek. Once the trays have been sealed, the ribbon is sheared into sections of two trays each. Each section of trays is then shaken by hand so as to spread the granular material evenly over the surface


Figure 5.—Equipment for tray processing and egg planting.

of the diet and then stacked in the sanitized rackveyors (Griffin 1979b) (Figure 6). Each rackveyor holds 896 of these trays.

The FFSM with auxiliary equipment is located in front of a wall module of HEPA filters (rated 99.9% efficient on particles > 0.3 microns). This location is necessary to provide an environment of clean air in the space where the sterile diet, egg suspension, granular material, tray plastic, and Tyvek are exposed during the planting operation.

The rolls of plastic and Tyvek are received from the supplier in a clean but not a sterile condition. Therefore, before use, they are fumigated with paraformaldehyde gas in a special chamber. The procedure reduces contamination of the diet.

Earlier, when petri dishes were used in rearing, the diet surface was scarified and dried so the young larvae would not drown in the moisture from the planting solution (Gast and Davich 1966, Griffin and Lindig 1978). The granular material mentioned previously absorbs the free moisture, provides a cover for the eggs

^0 J. G. GRIFFIN ETAL

Figure 6.--Rackveyor used for stacking and conveying planted trays.

and diet (Griffin and Lindig 1975), and serves as a base for the antibiotic agents used to control contamination (Sikorowski et al. 1980). Additionally, it provides an object for the small larvae to push against and allows them to begin eating from the surface of the diet, which they cannot do effectively unless the surface is scarified. The material used is a mixture of sand and corncob grits (8-16 mesh) in a ratio of 7:3 (volume) (S. Malone unpublished data) to which antibiotic agents are added.

The sand preparation local sand pits is dried sieve. It and the grits are combined; afterwards sterile containers in a mixing 8825 ml sand, 377 1.25 g neomycin sulfate (75% folpet) (Sikorowski be blended for 15 minute duce a homogenous mix. tainers until needed in

is as follows: washed, mason sand from and sifted through a 6.3-mesh screening are sterilized in an autoclave before they

, further handling or blending is done in clean air cubicle. A batch is prepared by 5 ml grit, 1.25 g streptomycin sulfate, (or the equal of these), and 6 g Phaltan 1982). One or two batches at a time can

s in a 0.03-m twin shell blender to pro- The mix is stored in closed 19-liter con- the egg planting operation.

As noted, the egg planting operation is performed in a separate room of the rearing facility. Entry to this room is restricted and the room is maintained as nearly as possible at the cleanliness of a "class 100 clean room (3.5 particles per liter of


air)." Therefore, the equipment involved in the planting operation is located in front of the clean air wall module. In addition, the conditioned air of the room is passed through HEPA filters because trays of diet that are contaminated at this point will be completely destroyed by the end of the regular larval development

period.

Development

After the rackveyors are loaded with planted trays, they are rolled into the first of the two development rooms to remain for the first 9-10 days of the larval development period. Then they are rolled into the second development room where they remain for the remainder of the 13-day period. By the 13th day after the eggs are planted, ca. 10% of the weevils have developed to the adult stage and are ready to leave the trays.

Both development rooms are held at 3r±rc and 50%±5% relative humidity, with continuous light, and both are maintained as near the cleanliness of a class 100 clean room as possible. The separate rooms are necessary because the trays of newly planted pre- adult-stage weevils must be separated from the trays containing older weevils that might escape as adults and contaminate the newly planted trays.

The air temperature, relative humidity, and circulation in all areas of both development rooms must always be at the proper levels to obtain uniformity in development and the maximum yield of weevils (Griffin et al. 1979). As noted, the air in the rooms is kept clean by passing the entering conditioned air through HEPA filters, and entry to the rooms is restricted.

The rackveyors are arranged in the development rooms so there is adequate space and ventilation between adjoining units. This arrangement means that the rearing medium will produce maximum yields of weevils.

Adult Emergence

Weevils from eggs oviposited and planted the same day never develop so uniformly that all adult emergence occurs the same day (Griffin et al. 1979). Emergence will usually occur over a 6- to 7-day period (13-20 days after eggs are planted), but in the mass rearing facility, trays are held in the emergence area for only 5 days. By this time, 90-95% of the adults will have emerged, and any emerging later have proved to be of poor quality.

Thus, the 13th day after eggs are planted, the rackveyor of trays is rolled from the number 2 development room to the tray preparation room in the emergence area. Here, while the trays are still on the rackveyor, a hole, ca. 1.3 x 2.5 cm, is burned in one

282 J. G. GRIFFIN ETAL.

end of each tray with an electrically heated charcoal lighter to provide a way for the adult weevils to leave the trays. Immedi- ately afterwards the rackveyor of trays is rolled into an emergence cubicle (Griffin and Roberson 1980).

The emergence cubicle has inside dimensions of 2.0 (width) x 2.4 (length) x 1.9 (height) m. Each can accommodate three rackveyors of trays, the equivalent of one day's planting. Access into the cubicle is through a 1.1 (width) x 1.8 (height) m door located in one wall. This wall also has twenty-eight 6.4-cm-diameter holes arranged in four columns of seven holes each (Figure 7). Jar lids (100 mm) with 6.4-cm holes in their center are mounted over these holes, and 3.8-liter plastic jars with a hole cut into the bottoms are screwed into the lids to serve as collection containers for emerging adult weevils. The bottom holes are covered with 5.5-mesh hardware cloth to allow for air circulation but make the opening weevil proof. Since the only light in the cubicle enters through the jars and since boll weevils are positively phototactic, the weevils are attracted from the trays.

At least once each day (more frequently if adult emergence is heavy), the weevils are removed from the jars and weighed to

Figure 7.—Emergence cubicles.


determine the number obtained. Later, they are distributed and used for colony maintenance or are sterilized. After the adults have been harvested, the rackveyors with trays are removed from the emergence cubicle and rolled into a small hot room maintained at ca. 66**C. They remain there for ca. 24 hours; that is, until any live weevils remaining in the trays have been killed. The trays of spent diet are then discarded.

The emergence cubicles are maintained at 31°±1**C and 50%±5% relative humidity. An exhaust fan exchanges the air inside the cubicles with the fresh air entering through the collecting jars. The cubicles also have an exhaust system vented above the roof of the building so the cubicles can be fumigated. The cubicles and rackveyors are cleaned and fumigated after each use.

A detailed list and a description of all production equipment used in the operations are given by Harrell and Griffin (1981).

MICROBIAL CONTAMINATION

One of the major problems encountered in mass rearing the boll weevil was microbial contamination, here defined as the harboring of or having contact with micro-organisms in the absence of a relationship that may be considered commensal istic, mutualistic, or parasitic (Steinhaus and Martignoni 1970). The microbial contaminants encountered are usually microbes that are otherwise nocuous. However, it is well-documented in the literature of animal pathology that micro-organisms normally considered nocuous can multiply extensively in the tissue of weakened hosts and so cause disease that may often be severe (Neter 1974). The boll weevil diet is a complex medium so it is subject to spoilage by many species of bacteria and fungi. Then since spoilage is the result of metabolic activity associated with microbial growth, the spoiled diet causes catabolism and release of products of digestion. In other words, the biochemical changes produced by microbes alter the nutritional value of the medium. In addition, microbial products such as bacterial toxins and myotoxins may interfere with weevil defense mechanisms or may damage weevil cells.

The cost of rearing weevils was greatly reduced by establishing an environmental sanitation program (Sikorowski 1975). How- ever, much of the information pertinent to this aspect of laboratory rearing of weevils has been obtained only recently and merits further study. Meanwhile, from present research results, sanitation is important in the mass rearing of boll weevils (and most other insects), and more attention will have to be given to strict enforcement of basic sanitary measures to achieve volume production of healthy insects.

The safety of employees must also be considered in designing environmental sanitation programs. A number of airborne micro- organisms such as Aspergillus, Pseudomonas, and Streptococcus,

284 J- G- GRIFFIN ET AL

which grow on almost any organic matter, are human pathogens too and constitute some degree of hazard to employees.

Sources of Contamination

The microbial contamination that causes problems in rearing laboratories is mostly generated by man and equipment. Humans are the primary source, and the level of contamination relates directly to the activity and density of personnel (Favero et al. 1966, 1968; Runkle and Phillips 1969). In fact, one healthy human body harbors millions of micro-organisms on the skin and in the mouth, respiratory tract, genitourinary tract, and intestines. Jawetz et al. (1978) arranged the normal microbial flora of the human body into two groups: (1) the resident flora, which consists of fixed types of micro-organisms regularly found in a given area and in persons of a given age; and (2) the transient flora, which consists of non- pathogenic or potentially pathogenic micro-organisms that inhabit the skin and mucous membranes for hours, days, or weeks. (This second group is derived from the environment, does not produce disease, and does not establish itself permanently on the surface.)

Our studies showed that freshly laundered and sterilized cotton uniforms do not stop the movement of bacteria through the cloth into the environment (Sikorowski 1975, Sikorowski and Thompson 1980) (Figure 8). Also, hairs from 50 persons (1 hair per person) each had from several to many bacteria; and cultures from hands always produce bacterial colonies, even shortly after normal washing. Talking, coughing, and sneezing likewise produce numerous moisture droplets, many of which contain bacteria. Finally, the malfunction of equipment or incorrect sterilization of equipment has usually been associated with massive contamination (Sikorowski 1975).

Microbial Flora of Weevils

In nature, adult boll weevils are solitary insects. They are seldom found together except when mating or when the food supply becomes scarce (Gast 1966). Laboratory-reared weevils, on the other hand, are always crowded together. In addition, insectary conditions are generally different from conditions in nature, which also contributes to the problem of microbial contamination (Shapiro 1982).

Field-Collected Weevils

The newly emerged boll weevil larva is sterile, but it immediately becomes bacterially contaminated because it feeds on decom- posing cotton squares. Thus field-collected larvae examined in the laboratory have very high numbers of bacteria per larva. However, the composition of the bacterial flora is simple and usually


(A) Freshly Laundered Uniform (B) Uniform Worn for Four Hours

Figure 8.—Plates showing microbes found on garments.

limited to two or three species of bacteria such as Erwinia herbicola (Geilinger)Dye and Enterobacter aerogenes Hormaeche and Edwards.

On the other hand, newly emerged adults from field-collected, surface-sterilized pupae have very low bacterial content. For example, 75% of field-collected adult boll weevils of various ages from Louisiana, Mississippi, and Texas were found by Sikorowski et al. (1977) and McLaughlin and Sikorowski (1978) to have fewer than 100 bacteria per insect. Hedin et al. (1978) reported that this low bacterial content can be attributed to antibacterial constituents such as gossypol, caryophyllene, gallic acid, and tannins that are found in the host cotton plants.

Likewise, diapausing weevils (250) collected during May and June of 1976 to 197 9 had low bacterial content as follows: 0 - 100 bacteria per weevil, 52%; 101 - 500, 13%; 501 - 1000, 4%; 1001 - 2000. 4%; 2001 - 5000, 3%; and 5000+, 24% (P. P. Sikorowski unpublished data).


Insectary-Reared Weevils

Weevils reared in an insectary, unlike field-collected weevils, are frequently contaminated with diverse species of aerobic and anaerobic bacteria. Thus, Sikorowski (1982) isolated many taxonomically unrelated species from apparently healthy insectary- reared boll weevils as follows: from the family Micrococcaceae, Micrococcus luteus (Schroeter) Cohn and Staphylococcus aureus Rosenbach; Streptococcaceae, Streptococcus spp., Leuconostoc mesenteroides Cienkowski van Tieghem; Bacillaceae, Bacillus sphaericus Neide; Lactobacillaceae, Lactobacillus plantarum (Orla- Jensen) Bergey et al.; Pseudomonadaceae, Pseudomonas aeruginosa (Schroeter) Migula; Enterobacteriaceae, Enterobacter aerogenes; and Coryneform Group, Cornynebacterium humiferum Seliskar. Later McLaughlin and Sikorowski (1978) tested 35 bacterial cultures, mostly from the American Type Culture Collection, for their ability to grow on the boll weevil diet. They found that 5 of 15 human pathogens and 7 of 20 saprophytes developed on the diet.

Effects of Microbial Contamination

Effects of bacterial contamination on weevil development and on amino and fatty acids, pheromone, and histopathology were examined by Sikorowski (1975), Gueldner et al. (1977), Sikorowski et al. (1977), Thompson et al. (1977), McLaughlin and Sikorowski (1978), Thompson and Sikorowski (1978), Sikorowski and Thompson (1979, 1980), and MacGown and Sikorowski (1980).

Weevil Development

The number of weevils that emerge from contaminated diets is influenced by the species of micro-organisms present, the stage of the insect at the time of contamination, the temperature, and other factors. However, the most conspicuous effects of microbial contamination are associated with the early developmental stages of the insect. For example, from 1972 to 1976 (the Gast rearing facility was completed in 1972), Aspergillus niger van Tieghem was present in the rearing medium for weeks or even months at a time. This contamination with A. niger, and occasionally with A. flavus Link, Pénicillium spp., yeast, and Rhizopus spp., was a serious problem when it occurred during early stages of larval development: larvae that were covered with conidia died, presumably from starva- tion. However, A. niger was normally present toward the end of the larval period when it did relatively little damage. Use of sand treated with Phaltan has since reduced A. niger contamination to almost zero (Sikorowski et al. 1980).

Bacterial contamination of the diet also will cause a reduction in yield per tray. P. P. Sikorowski (unpublished data) found that boll weevil diet contaminated with ^. aureus or Streptococcus


spp. at the time eggs were implanted produced 57 and 76%, respectively, as many weevils per petri dish as did uncontaminated diet. Similar values for the third and sixth days after hatch were 57 and 64% and 71 and 80%. In contrast, fast growing bacteria such as Leuconostoc spp. may overgrow an area of diet of about 700 mm during as little as 24 hours, meanwhile smothering all the larvae on the dish. Staphylococci (enterotoxin producers) also may have adverse effects on the larvae: the normal developmental time of 13 days from egg to adult weevil was extended to 14 or 16 days when diets were contaminated with such species of bacteria.

Amino and Fatty Acids, Pheromone, and Histopathology

Thompson et al. (1977) and Thompson and Sikorowski (1978) studied effects of Streptococcus sp., Micrococcus varians Migula, and E. aerogenes on the amino and fatty acid content of boll wee- vilsT They reported that all amino acids analyzed, except tyrosine and glutamine in females, were present in greater amounts in weevils free of bacterial contamination. The average reduction was 33% for males and 52% for females. The high levels of tyrosine and glutamine in contaminated female weevils were not explained. Comparison of individual fatty acids between groups showed a^decrease of up to 76% in highly contaminated insects (2.1 x 10 bacteria per insect).

Gueldner et al. (1977), P. A. Hedin and P. P. Sikorowski (unpublished data), and G. Wiygul and P. P. Sikorowski (unpublished data) examined the effects of bacterial contamination on pheromone production by the male boll weevil by measuring the amounts present in the feces and in the homogenate of the body. More pheromone was always isolated from the frass and homogenate of uncontaminated weevils than from the frass and homogenate of contaminated weevils. Then since pheromone production, and hence attractiveness of the sterile released weevil, is an essential characteristic, weevils that are bacterially contaminated would be expected to have greatly diminished value.

Also, McLaughlin and Sikorowski (1978), Sikorowski and Thomp- son (1979, 1980), and MacGown and Sikorowski (1980) examined the effects of bacterial contamination on the brush border of midgut epithelium of the boll weevil. In contaminated weevils, the brush border was frequently ulcerated and overgrown by bacteria. In addition, MacGown and Sikorowski (1980) showed Jhat though bacterial contamination and irradiation (10 krads of Cs ) both cause rapid deterioration of midgut epithelium of adult boll weevils, S.aureus and Streptococcus spp. greatly accelerated the effects of irradiation"^ The result was destruction of the tissues within a few days and subsequent premature mortality. R. A. Leopold (personal communication) has detected similar histopathological changes in bacterial ly contaminated boll weevils after irradiation.

288 J.G. GRIFFIN ETAL

Sanitary Measures

The principal objective of the sanitary methods used at the Gast rearing facility is to prevent entry and spread of microbes. The program includes maintaining a clean and sanitary environment by proper housekeeping, personal hygiene, proper waste disposal, proper use of gowns, gloves, and masks, and traffic control to minimize spread of microbes from area to area.

Numerous investigators have shown that the primary sources of microbial contamination within insectaries are: (1) human, (2) unsterilized diet, (3) insects, and (4) the facility itself. The significance of control of microbial contamination has been discussed by Steinhaus (1953), McEwen and Hervey (1960), Beard and Walton (1965), Gast (1966), Gast and Davich (1966), Ignoffo (1966), Lyon and Flake (1966), Martin (1966), O'Dell and Rollinson (1966), Raun (1966), Magnoler (1970), McLaughlin (1970), Helms and Raun (1971), Howell (1971), Sutter and Miller (1972), Sikorowski (1975), Stewart et al. (1976), Baumhover et al. (1977), and Shapiro (1982). In addition, Sikorowski (1975) described microbial monitoring and sanitary measures that are used at the Gast rearing facility. Also see reviews by Shapiro (1982), Goodwin (1982), and Sikorowski (1982) for extensive treatments of this subject.

Housekeeping

Micro-organisms settle from the air (onto floors, tables, shelves, external surfaces of equipment) and rise into the air again as a result of any movement in the room. The general housekeeping routine for minimizing contamination from this source is mopping and disinfecting floors. Litsky and Litsky (1968) and many other workers in the field of microbial contamination have demonstrated that flooding and wet-vacuuming is the most effective method of doing this. Portable vacuum cleaners may be used only if the vacuum cleaner exhaust is filtered at least as well as the air in the room. Sweeping and dry-mopping tend to stir up micro- organisms and should be avoided (Nagasawa et al. 1970). Runkle and Phillips (1969) recommended elimination of sweeping by use of dry or wet pickup vacuum cleaners equipped with high efficiency exhaust air filters. All floors in the Gast facility are mopped twice daily, in the morning and again in the afternoon (1 hour before the end of an 8-hour shift).

Personal Hygiene

Micro-organisms are usually shed with the human skin scales to which they are attached. Thus, personnel involved in handling insect diets and adult weevils and with planting eggs are required to wear caps and wash their hands frequently with medicated scrub soap. Workers handling weevil diets are also required to wear hair caps and face masks.


Sterilization of Equipment

Sterilization means the destruction of all life, and heat is the most reliable and universally used method of sterilization. Whenever possible, this is the method used at the Gast rearing

facility.

Large equipment such as the apparatus for processing medium that is permanently attached to the walls is sanitized immediately before and just after use to prevent entry of microbes into the apparatus. (On one occasion, improper sterilization of this equipment caused massive contamination of diet that resulted in loss of time, money, and insects.) Small instruments that cannot be auto- claved are sanitized by immersion in sanitizing solution.

Contaminant Monitoring Program at Gast Rearing Facility

The purpose of contaminant monitoring at the facility was to evaluate the effectiveness of the sanitary measures used there. The tests are made to determine (1) air microbial content, (2) sterility of diet, (3) surface sterility of weevil eggs, (4) micro- organisms on surfaces, and (5) presence of micro-organisms in adult

weevils.

Air Microbial Content

The two methods used to monitor the microbial content of the air in the facility were as follows:

(1) Membrane filter method: The air was filtered through a membrane filter (0.45-micron pore size) supported in a filter as- sembly. The filter was then placed in a 12- x 54-mra plastic petri dish with an absorbent pad saturated with mycological or plate count broth and incubated at 32'C for 24 hours. Afterwards the filters were removed from the dishes, air dried, and stained with méthylène blue solution; the levels of contamination were recorded. A sample consisted of 100 liters of air drawn through the filter.

(2) Agar setting plate method: An uncovered, agar-filled petri dish was allowed to remain open on a particular surface for 5 minutes. When airborne particles containing viable micro- organisms formed bacterial or fungal colonies on the agar medium after incubation, the colonies were counted, and the level of contamination was recorded. Microbial content of the air was monitored in egg planting and larval holding areas.

Sterility of Larval Diet

During preparation of the larval diet, 20-cc samples of diet were collected aseptically in sterile petri dishes every 15


minutes. The dishes were examined after 24-48 hours of incubation at Sy^C, and levels of contamination were determined.

Sterility of Eggs

Eggs were removed from the diet pellets as described by Grif- fin et al. (1979), surface sterilized with 10% formaldehyde (Siko- rowski et al. 1977), and planted on the diet (Griffin et al. 1979). Five samples of 2000 eggs each (each bottle of egg suspension contained 250 ml eggs plus 1750 ml planting solution) were planted in petri dishes with sterile trypticase soy agar and then incubated for 72 hours at 37*'C. A Gas Pak Anaerobic System (Bal- timore Biological Laboratory) was used for subsequent isolation of anaerobic bacteria. If a dish contained one or more colonies, contamination was considered to have been demonstrated.

Micro-organisms on Surfaces

Two methods were used for detection of bacteria on surfaces, the swab-rinse method and the agar contact method. In the first method, a cotton-tipped sterile swab was rubbed over the surface of the object to be sampled. Then the tip of the swab was broken into a tube containing sterile diluent, the tube was shaken, and the rinse fluid was plated on appropriate culture medium. Care was taken to avoid contaminating the swab.

In the second method, a rodac plate was used to monitor surface cleanliness. This plate was a modified petri dish that contained a raised nutrient agar bed. It was placed in contact with a surface; then the samples were usually incubated for 48 hours at 35**C before the colonies were counted. Trypticase soy agar with lecithin and polysorbate 80 medium was prepared for detection of surface contamination. (The lecithin and polysorbate 80 inacti- vated residual disinfectant collected with the specimen.)

Microbial contamination in the Gast rearing facility was found to vary depending on the area tested. In the egg planting and larval holding rooms where air was filtered through HEPA filters, the bacterial count was less than 10 colonies per plate. (The tests were made after wet cleaning and drying of the floor before any traffic was permitted.) The equipment, when properly cleaned and sanitized (Griffin et al. 1979), produced sterile medium. Formal- dehyde-sterilized eggs were almost free of microbial contamination, but eggs scored during extraction were occasionally infected with bacteria and fungi.


Micro-organisms in Adults

The criteria used by Sikorowski (1975) to evaluate quality of adult boll weevils were presence of bacteria, protozoa, viruses, and yeast.

Presence of bacteria.—A sample of 25 adults was frozen at -20°C for 15-20 minutes, surface sterilized with 0.5% sodium hypo- chlorite for 5 minutes, washed in two changes of sterile water (5 minutes each), and blended into 40 cc of sterile water for 30 seconds. The homogenate (40 ml) was then poured into a flask containing 30 cc of melted agar medium warmed to 45''C; then the mixture was poured into petri dishes. After incubation, the colonies were counted, and the level of contamination was determined.

Presence of protozoa (Microsporida).—A sample of 25 adults was blended into 25 cc of water. The suspension was then filtered through cheesecloth and centrifuged at 3000 r per min for 10 minutes. The resulting pellet was resuspended in a small quantity of water, smeared on slideè, and examined under a phase contrast microscope. For additional information, see Hazard and Oldacre (1975) and Poinar and Thomas (1978).

Presence of virus.—If a viral disease was suspected, the host tissue was examined with a light or electron microscope as required. Inclusion bodies of occluded viruses (nuclear and cytoplasmic polyhedroses, the granulöses, and the insect pox diseases) constituted one of the two broad groups of insect viruses and were easily detected with light or phase contrast microscopes. "Free"^ viruses, which are not embedded in a crystalline matrix and constitute the second broad group, can only be detected by using the electron microscope. M. E. Martignoni (personal communication) has since suggested an infectivity test as a more general and probably less expensive method of detecting nonoccluded viruses.

Presence of yeast.—When yeast contamination was suspected, the methods given by Poinar and Thomas (1978) were used.

Control

The importance of strict sanitation in controlling microbial contamination was recognized by Gast as early as 1961 when the mass rearing program was started at the Boll Weevil Research Laboratory (Gast 1966). However, only recently—with the use of HEPA filters and antibiotics and enforcement of sanitary measures—has microbial contamination been brought under control.

^^ J. G. GRIFFIN ETAL.

Use of Air Filters

High-efficiency particulate air (HEPA) filters were used to remove airborne contaminants generated or introduced by activities inside the facility. In fact, use of these filters in the egg planting and larval holding areas of the facility was a major factor m the final reduction of microbial contamination. For additional information see Griffin et al. (1979), Griffin (1982) and Roberson and Wright (1982). ^ ■^'>

Use of Antibiotics

Gast and Davich (1966) utilized methyl paraben and sorbic acid

(1966) tpl!r9n""TK-" -^ '•'^ ""^^ ^^^^^^ '^^^' ^y y^^^t- Gast (1966) tested 20 antibiotics for inhibition of Pseudomonas (tenta- tive identification), but only streptomycin sulfate inhibited growth of the bacterium, and it failed to control multiplication and spread Cast also tested antibiotics that might control Mat- 4#£ü |I|Edis McLaughlin but had no success. Childress and wñ- liams (1973) controlled L. mesenteroides contamination of boll weevil diets with erythromycin. Sikorowski et al. (1980) then used antibiotics to shield the growth medium of larvae of boll weevil from microbial contamination and found that they had no detectable adverse effects on insect development, egg production, hatch, and production of male pheromone. Today standard diet covered with

thin'sno K'^^" ^ '^''' ®^"^^^ """^y """^S^'^ ^^^îl« that have fewer than 500 bacteria per weevil compared with 18% obtained from diet not covered with medicated sterile sand.

PRODUCTION RESULTS

As far as is known, the Boll Weevil Research Laboratory (BWRL) was the largest producer of boll weevils before the Gast rearing

(M^rlh'I K'i i'^foô'""- ^°'' ^^^mle, during a 6-month period (March-August) m 1969. production at the BWRL was ca. 0.7 million weevils per week. Likewise, in 1970, 6-month production averaged

only 67 adults per petri dish planted with an average of 536 eggs (0. H. Lindig unpublished data).

Production was started in the Gast rearing facility during the summer of 1972, but problems were encountered because the rearing operation started before the facility was fully completed and while equipment was still being installed. The mechanical equipment in the building malfunctioned, personnel were new and inexperienced, and diet contamination was the rule. As a result, production reached only ca. 1.25 million weevils per week in 1972. and in ly/J, the rate was still disappointing. However, during June 1973 production reached ca. 1.8 million weevils per wêk (O. H. Lindig unpublished data) despite continuing problems with diet contamination and the loss of a high percentage of planted dishes.


Table 4.—Production data for Gast rearing facility

Parameters measured 1976 1977 ^979

Trays planted per week 14,468 17,880 7,027 Eggs placed per tray 2,595 2,415 2,100 Adults emerged per tray 346 349 643 Eggs per female per day 3.6 3.4 5.6 Percentage of production for

maintenance 32 25 14 Percentage of yield

(adults per eggs planted) 13.3 14.5 30.6 Percentage of trays with

microbial contamination 15.0 0.9 5.8

Finally, between 1973 and 1976, as noted, new and modified semiautomatic equipment and improved procedures replaced the manual equipment and inefficient procedures used during 1972 and 1973 (Griffin and Lindig 1974, 1975, 1977; Griffin 1978; Harrell et al. 1977).

Perhaps the most important equipment added to combat contamination losses was the in-line form-fill-seal machine plus auxiliary equipment, which allowed the change from rearing in petri dishes to rearing in plastic trays. The fact that the planting operations were thereafter done semiautomatically by machinery meant that all manual handling was eliminated and contamination caused by workers was reduced.

When the changes were tested in the trial production operations conducted in 1976 and 1977 and used in 1979 to rear the weevils for the Boll Weevil Eradication Trial (discussed earlier), production was as shown in Table 4 (J. Roberson unpublished data). V

Because the number of trays planted and of adults used in the brood colony depended on the number of adult weevils desired, maximum production potential was never reached. However, the increase in percentage yield is revealing.

CONCLUSION

The progress made in mass rearing boll weevils has brought us to the point that a viable operational system is available and proved capable of providing up to ca. 10 million per week. How- ever, more effort is needed to refine and advance present rearing technology, buildings, and equipment so greater numbers of high quality weevils can be produced more economically. Important information has already been gained regarding larval development, egg production, yields, contamination, and equipment needed when

294 j. G. GRIFFIN ETAL

producing weevils at a rate of 6-8 million per week, but if this number must be increased severalfold, care must be exercised. For example, problems might occur if some rooms and some equipment must be enlarged. In fact, difficulties were encountered when the rearing operation was increased from ca. 0.5 to 5-6 million weevils per week. Moreover, egg production and hatch tend to fluctuate from one batch of eggs to another so a uniform rate is difficult to maintain.

New production equipment must be designed and constructed so that It can be cleaned and sanitized with a minimum of effort and time. It must also withstand the required cleaning and sanitizing and still be available for continuous use.

The rearing facility must be divided into separated or isolated production rooms or areas, first for better sanitation and then for greater efficiency in handling materials or work movement. Building materials and construction must be such that cleaning and sanitizing are easy; they also must be durable.

A good housekeeping program is essential for successful production. Traffic must be restricted in the critical areas; e.g. those used for egg planting, larval development, and preparation'of eggs and planting solution.

The major problem is plainly microbial contamination, which must be held to a minimum. In an operation of this type, microbial contamination may be described as the occurrence and persistence of microbes in an environment where they are not wanted. The difficulty is that the weevil diets provide growth media for an almost infinite number of species of microbes. In addition, these microbial contaminants may have different effects upon the weevils depending upon vigor and age of the weevils and composition of the medium. Among the more frequent problems associated with microbial contamination are the following: (1) high mortality of early instars, (2) prolonged developmental time, (3) diminutive pupae and adults, (4) reduced production of pheromone, (5) reduced synthesis of ammo and fatty acids by the weevils, and (6) wide fluctuations m the quality of the insects.

The objective of an environmental sanitation program in an insectary is therefore elimination of the contamination that interferes with the rearing of healthy insects. Such a program must be planned carefully and based on research results. Then it must be carried out meticulously.

^ In the rearing operation at the Gast rearing facility, use of sanitation practices, HEPA (absolute) air filters, and antimicrobial agents has essentially eliminated microbial contamination of diets and insects. Consequently, the laboratory now has the technology to produce disease-free insects.


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303

Chapter 12

SAMPLING ARTHROPODS IN COTTON

J. W. Smith Bioenvironmental Insect Control Laboratory Agricultural Research Service U.S. Department of Agriculture Stoneville, MS 38776

W. A. Dickerson Boll Weevil Eradication Research Agricultural Research Service U.S. Department of Agriculture Raleigh, NC 27607

W. P. Scott Bioenvironmental Insect Control Laboratory Agricultural Research Service U.S. Department of Agriculture Stoneville, MS 38776

ABSTRACT This chapter deals first with arthropod sampling in general and addresses the problems of sampling locations, duration, methods, size, and statistical treatment. Next, specific problems having to do with arthropod sampling in cotton are discussed, and techniques are reviewed. Infor- mation is given about the efficiency of several often-used techniques.

Sampling for specific species of cotton pests and for beneficial arthropods is then reviewed.

The sampling methods actually used by the research teams associated with the Boll Weevil Eradication and Optimum Pest Management Trials are discussed in detail.

INTRODUCTION

Insect populations are usually sampled for two reasons: one is to determine whether an economic action level has been reached, and, hence, whether control measures should be initiated; the other is to obtain an estimate of the density of populations useful for

304 J. W. SMITH ET AL

research purposes. However, as Southwood (1966) points out, it is usually impossible to count all the vertebrates in a habitat; therefore sampling part of the population is necessary to obtain an estimate of a total population. Morris (1960) reminds us that "Sampling has no intrinsic merit but is only a tool which the entomologist should use to obtain certain information provided there is no easier way to get the information." Because several recent review publications (Sterling 1979, Kogan and Herzog 1980) have discussed sampling for economic thresholds and decision making extensively, we are concerned here primarily with sampling for research purposes.

Population sampling may be either extensive or intensive (Mor- ris 1960, Strickland 1961). Extensive sampling is usually necessary when large areas are to be surveyed and tends to be concerned with such problems as the relative abundance and distribution of insects among fields, their relationship to crop damage, or the efficacy of some areawide control measure. Intensive sampling, on the other hand, involves sampling of a specific population over time. The resulting data are often used to develop life tables, estimate changes in population growth parameters, or determine how a population is distributed within a field (Morris 1957, Southwood 1966, Harcourt 1969, Varley and Gradwell 1971).

ARTHROPOD SAMPLING FOR RESEARCH

The sampling methods selected by a researcher should be chosen according to the final goal. For example, methods used to determine economic thresholds and the need for control procedures are often not adequate for estimating population densities or measuring inherent variability of insect populations from location to location. Sampling for insects in cotton has been particularly vulnerable in this respect (Byerly et al. 1978). We need to develop sampling theory and application that will avoid bias and maximize statistical efficiency. Important considerations include location, duration, method, and size of the sampling done.

Sampling Locations

Ideally, population sampling should be done at a number of randomly selected locations so as to obtain a statistical estimate of the variance between locations. Indeed, since variance reflects the environmental influences associated with different sample sites, a population model for a pest species cannot be developed by sampling in just one location (Watt 1966). Moreover, as Mott (1963) points out, the selected locations should include not only model values of the variables in question but the extreme values as well.

However, the pattern of sampling needed is dependent on the objective of each program. If the objective is to obtain estimates of mean density for preparing life tables, then it is desirable to

SAMPLING ARTHROPODS IN COTTON 305

minimize variance (Southwood 1966). In addition, unrestricted random sampling is not efficient in minimizing variance because most of the samples might be taken from one area of the field. The method of stratified random sampling is, therefore, preferred for most ecological work (Healy 1962). ^Here the area is divided into a number of equal-sized subdivisions or strata, and one or more samples are randomly selected from each. This approach maximizes the accuracy of the estimate of the population, but exact estimates of sampling error can only be obtained if additional samples are taken from one strata.

Sampling Duration

When populations fluctuate irregularly, studies must continue long enough to permit observation of a sequence of increases and decreases so one can define the pattern of fluctuations. As collection of data proceeds, the sampling method should be tested and refined to ensure that deviations are accurately measured.

Sampling Methods

Watt (1966) suggested that each component of a biological system should be measured in such a way as to expose the real biological impact of the system. The problem is that the preliminary sampling and the analysis of the assembled data will provide a measure of many of the variables, but the actual decisions on technique must, in many cases, be a matter of judgment. As density changes, so will many of the statistical parameters, and a sampling method that is suitable at a higher density may be found inadequate as the population decreases. Therefore, sampling procedures must be flexible enough to deal with populations that vary in size.

Sampling Size

Obviously, the greater the sample size, the more reliable the estimates become. However, the cost per unit sampled may be substantial, and the collection of large samples may be unnecessarily costly. Thus, the smallest sample size that assures the desired reliability of the estimate should be determined in advance. Karandiros (1976) refers to this as optimum sample size. He also defined practical reliability in three ways and derived formulas for the first two; that is, mean and variance (general case). He then derived the formulas for the Negative Binomial, the Poisson, and the Binomial distributions as special cases.

Waters and Henson (1959) suggest taking sampling units of at least two sizes. One sample should tend towards the smallest possible limit, for example, a leaf or half a leaf, because a higher level of reproducibility is usually obtained (for the same cost) by taking more small units than by taking fewer large ones. In other cases, it may be necessary to increase the size of the sample unit


(Anderson 1965) to overcome the disadvantage of sampling by small units the number of zeros that may result at low densities. (This truncation may make analysis difficult though moderate truncation can be overcome by suitable transformation.) However, the decision to take larger samples must be related to the density of the population. Small sampling units may also increase precision by distinguishing between favorable and unfavorable microhabitats.

Before sampling is begun, the investigator must know whether different regions of the sampling area should be sampled separately. If the distribution of the population throughout the habitats is biased towards certain subdivisions, errors will arise when sampling is done randomly. These errors can be overcome by arranging the pattern so the number of samples taken from each subdivi- sion reproduces the gradient in the habitat or by regarding each part separately and correcting for it at the end. However, occasionally, such a large and constant proportion of the population occurs on one particular part of the plant that sampling may be restricted to this part. The taking of a certain number of samples randomly within a site, which is itself selected randomly from within a larger area, such as a field, is often referred to as nested sampling and may be on two, three, or more levels.

Morris (1955) laid down six criteria for a sample unit as follows:

(1) It must be such that all units of the universe have an equal chance of selection.

(2) It must have stability; if not, change should be easily and continuously measured.

(3) The proportion of the insect population using the sample unit as a habitat must remain constant.

(4) The sampling unit must lend itself to conversion to unit areas.

(5) The sampling unit must be easily delineated in the field.

(6) The sampling unit should be of such a size as to provide a reasonable balance between the variance and the cost.

Other Sampling Variables

The most serious biological problem in sampling arises when a part of the population has a behavioral pattern or habitat preference that is never sampled (MacLeod 1958). Less dangerous to the analysis (because the phenomenon will be recorded though it may well be misinterpreted) is the tendency for the behavior of the sampled insect to change. The behavior of insects is probably altered with age, weather, and even with the time of day, and these


changes may lead to a confusion in interpreting data. For example, the time of day when sampling is done may affect quality considerably because the diurnal rhythm of many insects causes them to move from one part of the habitat to another. Also, during the day, quite a proportion of active insects may be airborne (Southwood 1966). Clark et al. (1967) suggest that many sampling problems can be overcome, or at least additional information gained, if work is done at dusk and dawn rather than during conventional working hours.

TECHNIQUES FOR SAMPLING ARTHROPODS IN COTTON VEGETATION

Sampling methods for estimating population densities fall into three general groups: absolute methods, relative methods, and population indices (Roach et al. 1979). Population indices do not produce a count of insects; rather, they measure insect products or effects and are frequently used in making control decisions.

Absolute Methods

Accurate estimates of densities of arthropod populations are needed for almost all research-oriented sampling. Once an absolute method is devised, data obtained with relative methods can be compared and adjusted to provide estimates of density per unit of land area. Extensive reviews of absolute sampling methods and additional references can be found in Southwood (1978) and Ruesink and Kogan (1975).

An example would be the "clam shell" device (Leigh et al. 1970) suggested for estimating absolute insect populations on cotton. This method solved several problems: it prevented the escape of insects and allowed counting and identification in the laboratory. However, the plants must be removed from the study area, which is not desirable in most research situations.

A whole plant harvest technique was used to estimate adult cereal leaf beetles (Oulema melanopus (L.)) on grain (Ruesink and Haynes 1973) and on soybeans (Mayse et al. 1978). J. W. Smith (unpublished data 1972) used the same technique on cotton and compared it with the D-Vac and sweep net methods.

Smith et al. (1976) reported on an absolute unit area sampler that does not have the problems associated with the whole plant and clam shell methods. However, this sampler is not recommended as a sampling technique per se but rather as a method of establishing the relative efficiency of methods now being used.

Thus, absolute methods yield estimates such as density per unit of land area in the habitat, the type of data most often desired by population ecologists. However, such estimates must be

308 J- W. SMITH ET AL

made over time for nearly all studies of population dynamics of un- caged field populations.

Relative Methods

Most methods of sampling used today by cotton entomologists are relative methods that yield density per unit other than land area and must be converted to an absolute value. Often, this conversion cannot be done without correcting for the behavior of the insects or the effects of habitat, or both. For example, sweep nets, ground cloths, direct observations, and suction devices are widely used in sampling for insects in cotton. Direct observation can produce absolute (direct) population estimates for some species. The other methods constitute relative sampling, and the data need calibration against data obtained from reliable absolute sampling techniques before the results can be converted to estimates of density.

Another very important factor to consider when one is sampling arthropod populations in cotton is the intense interaction between the arthropods and the plants. Both the cotton plants and the arthropod populations change through the season (Byerly et al. 1978), and as the plants grow, they provide more places for arthropods to disperse. The combined result of plant growth and animal dispersion has great effect on the efficiency of most sampling methods.

Characteristically, cotton plants grow rapidly until the canopy closes, or they suffer carbohydrate stress because of the demands of large numbers of bolls (Gutierrez et al. 1975). Then, late in the season, plants may bend from the weight of maturing fruit or be blown down by wind. This phenology is likely to influence sampling efficiency in the following ways:

(1) When the plants are small and the canopy quite open, all sampling methods are likely to be quite efficient.

(2) As the canopy begins to close, some relative methods of sampling tend to sample only the populations on the upper part of the plant and so become less efficient.

(3) When the plants begin to bend, none of the methods of relative sampling are likely to provide adequate estimates of population size.

Whole Plant Survey

Whole plant examination is the oldest and most direct of all sampling methods for arthropods on cotton. Many entomologists have felt that it was the only accurate method. Recently, the method was used by Pieters and Sterling (1973) and Smith et al. (1976) to


sample cotton arthropods. Also, Mayse et al. (1978) used this method to study arthropod communities in Illinois soybean fields.

Kogan and Pitre (1980) gave a detailed description of a method of whole plant examination. Initially, nonadjacent randomly selected plants are scanned for large, often fast moving species of arthropods. Then both sides of each leaf on each of the plants are searched, as are the petioles, axils, and stems. The apical leaves are uncurled and searched for thrips, mites, and other small arthropods. Blossoms and fruiting forms are also searched. Numbers of each species, the stage of development, the relative position on the plant, and any other biological data of interest are recorded. The method can also be used to assess a population of a single species; in that case, the search strategy may be simplified by taking advantage of certain behavioral characteristics of the species of interest (Kogan and Pitre 1980).

Whole plant examination can be used early in the season when plants are small and tender without seriously damaging the plants. In addition, whole plant counts can be made for larger plants, though it becomes impossible to make them over a measured length of row. Mayse et al. (1978) found that they could survey the arthropod fauna on soybean from seedling emergence through physiological maturity by examining single plants; it was not necessary to remove any insects from the populations. Whole plant examination is the only method that allows correct positioning of the sampled organisms in the various strata of the canopy; and trophic relationships such as prey eaten by predators can be also observed and recorded (Kogan and Pitre 1980).

On the other hand, whole plant examination is dependent on the sampler's personal ability and visual acuity, factors that make it difficult to compare data gathered by different samplers. Moreover, the perception of small moving objects is greatly affected by wind. (Most sampling methods may be affected by wind, but direct counts are virtually impossible in winds above 8 mi. per hour.) An additional disadvantage is the chance for misidentification of certain species. Because the sampler quite often has only a glimpse of the sampled specimen, positive identification is often impossible (Kogan and Pitre 1980).

The simplest way to convert counts of arthropods on single plants to absolute populations is to multiply the counts per plant by the number of plants per unit of area. In crops like cotton and soybean, however, this cannot be done because the plants do not occur as discrete units in the crop space. Their branches and leaves crisscross, and plants in the late vegetative growth stages usually form a continuous canopy, at least along the rows. For this reason, it is difficult to isolate plants for sampling purposes (Kogan and Pitre 1980). Workers in Mississippi have used hills of cotton instead of single plants because of the variability of plants within a stand of cotton. Unfortunately, there tend to be one to two dominant plants in hills of cotton, which can cause sampling problems

310 J.W.SMITH ETAL

if the counts for these plants are not averaged out with those for the less dominant plants.

Portable tape recorders have been used in several Mississippi studies for recording data. This procedure facilitates whole plant examinations by leaving both hands of the sampler free.

Ground Cloth

The ground cloth sampling method is also known as the beat cloth, drop cloth, shake cloth, or plant shake method. The arthropods are forcefully displaced from the plants onto a sheet spread on the ground between two adjacent rows of plants so the specimens can be collected or counted (Kogan and Pitre 1980).

The ground cloth cannot be used to sample insects that will escape rapidly although it is an adequate technique for species that drop to the ground when disturbed. It is an excellent method for most lepidopterans (caterpillars), Chrysomelidae, Pentatomidae (particularly nymphs), Nabidae, and other insects with slow escape reactions. The method also has limited application when plants are small and becomes rather inefficient when plants become senescent and shed their leaves. On the other hand, results obtained by different researchers can be reasonably consistent because the main factor affecting the procedure is the rigor of the shaking action. Differences resulting from different samplers, however, should not be disregarded (Marston et al. 1979).

Sweep Net

For over a century, the sweep net has been the most widely used tool for sampling arthropods on small grain, forage, and many row crops. This is because no other method permits the capture of as many insects from vegetation per man hour at less cost and without damage to the crop (Ruesink and Kogan 1975). However, there are difficulties in quantifying and comparing data from sweep net sampling that stem from the many styles of sweeping though there are also some general procedures that may help one achieve a certain degree of standardization (Ruesink and Haynes 1973, Jenson 1976).

Also, there are difficulties of other kinds. Delong (1932) was among the first to study the efficiency of the sweep net as a tool in insect population studies on some field crops. He recognized that environmental factors such as temperature, humidity, wind velocity, position of the sun, plant size, density of the canopy, and pubescence of leaves and stems are responsible for variability of results. If the foliage is wet with rain or dew, it becomes very difficult to operate the sweep net, although this is also true for most sampling techniques.


Suction Net

Devices that use suction to remove arthropods from vegetation have been used for some time. One of the best known is the D-Vac suction net (Dietrick et al. 1959, Dietrick 1961).

Davis et al. (1966) compared the mean number of Miridae earlier sampled by visual in situ whole plant examination with the number collected by a D-Vac vacuum sampler and concluded that the visual technique was superior. Similar results were obtained by Shepard and Sterling (1972a) who were sampling for predaceous arthropods that were abundant on cotton. Callahan et al. (1966) concluded that the sweep net technique was superior to the D-Vac technique for collecting some insects that affect large plants.

On the other hand, Richmond and Graham (1969) compared methods of operating the D-Vac. Shepard and Sterling (1972b) showed that the D-Vac was the most economical method of obtaining reliable and repeatable results. Schuster and Boling (1974) used D-Vac sampling to determine phenology of both predatory and phytophagous cotton field insects.

J. W. Smith (unpublished data 1972) compared the results of visual whole plant and D-Vac sampling of cotton arthropods in Mis- sissippi. He concluded that no one method will give accurate population estimates for each of a diversified group of arthropods and that sampling techniques must be suited to the insect population (Pieters and Sterling 1973).

Studies by Harding and Dupnik (1976) and Fuchs and Harding (1976) conducted in the Lower Rio Grande Valley of Texas involved extensive D-Vac sampling.

Smith et al. (1976) included the D-Vac as one of the techniques compared in sampling populations of beneficial arthropods associated with cotton.

Pieters and Sterling (1973) compared the D-Vac and whole plant examination and stated that neither sampling method was more reliable nor more accurate than the other for coleopterans. However, the D-Vac nearly always provided a lower C.V. (Coefficient of Vari- ation) and a higher x (standard error of the mean) for Hemiptera and Homoptera than whole plant examination provided. They also found that the D-Vac method was more reliable than whole plant examination for sampling arachnids.

Devices rather like the D-Vac but much larger, some mounted on tractors, have been used to sample cotton insects. Some of the early ones were developed originally as control measures, primarily against the boll weevil (Anthonomus grandis Boheman). However, Parencia (1968), in field tests conducted in 1944, found that a collecting machine (Webb) captured only 40% as many boll weevils as

312 J.W.SMITH ETAL

could be located visually; and M. E. Merkl, E. P. Lloyd, and E. C. Burt (unpublished data 1966) found that the Nisbet bug catcher, an almost identical machine, captured ca. 50% of the weevils that had been found and marked by a field crew. Later, McCoy and Lloyd (1975) developed the McCoy Insect Collector (a dual directional blower and vacuum system) for use in detecting low level infestations of boll weevils. This device collected 130% more weevils than could be found by visual inspection.

Kogan and Pitre (1980) found that the suction net, like the sweep net, is operated in different ways by different researchers. Also, it is advisable to use the suction net in certain ways for specific conditions. Thus the interpretation of the results vary, just as with the sweep net. Since no one procedure is best for sampling all arthropods, preliminary tests should be made with the suction net to determine which procedure yields the most desirable results.

COMPARISON OF EFFICIENCY OF SAMPLING TECHNIQUES

Four sampling techniques were compared during one season (1978-79) of the Boll Weevil Eradication Trial (BWET) and the Opti- mum Pest Management Trial (OPMT). The unit area sampler was the standard for comparing the efficiency of the other three methods. The sweep net and the D-Vac methods were both included; the fourth method consisted of field observations by an entomologist with wide faunal experience who walked through a field and recorded numbers and species of all arthropods observed. Ten unit area samples were taken on each date in each sample field. D-Vac sampling (10 samples in each field) was done with a 10-inch collecting cone by vacuuming the plants from one side and from top to bottom while the operator moved along 10 feet of row.

Results are presented as ratios. For example.

Estimated numbers of arthropods per acre collected by D-vac = D/U Estimated numbers of arthropods per acre collectai

by unit area sampler

Variations in the ratios between months were greater in Mis- sissippi than in North Carolina, the two areas sampled. However, the season average of 0.50 was the same for both States.

The D/U*s for total important arthropods—after several numerous and less important species such as Thripidae had been removed from consideration—were as follows:


Mi ssissippi North Carolina Number Number Number Number

Sampling of of of of period fields samples D/U fields samples D/U

June 3 30 0.69 6 60 0.60 July 6 60 0.31 6 60 0.44 August 6 60 0.47 3 50 0.50 Total or averag( e 15 150 0.49 15 170 0.51

The D/U*s of arthropods known to be predaceous or parasitic were as follows:

M ississippi North Carolina Number Number Number Number

Sampling of of of of period fields samples D/U fields samples D/U

June 3 30 0.70 6 60 0.99 July 6 60 0.70 6 60 0.78 August 6 60 0.63 3 50 0.63 Total or averag( B 15 150 0.68 15 170 0.80

The D-Vac sampler was thus more efficient as a sampling device for important species of predators and parasites. It was less efficient when the entire insect population was considered.

Based on D/U's for Mississippi and North Carolina combined and on some extrapolations (numbers in parentheses) where less well sampled groups had similar behavior patterns with corresponding better sampled groups, the following ratios were developed:

Arthropod Group D/U Arthropod Group D/U

^ithonomus grandis Boheman Lathridiidae Conoderus vespertinus (F.) Systena spp. Chaetocnema Diabrotica undecimpunctata

howardi Barber

(0.50) Trialeurodes abutilonea (0.83) (Haldeman) 0.41 0.90 Aphidae 0.30 (0.48) Braconidae 0.50 (0.91) Chalcidoidea 0.36

Scelionidae (0.36) 0.34 Mjnmaridae (0.40)

314 J.W.SMITH ETAL

Arthropod Group D/U Arthropod Group D/U

Anthicidae 0.85 Coccinellidae 0.43 Phalacridae (0.43) Orthoperidae (0.83) Heliothis spp. (0.50) Pseudatomoscelis seriatus

(Reuter) (1.0) Lygus líneolarís (Palisot

de Beauvois) (1.0) Neurocolpus nubilus (Say) (1.0) Geocoris punctipes (Say) (1.0) Nabidae 0.66 Orius sp. 0.56 Fulgoroidea 0.44

Cicadellidae 0.36 Formicidae 0.94 Apis mellifera L. 0.08 Halictidae (0.17) Orthoptera (Saltatoria) (0.07) Thripidae 0.54 Psocoptera (0.40) Dolichopodidae 0.17 Chloropidae 0.17 Collembola (1.0) Araneida 1.0 Acariña (0.33) Other miscellaneous Arthropoda 0.47

Collections of beneficial arthropods from cotton with all four sampling methods are compared in Figure 1. The D-Vac sampler, in addition to providing an accurate estimate, provided an excellent system for collecting, counting, and careful identification of in- festing species.

SAMPLING MAJOR PEST SPECIES IN COTTON

Heliothis spp.

Heliothis zea (Boddie) and Heliothis virescens (F.) have become two of the most serious pest insects in the South, and both species now seriously limit the profitability of cotton production in many areas (Warren 1979).

Sampling of Heliothis spp. eggs on cotton, other row crops, or wild host plants is accomplished most efficiently through direct, visual examination. However, absolute density of eggs is difficult to determine because of the egg size and the large plant surface area available for oviposit ion. Relative estimates of egg abundance are, therefore, obtained by examination of the highly attractive terminal foliage. However, numbers change rapidly depending on oviposit ion, prédation, and hatching, and these conditions should be considered in making any judgments (Stinner et al. 1980).

Sampling of Heliothis spp. larvae on cotton is most successful when the terminal area, squares, blooms, and bolls (single plant on linear row) are examined visually. Other methods such as sweep net, suction devices, and ground cloth are less satisfactory because the larvae are frequently inside the fruiting structure. Although, first-instar larvae are difficult to see and most estimates are biased toward the later instars, numbers of large larvae collected from squares and bolls usually provide good estimates of absolute numbers.


Thousands

40 D Unit Area Sample • Whole Plant Exam V Sweep Net x 10 O D-Vac

Figure 1.—Number of predators per acre of cotton as determined by area sample, whole plant examination, sweep net, and D-Vac. Data taken from May 30 through September 17, 1979. Sweep net values were multiplied by 10 for comparison on the same scale used for other methods.

316 J.W.SMITH ETAL

Pupal sampling is difficult but has, nonetheless, been accomplished by soil sifting, soil scraping, and estimating numbers of prepupae that have emerged from fruiting forms (Stinner et al. 1980). Soil sifting provides the most precise information but is quite expensive in both time and labor required. Another technique, determination of the emergence of adult moths from various crops, requires the use of soil covers or cages (Roach and Ray 1976). This method, though it provides a good assessment of the size and source of the moth generation, requires considerable labor and is, at best, an indirect measure of pupal abundance.

Continuous sampling of populations of adult Heliothis spp. during their active period may be one of the best ways to follow and forecast the time and size of egg and larval populations (Hart- stack et al. 1979). Adults may be sampled by making visual counts at night, by disturbing the moths during sampling, or by using "sugar lines" to attract moths. However, light and pheromone traps are used most commonly to survey for populations of adults. The use of traps has recently been extensively revi€íwed by Hartstack et al. (1979). Two machines that have been used for area sampling of adult populations of Heliothis spp. are the Nisbet Insect Collector (Parencia 1968) and the McCoy Insect Collector (McCoy and Lloyd 1975) mentioned previously for control or sampling of boll weevils.

Southwood (1966) reviewed the mark, release, and recapture method used with traps in estimating populations and in dispersal studies. This method is now being employed in studies of 11. virescens dispersal in Mississippi.

Boll Weevil

The boll weevil, a key pest of cotton, has four stages: egg, larva, pupa, and adult. When conditions are favorable, a life cycle is completed in 2.5 or 3 weeks. Thus, in the extreme southern part of the Cotton Belt, there may be as many as seven generations during a crop season (Parencia 1978). In the spring, females lay eggs singly in cotton squares. Late in the season, eggs are laid both in squares and in young bolls. These eggs develop inside the square or boll and hatch in 3-5 days. Then the larvae feed 7-12 days inside the square or boll. After a 3- to 5-day pupal stage, adults cut their way out. The adults feed, mate, and begin depos- iting eggs in 3-7 days. This sequence continues until the plant is killed in the fall by cold weather. At about that time, adult weevils of the last generation move to ground trash or other suitable habitat where they overwinter in a physiological condition called diapause. Sampling for overwintering weevils is, therefore, normally accomplished by collecting ground trash from the hibernation sites and sifting it through a series of sieves. The separated material containing the weevils is then placed on heat tables where observers collect the weevils as they become active and crawl from the trash.


Overwintered weevils are most effectively detected by setting out pheromone traps in the spring. Sampling of subsequent generations of adult weevils in cotton fields may be accomplished by the shag method (a modified ground cloth technique), by vacuum sweeping, or by visual inspection of the squares, blooms, and bolls. Most cotton entomologists prefer visual inspection of fruiting forms.

Also, the tractor-mounted collecting devices discussed earlier (Nisbet and McCoy Insect Collectors) have been used extensively in research situations for sampling adult weevils (Parencia 1968, McCoy and Lloyd 1975).

Eggs and larvae of the boll weevil can be sampled by collecting fruiting forms that show signs of oviposition punctures or that have been shed from the cotton plant. (in most surveys made to determine economic thresholds, indices such as feeding and oviposition are used to assess levels of boll weevil populations.)

Plant Bugs

The tarnished plant bug (Lygus lineolaris (Palisot de Beau- vois)) is often considered a key pest in cotton because injurious numbers can occur during the early fruiting stage. The insecticides that are then applied for control may drastically reduce the numbers of predatory arthropods and thus leave the cotton crop vulnerable to subsequent infestations of the bollworm and the tobacco budworm.

The results of special research conducted during the OPMT and the BWET in which five sampling methods (ground cloth, visual inspection, sweep net, D-Vac, and unit area sampler) were compared in 1977, 1978, 1979, and 1980 showed that the D-Vac was an excellent device for collecting JL. lineolaris. Three times more of these plant bugs were collected by the D-Vac method than by sweep net, and five times more were collected by D-Vac than by visual inspection.

In general, tarnished plant bugs are similar in biology to the hemipteran predators that occur in cotton. Therefore, methods of sampling for these bugs are identical to those used to sample for other hemipteran species.

Secondary Pests

Sampling techniques for the secondary pests of cotton (thrips, leafhoppers, Aphididae, Aleyrodidae, and Tetranychidae) were discussed by Kogan and Herzog (1980). The earlier discussions in this chapter on general arthropod sampling apply to this group of occasionally important cotton arthropods.

318 J.W.SMITH ETAL

SAMPLING BENEFICIAL ARTHROPODS IN COTTON

Cotton fields contain a substantial entomophagous fauna. Indeed, it would not be economical to produce cotton if parasitic and predaceous species did not suppress the pest complex (Reynolds 1976).

An estimated 400-500 arthropod species are routinely associated with southern cotton fields. The surveys of predatory arthropods in Arkansas cotton made by Whitcomb and Bell (1964) revealed about 600 species associated with the crop, not including parasites.

Since the sampling of such arthropods requires basic knowledge of the biology and habitats of the parasites and predators involved, techniques must often be modified or devised.

Predators are free living throughout their life cycle and are capable of feeding on almost any prey they can capture. Also, some predators have both phytophagous and entomophagous habits. Para- sites are usually specific for one insect species or for a closely related group, and during their larval period, they are restricted to and dependent upon an individual host species. Thus, sampling for parasites may mean sampling the host(s) or sampling the parasite directly. Predators, however, must be sampled directly, regardless of the habitat or diversity of prey in the habitat.

Several workers have made extensive comparisons of sampling methods for predatory species in cotton (Leigh et al. 1970, Smith et al. 1976). Most of these techniques have been discussed earlier in this chapter under Techniques for Sampling Arthropods in Cotton Vegetation.

Experience in sampling for individual predators and groups of predators has shown that some techniques are especially useful.

Orius insidiosus (Say), described by Barber (1936) as the most important predator of Heliothis zea eggs, was the most numerous predator in a 1974 Mississippi study (Smith et al. 1976). It was also the most numerous predator found in the OPMT and BWET areas (Figure 2). However, the insect is so small, ca. 1.6 mm long, that sampling is difficult. Also, this predator typically lives in the terminal buds and is, therefore, not readily visible to direct observation. However, the D-Vac machine has proved to be effective in sampling this insect because the plant terminal can be entirely covered by the collecting cone while the suction dislodges both immature and adult Orius. (Sweep nets and ground cloths are less efficient.) Also, the D-Vac collected ca. 65% as many Orius as did the unit area sampler in the OPMT and BWET areas.

A big-eyed bug (Geocoris punctipes (Say)) was the most common predator in 3 of 4 years in the OPMT in Mississippi. Populations fluctuated from year to year, but peaks usually occurred from


O N. Carolina • Mississippi

Figure 2.—Orius spp. captured by D-Vac from cotton, Panola County, MS, and from the intensive sampling area of North Carolina,

1978.

mid-June to mid-July in both Mississippi and North Carolina; the pattern (Figure 3) was similar to that of other hemipteran predators. Because Geocoris is larger than Orius and spends more time in the open, it is easier to sample. Effective techniques include several relative methods including ground cloth, sweep net, and D-Vac. The high mobility of the adult Geocoris makes direct visual counts difficult.

The larval and adult stages of the convergent lady beetle (Hippodamia convergens Guerin-Meneville) and a spotted lady beetle (Colebmegilla maculata (De Geer)) are common predators in cotton. Because of their size and bright color, they are easily observed and can be sampled readily by visual examination and ground cloth. The sweep net and D-Vac are also useful relative methods of sampling for these predators.


Thousands

8

O N. Carolina # Mississippi

Figure 3.—Geocoris spp. populations collected by D-Vac from cotton, Panola County, MS, and from the intensive sampling area of North Carolina, 1978.

Adult Chrysopa spp. (primarily Chrysopa carnea Stephens) move into cotton quite early in the season (Smith et al. 1976), but reproduction in cotton does not become evident until midseason. Sev- eral workers have documented the effectiveness of C. carnea adults and larvae as predators of Heliothis spp. (Quaintance and Brues 1905, Whitcomb and Bell 1964, Ridgway et al. 1967, van den Bosch et al. 1969).

Several nabid species (primarily Reduviolus roseipennis (Reuter)) are common in cotton and are excellent predators of small Heliothis spp. larvae. Both adult and nymphal nabids are sampled well with suction devices, sweep nets, and ground cloths.

All spiders are predaceous and, for the most part, show no discrimination in the taking of prey; thus, most are just as likely to prey on beneficial insects as on pest species. A striped lynx spider (Oxyopes salticus Hentz), so-called for its rapid chase of prey, is the most commonly observed species of spider on cotton. Spiders are quite easy to sample, and suction devices are usually


satisfactory for collecting them. However, there are factors to consider such as time of day (many spiders are nocturnal) and time of year (many spider species are mature for only a few weeks out of the year, and immature spiders can seldom be identified as to species). Prey capture methods also differ. Some spiders are active hunters (Oxyopidae, Lycosidae, Pisauridae, Thomisidae, Salticidae); some are ambushers (Oxyopidae, Thomisidae), and many use a web to capture prey (Araneidae, Theridiidae, Dictyniodae, Linyphiidae, Tetragnathidae, Agelenidae). Vertical stratification likewise differs (different species prefer different strata of the cotton canopy). An excellent review of sampling techniques for spiders can be found in Kogan and Herzog (1980).

SAMPLING ARTHROPODS IN THE OPTIMUM PEST MANAGEMENT AND BOLL WEEVIL ERADICATION TRIALS

The North Carolina BWET and the Mississippi OPMT were conducted concurrently from 1978 to 1980. (Reports on these trials are found in Chapters 15 and 16 of this handbook.) In addition to the implementation of the BWET by the Animal and Plant Health In- spection Service and the OPMT by the Mississippi Cooperative Exten- sion Service, two research teams composed of personnel from Agri- cultural Research Service (ARS), U.S. Department of Agriculture collected extensive biological data on cotton and arthropods associated with cotton production in the test area. These data were then used in estimating and comparing the biological impact of the two programs and in evaluating the economic and environmental impacts. To collect representative data, the teams sampled ca. 193 cotton fields each year (219, 206, and 155 in 1978, 1979, and 1980, respectively) in North Carolina and 96 cotton fields each year in Mississippi. The number of fields sampled in North Carolina was greater because of the larger geographic area involved in the BWET. All fields were sampled at least once a week. A selected number of fields were sampled twice weekly to provide intensive monitoring data.

Because of the geographic separation and the large number of fields, accurate and consistent sampling procedures were a critical element in the evaluation of these Trials. Also, there was to be direct comparison between the Trial areas and nearby Current Insect Control practice areas. Therefore, the types of data collected and the sampling procedures were identical at all locations.

The primary methods of arthropod sampling were direct plant examinations and suction net (D-Vac). Plant examination was used to sample pest populations only. The suction net method was used to sample a broad spectrum of arthropods including pest, beneficial, and incidental species; it was chosen over other methods because the variability of sample quality due to sampler is less. This was important because so many individuals were involved in the sampling process.


Pest Arthropods

Arthropod pests of cotton were sampled by examining the whole cotton plant or selected portions of the plant depending on plant size and the pest species being sampled. Numbers of boll weevils (including egg and oviposit ion punctures), bollworms/budworms, fleahoppers, plant bugs, aphids, spider mites, thrips, and whiteflies were recorded. Other observed pests such as cutworms (Noctu- idae) and corn borers (Pyralidae) were also recorded. All species except aphids, spider mites, and thrips were counted and recorded as numbers found per row-foot. Populations of the excepted species were recorded as light—found on occasional plants; medium—found on numerous plants with slight damage; and heavy—found on numerous plants with damage easily observed.

The whole plant survey was the first pest sampling implemented during the season and was typically initiated 2 weeks before the cotton plant developed squares. Every cotton plant was examined in five randomly located 25 row-foot sections, a total of 125 row-feet per field. As plants grew larger and substantial square populations developed, the whole plant survey was replaced with square, boll, and terminal surveys where insect pest activity was centered.

The terminal survey was conducted in the same way as the whole plant survey, in five randomly located 25 row-foot sections. How- ever, only terminals were examined. This technique was continued throughout the remainder of the season since actively growing terminals are an ideal site for bollworm/tobacco budworm oviposition and for buildup of aphid populations.

The square survey was initiated when squares reached approximately 0.25 inch in diameter. A total of two hundred 0.25-inch or larger squares from all parts of the fields was examined. The top, middle, and lower portions of the plant were sampled. Since boll weevil egg and feeding punctures tend to be concentrated on squares, and bollworm/budworm eggs are frequently deposited on the outside of the bract (hatching larvae crawl inside and feed on the square, often at the protected base), the square survey was continued until the square population declined so much that collection of 200 representative squares from a field became difficult.

The boll survey was similar to the square survey: 200 bolls collected from throughout a field were examined. This survey was initiated shortly after blooming and continued throughout the season. Boll weevil oviposition and feeding punctures are found on young bolls as well as on squares. Bollworm/budworm larvae are especially important at the boll stage since the plant has less time to replace a lost or damaged boll than it has to replace damaged squares.


Beneficial Arthropods

Beneficial arthropods were sampled with a suction net machine (D-Vac). Weekly samples were collected in each survey field from four randomly located 10 row-foot sections, and some fields were sampled twice weekly to provide more intensive data. In this case, the 10 row-foot section was marked, and the second collection was made two rows over along a row that had not been disturbed.

As the sampling of each 10 row-feet was completed, a location- date-time tag was dropped into the bag. The bag was then removed from the suction machine and closed with a rubber band. When the sampling had been completed, the bags were tied together and placed in an ice chest containing dichlorvos (Shell No-Pest Strip). The day's samples were transferred to a freezer and delivered to the laboratory for identification. The combination of dichlorvos and cold temperature prevented additional prédation in the sample bags.

A combined total of over 100 miles of cotton row was sampled by the suction net machine in the BWET and OPMT. The collected arthropods were all identified, and representative collections were established at both the Mississippi and North Carolina laboratories and at the Agricultural Research Service cotton insect collection at Mississippi State University in the Mississippi Entomological Museum. All specimens collected during 1980 were preserved for future reference and study.

324 J.W.SMITH ETAL

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lation of the cotton fleahopper on wild hosts. Journal of Economic Entomology 62:525-526.

Ridgway, R. L., P. D. Lingren, C. B. Cowan, Jr., and J. W. Davis. 1967. Populations of arthropod predators and Heliothis spp. af-

ter applications of systemic insecticides to cotton. Journal of Economic Entomology 60:1012-1016.

Roach, S. H., J. W. Smith, S. B. Vinson, H. M. Graham, and J. A Harding.

1979. Sampling predators and parasites of Heliothis species on crops and native host plants. Southern Cooperative Series, Bulletin No. 231, p. 132-141. W. L. Sterling, editor.

and L. Ray. 1976. Pattern of emergence of adult Heliothis from fields

planted to cotton, corn, tobacco, and soybeans. Environmental Entomology 5:628-630.

Ruesink, W. G., and D. L. Haynes. 1973. Sweep net sampling for the cereal leaf beetle, Oulema melanopus. Environmental Entomology 2:161-172.

and M. Kogan. 1975. The quantitative basis of pest management: Sampling and measuring. Tn Introduction to Insect Pest Management, p. 309- 351. R. L. Metcalf and W. H. Luckmann, editors. John Wiley and Sons, New York.

Schuster, M. F., and J. C. Boling. 1974. Phenology of early mid-season predatory and phytophagous

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and W. Sterling. 1972b. Incidence of parasitism of Heliothis spp. (Lepidoptera: Noctuidae) in some cotton fields of Texas. Annals of the Ento- mological Society of America 65:759-760.

Smith, J. W., E. A. Stadelbacher, and C. W. Gantt. 1976. Comparison of techniques for sampling beneficial arthropod

populations associated with cotton. Environmental Entomology 5:434-444.


Southwood, T. R. E. 1966. Ecological methods, with particular reference to the study

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cotton, corn, soybeans, and other host plants. Southern Coop- erative Series, Bulletin No. 231, 159 p.

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329

Chapter 13

LOSSES IN YIELD OF COTTON DUE TO INSECTS

P. H. Schwartz National Program Staff Agricultural Research Service U.S. Department of Agriculture Beltsville, MD 20705

ABSTRACT Losses in yield of cotton due to insect pests despite best agricultural practices have been estimated. These are compared with losses calculated from research studies that included control plots and treated plots.

The boll weevil (Anthonomus grandis Bohe- man), the bollworm (Heliothis zea (Boddie)), and the tobacco budworm (Heliothis virescens (F.)) have been the predominant pests of cotton during this century and account for the greatest losses. The boll weevil accounted for losses of cotton that were greater than the 1976 value of U.S. production for any one of over 55 other crops.

Losses from cotton pests, if not controlled, were calculated to be: aphids (Aphis spp.), 19%; boll weevil, 51%; cabbage looper (Trichoplusia ni (Hubner)), 92%; cotton fleahopper (Pseudato- moscelis seriatus (Reuter)), 34%; Heliothis spp., 63%; pink bollworm (Pectinophora gossypiella (Saunders)), 61%; and spider mites (Tetranychus spp.), 21%. When these pests are controlled, it was calculated that losses still occur as follows: aphids, 8%; boll weevil, 21%; cabbage looper, 30%; cotton fleahopper, 12%; Heliothis spp., 15%; pink bollworm, 9%; and spider mites, 0.05%.

The amount of loss due to cotton insects is dynamic. Losses due to insects vary from year to year and from area to area. Losses from insect damage continue to occur at magnitudes that have not decreased appreciably over the past 30 years. Thus, the advances in insect control technology made during this period have made it possible for us to protect the cotton crop from greater losses while yields have increased significantly and production practices have changed dramatically.

330 P. H. SCHWARTZ

INTRODUCTION

The guidelines of the U.S. Department of Agriculture for the control of insect and mite pests (Hopkins et al. 1980) contain a list of 22 species of pests in cotton that may be controlled with chemical insecticides. Not all of these pests are seriously damaging to the crop at all times. However, experience has indicated that they may require some form of chemical control whenever a damaging population develops. My objective here is to bring together the information available in the literature on losses caused by these insect and mite pests (Table 1). This information is limited to losses in either yield or quality and the cost of controlling the pest. I will not deal with losses to society in general or with losses caused by pest control because of adverse environmental impacts.

The section on loss estimates by experts attempts to reflect the losses experienced under the best agricultural practice for the time periods when these estimates were made. The loss estimates calculated from field studies attempt to reflect the potential a pest population has in reducing yield under two regimes—with and without control.

LOSS ESTIMATES BY EXPERTS

One of the earliest reports on the losses caused by insects and mites to agricultural commodities in the United States was that of Marlatt (1904). Mr. Marlatt indicated that the principal insect pests on cotton were the boll weevil (Anthonomus grandis Boheman), the bollworm (Heliothis zea (Boddie)), and the cotton leafworm (Alabama argillacea (Hubner)). The bollworm was chiefly destructive in those southwestern States that were then producing cotton and was damaging 2-60% of the crop with an overall estimated loss of 4% in those States. From 1899 to 1902, the boll weevil caused losses of cotton yield ranging from 40 to 50% in Texas as compared with the zero losses in Louisiana, which was still free from infestation. (Louisiana first experienced heavy losses due to boll weevils in 1903 (Cramer 1967).)

Other experts have also estimated losses in cotton yield due to pests despite best agricultural practices. For the boll weevil, these losses range from 1.4 to 21% (Table 1). Tlie values given by the Cotton Foundation (DeBord 1977) and the U.S. Department of Agriculture Conference Report on Cotton Insect Research and Control (1980) are based on survey data or the best estimates of knowledgeable experts. The estimates by the U.S. Department of Agriculture in 1954 and 1965 are based on statistical surveys and records and on estimates by experts.

However, when estimates are presented on a national basis, as they are in Table 1, they tend to provide an overall average which is somewhat lower than the actual in those States where the pest

LOSSES DUE TO COTTON INSECTS 331

has been a serious problem. For instance, in the U.S. Department of Agriculture Conference Report on Cotton Insect Research and Control (1980), the average for the boll weevil is given as a loss in yield of 1.4%, but during the year of the study (1979), the State of Georgia estimated a 16% loss; Alabama and Louisiana each estimated 4%; Mississippi and South Carolina, 3%; Florida and Texas, each 1.5%; and Arkansas and North Carolina, each 0.05%. Missouri, Tennessee, Virginia, and Oklahoma reported no losses. Thus, the southeastern United States apparently suffered much higher losses from the boll weevil in 1979 than the national average indicates. (it is interesting that North Carolina had only a 0.05% yield loss estimated for 1979 whereas surrounding States had much higher losses. This may be attributed to the boll weevil eradication program in that State.)

This portion of the data in Table 1 therefore indicates that the boll weevil and bollworm have been the predominately important pests on cotton since 1904 and have accounted for the greatest losses. This is not to imply that the other pests listed in Table 1 are not capable of causing serious damage, but sizable infestations would appear to be more localized and sporadic and would thus require control less frequently.

A more detailed analysis of losses attributed by knowledgeable experts to the boll weevil for the various States where cotton is produced is presented in Table 2. Plainly these losses vary from State to State and from year to year (Table 2). Moreover, experts in all the States except Missouri estimate that the boll weevil has great potential for reducing yield if no chemical control is available. In fact, in 1974-76 (DeBord 1977), the boll weevil caused an average annual loss of yield of 201.6 million bales valued at $56.3 million plus control costs of $89.2 million for a total annual loss of $145.5 million. This is equal to an average annual 5.7% of the value of the cotton produced during that period.

The loss attributed by the experts to the boll weevil on cotton ($145.5 million) is thus greater than the 1976 value of U.S. production of any one of the following crops:

apricots artichokes asparagus avocados bananas beets broccoli brussels sprouts bush berries cabbage cantaloupe carrots cauliflower celery

cherries coffee cranberries cucumbers dates dry beans eggplant escarole figs filberts flax seed garlic honeydew melon hops

lemon lima beans lime macadamia nuts maple syrup nectarines olives papayas pears peas pecans peppermint peppers persimmons

plums pomegranates popcorn rye seed crops snap beans spearmint spinach tangelos tangerines temples walnuts watermelon

332 P. H. SCHWARTZ

Table 1.—Estimates of yield losses to cotton, caused by various U.S. Department of Agriculture has issued

Calculated y ield loss (%) Without control With control

From From Table 5 of Schwartz Table 5 of Schwartz

Pest Hopkins et al . and Klassen Hopkins et al and Klassen 1980 1981 1980 1981

Bandedwing whitefly

Beet armyworm Boll weevil 50.7 ± 10.4 30.9 ± 8.6 20.6 ± 6.8 19.0 ± 6.7 Bollworms 63.0 ± 7.7 90.8 ± 14.2 14.7 ± 3.2 12.1 ± 2.2 Cabbage looper 92.5 35 29.6 20 Cotton aphid 18.9 ± 14.8 4.8 ± 4.8 7.9 ± 12.3 0 ±0

Cotton fleahopper 34.2 ± 20.1 39.0 ± 11.6 12..4 ± 8.4 12.5 ± 3.9

Cotton leaf perforator 0 0

Cotton leafworm Cutworms Ground beetle

adults

Fall armyworm Garden webworm Grasshoppers Lygus bugs Lygus nymphs Pink bollworm 61.0 35.5 ± 13.5 9.2 10.0 ± 6.0

Saltmarsh caterpillar

Spider mites Stink bugs Thrips Yellowstriped

armyworm

21.3 ± 40.8 0 ± 0

67.8 ± 22.4

0.05 ± 0.09 0 ±0

18.0 ± 6.1

\_l Losses for boll weevil were extrapolated from $20,000,000


arthropod pests. (All arthropod species are included for which control guidelines (Hopkins et al. 1980))

Estimated loss (%) by experts despite best agricultural practices

Marlatt 1/ Hyslop USDA USDA USDA USDA DeBord USDA (1904) (1938) (1946) (1954) (1965) (1976) (1977) (1980)

0.2

6.7 10.9 8.7 10.1 8.0 8.0 3.0 1.4 4.0 2.0 4.0 4.0 3.3 3.0

2-50 0.2 1.4

0.2 0

0.7 1.4

0.3 0

0.2 0.7

7.5 13 0.2 0.3

loss figure presented in Marlatt (1904).

334 P. H. SCHWARTZ

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Methods

The information concerning calculated yield losses in Table 1 must be used with caution. The losses were developed from field studies in which yield and pest density data from an untreated plot were compared with yield and pest density data from insecticide- treated plots. The losses calculated for plots treated with the best control reflect control with the best insecticide/miticide evaluated in research plots; these may not necessarily be the most effective chemicals in commercial use. Thus, the losses do not reflect those that occur under best agricultural practices. Instead, they reflect the potential of a pest population to cause losses when no control is used and when the most effective chemical of those tested has been applied in research studies. It is important to bear in mind that the calculated losses in yield were generally obtained from studies in field plots chosen by researchers because of probable heavy pest infestation. Oftentimes these pest infestations may have been heavier than those normally found in other areas; thus the somewhat higher estimates. However, the data are useful in that they provide information concerning the potential impact these pests can have on cotton and the relationship between density of a pest population and yield.

The methods used to calculate losses and determine the relationship between pest density and yield loss were similar to those used by Schwartz and Klassen (1981). Thus, the Journal of Economic Entomology for the years 1945 to June 1980 and the Insecticide Acaricide Tests for 1976-80 were reviewed for studies containing data on cotton yield. Experiments were utilized wherein yield data were taken in conjunction with data on pest density and in which an untreated control was included.

However, various investigators have used different methods of measuring the density of a given pest and have sometimes used different methods of measuring yield. I therefore needed to trans- form the data for all studies involving a given pest to a common basis. For this, I used the equation

I = lOOT U

where I is equal to the index number for the yield or pest density; T is equal to the yield or pest density in the treated plots, and U is equal to the yield or pest density in the untreated plot.

With this equation, the yield for the untreated plot or the pest population equals 100. Then if the yield is greater in the treated plot than in the untreated control, the yield index is greater than 100; if the yield is less than that in the untreated control, the index is less than 100. Moreover, if the density of the pest population is greater in the treated plots than in the

336 P. H. SCHWARTZ

untreated plots, the pest population index is greater than 100. If the reverse is true, the pest population index is less than 100. The transformed data were then used in subsequent analyses to calculate losses. (The transformation did not affect the outcome of these calculations, but it did allow direct comparison of analyzed data across pests.)

For the purposes of this study, I assumed that a given pest population density would cause a corresponding loss in yield when the plant was attacked at a vulnerable stage in its growth. I also assumed that adequately reliable loss estimates could be made by treating this relationship as though it were linear. (Other workers have considered this relationship between the cotton plant and pests (DuRant 1979, Bailey et al. 1980).) Thus, as pest population densities increase, the losses in yield increase proportionally if the plant attacked by the pest is in a susceptible stage of growth. However, I recognize that under some circumstances there could be no cause and effect relationship or the relationship could be sig- moidal or very slightly curvilinear as Hartstack et al. (1978) found for damage to cotton by Heliothis spp. Therefore, data sets were only used when the correlation coefficient (r) was significantly different from 0 at the 5% level of probability. Schwartz and Klassen (1981) did not use a test for significance and summarized all their data (Table 1).

The relationship between pest density and yield or quality calculated by means of the linear equation:

was

Y + kP o

where Y is the yield index for any pest population density index P.

The regression coefficients were Y , which is the yield index when there is no pest infestation, and k, which reflects the change in Y per unit of P. (Also, the coefficient of determination (r ) was calculated.)

The coefficients Y and k were then used to calculate the losses when no treatments were applied (the untreated infestation) and when the most effective treatment in the study was used, as follows:

(1) % loss without controls = Y - Y,«^ ,^^ o 100 X 100 Y o

(2) % loss with best treatment = Y - Y ,^^ o X X 100

Y o

where Y is the yield index without any pest infestation, Y,^^ is the yield index when no control was applied (untreated check plot), and Y^ is the yield index for the most effective treatment.


Table 3.—Comparison of actual and transformed data

Insecticide

% boll weevil punctured squares 1/

Seed cotton _!./ Pest (pounds Yield index 2/ per acre) index 2/

A 59

B 29

C 27

D 57

E 66

Untreated 60

94

48

45

95

110

100

2346 122

2878 149

2678 139

2240 116

2204 114

1929 100

\_l Actual data from Table 4 of Roussel and Glower (1957), 2/ Transformation.

When the computed percentage loss was less than 0, it was rounded off to 0%; when it was greater than 100, it was rounded off to 100%. For each pest situation, a standard error of the mean times the t^ value at the 0.05 level of significance with n-1 degrees of freedom was computed with three or more data sets.

The results obtained when these concepts were applied can be demonstrated by comparing the actual data obtained by Roussel and Glower (1957) and the transformations (Table 3). This study was one of the very few in my analysis of the 37 data sets which had a significant correlation and which was concerned only with the boll weevil. The information concerning this study is taken from Table 4 for the St. Joseph location in 1956, which involved 13 applications of five insecticides and insecticide combinations. The specific data are shown in Table 3.

Two regression analyses were then conducted on these data, one by using the actual data and one by using the pest index. The calculations are shown in Table 4.

One can see that there are no differences between the index data and the actual data when an _n of 5 was used and the check for the actual data was excluded in calculating the index data. There is a slight difference, as would be expected, when the check is included because of the addition of another set of variables to the regression equation. However, elimination of the data from the check plots helps to lessen the impact of the influence of heavy pest populations on the prediction of percentage losses.

338 P. H. SCHWARTZ

Table 4.—Analysis of actual and transformed data

Actual data Actual for treated

Parameter Index data 1/ for and control calculated data treated plots plots

Y 0

(3198 165.83 .86 pounds)

3198.82 pounds 3263.94 pounds

k -0.48 -15.33 -17.81 2

r 0.90 0.89 0.78 % loss without

control 28.81 28.68 32.75 % loss with

control 12.96 12.94 14.74 n 5 5 6

IJ Actual data from Table 4 of Roussel and Glower (1957),

Results and Discussion

The data I developed concerning loss with and without control are given in Table 5, which shows the results of my analysis of 251 field experiments for the boll weevil reported in the literature since 1945. Of these, only 37 (15%) had correlation coefficients that were significantly different from 0. These are reported in Table 5 as are significant correlations for other pests.

The parameter Y is of particular interest because it gives the percentage of change in yield that results from an infestation and from an untreated plot when no pest population is present. Any value of Y^ that is 100 or less in Table 5 is an indication that the pest does not cause any reduction in yield. Conversely, any value of Y^ that is over 100 is an indication that the pest is capable of causing a reduction in yield.

The data in Table 5 indicate that the boll weevil has the greatest potential for reducing yield (an average 546% above an untreated check) when no control is used. However, the data for these 37 sets were highly variable; the range was 88.8-1002.8%. Heliothis spp. has the next greatest potential for causing losses in yield of cotton: the gain would be 456.1% over all untreated checks without an infestation. Also, the data for Heliothis spp. plots were much less variable than those for boll weevil plots since the range was 341.6-570.6.

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My results appear to be consistent with data developed by other workers (Table 6). For example, a comprehensive report on cotton losses was presented by Cramer (1967). He indicated that the boll weevil accounted for two-thirds of the 12% loss in yield due to insects attacking cotton during the period 1942-51. For the period 1951-60, he reported that the proportion of the loss due to the boll weevil dropped to 42%, whereas bollworms were responsible for 20%; the remaining losses were attributed to the infestation of all other species such as plant bugs (Lygus spp.), thrips (Thripi- dae), and spider mites (Tetranychus spp.). He based his figures on data in Losses in Agriculture (U.S. Department of Agriculture 1954, 1965). During these two periods, it was estimated that insect pests on cotton caused losses amounting to 12 and 19.0%, respectively.

Cramer (1967) developed an equation for estimating the losses that would be obtained in the absence of any control measures as follows:

X + (52x) = 696 100

where 52 is equal to the percentage increase when control measures are used, and 696 is the average nationwide yield per unit area.

From this, cotton production during the period 1951-60 could have been increased by approximately 20% provided modern control measures against insects had been applied to the entire acreage. Instead Cramer estimated from his equation that the equivalent reduction was 34% of the potential yield per area.

Other workers too have undertaken to develop experimental data to determine losses from cotton pests. Their results are shown in Table 6. Fye et al. (1962) published results of experiments undertaken from 1928 to 1958 in South Carolina in their study of the effects of insecticides on cotton yields and on control of cotton insect pests. The boll weevil and the bollworm were emphasized. Between 1928 and 1945 when the test plots were being treated with inorganic insecticides, average yield was 1225 pounds of seed cotton per acre each year for treated plots and 955 pounds for untreated plots, or an increase of 23.6%. Between 1946 and 1958, the test plots were treated with inorganic insecticides, and average yield was 1441 pounds of seed cotton per acre for treated plots and 953 pounds for untreated plots, or an increase of 53.9%. However, analysis of the results for the different years showed that the differences between the yields of the treated and untreated plots were especially large in years when infestations were above average. For example, in 1929, 1938, 1941, 1946, 1949, and 1950, years of severe boll weevil infestation, the average yield was 1146 pounds per acre in treated plots and 756 pounds per acre in untreated plots, or an increase of 52%. In those years when boll weevil infestations were below average, the average yield was 1363 pounds per acre for treated plots and 1211 pounds per acre for untreated plots, or an increase of only 12.5%.

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342 P. H. SCHWARTZ

C. R. Parencia, Jr., (1959) obtained similar results in a study carried out from 1939 to 1958 in Texas. A total of 320 comparative experiments was undertaken. Data were obtained from 787 untreated plots covering an overall area of 2177 acres and from 1385 treated plots covering a total area of 6102 acres. Over the 20-year period, the untreated plots produced an average of 740 pounds per acre, and the treated plots yielded 1049 pounds per acre, equivalent to an increase of 41.5%. From 1939 to 1945, the test plots were treated with arsenical compounds from 1946 to 1954 with chlorinated hydrocarbons, and from 1955 to 1958 with organophosphates. The average increase in yield of treated plots, as reflected by losses in Table 6 for these three periods, was as follows: 1939-45, 21.6%; 1946-54, 48.8%; 1955-58, 52%.

Gaines (1959) reported a similar study made in Louisiana from 1920 to 1956. The use of insecticides increased the annual yield of seed cotton an average 26.4% between 1920 and 1945 and an average 41.7% between 1946 and 1956. Parencia and Cowan (1972), in a review of the comparative yields of cotton in treated and untreated plots in central Texas for the period 1939-70, found that in plots treated with an average 6.1 applications of insecticides, yield was 54.3% greater (366 more pounds of seed cotton per acre) than in untreated plots. During this period, the insects of primary importance were the boll weevil, bollworm, and tobacco budworm (Helio- this virescens (F.)). However, the tobacco budworm became considerably more important over time and often was the predominant species, especially after it developed resistance to several of the recommended insecticides. The cotton fleahopper (Pseudatomoscelis seriatus (Reuter)) also increased in importance as it developed resistance to the organochlorine insecticides.

Canerday and Arant (1964) showed that yield losses of seed cotton caused by the carmine spider mite (Tetranychus cinnabarinus (Boisduval)) ranged from 14 to 44% and were directly related to population density and duration of infestation.

Lukefahr and Martin (1963) evaluated the damage to lint and seed cotton caused by the pink bollworm (Pectinophora gossypiella (Saunders)). The data indicated that the value of the cotton crop was reduced 34% when at least 60% of the bolls were infested and that reductions in staple length, strength, and fineness or imma- turity of fiber were directly related to the levels of infestation. In artificially infested bolls, the degree of damage was related to age of boll and number of larvae per boll. Tsao and Lowry (1963) estimated losses in yield due to the pink bollworm by using the equation:

Y = lOOy/p and loss = Y - y, where y equals actual yield, p equals percentage of locks pickable, and Y equals potential yield.

In the application of this formula, they found that potential yield was 1379 pounds per acre from a potential check plot yield of 696.9 pounds per acre. The loss per acre caused by the pink


bollworm (potential yield minus actual yield) was 681 pounds for the check plot and 296 for the treated plot. In 1959 and 1960, the loss per acre was 738 pounds in the check and 238 in treated plots. Thus, the data of Tsao and Lowry (1963) indicate that the potential loss in yield from untreated plots was 49% in 1959 and 60% in 1960; that in treated plots was 22% in 1959 and 24% in 1960.

In other studies not reported above, Brazzel and Gaines (1956) likewise studied the effect of three levels of pink bollworm infestations and an insect-free check on yield and quality of cotton. Their data indicated that heavy infestations caused large reductions in the value of cotton. If 100% of the bolls were infested with an average 6.4 or 9.6 larvae per boll, most of the loss in the value of cotton was the result of reduced quality. When the infestation reached 12.9 larvae per boll, the reduced yield accounted for more of the loss than the reduced quality. Subsequently, Brazzel and Gaines (1957) further evaluated cotton yield and quality losses caused by various levels of pink bollworm infestations. They found that when ca. 50% of the bolls were infested at a rate of less than two larvae per boll, the value of the cotton decreased little. Yields per acre of both lint and seed decreased slightly with increased levels of insect infestations in both of their experiments. However, these differences were not significant though a trend to decreased yields with increased bollworm infestations was indicated.

DuRant (1979) studied the effectiveness of selected insecticides used in combination against three species of insects on cotton. He found that highly significant correlations existed between the degree of Heliothis spp. control and yield but no correlation existed between beet armyworm (Spodoptera exigua (Hübner)) control and yield. On the basis of his data, Heliothis spp. and beet armyworms caused an average yield reduction of 81% compared with the untreated check.

Adkisson et al. (1964) studied the effect of the bollworm on the quality of cotton. They found that losses in cotton due to attack of the bollworm are more likely to be in yield than in quality. Moreover, relatively small numbers of bollworms may cause significant yield losses. Under the conditions of their experiment, significant yield losses were caused when infestations averaged 8-10 bollworm larvae per 100 plants or more than 2 per foot of row. On the basis of their data, significant yield loss did not occur until damage counts exceeded 3% of the squares or 3% of the bolls. Severe yield loss occurred when more than 5% of the bolls were damaged for prolonged periods. Thus, light, medium, and heavy infestations of bollworms caused losses of 8, 23, and 41%, respectively.

Bailey et al. (1980) studied 16 cotton genotypes and the effect of insect populations on yield. They found that significant correlations existed between lint yield and insect populations for untreated plots infested with adult tarnished plant bugs (Lygus

344 P. H. SCHWARTZ

lineolaris (Palisot de Beauvois)), tarnished plant bug nymphs, and the total number of tarnished plant bugs in the plots. Also, in the treated plots, lint yield and populations of these pests as well as whiteflies showed significant correlations. Under the conditions of these tests, correlations were insignificant for yield and populations of Heliothis spp. larvae, Heliothis spp. eggs, and cotton fleahoppers. Untreated plots yielded an average 33% less lint than plots treated with insecticide.

Hartstack et al. (1978) studied the damage done to cotton by the bollworm and tobacco budworm. Their data showed relationships between the number of larvae present and the percentage and number of damaged squares and bolls. A highly significant relationship was also shown between the number of larval days (number of larvae counted times number of days observed) and percentage of lint lost. They showed that an average of 2% damaged squares and bolls and 60,000-70,000 larval days could be tolerated without loss. They also found that the percentages of lint loss v. damaged squares, damaged bolls, and total number of larval days were curvilinear relationships. Yield losses ranged from 0 to 72% with larval infestation levels of an average of 1-12 per acre. Therefore, with 25% damaged squares, a loss in yield of about 70% can be anticipated with 25% damaged bolls. With 10% damaged squares or bolls, yield loss was calculated to be about 30%.

Lloyd et al. (1962) studied the effect of four levels of boll weevil infestations on yield and quality of cotton. Small plots of cotton fields were caged as soon as the first young squares became visible, and different numbers of boll weevils were introduced into the cages with the intention of obtaining infestation levels of 25, 50, and 75%. The exact infestation levels actually attained were not those desired. Their data indicated an inverse relationship between total yield and percentage of squares damaged throughout the season. However, infestation levels of approximately 27% resulted in 30 and 15% yield reductions for 1959 and 1960, respectively; and infestation levels of 40 and 48% resulted in reduced yield levels of 44 and 18%, respectively. At infestation levels of 62 and 67%, reductions of 59 and 52% were obtained.

Lloyd and Merkl (1966) made a 2-year replicated field cage study of the population dynamics of the boll weevil. Their data indicated that first-generation progeny from boll weevil populations estimated at 0, 14, 25, 50, and 100 weevils per acre damaged 0, 28, 46, 66, and 83% of the squares, respectively. Second-generation weevils damaged from 84 to 96% of the squares. Seed cotton harvested from the respective treatments averaged 2802, 1875, 1678, 1380, and 479 pounds per acre; yields were reduced 33, 40, 53, and 70% with 28, 46, 66, and 83% damage of the squares, respectively. They also detected differences in lint quality between plots infested with 100 overwintered weevils (83% damaged squares) and those infested at the other four levels. No other differences in quality were observed.


The general conclusion therefore is that cotton insect loss data are dynamic; they change from year to year in geographical areas. Losses due to insect damage continue to occur at magnitudes that have not decreased appreciably over the past 30 years, even with the increased intensity of cotton plantings. While some cotton pests may cause increased losses now because of the increased importance of one pest species over another pest species due to resistance, climatological factors, or cultural practices, the magnitude of the losses has not shifted downward to any extent. Also, the boll weevil and the bollworm continue to be the insects that cause major losses to cotton. This means that we are barely stay- ing abreast in the control of these insect pests by the research, development, and implementation of pest management programs. There are times when cotton insects can tip the scales in their favor as evidenced by the atypical year Georgia had in 1977. In that year, the State of Georgia reported severe losses to many crops (Todd and Suber 1981). There was an extended drought which favored insect development, making infestations more severe than normal. Cotton and corn were heavily damaged. In 1977, Georgia harvested 170,000 acres of cotton at a production value of approximately $18.5 million. The control and yield reduction costs for that crop amounted to $26.7 million, a loss of 144%.

There is a continual need to apply pest control technologies to cotton pests and to maintain a strong research program directed toward a reduction in losses caused by these pests. In addition, research should be directed toward the refinement of the cost of application of these technologies to maximize cotton yields by reducing pest control costs to a minimum.

346 P. H. SCHWARTZ

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348 P. H. SCHWARTZ

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SELECTED REFERENCES

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Becnel, I. J., H. S. Mayeux, and J. S. Roussel. 1947. Insecticide tests for the control of cotton boll weevil

and cotton aphids in 1946. Journal of Economic Entomology 40: 508-513.

Bell, M. R., and C. L. Romine. 1980. Tobacco budworm field evaluation of microbial control in

cotton using Bacillus thuringiensis in a nuclear polyhedrosis virus with a feeding adjuvant. Journal of Economic Entomology 73:427-430.

Bottger, G. T., A. J. Chapman, R. L. McGarr, and C. A. Richmond. 1958. Laboratory and field tests with Sevin against cotton in-

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Bull, D. L. 1980. Fate and efficacy of sulprofos against certain insects as-

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V. S. House, J. R. Abies, and R. K. Morrison. 1979. Selective methods for managing insect pests of cotton. Journal of Economic Entomology 72:841-846.

Calhoun, S. L., and E. W. Dunnam. 1953. Heptachlor and other insecticides for control of cotton

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organic insecticides applied as concentrated sprays. Journal of Economic Entomology 43:606-610.

Cowan, C. B., Jr., and J. W. Davis. 1963. Control of several late-season cotton pests in field ex-

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Cowan, C. B., Jr., J. W. Davis, and C. R. Parencia, Jr. 1957. Control of the boll weevil and bollworm with chlorinated hydrocarbon and phosphorus insecticides in 1956. Journal of Economic Entomology 50:663-666.

J. W. Davis, and C. R. Parencia, Jr. 1960. Field experiments against several late-season cotton in-

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C. R. Parencia, Jr., and J. W. Davis. 1956. Late-season control of the boll weevil and the bollworm with new insecticides in 1955. Journal of Economic Entomoloev 49:783-785.

C. R. Parencia, Jr., and J. W. Davis. 1959. Field experiments for control of late-season infestations

of several cotton insects. Journal of Economic Entomoloev 52: 975-977. -^

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Davis, J. W., and C. B. Cowan, Jr. 1972. Field evaluation of three formulations of aldicarb for

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C. B. Cowan, Jr., and C. R. Parencia, Jr. 1962. Field experiments with insecticides on cotton for control

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Fife, L. C, and R. L. Walker. 1954. Comparative effectiveness of various phosphorus and chlo-

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R. L. Walker, and S. F. Bondy. 1949. Boll weevil control with several organic insecticides dur-

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Richmond, C. A. 1956. Tests with phosphorus insecticides for control of pink

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Ridgway, R. L., H. J. Walker, R. L. Hanna, and W. L. Owen. 1967. Fertilizers impregnated with systemic insecticides for

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Schwartz, P. H., and D. R. Hamel, editors. 1980. Guidelines for control of insect and mite pests of foods,

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1976b. P. gossypiella control in cotton, 1975. Insecticide and AcaricTde Tests, Volume 1, Paper No. 125, p. 93.

Watts, J. G. 1948. Cotton insect control with organic insecticides. Journal


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123.

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358 P. H. SCHWARTZ

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359

Chapter 14

MODELS FOR COTTON INSECT PEST MANAGEMENT

A. W. Hartstack and J. A. Witz Pest Control Equipment and Methods Research Agricultural Research Service U.S. Department of Agriculture College Station, TX 77843

ABSTRACT Systems science techniques such as computer modeling are helping scientists take a new look at insect control, a major problem in cotton production. Models relating to the cotton plant, to important cotton insect pests, and, more recently, to beneficial insects have been developed. MOTHZV, a model for the bollworm (Heliothis zea (Boddie)) and tobacco budworm (Heliothis virescens (F.)), has been used successfully for 5 years in a statewide extension program in Texas. Updates to this model, including an improved cotton fruiting model, SIM- PLECOT, and a Heliothis spp. damage model, have recently made new research studies possible.

INTRODUCTION

Dramatic changes have been made in the control of cotton insect pests during the last 10-15 years because of developing insect resistance to insecticides, the increasing cost of energy, and concern over environmental quality. As a result, the cotton industry has been searching for alternative methods of producing a satisfactory crop, and several new systems have been proposed and tested. For example, cotton varieties having early, more rapid fruiting characteristics are being examined as are more efficient use of fertilizer and water, judicious use of insecticides, and maximum reliance on naturally occurring insect control agents. However, as this work has progressed, it has become clear that no single method of control can be expected to provide an acceptable solution to all cotton insect problems. The entire cotton production system must be examined, and many factors such as ecology and behavior must be considered in deciding what techniques are likely to be feasible and practical against a given pest (Knipling 1979). As a result, a new discipline, integrated pest management, based on the philosophy of total system consideration and multiple control techniques, has developed.

360 A. W. HARTSTACK AND J. A. WITZ

In this chapter, after a discussion of the basic concepts un- derlying the systems approach, we describe several of the larger computer models that have been developed in the United States to study cotton pest management. A specific example, the cotton- Heliothis model, MOTHZV, is then described in some detail. We conclude with a discussion of the Texas Agricultural Extension Service program in which the MOTHZV model is used.

THE SYSTEMS APPROACH

Systems modeling has emerged from man's need to study and control large and complex systems. The National Aeronautics and Space Administration moon exploration program is a prime example. Multi- discipline teams with specialized knowledge worked together with the aid of sophisticated computers and equipment to solve complex problems (Witz 1973). DeMichele and Bottrell (1976) discuss in considerable detail how the same approach can be used in cotton pest management to unify and guide research and produce a better understanding of interactions and the consequences.

The systems, or modeling, approach usually begins with simple mental models that a person formulates on the basis of his experience (witz 1973):

"Watch out for the July 4th bollworm egglay." "Full moon occurs on July 10 so there will be large Heliothis spp. egglays about 2 to 4 days after the 10th."

"These summer showers will really bring on the boll weevil."

If these mental models are transformed to a flow chart, a set of equations, or a computer program, they become tangible and can be communicated to and used by other people. Several such tangible models may then be combined into more complex models through the use of computer and systems analysis techniques (Witz 1973).

The investigation of complex systems may result in the development of multiple models, each at different levels of detail. The level used in a given situation must be determined on the basis of both the intended purpose and the current knowledge available. The study of an animal or plant, for example, can be subdi- vided into basic physiological processes, which, in turn, relate to various components or organs. Each organ can then be studied and modeled at the cellular level, the biochemical level, or, possibly, the molecular and atomic levels. Models developed at one level can often be simplified and made useful for applications at levels that require less precision.

MODELS FOR COTTON INSECT PEST MANAGEMENT 361

REVIEW OF COTTON PEST MANAGEMENT MODELS

The cotton plant (Gossypium hirsutum L.) is usually an integral part of any modeling study of a cotton insect pest. On the one hand, the behavior and population dynamics of a given pest are affected by the plant; on the other hand, the insect affects the growth of the plant. For this reason it is important to our purpose here to review the development of several cotton plant models.

The first digital computer simulation of cotton growth was reported by Stapleton (1970) and Stapleton et al. (1973). It was used to study the effect of machinery design alternatives on the yield of cotton. SIMCOT, another early model, was developed by Duncan (1971) to calculate daily production and distribution of photosynthate as the cotton plant developed. McKinion et al. (1974, 1975) then used the same approach as Duncan (1971) in developing Simcot II but included many additional factors that affect plant growth and maturity, among them the location and condition of individual fruiting points on the plant.

GOSSYM (Baker et al. 1977) is a more recent cotton plant model that stemmed from the SIMCOT research program. Many of the functional relationships are carried over from SIMCOT II, but a new plant growth dynamics algorithm is used, and a highly detailed model of soil, water, and plant-root relationships has been added.

A simpler, less detailed approach was reported by Wilson et al. (1972). By simulating the typical fruiting pattern of the cotton plant, they are able to adjust the rate of fruiting parametri- cally to simulate different varieties or different environments. In addition, the indeterminate behavior of cotton is modeled with a simple feedback mechanism, so the model can simulate regrowth subsequent to programmed removal of fruit. Thus, it has sufficient precision to be useful in many pest management applications.

In the early 1970's, SIMCOT II was revised by Gutierrez et al. (1975) to fit the California environment and cotton varieties. Calculation of fruit was converted from a single, average plant to a total field basis. Gutierrez et al. (1975, 1977a, 1977b) then incorporated several simple insect models into this revised version so they could study plant interactions with cotton defoliators such as the beet armyworm (Spodoptera exigua (Hübner)) and cabbage looper (Trichoplusia ni (HÜbner)) and fruit attackers such as Lygus hesperus Knight, Heliothis spp., and the pink bollworm (Pectinoph- ora gossypiella (Saunders)).

At about the same time, Stinner et al. (1974) described a Heliothis model that included a spatial grid of fields and crop types. Each crop was modeled on a field basis by using a measure


of the attractance of that crop for Heliothis spp. No prediction of yield was possible, but the approach allowed study of the movement of the insect population.

Jones (1975) and Jones et al. (1977) reported a detailed simulation model of the influence of weather, crop status, and management practices on populations of the boll weevil (Anthonomus grandis Boheman). This model has since been combined with a modified version of the SIMCOT II cotton model (Jones et al. 1980) and with a Heliothis spp. model derived from MOTHZV (Hartstack et al. 1976). It is being used to study improved pest management strategies (Brown et al. 1979) and is discussed in detail in Chapter 17 of this handbook.

Most recently, a cotton crop-boll weevil model has been developed that is concerned with natural and induced mortality of the boll weevil in the field (Curry et al. 1981). Row spacing and orientation are used to calculate light penetration through the crop canopy so as to achieve a more accurate measure of the microclimate under the plant where the immature boll weevil develops. Damage to the plant is estimated based on the size of the adult population, and yield can be predicted. This model is currently being field tested and will be used to test alternative control strategies.

THE HELIOTHIS POPULATION MODEL: MOTHZV

The model for Heliothis spp. designed by Hartstack et al. (1973), as shown by flow diagram in Figure 1, was not complex. However, Hartstack and Hollingsworth (1974) converted it to mathematical equations and used a computer to predict the number and time of emergence of the subsequent generation of adults. A degree-day concept was used with development times to calculate the total length of each generation (adult to adult). For example, rates of increase were input as constants for each day by using light trap data collected at College Station, TX. Moonlight was the only other factor considered to affect rate of increase. Timing and size of future generations were accurate for College Station, TX, but this regression-type model lacked versatility and could not be used at other locations.

The 1975 Version: MOTHZV-2

MOTHZV-2, a descendant of the original MOTHZV, was described by Hartstack et al. (1976). It incorporated considerably more detailed population and physiology algorithms (Figure 2). It also included three simple crop models—corn (Zea mays L.), cotton, and sorghum (Sorghum bicolor (L.) Moench). The FORTRAN computer program for MOTHZV-2 consisted of a main computer program and 16 subroutines.


Input Catch Per Trap Corn, Cotton,

etc. Day "A"

Convert Trap Catch to Moths Per Acre

I Calculate Generation Length Expected fron^i

Day "A"

I M Store Day "B" Next Generation

Day No.

Calculate Rate of Increase Expected from Day "A" to Day "B" for

Each Crop H (Rate of Increase in Each Crop) x (No. Moths/

Acre in Crop)

Sum Projected Populations in

Each Crop

I M I

(Projected Population) x (% of Crop in Area)

Calculate Moonlight Effect and Adjust

Projected Population

I Calculate Longevity

of Projected Population and Store Accordingly

Output Population Projected

and Day "B"

Stop j Figure 1.—Flowchart of original MOTHZV concept (Hartstack et al.

1973).

364 A. W. HARTSTACK AND J. A. WIT2

Mk/UL.1

C

D

S n

V® ¡ GENLN

V© ;\© i VS Ï V2 Ä 0 TEMP 50

EGGS 0 TEMP 50 0 TEMP. 50 0 TEMP. 50 0 TEMP. 50

1-3 INSTAR 4-5 INSTAR PUPA PREOVIPOSITION O D

S 0

D TEMP. 50 OVIPOSITION

0 0 y ^''^^'^S ' LARVAE

CANNIBALIS

CANBAL

-u °' NAT MOF

365 1TALITY

Figure 2.—Flowchart of MOTHZV-2 (Hartstack et al. 1976).


With MOTHZV-2, predictions concerning the timing and size of future generations of Heliothis spp. were made by using expected (long-term average) temperatures and projected crop phenology. Simulations were initialized with numbers of eggs or moths and were carried through the number of generations that occur at a given locality during one season. A bookkeeping system was used to record the number of eggs, first- to third-instar larvae, fourth- and fifth-instar larvae, pupae, preovipositing adults, and ovipositing adults for each day of the simulation. Each stage of the insect could be advanced one calendar day at a time by using the degree- day concept so daily mortality (natural, insecticide, parasites, and predators) could be considered. The output of MOTHZV-2 consisted of tables or graphs showing the numbers of Heliothis spp. of each stage present on each day.

The three crop models, like MOTHZV-2, were temperature dependent, and the degree-day concept was used to predict crop phenology (e.g., first square, boll, and open boll). These events were then used to predict the relative attraction of the crop to Heliothis spp. females, since this attraction has a considerable effect on oviposition. No prediction of yield was possible, and a separate run of the model was required for each crop. However, the numbers of adult Heliothis zea (Boddie) predicted to migrate out of corn or sorghum were held in a vector that could be used as input for a subsequent run with the cotton model.

Rather than attempt an in-depth mathematical description of the model, we refer readers to the reports of Hartstack et al. (1973, 1976).

The 1978 Version: MOTHZV-3

In 1978, MDTHZV-2 was revised by replacing the original cotton model with a more dynamic crop model and by adding a Heliothis damage model. This revision allowed the user to study changes in cotton yield caused by Heliothis. Since this latest version has not been reported, the changes are described here in detail.

The Cotton Submodel: SIMPLECOT

The submodel for cotton fruiting behavior, SIMPLECOT, was derived from the earlier model developed by Wilson et al. (1972). The number of new fruit-per-plant per degree-day (FRT) was given

by: FRT=(V+0.00288xFRTMX)x(l-0.0003xFRTPTxTOTBOL) (1)

where V = Variety factor: 0.054 - 0.072 for Delta varieties, e.g., Stoneville 213 0.072 - 0.100 for short-season varieties, e.g., TAMCOT-

SP37


FRTPT = Accumulated fruiting points per plant - a measure of the size of the plant

TOTBOL = Total number of bolls (small, large, and open) on plant

FRTMX = The smaller of the values FRTPT and 41.38xYIELD YIELD = The expected yield in bales per acre

The FRTPT in combination with the TOTBOL thus cut off square production when all the photosynthate production had been used for maintenance of the plant and its fruit load. If the calculation of fruiting points became negative, it was set to zero.

Natural shedding of fruit was based on the load of green bolls and temperature The probability of fruit survival was calculated as:

PRSUR = (0.9995-0.0001xTOTGRB)xDDAY (2)

where TOTGRB = Total green bolls. (With average conditions, about 75% of

the total fruit produced would be shed.) DDAY = Degree-days for each day. (Degree-days were calculated

by using 12.6 C and 33.3 C as lower and upper thresholds, respectively, as described by Hartstack et al. (1976) for Heliothis development.)

Although soil type, fertility, and moisture influence the rate of production and retention of fruit, they were not included in this model. Rather, they were assumed to be adequate to produce the expected yield.

The plant model was converted to a per acre basis since all the insect data in MOTHZV-3 were calculated on that basis. Multi- plying the fruit production by the expected yield per acre for average conditions gave the accumulated fruit per acre as:

FRUIT = FRTPTx5000xYIELD. (3)

The model thus must show production of about 150,000 open bolls for each 1.0 bale of predicted yield.

The SIMPLECOT routine was not called up by MOTHZV unless squaring had commenced. It was assumed that 378 degree-days were required from planting to first square, 317 degree-days from first square to first boll, 173 degree-days from first boll to large green bolls, and 448 degree-days from large green boll to open boll. The rate of production of fruit was adjusted by expected yield in bales per acre and the variety factor. Each cohort of fruit was moved from one stage to the next as a group (no distribution). The model tabulated the age and number of each fruit cohort as it developed.

Fruiting curves generated by the model for two cotton varie* ties are shown in Figure 3. In this case, the variety factor (V)


Relative number of fruit

Squares

1 140

I 150

1 160

1 170

1 180

1 1 190 200

Day no.

1 210

1 220

"H T" 230 240

—I 1 250 260

Figure 3.—Comparison of fruiting curves produced by SIMPLECOT for TAMCOT-SP37 and Stoneville 213 cotton varieties.

was set at 0.054 to simulate a traditional Delta variety, e.g., Stoneville 213, and set at 0.1 to simulate a newer, faster fruiting, more determinant variety, e.g., TAMCOT-SP37. The yield was projected at 2 bales per acre for each.

The simulation produced by the submodel is compared in Figure 4 with actual field counts of squares and bolls produced by Stone- ville 213 at two locations (Figures 4a and 4b) and by TAMCOT-SP37 at College Station, TX (Figure 4c).


100000

"X Field \ Counts Model

\ ° Sq. \ ■ Gr. Bolls

\ —— Op. Bolls

1 1 I 230 240 250

Figure 4a.—Comparison of field counts of cotton fruit with output from SIMPLECOT, Stoneville 213, Pearsall, TX, 1973.

800000

600000

400000

200000

-| ^ I I I I I I I ^ I

140 150 160 170 180 190 200 210 220 230 240 Day no.

Figure 4b.—Comparison of field counts of cotton fruit with output from SIMPLECOT, Stoneville 213, College Station TX, 1974.


800000" Field

0 Counts Model o o Sq.

■ Gr. Bolls A ——Op. Bolls

600000-

400000

200000

140 150

Figure 4c.—Comparison of field counts of cotton fruit with output from SIMPLECOT, TAMCOT-SP37, College Station, TX, 1976.

The Damage Submodel

The larval stage of Heliothis spp. causes the actual damage to the cotton fruit. Townsend (1973), in an extensive study of Heliothis spp. larvae, found that the number of fruit eaten tended to increase linearly as physiological age increased and that older larvae would eat older fruit when younger fruit was not readily available. This relationship is shown in Figure 5 (larval stages assumed to last 16 days). The data from Townsend (1973) also indicated that a larva that was 8.5 physiological days old damaged one fruit per day. Accordingly, for the damage submodel, the numbers of small and large larvae were each weighted by their age divided by 8.5. All cohorts were then summed and stored as equivalent 8.5-day-old small or large larvae (EQSL and EQLL, respectively) .


Relative damage (fruit/larvae)

2.0

n 1 1 1 r 5 6 7 8 9 10 11

Physiological age of larvae in days

T 1 1

13 14 15 16

Figure 5.—Cotton fruit per day eaten by Heliothis spp. larvae v. age (Townsend 1973).

The square preference function determined from the data of Townsend (1973) and Baldwin et al. (1974) is shown in Figure 6. The probability data were calculated by comparing the relative damage done to squares and bolls during the season (early, middle, and late) when populations of squares were high, equal to, and low, respectively, compared with populations of bolls. This interaction of fruit age and larval age was modeled (without undue use of computer time) by making the following assumptions: (1) one equivalent larva will not damage more than one square or boll per day; (2) small larvae (1-3 instar) damage only squares; (3) large larvae (4-5 instar) damage squares and bolls but prefer squares if^ available, and they will damage small green bolls before they will damage large green bolls; and (4) larvae over 14.5 days old do no

damage.

Also, the probability that an equivalent larva will find a square or boll was assumed to be Poisson (random) distributed with

U= 1.0-EXP(-O.000028571xSQUARE)

where SQUARE = Number of squares per acre present.

(4)


Probability of square damage

1.0

-T —I \ 1 1 -r •3 .4 .5 .6 .7 .8 .9 1.0

Proportion of bolls in fruit population

Figure 6.—Square preference of large larvae as a function of boll and square populations.

This equation affected the damage prediction when numbers of squares were low and had a negligible effect when numbers of fruit were medium or high.

The squares per acre damaged by small larvae (DAMSQ) were estimated by the following:

P2 = 1.0-(U SQUARE) (5) DAMSQ = (1.0-EXP(EQSLxLOG(P2)))xSQUARE (6)

where P2 = Probability that a larva will not find any square.

Equations 4, 5, and 6 were also used to calculate total damage to fruit by large larvae, but total fruit (squares plus green bolls) was substituted for SQUARE, and EQLL was substituted for EQSL. In addition, square preference was used to distribute damage between squares and green bolls by introducing the probability that a large larva damaged a square rather than a boll (SQPREF):

SQPREF = l.-(0.548+(0.738-(1.19xPBOL)xPBOL)xPBOL) (7)

where PBOL = Proportion of bolls in total fruit load.


The total damage to squares and green bolls thus calculated was used to reduce each cohort of fruit to complete the damage algorithm.

Results of tests made to validate the damage model are shown in Table 1. The values compare favorably with the data of Townsend (1973) and Baldwin et al. (1974). Moreover, Quaintance and Brues (1905) found that on the average, one larva would damage eight squares, 1 2/3 bolls, and one flower (considered a boll), precisely what the model predicted.

The addition of a dynamic cotton crop model,, SIMPLECOT, and the Heliothis spp. damage model made possible new studies with MOTHZV-3 that were not previously possible. The cotton model can be adjusted for a particular simulation by varying the two input parameters, variety factor, and yield. A base run with no damage can be made. Then the effect on yield of various insect populations or pest management decisions can be studied by comparing subsequent runs with the base run or to each other.

A STATEWIDE EXTENSION PROGRAM: BUGNET

BUGNET, a computerized pest management delivery system, was developed for use in Texas by entomologists of the Texas Agricul- tural Extension Service and research cooperators. It consists of making computer models such as MOTHZV and other BUGNET programs available to the personnel of the Extension Service and thereby to producers across the State for use in making decisions about pest control.

A statewide pest management plan of this type was first proposed for Texas (Frisbie and Adkisson 1975) in 1974 and was tested in pilot programs in 1973, 1974, and 1975. Results of these tests were so encouraging that the Texas Association of Cotton Producer Organizations asked the Texas Agricultural Extension Service, the Texas Agricultural Experiment Station, and the Texas Department of Agriculture to develop and implement such a plan. This was done in 1976.

Table 1.—Validation of the damage model

Test Squares Bolls No. damaged per larva season per acre per acre Squares Bolls

Early 100,000 Mid 270,000 Late 200,000

0 10.5 n.a. 70,000 9.5 1.3

200,000 8.0 2.8


The statewide plan consisted of 10 subplans developed by individual subcommittees. Nine of the plans were local, that is, they were tailored for the nine geographic areas of Texas that are involved in cotton and sorghum production. The tenth plan, TAMU- BUGNET, was designed to investigate the potential of a computer- based system for forecasting populations of insect pests and crop yields. The goal of all 10 plans was to aid farmers in making decisions concerning insect control and crop management.

Phase One

The intent of BUGNET was to make models such as MOTHZV available to the county extension entomology specialists. Phase One of BUGNET was operated from a headquarters in College Station, TX, and the central computer at Texas A&M University was used to run the models.

Necessary information was obtained by installing insect traps in each of the areas and having the specialist monitor the number ^^ Heliothis spp. taken in each daily catch. The traps were installed as early as possible in the spring so as to monitor the emergence of the diapausing (overwintered) moths. The time the traps were put out ranged from February for the Rio Grande Valley to May for the Rolling Plains area. Traps were located within early-season hosts of H_. zea (corn or sorghum or both), depending on which was the major crop in the area. When cotton began to square or when the corn or sorghum became mature, the traps were moved into cotton.

Additional input data gathered by the specialist for MOTHZV were as follows: (1) minimum and maximum daily temperature; (2) planting date, emergence date, and date of first fruit (silk, bloom, square, boll) for each of the three crops (corn, sorghum, cotton) present in the area; and (3) the percentage of each of the three crops in each area (one or multiple counties).

The first batch of data was available for use about 60 days after the traps were installed. Data were mailed to the headquarters by the extension entomologist. Thereafter, data were for- warded whenever it seemed advisable to update a forecast, usually every 7-14 days.

As soon as the data arrived at College Station, they were punched on computer cards, and MOTHZV (stored online on disk at the Texas A&M Data Processing Center) was run. The output, that is, the forecast, was then mailed to the extension entomologist and other interested personnel. The forecast included the time of occurrence and the relative size of the expected egg and larval populations of 11. zea and H. virescens for the entire season. Recipi- ents were cautioned that the numbers indicated the anticipated trend and should not be used as predictions of actual numbers in specific fields.


In 1976, three light traps (Hollingsworth and Hartstack 1972) were installed at each of five test areas. The egg peaks forecast by MOTHZV-2 on the basis of the data obtained at these locations predicted peaks that actually occurred within 3 days of the prediction. Figure 7 shows an example of the predicted and actual egg counts of tl. zea for one location. The successful results of this first year were reported by Hartstack et al. (1977).

In 1977, the BUGNET-MOTHZV program was expanded from 5 areas to a total of 15. In addition, two or three electric grid pheromone traps (Wolf et al. 1972) baited with virelure (Tumlinson et al. 1975, Hendricks et al. 1977), a synthetic attractant for ji. virescens, were installed at each location. The catches of these pheromone traps were used as inputs to MOTHZV-2 for predictions of E, virescens oviposition.

In 1978, MOTHZV-2 was replaced with MOTHZV-3, which included the more dynamic cotton model, SIMPLECOT. The next year the grid traps were replaced with cone traps (Hartstack et al. 1979) that required no electricity and thus were much more versatile. The program has continued to operate in about 15 areas since 1977.

Relative number of eggs

— Predicted June 2,1976—MOTHZV-2 Actual Egg Counts (Hillsboro Area)

—r~ 21

—T" 11

.-./-y^ April May

31 20 June

Figure 7.—A comparison of the June forecast of Heliothis zea oviposition with the actual field egg counts, Hillsboro, TX, 1976.


Phase Two

The second phase of the overall BUGNET program was begun in 1977. Computer power was placed directly in the hands of the area and county extension specialists by purchasing and installing IBM 5100 minicomputers at three locations. In 1979, MOTHZV-4, a simplified version of MOTHZV-3 written in APL, was sent to the field for use on these minicomputers. The version lacked much of the versatility of MOTHZV-3 but could successfully predict timing of Heliothis spp. oviposit ion. Phase Two was expanded in 1980 by adding four new computers and upgrading the original three so that seven IBM 5110 computers are now available to area and county extension personnel at seven locations. Other software packages made available to BUGNET users include a Cotton Budget Generator, an Insecticide Compatibility Chart, Cotton Production Games, an IBM Statistics Pack, and a Boll Weevil Model.

Five Years of BUGNET: The Results

Forecasts during the first year of BUGNET were of limited use to farmers, both because there was doubt about reliability and because populations were low and of little economic importance except for a few isolated locations. However, confidence in the program has grown steadily each year. Over the 3 years, 1977-79, the predictions on the timing of peak egg production were within 4 days of the actual field peaks ca. 70% of the time, this despite the fact that in some areas and in some years, Heliothis spp. populations were low, and there actually were no significant peaks in the field. When populations were low, the probability of error was as great in the field data as in MOTHZV. Thus, some misses might not have occurred if more accurate egg peaks could have been determined from field data.

Although MOTHZV has never been recommended as the exclusive basis for a decision to apply insecticide for control of Heliothis spp., the advance information concerning possible infestations alerted producers who then could intensify scouting efforts. Also, in areas where crops were irrigated, early warning of Heliothis outbreaks has been valuable to those who need this knowledge to time irrigations properly (Slosser 1980). This was because the rapid plant growth and lush foliage that resulted from irrigation were extremely conducive to Heliothis spp. egg lay. Thus it was advisable to avoid irrigation when adult insect populations were high.

Finally, in areas where other insect pests such as the boll weevil and the cotton fleahopper (Pseudatomoscelis seriatus (Reu- ter)) were problems early in the season before Heliothis spp. infestations occurred, any application of pesticides for control of these early-season pests must be terminated several weeks before Heliothis spp. populations build up so populations of beneficial insects can recover enough to help with their control. Advance


knowledge of when Heliothis spp. were likely to build helped determine the best cutoff date.

The Texas Agricultural Extension Service released the following statement in 1979:

"In 1979, approximately 5,740 cotton producers in 91 counties used this tool (MOTHZV) to help manage 4,069,300 acres of cotton. It is conservatively estimated that these producers realized a combined net benefit of $4,967,000. In addition to this, there are intangible benefits (i.e., peace of mind from knowing you*re doing the right thing) that cannot be measured in dollars. It is reasonable to assume that net benefits comparable to this have also been realized in 1977 and 1978, as MOTHZV has enjoyed the same widespread use over the past three years."

The Future for MOTHZV and BUGNET

Although the value of the systems approach to pest management in cotton has not been fully tested and evaluated, research gaps and priorities have been identified. The model itself needs improvement; it is especially lacking in regard to the impact of beneficial insect species and the effects of rainfall and soil moisture. In addition, early-season trapping data are not as precise as they should be.

At present, natural insect predators and parasites are being studied to determine their occurrence and their ability to control pest species; however, little basic biological data are available concerning these beneficial species. Such information will be required if these native beneficial insects are to be managed and augmented by distribution of reared beneficial species. Also, improved methods of sampling beneficial populations to determine their occurrence and number will be necessary before management and releases of beneficiáis will become practicable on a large scale.

MOTHZV-3 does not consider the effect of rainfall and soil moisture on the growth of the crop despite the obvious effects of soil moisture on lushness and the number of eggs laid by Heliothis spp. moths. Moisture also affects mortality of eggs and larvae. However, before these factors can be incorporated in the model, methods of monitoring rainfall and soil moisture over a wide area are needed. Remote sensing might be useful in this application.

The matter of early-season trap catches is another problem. Light traps (Hartstack et al. 1971, 1973) have proved useful in monitoring numbers of Heliothis spp. adults, but there are problems. Such traps must have an electrical power source, which often interferes with field operations. Moreover, the catches are sometimes


difficult to identify. In addition, experience with MOTHZV-BUGNET has shown that at least 3 and perhaps 5-10 traps must be operated within each area to achieve adequate data. That would be expensive, time consuming, and troublesome so numbers have usually been sacrificed for convenience. Finally, the matter of locating the traps in the proper crop and at the proper place can be difficult because of power requirements. These problems, plus irregu- lar servicing, have contributed substantially to prediction errors.

The pheromone traps (Hartstack et al. 1979) and synthetic sex pheromones (Klun et al. 1979) that have recently been developed for H. zea and H. virescens may provide a more convenient and effective way to monitor Heliothis spp. adults. The traps are highly efficient, simple to construct, inexpensive, and portable (requiring no power). Also, only a single species of Heliothis is attracted, which makes identification and counting quick and easy. Since these pheromones are now commercially available, the desired array of 5-10 traps per area can be located within the proper crops, and monitoring should not be difficult. Additionally, with pheromone traps, spring emergence of moths can be detected 2-3 weeks earlier than with light traps.


LITERATURE CITED

Baker, D. N. , J. R. Lambert, C. J. Phene, and J. M. McKinion. 1977. GOSSYM: a simulator of cotton crop dynamics. Tn Compu-

ters Applied to the Management of Large Scale Agricultural En- terprises. Ln Proceedings, United States-Union of Soviet So- cialist Republics Seminar, Moscow, Riga, Kishinev, p. 100-133.

Baldwin, J. L., J. K. Walter, J. R. Gannaway, and G. A. Niles. 1974. Bollworm attack on experimental semidwarf cottons. Texas A&M University. Texas Agricultural Experiment Station Bulletin No. 1144, 11 p.

Brown, L. G., R. W. McClendon, and J. W. Jones. 1979. Computer simulation of the interaction between the cotton

crop and insect pests. Transactions of the ASAE 22:771-774.

Curry, G. L., P. J. H. Sharpe, D. W. DeMichele, and J. R. Cate. 1981. Towards a management model of the cotton boll weevil eco-

system. In IIASA Pest Management Network, Volume 6. [in press.]

DeMichele, D. W., and D. G. Bottrell. 1976. Systems approach to cotton insect pest management. Iri In-

tegrated Pest Management, p. 197-232. Plenum Press, New York,

Duncan, W. G. 1971. SIMCOT: a simulator of cotton growth and yield. In Pro-

ceedings, Workshop on Tree Growth Dynamics and Modeling, Duke University, October 11-12, 1971, p. 115-118.

Frisbie, R. E., and P. L. Adkisson. 1975. Summary: statewide pest management plan. Texas Agricul-

tural Extension Service, Texas A&M University System, College Station.

Gutierrez, A. P., G. D. Butler, Jr., Y. Wang, and D. Westphal. 1977a. The interaction of pink bollworm (Lepidoptera: Gelichi-

idae), cotton, and weather: a detailed model. Canadian Ento- mologist 109:1457-1468.

L. A. Falcon, W. Loew, P. A, Leipzig, and R. van den Bosch.

1975. An analysis of cotton production in California: a model for Acala cotton and the effects of defoliators on its yield. Environmental Entomology 4:125-136.

T. F. Leigh, Y. Wang, and R. D. Cave. 1977b. An analysis of cotton production in California: Lygus hesperus (Heteroptera: Miridae) injury—an evaluation. Cana- dian Entomologist 109:1375-1386.


Hartstack, A. W., Jr., J. L. Henson, J. A. Witz, J. A. Jackman, J. P. Hollingsworth, and R. E. Frisbie.

1977. The Texas program for forecasting Heliothis spp. infestations on cotton. ^E Proceedings Beltwide Cotton Production Research Conference (National Cotton Conference, Memphis, TN), p. 151-154.

and J. P. Hollingsworth. 1974. A computer model for predicting Heliothis populations. Transactions of the ASAE 17:112-115.

J. P. Hollingsworth, R. L. Ridgway, and J. R. Coppedge. 1973. A population dynamics study of the bollworm and the tobac-

co budworm with light traps. Environmental Entomology 2:244-

252.

J. P. Hollingsworth, R. L. Ridgway, and H. H. Hunt. 1971. Determination of trap spacings required to control an in-

sect population. Journal of Economic Entomology 64:1090-1100.

J. A. Witz, and D. R. Buck. 1979. Moth traps for the tobacco budworm. Journal of Economic

Entomology 72:519-522.

J. A. Witz, J. P. Hollingsworth, R. L. Ridgway, and

J. D. Lopez. 1976. MOTHZV-2: a computer simulation of Heliothis zea and Heliothis virescens population dynamics. Users manual. U.S. Department of Agriculture, ARS-S-127, 55 p.

Hendricks, D. E., A. W. Hartstack, Jr., and T. N. Shaver. 1977. Effect of formulations and dispensers on attractiveness

of virelure to the tobacco budworm. Journal of Chemical Ecol- ogy 3:497-506.

Hollingsworth, J. P., and A. W. Hartstack, Jr. 1972. Effect of components on insect light trap performance.

Transactions of the ASAE 15:924-927.

Jones, J. W. 1975. A simulation model of boll weevil population dynamics as

influenced by the cotton crop status. Ph.D dissertation. North Carolina State University, Raleigh, 254 p.

H. D. Bowen, R. E. Stinner, J. R. Bradley, Jr., and J. S. Bacheler.

1977. Simulation of boll weevil populations as influenced by weather, crop status, and mangement practices. Transactions of the ASAE 20:121-125, 131.


Jones, J. W., L. G. Brown, and J. D. Hesketh. 1980. COTCROP: a computer model for cotton growth and yield.

Chapter 10. _In Predicting Photosynthesis for Ecosystems Mod- els. CRC Press, West Palm Beach.

Klun, J. A., J. R. Plimmer, B. A. Bierl-Leonhardt, A. N. Sparks, and 0. L. Chapman.

1979. Trace chemicals: the essences of sexual communication systems in Heliothis spp. Science 204:1328.

Knipling, E. F. 1979. The basic principles of insect population suppression and management. U.S. Department of Agriculture, Agriculture Hand- book No. 512, 659 p.

McKinion, J. M., D. N. Baker, J. D. Hesketh, and J. W. Jones. 1975. SIMCOT II: a simulation of cotton growth and yield. In

Computer Simulation of a Cotton Production System. Users manual. U.S. Department of Agriculture, ARS-S-5^, p. 27-82.

J. W. Jones, and J. D. Hesketh. 1974. Analysis of SIMCOT: photosynthesis and growth. Tn Pro-

ceedings, Beltwide Cotton Production Research Conference (National Cotton Conference, Memphis, TN), p. 117-124.



Slosser, J. 1980. Irrigation timing for bollworm management in cotton. Journal of Economic Entomology 73:346-349.

Stapleton, H. N. 1970. Crop production in system simulation. Transactions of the ASAE 13:110-113.

D. R. Buxton, F. L. Watson, D. J. Nolting, and D. N. Baker.

1973. COTTON: a computer simulation of cotton growth. Arizona Agricultural Experiment Station, Technical Bulletin No. 206, 124 p.

Stinner, R. E., R. L. Rabb, and J. R. Bradley. 1974. Population dynamics of Heliothis zea and H. virescens in North Carolina: a simulation model. Environmental Entomology 3:163-168.

Townsend, J. R., Jr. 1973. Economic threshold studies of Heliothis spp. on cotton. M.S. thesis. Department of Entomology, Mississippi State Uni- versity, Mississippi State, 72 p.


Tumlinson, J. H., D. E. Hendricks, E. R. Mitchell, R. E. Doolittle, and M. M. Brennan.

1975. Isolation, identification and synthesis of the sex pheromone of the tobacco budworm. Journal of Chemical Ecology 1: 203-214.

Wilson, A. G., R. D. Hughes, and N. Gilbert. 1972. The response of cotton to pest attack. Bulletin of Ento- mological Research 61:405-414.

Witz, J. A. 1973. Integration of systems methodology and scientific re-

search. Agricultural Science Review 11:37-48.

Wolf, W. W., H. H. Toba, A. N. Kishaba, and N. Green. 1972. Antioxidant to prolong the effectiveness of cabbage looper

sex pheromone in the field. Journal of Economic Entomology 65: 1039-1041.

SECTION IV ALTERNATIVE PROGRAMS

385

Chapter 15

OPTIMUM PEST MANAGEMENT TRIAL IN MISSISSIPPI

J. L. Hamer, G. L. Andrews, R. W. Seward, D. F. Young, Jr., and R. B. Head Mississippi Cooperative Extension Service Mississippi State, MS 39762

ABSTRACT The 3-year Optimum Pest Management Trial (OPMT) provided a thorough test of available technology for suppression of the boll weevil (Anthonomus grandis Boheman) during the period when it enters diapause in the late summer and fall and for in-season management of other insect and arthropod pests of cotton. The number of in-season insecticide applications was lowered to an average of 3.3 by the end of the Trial. In 1978, the total insect control cost for 3.3 applications including the scouting fee was $20.47 per acre. During 1979, the total insect control cost for 3.41 treatments was $19.36 per acre. In 1980, the total insect control cost for an average of 3.01 applications was $17.50 per acre. In addition, the presence within the Trial area and efforts of well trained Extension pest management specialists who worked closely with producers, private consultants, aerial applicators, county Extension personnel, and others achieved a unified effort by all cooperators. These cooperative efforts resulted in an expansion of cotton acreage from 32,075 to ca. 39,000 acres from 1978 to 1980. Participation by growers in the scouting program increased each year of the Trial—98.7, 99.6, and 99.7% of the cotton acreage was included in 1978, 1979, and 1980, respectively. Yields of lint were increased an average of 84 pounds per acre during the Trial period and an average 34 pounds per acre above the 10-year average.

Through the use of correctly timed pinhead square and diapause control applications and precise monitoring of boll weevil activity with pheromone traps, significant boll weevil suppression was attained. Modified Mitchell traps were used to monitor weevils in both

386 J. L HAMERETAL

Pontotoc, a Current Insect Control Practice Area, and Panola County, the test area. Dur- ing the fall of 1978, 1979, and 1980, up to four diapause applications were applied on most of the participating acreage in Panola County. As a result, in the spring of 1979 and 1980, weevil captures were 78 and 94% lower, respectively, in Panola County than in Pontotoc Coun- ty. Also, weevil captures in line traps installed at 2-mile intervals extending into four counties in north, south, east, and west directions from Panola County indicated higher weevil numbers near or outside the boundaries of Panola County. The need for pinhead square treatment in the test area was limited because the areawide diapause control treatments proved highly effective. Only 57 acres received a pinhead square insecticide treatment during the the Trial, and that was in 1980.

Participation in the Trial required that producers have their acreage scouted. Private consultants scouted 75% of the acreage and producers, 15%; the remaining 10% was monitored by the Panola County Pest Management Society.

Other benefits of the program to the producers included improved understanding of the role of beneficial arthropods, economic thresholds, and timing of insecticide treatments in the control of cotton insect pests. In addition, there was improved understanding of related agronomic practices such as matching plant densities to soil types and the advantages of new methods of fertilization and weed control.

INTRODUCTION

In 1976, States in the Cotton Belt were invited by the U.S. Department of Agriculture Boll Weevil Interagency Working Group to submit plans for a State pest management program that would include all implementable technological advances. This pest management program received the title "Optimum Pest Management (OPM)." Re- sults would be compared with those of the Boll Weevil Eradication Trial (BWET), which was to be carried out concurrently in North Carolina. After extensive evaluation of the responses submitted, the Panola-Pontotoc area of Mississippi was selected as the area where the program would be conducted because it was similar to the

OPTIMUM PEST MANAGEMENT TRIAL IN MISSISSIPPI 387

area in North Carolina where the BWET was to be conducted. Both trials took place during the same 3-year period and were evaluated as alternative methods of improving cotton insect management throughout the Cotton Belt. Panola County was the site of the Op- timum Pest Management Trial (OPMT); Pontotoc County, a comparable area in Mississippi, was the control (Current Insect Control; CIC), that is, the producers in this county used their normal procedures. Panola County is located ca. 50 miles south of Memphis, TN, in the edge of the Delta foothills. About 65% of the acreage in Panola County is hill or river bottom; the Mississippi Delta makes up the rest of the acreage. In 1977, 32,075 acres of cotton were planted in Panola County. However, this acreage can be expanded (to more than 40,000 acres) if profit margins are such as to make cotton a more desirable crop. The average field size is ca. 25 acres with a range from 1 to 100 acres per field. Before the Trial, organized scouting was conducted in the county by private agricultural consultants, producers, business firms, and Extension Service personnel.

Past experience has shown that in Mississippi effective use of pest management strategies will improve net profits for producers (Collins et al. 1976). For example, prior to 1972, some Missis- sippi cotton producers relied heavily on insecticides to protect their crops: they made as many as 18 scheduled applications without regard to thresholds or scouting (Moody et al. 1973). Other producers did not treat at all and so had lower yields. With the introduction of pest management concepts and their gradual adoption since the pilot pest management project in 1972, insecticide usage has been reduced significantly, and yields have increased. Similar benefits have been derived from other pest management programs throughout the Cotton Belt (Smith 1969, Carruth and Moore 1973, Barnes et al. 1974, Black and Burton 1974).

The experience of such successful pest management programs and support from advisory committees and others helped in planning and implementing the OPMT.

Cotton in the OPMT area is infested by the same insect pests that are present in other hill areas of the State. Populations of boll weevils (Anthonomus grandis Boheman) often reach treatment level during early season and will seriously damage fields that do not receive proper management. The bollworm (Heliothis zea (Boddie)) usually requires more frequent midseason and late-season insecticide applications than other pests. This is especially true in fields where it has been necessary to make repeated applications for early-season boll weevils. Control measures for plant bugs (Lygus spp.) may be required in some fields during early season. Whiteflies (Aleyrodidae), spider mites (Tetranychus spp.), and aphids (Aphis spp.) occasionally reach damaging levels and must be controlled.

^^^ J. L HAMERETAL

OBJECTIVES

The objectives for the OPMT were;

(1) To develop and demonstrate the technological and operational capability to implement a community-wide optimum cotton insect management program to maintain boll weevils and other insects below treatment levels through voluntary participation of producers.

(2) To make available to evaluation teams biological, environmental, and program cost data collected in the operation of the Trial as part of the information necessary in estimating costs and benefits of a beltwide cotton insect management program.

GOALS

To achieve the objectives for the OPMT, several goals were established. These were:

(1) Maintenance of boll weevils and other cotton pests below treatment levels as recommended by the Mississippi Cotton Insect Control Guide.

(2) Higher net returns for participating growers than for nonparticipating growers.

(3) Ninety percent grower participation in the demonstration area at the end of the first year, 95% by the end of the second year, and 100% by the third year.

(4) Complete cooperation of all agencies and personnel involved in the Trial.

(5) Implementation of other pest management practices by par- ticipants in the Trial. Agronomic and other pest control practices would include those currently recommended by the Mississippi Coop- erative Extension Service (MCES) to increase cotton profits.

PERSONNEL

Operations

During early planning for the OPMT, personnel required for actual operations were projected on the basis of land area, potential acreage to be included, number of participating clientele expected, and resource personnel located in the program area. The minimum necessary was determined to include an operations chief and five unit employees. The unit employees were used in operating traps collecting field data, and scouting (after summer scouts returned


to school); they also had other duties as assigned by the operations chief. The operations chief assisted in supervision of employees, helped analyze data, and worked closely with aerial applicators, consultants, producers, chemical suppliers, and Extension personnel. He had primary responsibility for maintenance of an effective, well-coordinated program. An Area Pest Management Specialist was in charge of the Trial and worked closely with the county Ex- tension agent, associate agent, and other Extension personnel in conducting the program. He also worked closely with all clientele in Panola County to insure operational success. Backup support was provided by the Extension cotton entomologist and pest management specialist at Mississippi State University. Personnel relationships are illustrated in Figure 1.

Advisory

All aspects of the OPMT were under the supervision of support- ive advisory committees. Both State and regional advisory personnel participated in scheduled meetings during the 3-year Trial period. The State Pest Management Advisory Committee, established in 1972, functioned in an advisory capacity by assisting in Trial planning and guidance. The Regional Extension Educational Advisory Committee consisted of one representative from each of the 11 boll weevil-infested States. Twice each year this committee reviewed the progress of the Trial and offered suggestions for improvements. The State Working Group included representatives from Extension, research and regulatory groups, private consultants, and the chemical industry. This group attended a meeting held monthly in the Trial area. Public attendance was also encouraged.

PUBLIC AWARENESS AND EDUCATION

The collection of baseline data in 1977 by members of the several teams that would be evaluating the OPMT alerted many producers to the fact that the Trial would probably begin in Panola County in 1978. In addition, during the fall of 1977 and throughout 1978, educational efforts were undertaken by 0PM personnel. County meetings with producers, programs for civic clubs and ginning groups, and informal meetings with producers were means of communication used in informing growers and the public of the OPMT program. News releases describing the program were submitted to regional and national magazines and local newspapers.

The operations chief, a person knowledgeable in pest management, and the five unit employees, local individuals holding B.S. and M.S. degrees, were hired in the spring of 1978. These people carried out the operational components of 0PM and gained the confidence of the farm community. In addition, 0PM personnel met in- formally with producers, consultants, aerial applicators, and others and discussed the potential role of the OPMT as it related to their particular interests. These informal communications

390 J. L HAMERETAL

Regional Extension

Educational Advisory

Committee

Dr. David F. Young, Jr. Leader, Extension

Entomology

Dr. Jim Hamer Pest Management

Specialist

State Pest Managernent

Advisory Committee Other State

Cooperatives

Dr. Gordon Andrews Area Pest Management Specialist

Dr. H. C. Mitchell (Deceased)

Dr. Robert Head Extension Entomologist

Joe Hensley County Agent Panola County

Government Cooperators (ASCS, MDA-DPI, Evaluation Teams)

Producers Aerial Applicators

Chemical Suppliers

Figure 1.—Optimum Pest Management Trial Cooperators: ASCS = Agri- cultural Stabilization and Conservation Service. MDA-DPI = Mis- sissippi Department of Agriculture and Commerce, Division of Plant Industry.


assisted in solving specific problems with producers. Also one-on-

one meetings were frequently used to inform growers and other interested individuals of insect problems throughout each growing season and to help maintain effective interactions between program personnel and growers. Interest increased as producers observed

reduced costs and excellent yields on their own farms.

Scout training received emphasis throughout the 3-year Trial. At least three scout training workshops were conducted for scouts employed by the county Extension personnel or by private consultants. Training sessions were held at night so farmers could at- tend. Follow-up scout training continued throughout the season as Extension personnel visited with scouts and consultants to work out recommendations for special situations that arose.

Because of the educational activities undertaken by the 0PM staff and the county Extension personnel in Panola County, the levels of participation by growers in the OPMT were high. In 1978, 1979, and 1980, participating growers accounted for 98.7, 99.6, and

99.7%, respectively, of all cotton acreage.

CONTRACTUAL AGREEMENTS

Funds allocated for the OPMT covered chemical and application costs for up to one pinhead square application (if needed) and four diapause control applications. Contractual agreements for disburs- ing these funds were necessary to improve efficiency in payment and

record keeping, to insure effective use of chemicals, and to make all parties legally bound to a contract. The MCES made contracts with aerial applicators and producers, and the contracts were used to inform the operations chief of the aerial applicator selected by

each producer.

At the beginning of each season, bids were solicited for the cost of the chemicals and the applications (on a per acre basis). Bids were then averaged, and the average cost became the fixed price for the season for all cooperators in the county. Pajmients for chemicals were made directly to the producer. Payments for applications were made to the aerial applicator chosen by the producer. This procedure did not disrupt the regular channel of trade of the producer and proved to be a sound approach for a voluntary

program.

MAPPING

Mapping of cotton acreage is a prerequisite to an effective scouting program. However, locating and mapping approximately 39,000 acres of cotton in an area as large as Panola County required considerable effort and so could not be done entirely by 0PM personnel. Private consultants and county Extension personnel

392 J. L HAMERETAL

cooperated by specifying the acreage they were scouting. Only the acreage scouted by producers was actually mapped by OPMT personnel.

Sixteen orthophotoquad maps were used to map the acreage in the county. With these maps, any point in the county could be located with longitude-latitude coordinates. 0PM personnel were thus able to pinpoint fields and traps and to assign them unique coordinates for identification. In addition, computer storage of data and retrieval of data in map form (Figure 2) made it possible to survey the entire county each week to determine trap captures.

The accurate data from precise locations produced from the mapping effort were essential to decision making in the program. They should also be analyzed carefully before other larger programs are initiated. Weevil populations in the county can be precisely located, and such information can be invaluable in determining how much isolation is needed for a diapause program.

Components used during the 3-year period of the 0PM Trial were as follows:

(l) Trapping

(A) Pheromone traps

(1) Modified Mitchell trap (about 1500 peripheral field traps monitored weekly from April 15 to July 15 and September 11 to December 1.

(2) Leggett traps at different distances from the county lines (72 monitored).

(3) Cone Heliothis spp. traps.

(B) Blacklight traps (three traps used to detect Heliothis spp. activity during the soason).

(II) Planting dates (producers encouraged to plant in as short an interval as possible once planting initiated).

(Ill) Pinhead square application (paid from 0PM funds, if needed).

(IV) Scouting.

(V) In-season control of boll weevils, bollworms, plant bugs, spider mites, and other pest complexes based on scouting reports (costs of chemical and application borne by producers).


fftt^-fttt^ ^ '^ ^V '^^l ^^'^'^l -f f- -ft^f^ 1^2^'^^^'^''^^ ^ ^ 1 ^ -f i^ttttti^t't i^ \r t i^ t t l i^

-^-^ ^ T t r t t i\i^ t t t t t

t^-rt] rr-firi'-f'f \ -f -f r l^'^ t t t ^\2

^ * 1- 1 1 1- ^ 1 ^ ^/i 1 ^ 1

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- 2212^M ^M -f + + 1 'f',_-..-...^ ^1^1^ 2 1 * /--i _^...^ ^-2"

\4 3 1 ...1 i-^-^--^~iJr 1 1 -2^23 \-"2 2332^^ r 1^ t t -r

\22233 2 1^ 1^ 1^ 1- 1 X 1 1 2 2 '^ 'i' ^ 31 34411 ^ 2 52 325M 1 M ^ 1 M 1 1 3 \ M M 1 1 1 1 1 1 \ M12^^2^^^2 \ ^ i~±-i—■ '

Figure 2.—A 1979 computerized map of Panola County showing average captures in pheromone traps during the week (5/29/78-6/4/78) of peak spring emergence of boll weevils.

394 j. L HAMERETAL

(Vl) Diapause control of boll weevils in late summer and fall with insecticide (three or four treatments). Diapause control treatments applied at no expense to producers.

(VII) Stalk destruction.

TECHNOLOGY USED IN OPMT

Trapping

As noted, Mitchell and Leggett pheromone traps were used in the 0PM program to monitor weevil populations. The modified Mit- chell pheromone traps (McKibben et al. 1971, Mitchell and Hardee 1974, Frisbie 1976, Mitchell et al. 1976, Dickerson et al. 1981) were distributed at a ratio of one trap per 20 acres of cotton in Panola County. In order to compare the size of boll weevil populations in the OPMT and the CIC areas, the research team collecting biological evaluation data used the same trapping density in sampling fields in Pontotoc County. Each spring, these field-oriented pheromone traps were placed on the periphery of the fields that had been planted in cotton the preceding year and were used to determine the need for a pinhead square application of insecticide for the control of overwintered boll weevils. The detection of five weevils per week in May was a signal to alert consultants and producers. Row-foot counts were then undertaken in fields that were threatened. The treatment threshold recommended was 25 weevils per acre.

In addition, a line of traps radiating from 8 miles within the county to 2 miles outside the county in all compass directions was operated at ixentical sites throughout the 3 years of the 0PM program to monitor movement of weevils into the Trial area. These trap lines consisted of three Leggett traps at trapping stations that were positioned at 2-mile intervals (Leggett and Cross 1971, Leggett et al. 1975, Leggett 1979). Since there were no buffer zones in this program, trap lines were used to evaluate suppression of normally managed weevil populations at various distances outside the county.

The three blacklight traps and the cone pheromone traps (Roach 1975, Hollingsworth et al. 1978, Hartstack et al. 1979) were used to monitor populations of adult bollworms and to alert producers, consultants, and scouts of possible bollworm activity.

The pheromone trapping program of the OPMT was the largest pheromone trapping program for boll weevils ever conducted. It provided 0PM personnel with current information on the selective density of populations throughout the county. Figure 3 shows the


Average weevils/trap/week

5

Ponotoc '80

Panola '80

Ponotoc '79

Panola '79

May June

Figure 3.---Captures of boll weevils in peripheral traps, Optimum Pest Management Trial, spring 1979-80.

396 J. L HAMER ETAL

trend of catches in the peripheral traps in Panola and Pontotoc Counties during the spring emergence of weevils from ground trash. In both areas, the severe winter of 1977 had reduced boll weevil populations to a low level. Then in the fall of 1978 and 1979, insecticides for diapause control were applied to participating acreage in Panola County. Figure 3 shows the difference between boll weevil populations in the two counties as the 0PM program progressed. In the spring of 1979 and 1980, weevils were 78 and 94% lower, respectively, in Panola County than in Pontotoc County.

The gradients of weevil captures in line traps during the spring trappings of 1978, 1979, and 1980 are shown in Figure 4.

Average weevils/trap

1.575

.175

.025 1 \ I \ r 2 0 2 4 6

Outside Panola County I Inside Panola County

Station positions (miles)

Figure 4.—Captures of boll weevils in line traps during spring emergence. Optimum Pest Management Trial, 1978-80.


Fewer weevils were taken in traps outside the county than in traps inside Panola County in 1978, the first year of the program. How- ever, the numbers taken outside increased each spring thereafter. Meanwhile, traps 4 miles or more inside Panola County captured fewer weevils in 1979 and 1980 after fall diapause control treatments.

Planting Dates

Uniform planting dates were part of the effort to improve insect pest management in Panola County during the OPMT since fields of cotton that are at two stages of growth frequently offer an insect population a chance to develop in one field and then move to the later-planted field, which now may be in a more attractive stage. Moreover, in Panola County, producers must plant as soon as soil temperatures are suitable so full benefit can be received from the short growing season. However, weather, equipment, and available labor determine how quickly the cotton crop can be planted.

In all 3 years of the OPMT, cotton was planted by cooperating growers as soon as soil temperatures would allow.

Pinhead Square Application

The procedures used in the OPMT were designed to prevent damaging infestations of boll weevils from occurring before the onset of large Heliothis spp. populations made it necessary to apply insecticides. Applications early in the season destroy beneficial insects, thus releasing other insect pests, principally bollworms, which then must be controlled with insecticides. Therefore, a pinhead square application of insecticide was used only when populations of overwintering weevils were large enough to produce a damaging first generation of boll weevils. Also, the application was timed to kill overwintering weevils before egg laying and at a time when it would not disrupt the development of the beneficial insect populations needed to suppress bollworms in late July and August.

During the 3 years of the 0PM program, more than 105,000 acres of cotton were planted in Panola County, and it was only necessary to use the pinhead square application on ca. 57 acres of cotton (in 1980). This cotton was near other cotton that was planted at the county border and so had not received diapause control treatments in 1979.

Scouting

Scouting is an important and difficult component of any cotton pest management program, but necessary control decisions can only be made if fields are thoroughly scouted. The most useful data are obtained by scouts who are highly motivated, well trained.

^^Ö J. L. HAMERETAL

experienced, and observant. When such scouts are available, data collected from each day of scouting can be used with confidence though previously collected data, the stage of the crop, current growing conditions, past history of the crops, potential yields, and previous crop input must also be considered in making an accurate control decision.

The only requirement for participation in the OPMT was that the producer have his cotton scouted and that a weekly scouting report be filed with the operations chief throughout the season. The Extension agricultural agent for Panola County encouraged growers of large acreages to hire private consultants. The Panola County Pest Management Society worked with producers who had not previously scouted their acreage. There was some concern at the beginning of the program that scouting done by such diverse groups would result in a diversity of recommendations. However, formal and informal communications between the Trial personnel and other scouts resulted in early identification of localized insect problems. Careful consideration of the problems by all groups then resulted in general agreement concerning recommendations to be made to growers.

During the 3 years of the OPMT, the percentage of the acreage scouted remained fairly constant. Approximately 75, 15, and 10% were scouted by private consultants, producers, and the Panola County Pest Management Society, respectively. There were 1250, 1339, and 1469 scouted fields in 1978, 1979, and 1980, respectively. Although the number of acres scouted by the Panola County Extension Pest Management Society was relatively low, this service was provided at actual cost to producers with small farms, a decision that improved overall management of cotton insects in the Trial area significantly. Figures 5 and 6 show the percentage of squares damaged by boll weevils and bollworms, respectively, as reported by the 0PM scouts. Plainly the populations of both pests fluctuated from year to year and were, on the average, below threshold levels.

In-Season Control

Natural factors such as disease and beneficial insects (Dink- ins et al. 1970) are important in management of insect pests. They are especially effective in suppressing the first and second generations of bollworms in cotton when disruptive insecticides are not applied. As noted, if one is to avoid early use of insecticide, boll weevils must be managed by using pinhead square applications or by diapause control. When weevil infestations can be held below the economic threshold, fewer applications of insecticide will be needed to control bollworms though there may still be a need for occasional control of infestations of plant bugs, spider mites, whiteflies, or aphids before onset of heavy bollworm pressure. However, the damage caused by these pests usually does not affect as much acreage as the damage done by boll weevils and bollworms.


Percent

20 1978 1979 1980

15-

6-11 6-25 7-09 7-23 8-06 Week

8-20 9-03 9-17

Figure 5.—Percentage of squares damaged by boll weevils reported by Optimum Pest Management Trial scouts, 1978-80.

Percent

20 1978- 1979- 1980

15-

10-

Figure 6.—Percentage of squares damaged by bollworms reported by Optimum Pest Management Trial scouts, 1978-80.

400 J. L HAMERETAL

In 1978, weevil populations were maintained below economic threshold during the season so insecticides did not have to be applied to control bollworms until the first of August or later. Only a few fields required treatment for plant bugs. Then four fall diapause control applications were made to most of the cotton acreage to lower the weevil population before overwintering.

In the spring of 1979, weevil emergence was low, and populations were insufficient to justify a pinhead square application. Then during the season, extremely wet conditions prevailed so the cotton had difficulty in fruiting. Also, wild hosts remained attractive to plant bugs longer so relatively large populations were ready to move into cotton when it was fruiting. As a result, plant bugs required control in most fields in 1979, but treatments were usually not applied until after the first generation of bollworms was reduced by beneficial arthropods. Also, the bollworm population did not reach a damaging level until late in the growing season and thus caused few problems. Boll weevils remained below treatment level during the season in almost all fields. Three diapause applications and a partial fourth application were made to all acreage in the Trial area. (An early freeze was the main factor in the decision to cease the fourth application to some acreage.)

In 1980, populations of boll weevils increased greatly over much of the hill acreage outside the Trial area in Mississippi. This resurgence made it necessary to make more frequent in-season applications to control this pest in the surrounding counties and also resulted in larger numbers of boll weevils near the Panola County line. It was for this reason that the pinhead square application had to be used on 57 acres of cotton near the border of the Trial area. Nevertheless, in 1980, infestations of boll weevils in the Trial area were maintained below the economic threshold and did not require treatment during most of the season. A small percentage of the acreage was infested by spider mites and required treatment. The plant bug was of little significance as a cotton insect pest in 1980.

Producers in the OPMT therefore benefited from reduced weevil populations because they had to make fewer applications of insecticide. For example, in 1978, the average number of foliar applications was 3.3 on fields selected for evaluation, and total cost of insect control, including scouting, was about $20.47 per acre. In 1979, the average number of applications was 3.4, and the cost was $19.36 per acre. In 1980, the average was 3.0 applications, and the cost was $17.50 per acre. In addition, yields in the Trial area were higher than yields in all surrounding counties where more or the same number of insecticide applications were applied in 1980 (Figure 7). In the 3 years of the OPMT area, yield of lint cotton increased by an average 84 pounds per acre per year, which equalled an average increase of 34 pounds of lint per acre compared with the 10-year average yield (Tables 1 and 2).


Figure 7.—Estimated yields (x), insecticide applications (y), and cotton acreage (z) for representative counties in north central Mississippi in 1980. Estimates based on survey of county agents, fall 1980. Data based on Current Insect Control programs, which included organized pest management programs.

Diapause Control

As noted, as many as four diapause control treatments were provided at no cost to the producer and with little interference to his normal routine. The producer could choose his aerial applicator and could purchase chemicals from the dealer he normally used.

All diapause applications were applied aerially to insure ad- herence to the schedule. The first application was scheduled 10 days after the producer had ended in-season control. The second followed the first by 10 days. The third and fourth were applied 15 days after the preceding application. (Most producers included a defoliant in one of the applications.) Methyl parathion was selected for diapause control and was used at a rate of 0.5 pound of active ingredient per acre. In 1978, all applications were made at a rate of 1 gallon total volume per acre, but the rate was increased to 2 gallons per acre in 1979 and 1980 to achieve better plant coverage. The schedule for the first two applications was adhered to closely. Only routine weather problems such as rain and

402 J. L HAMERETAL

Table 1.—Lint yields and averages for 3 years of Optimum Pest Man- agement Trial y V. 10-year average 2/

Year

1978 1979 1980 Three-year average Ten-year average Difference between

10- and 3-year averages

Lint yie Ids (pounds per acre :)

Panola Pontotoc County County

630 533 582 485 582 436 598 485 514 422

84 63

]_l Yield estimates obtained from Biological Evaluation Team of OPMT. A value of 485 pounds lint per bale was used as a conversion factor.

2./ Ten-year average yield data taken from Mississippi Crop and Livestock Reporting Service reports.

wind caused short delays. Later in the season during the period when the last two applications were scheduled, temperature became a critical factor and caused some delays. For example, if predictions did not indicate that the temperature would reach 70**?, applications were delayed. All diapause applications were halted after a killing frost or if the stalks were destroyed in a field.

Table 2. -Lint yields and averages for 3 years of Optimum Pest Man- agement Trial and 10-year averages 1/

Year

1978 1979 1980 Three-year average Ten-year average Difference between

10- and 3-year averages

Lint yie Ids (pounds per acre i)

Panola Pontotoc County County

557 500 602 411 485 348 548 420 514 422

+34

J_/ Data taken from Mississippi Crop and Livestock Reporting Ser- vice reports.


Areawide diapause control treatments were applied for the first time in the Trial area in 1978. Since the crop had matured early, the initial treatment was applied beginning September 10. Because of the warm fall and this early starting date, all four diapause applications were needed except in a few fields where the stalks were destroyed. In 1979, the late maturing crop and bad weather put off the first diapause application to September 20. That year an early freeze stopped applications in the middle of the fourth application. In 1980, diapause applications were started September 10, and all four applications were made except on 4034 acres where stalks had been destroyed before the completion of the treatments. The catch of overwintered weevils in pheromone traps reported previously shows the effectiveness of the diapause control applications.

Stalk Destruction

Stalk destruction is a method of eliminating the food that weevils must have to attain firm diapause, but those planning future management programs should take into account the time available for destruction after the crop of cotton is produced and the harvest is completed. In 1978, cotton matured early in the OPMT area, and harvesting was in progress by the middle of September. As a result, about 80% of the stalks were destroyed before the first killing frost. In 1979, harvest did not begin until late September, and the early frost that occurred during harvest made stalk destruction impractical. In 1980, about 70% of the stalks had been destroyed by the time of the first killing frost.

Stalk destruction in the fall was also affected adversely by two problems: (1) rented land was leased on a year-to-year basis, and (2) producers were not sure how much cotton they would plant the next season because of fluctuating prices.

Stalk destruction must take place before the first killing frost, but during most years, producers in Panola County are still harvesting when the frost occurs. The technique is therefore of little value in many areas of the Cotton Belt.

TRIAL SUPPORT

Regulatory

The Mississippi Department of Agriculture and Commerce, Divi- sion of Plant Industry (MDAC-DPI), a cooperating agency, is charged with State regulatory activities. No regulatory functions were involved in the OPMT, but this agency provided support by insuring "up-to-standard" pesticides and usage in accordance with labeling. Other responsibilities included periodic checks of aerial application equipment with emphasis on drift, dosage, and application

404 J. L HAMERETAL

procedures. The MDAC-DPI issues all new and renewed licenses for aerial applicators.

This agency provided much assistance during the 3 years of the Trial and should continue to be included in future programs.

Research

Special projects and recurring State pest management programs are strengthened by a productive relationship between research and Extension entomologists. This relationship has been effective in Mississippi throughout the years and was equally effective during the OPMT.' The MCES sought the advice of and was fully supported by research personnel.

Various agencies and groups that were associated with the Trial and their activities were as follows:

Boll Weevil Research Laboratory

ARS, USDA Starkville, MS

Bioenvironmental Laboratory

ARS, USDA Starkville, MS

Mississippi Agricultural and Forestry Experiment Station

Mississippi State University

Computer Center Mississippi State

University

Animal and Plant Health Inspection Service, USDA

(1) Overall and biological evaluation

(2) Weevil trapping

(3) Coordination of data retrieval and storage

(4) Research (a) Host plant resistance (b) Weevil trapping (c) Cotton insect ecology

(1) Biological evaluation

(2) Research (a) Bollworm pheromone trapping (b) Cotton insect ecology

(1) Economic evaluation

(2) Research - cotton insect ecology

(1) Data storage

(2) Data summarization

(3) Modeling

(1) Environmental monitoring and evaluation


Mississippi Cooperative (1) Program education Extension Service

Panola County, MS (2) Cotton scouting

(3) Advice and support

(4) Chemical demonstrations

EVALUATION

In 1979, a questionnaire was mailed by the operations group of the OPMT to cotton producers who had participated in the Trial. The intent was to help operations personnel evaluate their efforts and to obtain information pertinent to the overall evaluation of the trial. Significant statements derived from analysis of the returned questionnaires were:

(1) Producers shifted from no routine scouting to some form of regular scouting.

(2) Private consultants were used by a higher percentage of producers, and the percentage of fields scouted has increased by 25% since 1975.

(3) Producers decreased the total number of insecticide applications and the number directed specifically against boll weevils.

(4) Of the producers responding, 91% indicated they will continue the program after public funding is withdrawn. Producers responding "No," indicated that the reason was the location of their farms; that is, they were near a county where infestations were not to be controlled or they farmed acreage in two counties.

Other methods of evaluation of the program included summaries of weekly infestation records from each field. This information was compiled annually and in a final report at the end of the 3- year trial period. These reports will be available to evaluation teams and to others interested in the OPMT.

406 J. L HAMERETAL

LITERATURE CITED

Barnes, G., W. P. Boyer, J. J. Kimbrough, H. R. Sterling, and M. L. Wall.

1974. Cotton pest management program. Arkansas Agricultural Ex- tension Service, Leaflet No. 52 (Revised), 12 p.

Black, J. H., and V. E. Burton. 1974. Pest management, what it really is and how it is working

in California cotton. Agrichemical Age, September, p. 6-9.

Carruth, L. A., and L. Moore. 1973. Cotton scouting and pesticide use in eastern Arizona. Journal of Economic Entomology 66:187-190.

Collins, H. L., R. J. Moody, C. F. Sartor, D. F. Young, and J. L. Hamer.

1976. Results of a three-year cotton pest management program in the hill section of Mississippi. U.S. Department of Agricul- ture, Animal and Plant Health Inspection Service, Plant Protec- tion and Quarantine Programs, p. 81-86.

Dickerson, W. A., G. H. McKibben, E. P. Lloyd, J. F. Kearney, J. J. Lam, Jr., and W. H. Cross.

1981. Field evaluations of a modified in-field boll weevil trap. Journal of Economic Entomology 74:280-282.

Dinkins, R. L., J. R. Brazzel, and C. A. Wilson. 1970. Seasonal incidence of major predaceous arthropods in Mis-

sissippi cotton fields. Journal of Economic Entomology 63:814- 817.

Frisbie, R. E. 1976. Role of pheromone traps in survey, detection, program

evaluation, and related biological studies. Texas Agricultural Experiment Station, Research Monograph No. 8, p. 32-36.

Hartstack, A. W., J. A. Witz, and D. R. Buck. 1979. Moth traps for the tobacco budworm. Journal of Economic Entomology 72:519-522.

Hollingsworth, J. P., A. W. Hartstack, D. R. Buck, and D. E. Hen- dricks.

1978. Electric and non-electric moth trap baited with synthetic sex pheromone of the tobacco budworm. U.S. Department of Agri- culture, ARS-S-173, 13 p.

Leggett, J. E. 1979. Boll weevil: some new concepts in trap design and evalua-

tion of trap efficiency. Environmental Entomology 8:70-72.


Leggett, J. E., and W. H. Cross. 1971. A new trap for capturing boll weevils. U.S. Department of Agriculture, Cooperative Economic Insect Report No. 21:773-774.

W. H. Cross, and H. C. Mitchell. 1975. Improved traps for capturing boll weevils. Journal of the Georgia Entomological Society 10:52-61.

McKibben, G. H., D. D. Hardee, and T. B. Davich. 1971. Slow-release formulation of grandlure, the synthetic pher-

omone of the boll weevil. Journal of Economic Entomology 64: 317-319.

Mitchell, E. B., and D. D. Hardee. 1974. In-field traps: a new concept in survey and suppression

of low populations of boll weevils. Journal of Economic Ento- mology 67:506-508.

E. P. Lloyd, D. D. Hardee, W. H. Cross, and T. B. Davich.

1976. In-field traps and insecticides for suppression and elimination of populations of boll weevils. Journal of Economic En- tomology 69:83-88.

Moody, R. J., H. Collins, J. Hamer, C. F. Sartor, and D. F. Young. 1973. Mississippi cotton pest management first annual report, Mississippi Cooperative Extension Service, Mississippi State.

Roach, S. H. 1975. Heliothis zea and JH. virescens: moth activity as measured by blacklight and pheromone traps. Journal of Economic Ento- mology 68:17-21.

Smith, R. F. 1969. The importance of economic injury levels in the development of integrated pest control programs. Qualitas Plantarum et Materiae Vegetabiles 17:81-92.

409

Chapter 16

ANALYSIS OF TECHNOLOGY AVAILABLE FOR ERADICATION OF THE BOLL WEEVIL

E. F. Knipling Agricultural Research Service U.S. Department of Agriculture Beltsville, MD 20705

ABSTRACT The technology for eradication of the boll weevil (Anthonomus grandis Boheman) has been demonstrated. It has focused on the highly vulnerable overwintering generation. Properly scheduled insecticide applications after the regular growing season reduced populations by next spring to an average of a few per acre. Grandlure traps along field borders further suppressed survivors and also identified fields where boll weevils were most prevalent. Diflubenzuron was applied, if necessary, where field populations seemed higher than can be effectively suppressed by sterile boll weevil releases. The sterile boll weevils at high sterility-to-fertile ratios are counted on to inhibit reproduction by most of the low surviving population. However, infield traps at the rate of one or two per acre will assure early detection of any infestations that may occur. Infield and border field traps have such high technical capability that possible reintroduction can be discovered before infestations increase to high levels and become widespread.

INTRODUCTION

The technology employed in the Boll Weevil Eradication Trial (BWET) conducted in North Carolina during 1978-80 involved the use of chemical insecticides and defoliants, pheromone of the boll weevil (Anthonomus grandis Boheman), and the release of sterile boll weevils. Limited use was also made of the growth regulating chemical, diflubenzuron (Dimilin). The general plan was to suppress the boll weevil population during Year 1 to a very low level by the use of insecticides and cultural measures and then eliminate the reduced population during Year 2 by the use of at tractants, sterile boll weevil releases, and limited use of chemical insecticides.

410 E. F. KNIPLING

In terms of numbers of pests destroyed, chemical insecticides have their greatest efficiency when the pest population is high; the attractant and the sterile boll weevil release components have their greatest efficiency when the population is low. Therefore, the two control procedures are highly complementary. The suppressive pressure was directed against the overwintering generation, the most vulnerable period during the annual cycle of the boll weevil.

The basic technology, then still in the early stages of development, was first tested in the Pilot Boll Weevil Eradication Experiment (PBWEE), which took place in southern Mississippi during 1971-73. The results of the PBWEE were evaluated in reports of the Technical Guidance Committee (Knipling 1976b) and the Entomological Society of America (ESA) Review Committee on the Pilot Boll Weevil Eradication Experiment (Eden 1976).

The Technical Guidance Committee for the PBWEE concluded that it was technically and operationally feasible to eliminate the boll weevil as an economic pest in the United States by the use of techniques that are ecologically acceptable. This conclusion seemed justified in view of the extremely high boll weevil population in the experimental area and the difficult circumstances under which the experiment was conducted. Even though the techniques used were still under development, the experiment demonstrated that by methods then available a population could be suppressed below the level of detection in all 170 cotton fields that were 25 miles or farther from heavily infested cotton. However, the Committee also recognized the need for improvements in the techniques and identified the following research needs:

(1) Improved mass rearing procedures to assure the capability of producing adequate numbers of high-quality boll weevils for sterilization and release.

(2) Improved sterilization techniques to assure the attainment of maximum (and consistently high) levels of sterilization with minimum detrimental effect on the vigor and mating competitiveness of the males.

(3) New methods of sterilizing both sexes of the boll weevil so as to obviate the cost of separating sexes and reduce costs and logistic problems associated with feeding boll weevils for 6 days before release.

(4) Continued investigation of grandlure (boll weevil pheromone) to develop the most effective and least costly method of using the attractant for: (a) suppression, (b) detection and population assessment, and (c) monitoring progress in population suppression.

The ESA Review Committee for the PBWEE did not agree on whether technical feasibility of eradication of boll weevil populations

TECHNOLOGY FOR ERADICATION OF BOLL WEEVIL 411

was demonstrated. It recognized the same research needs specified by the Technical Guidance Committee. It concluded that an attempt to eradicate the boll weevil should be a sociopolitical decision. It recommended that all members of the ESA inform themselves as to the long-range environmental and economic benefits that would result from a successful eradication program and weigh the benefits against the costs involved.

Following completion of the PBWEE and before initiation of the BWET in North Carolina, major technical advancements were made which significantly improved the probability of success of the BWET while reducing costs as well. The major improvements, all discussed in this handbook, are:

(1) Improved rearing procedures (Griffin et al. Chapter 11) resulted in production of large numbers of quality boll weevils for sterilization.

(2) Improved procedures for sterilizing the boll weevil (Wright and Villavaso Chapter 7) resulted in a highly sterile weevil which is fairly competitive.

(3) The insect growth regulator, diflubenzuron, was developed as an additional suppressive component. When applied as a foliar spray, the chemical prevents hatch of eggs deposited by females while not interfering with release of sterile weevils (Bull et al. Chapter 9).

(4) A highly sensitive detection system that consisted of as few as one infield trap per acre was developed. It has a 94% probability of detecting F, progeny and a 100% probability of detecting F- progeny of a single female weevil (Lloyd et al. Chapter 8).

No other eradication or management procedure for an insect has ever been put to such elaborate and demanding tests as a prelude to possible wide-scale practical application. However, no other previously proposed eradication program has involved the same techniques and basic principles of suppression that were applied in the two trial programs.

The purpose of this chapter of the handbook is to describe and analyze in detail the nature and function of the methods of suppression employed and to point out what the several suppressive measures can contribute individually and collectively to eradication, in the event a national effort to eradicate the boll weevil is undertaken. While the techniques and principles are applicable to eradication, they could be equally relevant to effective and ecologically acceptable boll weevil population management programs.

The magnitude of the boll weevil problem has caused Federal, State, and private institutions to spend millions of dollars in efforts to develop effective and acceptable solutions to the problem.

412 E. F. KNIPLING

The boll weevil ranks high among the nation's most damaging pests and, without question, is the most objectionable from the standpoint of the adverse effect it has had on the quality of our agricultural environment, because of the necessity of using a variety of ecologically disruptive chemicals for boll weevil control year after year for almost a half century. This effect takes into account the impact such use of insecticides has had on Heliothis spp. and other insect problems.

SOME FUNDAMENTAL PRINCIPLES OF INSECT POPULATION SUPPRESSION AS IT RELATES TO THE BOLL WEEVIL

The application of insecticides, together with the use of cultural measures in some areas, has been relied upon for boll weevil control since the development of arsenicals. Before chemicals became available, the fast-maturing cotton varieties were grown to obtain reasonable yields before overwintered populations increased to highly damaging numbers. From the mid-1940's to the present, a dozen or more highly effective insecticides came into use (Parencia et al. Chapter 10 in this handbook). These insecticides have served their purpose reasonably well when viewed from the standpoint of profitable cotton production. However, as used, insecticides do not provide a satisfactory solution to the boll weevil problem. Annual costs for control, inevitable losses due to grower neglect or miscalculations, unavoidable variations in boll weevil abundance due to weather and other causes, risks of insecticide resistance, and the ecological impact of broad-spectrum insecticides all contribute to a continuation of one of the nation's most costly and obnoxious insect pests. Indirectly, its presence makes it more difficult to manage Heliothis spp. and other pests on cotton or even in adjacent crop ecosystems because of the ecological disruption resulting from broad-spectrum insecticides used for its control.

It has long been my contention that the boll weevil has been a costly pest year after year, not because of a lack of effective control measures but rather because of the way the available control measures have been used. In 1958, I began studies involving the use of simulation boll weevil population models in an effort to gain a better understanding of the dynamics of the boll weevil in quantitative terms. Such information is necessary to explain why the pest continues to be so costly and destructive despite the availability and intensive use year after year of highly effective boll weevil insecticides by most growers in areas where the problem is severe. The most important conclusion reached from these studies was that the boll weevil will continue to be a major pest indefinitely unless the total population is adequately suppressed in an organized and systematic manner. As noted (Knipling 1960), the dynamics of boll weevil populations are such that if only 10% of the farmers in a cotton community fail to control the pest, enough boll weevils can develop by generation 3 to infest all bolls and squares throughout the community even if 90% of the farmers


apply insecticides and obtain near 100% control on their cotton. In contrast, on the basis of the postulated dynamics of the pest, if all growers applied insecticides diligently and moderately and obtained 90% control each generation, there would be 100 times fewer boll weevils in the community by the end of one season and at the beginning of the next. More convincingly, if the insect is not controlled on 1% of the cotton in a community, 10 times more boll weevils will likely exist than in a similar community where all cotton is subjected to moderate and consistent boll weevil suppression.

This simple basic principle of insect population suppression in relation to the dynamics of the pest was largely ignored for many years by research workers, by growers, and by pest management advisers in developing systems of management for the pest. How- ever, it convinced me that an organized and fully coordinated approach to the management of a key and dynamic pest like the boll weevil will be necessary to maintain populations at levels of little or no economic consequence. This fundamental principle holds regardless of the nature of the suppressive measures used.

Reliance on insecticides alone to achieve eradication or rigid management of the boll weevil could lead to ecological problems and possibly intensify insecticide resistance. Hence, supplemental suppression measures that avoid ecological disruption and reduce chances of resistance are necessary before one can advocate areawide eradication or management practices. These goals have now been reached. Thus, on the basis of current technology, there are two alternatives to the boll weevil problem: (1) continue to rely on ecologically disruptive chemicals for an indefinite period of time, or (2) attack the pest on an areawide basis by making optimum use of alternative suppressive techniques.

USE OF SIMULATION MODELS AND INDIRECT CALCULATIONS AS AN AID TO EVALUATION OF BOLL WEEVIL SUPPRESSION MEASURES

In eradication, containment, or rigid pest population management programs, the pest numbers generally reach such low levels that detection of those remaining becomes a major problem. In the PBWEE in southern Mississippi, boll weevils could not be found in fields 25 miles or more from infested cotton with the detection methods then available. However, because of limitations in the sensitivity of the detection methods, complete absence of reproduction could not be assured with a high degree of confidence. Simi- lar detection problems have been encountered in many other insect eradication or containment programs conducted in the past. The lower the density of the target pest the more difficult it becomes to establish presence or absence of a pest in specific areas or to make valid determinations of actual numbers of insects remaining. Consequently, research workers and pest managers are confronted with the problem of providing "scientific proof" of success to those who must endorse a new approach to a problem.

414 E. F. KNIPLING

The difficulty of obtaining reliable, quantitative data to support pest management procedures is a problem that must be given adequate attention and analysis by entomologists because it is relevant to the concepts of pest population eradication and containment and, in some cases, may be equally relevant to rigid pest population management. However, it should be emphasized at the outset that absolute "proof" of eradication of any pest population is not scientifically possible. It is no more possible to prove complete absence than to prove that a chemical is completely free of hazards. This is also a matter of grave concern to toxicolo- gists concerned with the use of chemicals as pesticides.

The outstanding recent advances in research on insect sex pheromones have made possible great progress in the sensitivity of detection methods for a wide range of insect pests, but better interpretation of the data in quantitative terms is still needed. As progress continues, this should lead to less uncertainty concerning the validity of results obtained in eradication or pest management programs. This surely should be the case for the boll weevil. The advances that have been made in detection methods for this pest are reported in the section on the role of the sex and aggregating attractant as a suppressive measure (Lloyd et al. Chapter 8).

As noted, the conventional methods used to detect many insect pests have had limited reliability. This has made it difficult to determine in quantitative terms the degree of success of various suppressive measures under consideration. Accordingly, I have made extensive use of simulation population models based on assumed numbers of insects present in an effort to determine the mechanism of action of various techniques of insect control and to estimate in numerical terms the results to expect from various methods of suppression. Such models have been used to estimate the impact on insect populations subjected to suppression by the use of insecticides, insect attractants, programmed release of parasites, growing resistant plant varieties, and the release of sterile or genetically altered insects. They have also been used to show the great advantage of concurrent use of two or more compatible or complementary methods of control. The various procedures used to make such a determination have been described in a recent publication (Knip- ling 1979).

Entomologists have not yet made extensive use of, and many do not have confidence in, indirect modeling procedures as an aid to the evaluation and interpretation of data obtained in suppression experiments or programs. They still prefer or expect direct quantitative data that are virtually impossible or impractical to obtain after pest populations reach a certain minimum. In my view, simulation models are almost essential to fully appraise and explain how and why different suppression techniques achieve certain results. In the final analysis, eradication, or even rigid management of pest populations, involves a game of numbers, which often defies accurate determination by conventional collection of data. Therefore, in discussing the various techniques of suppression that


may be used in boll weevil eradication programs and what they can contribute to suppression, I will make maximum use of simulation models that are based on reasonably well-established parameters.

INFLUENCE OF BOLL WEEVIL MOVEMENT ON ERADICATION

The movement of insects can account for the failure or apparent failure of many eradication experiments, even though the techniques used may have been capable of achieving eradication of isolated populations. It is axiomatic that eradication of a pest cannot be achieved unless the total population in the area of permanent survival is subjected to suppression. Entomologists have consistently underestimated, or in some cases have not taken into account, the extent of insect movement. When the rate of infiltration is below the level of detection and when insects still remain, scientists almost invariably attribute such presence of insects to a failure of the technology tested. The controversy over the success or lack of success of the PBWEE in southern Mississippi was in large measure due to the presence of some boll weevil reproduction in portions of the originally defined eradication area. Actually, infestations were detected only in cotton fields that were within 25 miles of heavily infested areas. The entire core area was assumed to be adequately isolated, but this subsequently proved not to be the case. In fact, the extent of movement of the boll weevil has been a major subject of investigation in connection with the different eradication trials. However, eradication, or even highly effective management of boll weevil populations, will never be accomplished unless the areas under suppression are adequately isolated or are large enough to avoid direct infiltration of large numbers of the insects into substantial portions of the area under suppression. In the planning for the North Carolina trial program, movement of boll weevils 45 miles or more was considered a probability because records of this extent of movement had been obtained; therefore, a barrier zone approximately 85 miles deep was established to prevent or minimize the possibility of infiltration into the eradication zone. Present movement studies now indicate some movement for up to 65 miles, so the possibility that some boll weevils will disperse a greater distance cannot be ruled out unless the population at the source is strongly suppressed. The introduction of boll weevils as hitchhikers or on infested commodities was, of course, recognized.

CHARACTERISTICS AND FUNCTION OF VARIOUS SUPPRESSION COMPONENTS CONTRIBUTING TO ERADICATION

The techniques currently envisioned for the use in boll weevil eradication programs differ in suppressive action. They also vary in efficiency, depending on the density and distribution of the insects in the natural population. This makes it possible to achieve greater efficiency by employing two or more techniques concurrently or sequentially instead of relying on only one method. Indeed,

416 E. F. KNIPLING

techniques that are potentially effective and highly desirable from an ecological standpoint, such as the use of sex pheromones or genetically altered insects, may have relatively little practical value for eradication or management of well-established insects unless they are employed as supplements to insecticides, cultural and sanitary measures, or host plant resistance, methods of control with essentially the same efficiency at all levels of pest density. In order to clarify the practical significance and the potential value of different techniques of suppression when appropriately integrated, I will discuss in detail the characteristics, action, and function of each of the several methods used for boll weevil suppression in the North Carolina trial program.

Insecticide Suppression Component

Insecticides are highly effective for the control of boll weevils when used at approved dosages on proper spray schedules. When eradication or a high degree of suppression is the objective, it is obvious that applications must be thorough. In the PBWEE, it was found during Year 1 that aerial applications alone did not produce a high degree of suppression because of natural and man-made obstacles such as tall trees, power lines, and others. However, supplemental sprays applied with ground equipment resulted in a very high degree of suppression. It was also found that highly effective suppression with insecticides cannot be expected unless the behavior of the pest is taken into account and applications are appropriately timed to disrupt boll weevil development.

Brazzel and Newsom (1959) determined that adult boll weevils enter a state of diapause in the late summer and early fall. In this state, they feed on squares and bolls for a period of 10-14 days or longer to build up fat reserves. They then leave the cotton fields for overwintering quarters. In view of this behavior, Brazzel (1961) and Brazzel et al. (1961) proposed the diapause spray schedule and demonstrated that four appropriately timed applications of spray at about 10- to 14-day intervals in the fall would reduce overwintered populations by ca. 90%. This substantial control reduced the number of in-season applications required the following season. However, reproducing boll weevils are also present in the late summer and early fall. Therefore, spray intervals of 10 days or more permit considerable reproduction because the preoviposition period of the boll weevil may be as short as 5-6 days, even in the fall. Accordingly, on the basis of results of earlier simulation control models, I proposed modifications to the diapause spray schedule so as to limit reproduction by the last generation that produces most of the diapausing population (Knip- ling 1968). I also proposed that applications should be continued long enough to kill most of the surviving progeny before they leave the cotton fields for hibernating quarters. It was calculated that if four spray applications at intervals of 10-14 days to kill diapausing boll weevils will achieve about 90% suppression, seven applications properly scheduled to also limit reproduction of the


last reproducing generation will achieve higher than 99% suppression. The general validity of the calculations was subsequently verified in boll weevil suppression programs undertaken by regulatory agencies in the Presidio and High Plains areas in Texas (Adkisson et al. 1966, Fye et al. 1968).

Although most of the diapausing boll weevils are produced in the late summer and early fall, a certain percentage of the population may diapause and leave cotton fields for hibernation quarters before the time that a reproduction diapause spray schedule is initiated. This seemed to be the case with the high populations present during Year 1 of the PWBEE. (Many of the growers did not carry out a good in-season control program, and boll weevil populations were very high.) Considerable numbers of boll weevils apparently entered hibernation when squares and bolls became scarce before the normal diapause period. Therefore, during Year 2, all cotton was properly monitored and sprayed during the growing season since a good in-season spray program protects the crop and also assures that few, if any, boll weevils will enter diapause and leave the field for overwintering sites during July and August. This in-season program was then followed by properly timed sprays to limit the rate of reproduction of the last reproducing generation and to kill most of the greatly reduced population of diapausing progeny before it could complete development and leave the fields for hibernating quarters. The result was a drastic reduction in the overwintered population.

The BWET conducted in North Carolina was carried out under close supervision by U.S. Department of Agriculture and cooperating State personnel. In the first year (1978), there was critical monitoring of cotton insect infestations, and in-season applications of insecticides were made for the control of Heliothis spp. and other pests, as well as for control of the boll weevil. However, the boll weevil population was abnormally low because the two previous winters had been severe and because insecticides had been used intensively in 1977 for control of the bollworm (Heliothis zea (Boddie)); thus the 1978 in-season program included an average of 3.7 applications for bollworm control and 2.2 for boll weevil control. These treatments further reduced the boll weevil population. Nevertheless, the regular in-season program was supplemented by five sprays properly timed for maximum suppression of both reproducing and diapausing boll weevils. Defoliants were also applied to limit available food for diapause development.

In the spring of 1979, only seven overwintered boll weevils were captured in 16,676 survey traps around North Carolina cotton fields totaling 12,485 acres of cotton. However, an accurate estimate of the total surviving overwintered population cannot be made because it is not known what proportion of the overwintered survivors was captured in the border field traps before the first releases of sterile boll weevils. After sterile boll weevil releases are made, much of the competitiveness of the traps is lost because of the competing pheromone produced by released males. However,

418 E. F. KNIPLING

it is probable that up to 50% of the overwintered boll weevils had emerged from hibernating quarters by the time the first sterile boll weevil releases were made. E. P. Lloyd (personal communication) estimated that pheromone traps placed along field borders in the earlier PBWEE program captured 25% of the overwintered boll weevils.

If it is conservatively assumed that seven captured boll weevils equaled 25% of the total overwintered population in the eradication area, the total number of overwintered survivors would have been of the order of 28 in an area having 15,222 acres of cotton during the 1979 season. While this estimate may not be highly accurate, it is accurate enough to allow the conclusion that vir- tual annihilation of the boll weevil population had been achieved by the insecticide applications and defoliant treatments during 1978.

It has long been my view that during the first year of a program designed to eradicate the boll weevil, the overwintered populations should be reduced to an average level of one or two boll weevils per acre. I believe that such a low population can be readily eliminated the next season by the use of pheromone traps, sterile male releases, and strategic use of insecticides where needed. The very low capture rate in the spring of 1979 in North Carolina indicated that the overwintered population there had been reduced far below a level of one per acre. If the surviving overwintered population was of the order of 28, as estimated, this would mean the survival of only one boll weevil on about 445 acres of cotton, (it should be pointed out that if the population had been 100 times higher but a comparable reduction had been attained, the overwintered surviving population of 2800 would still have been much lower than the average of one or two boll weevils per acre which I have arbitrarily set as the desired degree of suppression during Year 1.) This analysis indicates in numerical terms the degree of success of the first year of suppression.

As noted earlier, the boll weevil population in the BWET area was abnormally low. Therefore, it would be presumptuous to assume that similar low populations will be encountered in all areas if an eradication program is extended. For this reason, it seems important to consider the results to expect from the use of insecticides when the boll weevil population during Year 1 is much higher.

The population in the Trial area was abnormally low when the eradication treatments were started, but the actual number of boll weevils present is not known. A total of 1009 boll weevils were captured in 2293 traps operating in 1978 during the fall insecticide treatment period. W. H. Cross (personal communication) estimated 2% capture of available boll weevils with the density of traps employed. On this basis, the total population was of the order of 51,000, or 4-5 per acre.


With these data, we can establish numbers that will be reasonably representative of maximum densities likely to be encountered in areas of severe boll weevil infestation and then calculate the results expected of a well-monitored in-season control program followed by a thorough, well-timed spray schedule designed to reduce the overwintered population to a practical minimum. This can be done by the use of simulation models based on conservative parameters such as the level of kill that will result from insecticide treatments.

In-season boll weevil applications are usually started when the square puncture level is ca. 10%. Therefore, it is assumed that this level of infestation can be maintained in areas planned for eradication if a well-conducted in-season control program is implemented. When the crop has largely matured and squares are relatively scarce, as few as 200 boll weevils per acre can account for a square puncture rate of ca. 10%. Therefore, this is assumed to be representative of the level of density when actual eradication treatments are started. It is also assumed that each insecticide treatment will kill 95% of the weevils present at the time of each treatment, both reproducing and diapausing forms. The increase rate for highly favorable boll weevil reproduction is estimated to be tenfold. Therefore, each reproducing pair can account for 20 diapausing boll weevils. The diapausing boll weevils are estimated to have 90% natural mortality from the time of emergence in the fields until they enter the fields the next spring. These basic parameters were discussed with J. R. Brazzel and E. P. Lloyd who participated directly in both the North Carolina trial and in the PBWEE. These two authorities (personal communication) consider the basic parameters as being on the conservative side since they are of the opinion that thorough insecticide treatment of the type applied will achieve higher than 95% kill of weevils present. How- ever, it seems desirable to use parameters that are conservative.

On the basis of the assumed number of boll weevils per acre and the effectiveness of the spray treatments, I estimated the results to expect when a population is more representative of normal density than that encountered in the North Carolina trial. For these calculations, a cotton growing area consisting of 25,000 acres is assumed. Then, in order to clearly indicate the expected impact of the insecticide and cultural control components during the first year, I developed a basic model that reflects an otherwise uncontrolled population after a well-executed in-season program has been followed. (This hypothetical population is not subjected to suppression during the diapausing period, which is characteristic of boll weevil management in many areas.) The model can then be used to project the effect of the insecticide application on a similar population when the applications are directed against the last reproducing generations and the surviving diapausing progeny. On the basis of the parameters given, the calculations show the relative number of overwintered boll weevils per acre for an uncontrolled and a suppressed population that would enter hibernation

420 E. F. KNIPLING

and emerge to enter cotton fields the next spring. A natural winter mortality of 90% is assigned to each population.

Uncontrolled population (per acre)

Reproducing boll weevils during generation 4 (F^) = 200

Number of diapausing progeny = 2000

Winter mortality = 90%

Overwintered boll weevils per acre entering cotton fields the next spring = 200

Suppressed population (per acre)

Reproducing boll weevils during generation 4 (F^) = 200

Reproducing boll weevils surviving treatment = 10

Number of diapausing progeny = 100

Number of diapausing progeny surviving treatments = 5

Winter mortality = 90%

Overwintered boll weevils per acre entering cotton fields the next spring = 0.5

This estimated effect of Year 1 suppression is based on realistic numbers of boll weevils likely to be present in areas under good boll weevil management. The assigned rate of increase seems reasonable. The results assumed after thorough, well-timed insecticide applications are probably conservative. The natural mortality also seems reasonable. Therefore, the calculations should indicate in numerical terms the minimum effect expected from the insecticide treatment phase during the first year of an eradication program. This estimated average overwintered population of 0.5 boll weevils per acre would represent a drastic reduction, but it would still mean some 12,500 boll weevils in the hypothetical area, and these would require additional suppression during Year 2 in order to achieve eradication. It is obvious that the number of survivors per unit area will vary greatly in different cotton fields, both in the fall and spring. However, it is the function of the detection component to identify fields where surviving populations are above average so suitable adjustments can be made in the


intensity and type of control measures to apply. For example, in fringe areas where populations are very low, fewer applications of insecticides should be necessary to reduce overwintered populations to a very low level. Also, if some fields have higher than average overwintered survivors, supplemental insecticide applications may be necessary. In any event, the model depicts the drastic accumulative impact of the suppressive procedure used and indicates that prehibernation î)opulations 100 times as high as those occurring in the trial program should be reduced to less than one overwintered

boll weevil per acre.

It might be mentioned that if each insecticide application

kills 98% of the boll weevils, as J. R. Brazzel and E. P. Lloyd contend, the surviving overwintered population would be reduced to

a level of 0.08 boll weevils per acre instead of 0.5 per acre. This would mean an average of one overwintered boll weevil on 12 acres of cotton or about one boll weevil in an average-size cotton field; nevertheless, in an area consisting of 25,000 acres of cotton, this would still mean the survival of some 2000 boll weevils that must be killed or whose reproduction must be inhibited if

eradication is to be obtained.

Suppressive Measures Directed Against the Overwintering Generation Versus In-Season Generations

In the previous section, a simulation model was presented to depict the effect of properly scheduled insecticide treatments to reduce the number of diapausing boll weevils that can survive to enter hibernating quarters. It was stated that the diapausing progeny of the last reproducing generation in the fall constitutes a highly vulnerable portion of the population of the pest. The model depicted the effect of in-season suppression of an in-season population to a level of 200 boll weevils per acre until the last reproducing generation in the fall and showed that 95% control of reproduction plus 95% control of the diapausing progeny produced overall suppression of 99.75%. In addition, natural mortality of 90% would limit the number of overwintering survivors. However, it is difficult to fully appreciate the accumulative impact of the factors that cause such high mortality by considering percentages alone. Therefore, it is important to convert percentages to representative numbers. If a boll weevil population is uncontrolled, one can expect an overwintering population of 1000 per acre. If this potential overwintered population were reduced by 99.75%, the overwintered population would be reduced to an average of 2.5 boll weevils per acre. But the fact is that in most areas, cotton growers today achieve reasonably good control, especially under present supervised integrated pest management (IPM). Under such programs, an overwintering population is not likely to exceed 200 per acre, and 99.75% suppression would mean a reduction to 0.5 boll weevils

per acre, as previously discussed.

422 E. F. KNIPLING

Unless appropriate simulation models are established, it is difficult to visualize the relative effect of different strategies for suppressing the boll weevil. The traditional method of controlling the boll weevil has been to attack the in-season generations. Nevertheless, from the standpoint of the dynamics and behavior of the boll weevils, suppressive measures applied during this period are much less efficient than suppressive measures directed against the overwintering generation. Indeed, the advantage of the attack on the overwintered generation, as proposed for eradication programs, is so impressive that it seems important to analyze the relative efficiency of the two approaches to boll weevil suppression.

We assume, as before, that each application of insecticide kills 95% of the boll weevils present at the time of treatment. We also assume, as before, that reproducing survivors will increase tenfold per generation. The hypothetical overwintering population starts with 200 boll weevils per acre, which is considered representative of a normal population in an area with a severe infestation. Insecticide applications are programmed at 5-day intervals through five generations, including the F« generation, which is assumed to be the last reproducing generation that produces the diapausing progeny.

This model thus assumes an intensive attack during the growing season but no control of the diapausing population. If we allow 21 days per generation and if insecticide applications are necessary at 5-day intervals to achieve 95% control of a generation, a total of about 18 applications of insecticides will be required to achieve the results shown in Table 1.

Table 1.—Accumulative impact on the dynamics of a boll weevil population subjected to intensive suppression of the pest with insecticides during the regular growing season

Gener- ation

Boll weevils per acre (No.)

Degree of

control (%)

Repro- ducing boll

weevils (No.)

Progeny (No.)

Year 1 1 1/ 200 95 10 100

1.25

2 100 3 50 4 25

95 5 50 95 2.5 25 95 1.25 2/ 12.5 ar 2 3/

Ij Overwintered. 1/ Diapausing. 3_l Natural winter mortality = 90%.


Therefore, the intensive attack against all the reproducing generations would greatly reduce the overwintered population. How- ever, there would be 2.5 times as many overwintered survivors during Year 2 as there would be after the application of about six or seven properly scheduled insecticide applications directed against the overwintering population in the fall. (There is also an ecological advantage in concentrating suppression against the population after the cotton crop is made.)

Obviously, the difference in effectiveness of the two approaches to boll weevil suppression cannot be readily visualized and would be difficult and costly to measure in conventional field trials because of the low numbers of survivors per unit area that would be involved under either method. However, appropriate use of simulation suppression models that depict populations in numerical terms clearly indicates the advantage of one suppressive procedure over the other. This is an excellent example of the way simulation models can be used to guide research and development and operational strategies.

Pheromone Trapping Component

Role of the Sex and Aggregating Attractant for Detection

The identification and synthesis of the pheromone of the male boll weevil, grandlure, and the demonstration of the value of grandlure for detection are among the major developments in boll weevil research. This use of grandlure has great practical significance to the concept of boll weevil eradication and to management. The history of the research is reviewed by Lloyd et al. in Chapter 8 of this handbook.

Grandlure provides us with a method of detection that has such a high degree of sensitivity, particularly when it is used in infield traps, that the problem of determining whether and where low level infestations still exist is no longer a matter of major concern in eradication and containment programs. There is little question that technology is available for eliminating incipient boll weevil infestations if it is known where they exist. It is also highly important from the standpoint of optimum efficiency in the conduct of an eradication program to know with a high degree of certainty where the boll weevils no longer exist within an eradication area. In fact, detecting boll weevils in cotton fields was still a major problem when results of the PBWEE were interpreted. This was one reason many pest management authorities were reluctant to accept the results of the Mississippi experiment as a valid demonstration of the feasibility of eradicating the boll weevil. The methods then used were based on visual detection of adult boll weevils or detection of fertile egg punctures in squares.

The sensitivity of the border and infield traps now used for detection is discussed by Lloyd et al. in Chapter 8 of this

424 E. F. KNIPLING

handbook and will not be discussed in detail here. However, it is important to note that though even one infield trap per acre will detect reproduction by a single female by the F^ generation, an average of slightly under two infield traps per acre (30,244 traps in 15,222 acres) were used in 1979 in the North Carolina trial. No reproduction was detected during at least three generations of boll weevil development during Year 2. Thus, it can be assumed with virtually 100% certainty that the boll weevil population was eradi- cated from the eradication area by Year 2, rather than Year 3, which was the original goal. In the absence of the newly available detection technology, this conclusion could not have been reached during Year 2 and with such high degree of confidence.

One reproducing clump of boll weevils was discovered in Sep- tember 1980 (Year 3) in one field. However, the failure to detect the presence of boll weevils in infield traps during at least three generations in 1979 and at least two generations in 1980 plus the failure to detect boll weevils in border traps in the spring and fall of 1979 and the spring and summer of 1980 makes it possible to attribute the infestation discovered in Year 3 to long-range dispersal from heavily infested cotton or accidental movement from an infested area. In view of the probability of detecting the presence of boll weevils during each of these generations and periods, the chances are of the order of 1,000,000:1 that the infestation was the result of an introduction rather than a surviving population.

The capability of detecting the absence of or existence of reproduction in cotton fields at the lowest reproducing level offers prospects for optimizing the effectiveness and efficiency of the various procedures available for boll weevil suppression.

Role of the Sex and Aggregating Attractant as a Suppressive Measure

The potential role of pheromone traps for the control of very low overwintered boll weevil populations has not yet been fully ex- ploited. However, available information and general observations indicate that border field traps used at a rate of one per acre and subsequent infield traps used at a rate of three to four per acre after cotton fruiting begins would make a major contribution to suppression of very low populations.

On the basis of the competitive theory of attraction (Knipling and McGuire 1966), the efficiency of pheromone traps baited with the synthetic replica of a natural pheromone is inversely correlated with the. density of the insects that produce the competing natural pheromone. The validity of this theory has been confirmed in principle by studies conducted by Lloyd et al. (1972). Thus, the lower the population of overwintered boll weevils, the greater will be the suppressive action of a given density of traps. Knipling (1976a) developed models to estimate the effect of infield traps


used against low-level overwintered populations. The calculations indicate that at a trap density of 10 per acre, a high degree of suppression can be expected when the overwintered population has been reduced as low as 10 per acre. It was also calculated that ca. 98% control could be expected when the overwintered population was as low as two per acre. Since a properly executed Year 1 program of suppression of the boll weevil can be expected to reduce an overwintered population well below an average of two boll weevils per acre and since the lower the overwintered population, the more effective a given number of traps will be, the prospects seem excellent that a border and infield trapping system could have a vital role in both detection and suppression of a low density boll weevil population.

The validity of the theoretical models has not been fully confirmed, but Lloyd et al. (1980) obtained encouraging data concerning the effectiveness of infield traps used against simulated "clumped" F, progeny from single reproducing females in small cotton fields of about three acres. Although these studies were designed to determine the effectiveness of infield traps for detection, the results also indicated that four infield traps per acre will capture more than 90% of an average population of ca. eight female boll weevils emerging in each cotton field. These data, while preliminary, suggest that the parameters used in early calculations of trap density may have been conservative and that the probability is high that pheromone traps could make a major contribution to the elimination of overwintered boll weevils when densities average less than one per acre. I will consider this possibility later in connection with a discussion of opportunitier for further improvement in eradication technology.

Sterile Boll Weevil Release Component in Eradication

Although the number of overwintering boll weevils surviving the insecticide suppression component of an eradication program may be at a very low level, reproduction by the few survivors must be inhibited. When suppression measures that are equally effective at all pest densities are employed, it may take as much effort and cost to kill 1% of a surviving population as it requires to suppress the first 99-99.9%. Nevertheless, even when a boll weevil population reaches an average density of one per acre, there are thousands of survivors in an ecosystem consisting of thousands of acres of cotton. These survivors must be eliminated to achieve eradication, but reliance on insecticides to achieve this purpose would be inefficient and could be objectionable from an ecological standpoint.

In contrast, the sterile insect technique becomes increasingly efficient as a population declines. Also, boll weevil rearing has reached such efficiency that the cost of rearing is not likely to exceed $2-$3 per thousand (Griffin et al. Chapter 11 in this handbook). Therefore, when natural populations reach an average level

426 E. F. KNIPLING

of one or fewer boll weevils per acre, an overwhelming ratio of sterile to native boll weevils can be achieved at low cost. This is important because sterilized males may not approach the competitiveness of the native males. However, when native boll weevils can be outnumbered by a factor of several hundred, release of weevils that are only 5-10% as competitive will still prevent reproduction in virtually all cotton fields.

As previously noted, only seven native overwintered boll weevils were captured in the North Carolina eradication zone. It was postulated that the total native boll weevil population in 15,222 acres of cotton was likely of the order of 28. Since a total of about 11 million sterile boll weevils was released, the sterile to fertile ratio achieved was of the order of several hundred thousands to 1. When the native population is at such a low level, there is no way to make a statistical measurement of the effect of the sterile boll weevils. Neither can one measure the effect of sterile boll weevil releases on the basis of overall ratios since that depends on the ratio of fully competitive sterile weevils to fertile weevils in the specific habitats of the native boll weevils. Even so, the release of sterile boll weevils provides an efficient system for final elimination that is ecologically safe and highly complementary with other suppression techniques.

Sterile boll weevils in cotton fields may do more than interfere directly with reproduction of native females when the native population is greatly reduced. Their presence should prevent the normal aggregation of the few native boll weevils remaining. It is not possible to obtain statistical data concerning this effect that are adequate for analysis. Yet, by rationalization as well as by observation, aggregation of overwintered boll weevils is a natural behavior of boll weevils. It undoubtedly evolved to increase opportunities for mating in natural low and widely scattered populations. In view of the high degree of attractiveness of the pheromone produced by the boll weevil, mate finding may not be a serious problem to successful reproduction, even when a single male and female are present in an average-size cotton field. However, in the presence of several hundred sterile boll weevils, it seems highly unlikely that so few native males and females could aggregate because of the competing pheromone produced by the released males. This same effect could result from high density trapping. For example, if a native population averages one male and one female per 10 acres and if a thousand or more sterile boll weevils are present that produce the pheromone, matings may seldom occur, even if the males have a low level of mating competitiveness. Ran- dom distribution predicts the presence of two males only in about 25% of the cotton fields, two females in 25% of the fields, and one male and one female in ca. 50% of the cotton fields. (Such calculations ignore the probability of more or fewer boll weevils in some fields.) However, even in fields with several of each sex, the probability of encounters between native males and females may be nil in the presence of several hundred sterile males that would interfere with the normal aggregation of low density populations.


These effects have not yet been investigated, but they are likely to be of very great practical significance in the final elimination of boll weevil populations.

Finally, it should be pointed out that the sterile boll weevils may reduce the opportunity for reproduction of any native boll weevils that have survived exposure to insecticides because of an insecticide-resistant gene or genes. In the absence of competing sterile boll weevils, a few survivors carrying genes for resistance would have the opportunity to reproduce, which would immediately increase the frequency of resistant genes. This will not be the case if the few surviving weevils with resistant genes mate with sterile boll weevils.

Diflubenzuron Component in Eradication Programs

The development of the growth regulating chemical, diflubenzuron, as a control measure for the boll weevil added a new component that could be valuable in boll weevil eradication (Bull et al. Chapter 9 in this handbook). The initial plans were to make substantial use of the material as a supplementary suppressive measure in individual cotton fields where trapping data indicated the presence of enough overwintered survivors so sterile males might not control reproduction adequately. In fact, the capture of native boll weevils in survey traps was so low there was little need for supplemental diflubenzuron applications. Nevertheless, about 900 acres of cotton were treated with diflubenzuron as a security measure in areas where the few overwintered boll weevils were captured.

Although the need for diflubenzuron did not materialize in the North Carolina trial, the potential value of this chemical to any eradication program should not be discounted. Diflubenzuron has relatively little effect on beneficial insects, a feature of great importance in cotton insect management or eradication, since broad- spectrum insecticides destroy the beneficial insects that hold such secondary pests as Heliothis spp. in check. Thus, when supplemental chemical treatments were needed during the growing season, diflubenzuron would be preferred. This growth regulating chemical has little adverse effect on adult boll weevils, but females cannot produce progeny for a week or longer after exposure to the material. Therefore, a series of applications superimposed on releases of sterile males would have a compounding effect and result in greater suppression than can be obtained by either technique used alone.

Diflubenzuron also is important in producing sterilized boll weevils for release (Wright and Villavaso Chapter 7 in this handbook). Irradiation alone at an acceptable dosage level does not assure near 100% sterility of female boll weevils. However, irradiation plus diflubenzuron in the adult diet assures virtually 100% sterility of both females and males.

428 E. F. KNIPLING

OPPORTUNITIES FOR IMPROVEMENTS IN BOLL WEEVIL ERADICATION TECHNOLOGY

New technology in any field of science is never fully perfect- ed until all aspects of the technology are thoroughly investigated and until adequate experience is gained to permit optimal use of technology that may be available. Therefore, it would be reasonable to assume that the technology used in the North Carolina trial can be made more effective and more efficient through additional research and development. Although there is every reason to have full confidence in our ability to eradicate the boll weevil on the basis of available technology and experience, it is my view that the probability is very high that substantial improvements can be realized through further research and operational experience. The same opportunity should exist for the improvement of management procedures. It would seem important that the possibilities for improvements in technology be kept in mind by those who will have the responsibility for making a decision on boll weevil management or eradication. However, my analysis here deals primarily with eradication technology.

I have already alluded to several opportunities for increased efficiency. For example, the degree of suppression in terms of survivors during Year 1 in the North Carolina trial was of the order of 100 times as high as would have been necessary to reduce the population to a level that could readily have been eliminated by the suppressive components available for Year 2. Therefore, substantial savings in cost, especially in areas with low boll weevil density, can in all likelihood be realized by reducing the number of insecticide applications.

There are opportunities for increasing the vigor and competitiveness of sterile boll weevils which could mean greater efficiency or less cost of the sterile male component. For example, research is underway at the ARS Metabolism and Radiation Research Laboratory, Fargo, ND, in cooperation with scientists of the Uni- versity of Minnesota, in an effort to select a strain of boll weevil that will survive longer after the application of a sterilizing dosage of irradiation. The preliminary results are encouraging.

Then modified cotton culture and host plant resistance, as discussed by Namken et al. (Chapter 4 in this handbook), could contribute to eradication in certain areas. In particular, appropriate cultural measures designed for the southern portions of the boll weevil area could contribute materially to eradication and the maintenance of eradication. It was mentioned earlier that infield traps may be used to eliminate low density boll weevil populations and at the same time provide highly sensitive detection. Indeed, four infield traps per acre will capture more than 90% of the F females from a single reproducing overwintered female. If this degree of efficiency against clumped F. boll weevils can be obtained by so few traps per acre, it is probable that an even higher capture efficiency can be achieved by the same number of traps


operating against a low density overwintered population. For example, at least some males are likely to respond to infield traps as they do to border traps. Also, boll weevils entering trapped cotton fields from hibernation are likely to enter in a distributed pattern rather than a clumped pattern because the pheromone emanating from the traps would interfere with normal aggregation. The data indicate that at a density of four well-distributed traps per acre, each trap baited with the optimum amount of pheromone will equal or exceed a competing male in attracting females. On the basis of these preliminary results, which will be given more intensive study, it may be possible to use infield traps as a highly sensitive method of detecting overwintered boll weevils and as a method of providing control when densities are reduced to levels below an average of one boll weevil per acre. The use of infield traps may therefore obviate the need for releases of sterile boll weevils, especially in areas where boll weevil populations are

normally low.

In view of the excellent prospects of making greater use of infield traps for both detection and elimination of very low surviving overwintered populations, a theoretical suppression model has been developed as depicted in Table 2. The model is based on the assumption that by the time cotton fruiting begins, overwintering survivors will average 0.4 boll weevil per acre or four weevils per 10-acre field. This is the approximate population level calculated for the controlled population described in my first model. Insecticides would be applied when squares are first subject to infestation in order to destroy all early emerging boll weevils not

Table 2.—Theoretical control of 40 overwintered boll weevils entering a 100-acre cotton field in which 400 infield traps are operating. Parameters are discussed in the text

Proba- Proba- bility bility

No . of No. of Ratio of of native of

boll weevils traps in traps to female female

Day Male

2

Female operation males matings capture

1 2 400 200:1 0.005 1.995

2 4 2 400 100: 0.010 1.990

3 6 2 400 67: 0.015 1.985

4 8 2 400 50 0.020 1.980

5 10 2 400 40 0.025 1.975

6 12 2 400 33 0.030 1.970

7 14 2 400 29 0.034 1.966

8 16 2 400 25 0.040 1.960

9 18 2 400 22 0.046 1.954

10 20 2 400 20 0.050 1.950

Accumulative probability 0.275 19.725

430 E. F. KNIPLING

captured in border field traps. The infield traps would be used at the rate of four per acre, or 400 traps on 100 acres. The larger acreage is assumed in order to deal with larger numbers of boll weevils and minimize the use of fractions in making calculations. To further simplify calculations without significantly changing the results, I have assumed that emergence will occur at a given rate during each of 10 days. The model shows the high ratio of traps to competing native males for the attraction of the relatively few females as the males and females enter the trapped fields. Although this ratio will decrease as the native males accumulate, the total theoretical effect will be to prevent reproduction in about 99% of the fields. This would mean that no reproduction would occur in most cotton fields. However, even if occasional females in an area consisting of thousands of acres of cotton are successful in mating, which would be expected, the traps would, during the period of F. emergence, identify the sites where reproduction had occurred and, at the same time, provide a high degree of control. In any event, if F, progeny are captured in any of the fields, supplemental treatments with an appropriate insecticide could eliminate the infestation. It should be noted that the suppression model assumes that none of the males would be captured. If a significant number of males are captured, the ratio of traps to competing males would be higher which, in turn, should result in the capture of a higher proportion of the females.

TECHNOLOGY FOR MAINTAINING AREAS FREE OF BOLL WEEVILS

Some question the rationale of undertaking boll weevil eradication on the grounds that even if successful, the pest will become reestablished after the eradication program terminates and that another eradication program of a similar magnitude and cost would again be necessary. It may also be argued that a continuing program of surveillance and eradication to prevent reestablishment of the pest in vulnerable areas would be so costly that little would be gained from eradication. These are highly speculative assumptions, of course. Nevertheless, such questions and implications may well be a matter of major concern to agricultural administrators, budgetary officials, and others in decision-making roles. Therefore, it seems highly important to analyze this possibility. Likewise, it would be unfortunate if boll weevil eradication programs were discouraged on the basis of a continuing cost. Such cost might well amount to several million dollars annually, but such a sum is a very small fraction of the continuing annual cost of $200 million to $300 million that can be expected if eradication is not undertaken, to say nothing of the adverse ecological effects of wide-scale, intensive use of chemical insecticides for the indefinite future.

For maintenance, a good monitoring program will obviously have to be instituted in the Rio Grande Valley for an indefinite period to serve as a guide to the nature and intensity of


suppressive measures that will be required to keep the pest at a low level. This cotton growing area is in direct flight range of boll weevils developing on cotton (and perhaps on wild host plants) in Mexico or in some areas in south Texas. The suppressive measures that would be used, if required, should make optimum use of available technology, including the use of insecticides that have minimum effect on nontarget organisms, the use of pheromoiie traps, the application of cultural measures, and the growing of short- season varieties of cotton. The release of sterile boll weevils on a routine basis may also assure the degree of suppression necessary to prevent infiltrating boll weevils from reaching high levels. The objective would be to maintain infestations at a practical minimum, partly to protect crops in the Valley region from excessive damage but primarily to minimize the possiblity of boll weevil spread to cotton growing areas north of the Valley. Fortunately, cotton-free ranch land extends for a distance of about 50 miles from Valley cotton to other cotton growing areas in southern Texas, and this natural barrier and a low boll weevil population at the source of possible spread should assure minimum dispersal. Even so, an adequate surveillance program will, no doubt, have to be maintained throughout south Texas to detect any boll weevil reproduction that may result from dispersal from infested cotton grown in the Valley and in Mexico border regions or possibly from wild host plants. Any infestations that might be detected north of the Rio Grande Valley would require prompt elimination.

Also, pheromone traps should be used for at least several years in all cotton growing areas in order to detect infestations that may occur because of shipment of infested commodities or hitchhiking boll weevils. Only experience will tell us how long and to what extent surveillance will be necessary in the various cotton growing regions. However, the cost of maintaining at least one trap per cotton field in uninfested areas is not likely to be excessive and could be made a part of a general IPM monitoring

program for cotton and other crops.

In sum, it is by no means certain that season-long suppression of boll weevils on the total acreage of cotton grown in the Rio Grande Valley region adjacent to Mexico would be necessary. How- ever, on the basis of available information about the flight range of the boll weevil, it must be assumed that the pest will continue to infiltrate into the Valley in sufficient numbers to require continuing suppressive efforts so long as uncontrolled populations exist in cotton or wild host areas within 50 miles or more of the border area. A well-organized, well-executed boll weevil suppression program designed to maintain populations at a very low level so as to minimize the chances of spread may.cost little, if any, more than the average losses due to the pest under present management practices. In fact, an organized program designed to minimize reinfestation and spread of the pest from Mexico might actually reduce costs. It seems apparent that in the event the boll weevil is pushed back to the border region, a joint boll weevil management

432 E. F. KNIPLING

effort by Mexico and the United States would be considered; and this might minimize the possibility of continuous infestations in the Valley.

Some argue that the boll weevil is likely to become widespread before any reintroduced populations are detected and that the need for costly eradication will recur frequently. The experience of the North Carolina trial is highly reassuring in both respects. The single infestation discovered near the North Carolina/Virginia line in 1980 was detected before the population had reached a high level and spread. The discovery of only one established reintroduction during two seasons in some 40,000 acres of cotton indicates that reintroductions are not likely to be frequent. This is especially reassuring because there was heavily infested cotton within 100 miles of the eradication zone. In any case, use of the highly sensitive detection methods now available should virtually assure that infestations will be detected before they reach high levels and become widespread. Finally, as to possible concerns about the difficulty of eliminating reestablished infestations, if we have the technology to eliminate well-established infestations on millions of acres of cotton, we surely have the capability of eliminating any possible incipient reintroduced infestations. The key to preventing the reestablishment of any pest that has been erad- icated is to maintain adequate surveillance and to take prompt action to eliminate any reintroduced infestations before they become widespread.

GENERAL SUMMARY AND CONCLUSIONS

Technology for possible use to eradicate an insect has never before been tested so thoroughly as was the technology proposed for use against the boll weevil in the event an eradication program is undertaken. On the basis of highly favorable results obtained in North Carolina, it can be stated without reservations that adequate technology for boll weevil eradication is available. It has the following components: Year 1 : (1) a well-monitored, well- executed, in-season boll weevil management program; (2) an intensive insecticide and cultural spray schedule involving an average of about six or seven applications of chemical following the in- season control program that is directed against the hibernating population. Year 2: (1) the use of pheromone traps for detection and to further suppress the low number of surviving overwintered boll weevils; (2) when cotton starts fruiting, release of sterile boll weevils at a rate of about 100 per acre per week for a period of ca. four weeks; (3) the use of infield boll weevil traps following the termination of sterile boll weevil releases, in order to detect and subsequently eliminate any boll weevil reproduction that may persist; (4) the supplemental use of chemical insecticides as needed.

In view of the abnormally low boll weevil population that existed at the beginning of the trial program in North Carolina, the


procedure used in the trial program during Year 1 virtually eliminated the population by the use of chemicals alone. However, simulation models were developed to estimate the degree of suppression that might be expected from available technology when the boll weevil population is representative of normal numbers likely to be encountered in severely infested boll weevil areas. The simulation models suggest that if a boll weevil population were 100 times higher than that in the North Carolina trial, a thorough in-season management program followed by about five to seven properly timed insecticide treatments would still have reduced the overwintered population to an average of less than one boll weevil per acre. Such low populations should be readily eliminated by the pheromone traps, sterile boll weevil releases, and strategic application of insecticides used during Year 2.

The high degree of effectiveness of the several suppressive measures, when properly integrated, is attributed in large measure to the strategy of concentrating suppressive efforts against the overwintering generation before and after the insects leave the hibernating quarters. The overwintered population is also subject to high natural mortality due to winter hazards, which adds greatly to the suppressive efforts. The compounding effect of the several mortality factors can reduce very high potential populations to near zero.

Although available technology for boll weevil eradication has been well demonstrated, the possibilities are excellent for further improvements and reduced costs. There are possibilities for making optimal use of insecticides and cultural measures during Year 1. There are also possibilities for improving the competitiveness and quality of sterile boll weevils. The use of pheromone traps, both for detection and as a suppressive measure, offers unusual opportunities for possible application against surviving populations that may average less than one boll weevil per acre.

The unusually high boll weevil detection capability of pheromone traps placed around borders of cotton fields and inside the cotton fields is considered one of the most important developments in optimizing the efficiency of boll weevil eradication procedures and for detecting and making possible prompt elimination of any reintroduced infestations that may occur in areas free of boll weevils. The experience in the trial program indicates that reintroductions into areas free of boll weevils are likely to be infre- quent. Only one reintroduction was discovered in the eradication zone during two seasons despite the existence of normally infested cotton within 100 miles of the eradication zone.

434 E. F. KNIPLING

LITERATURE CITED

Adkisson, P. L., D. R. Rummel, W. L. Sterling, and W. L. Owen, Jr. 1966. Diapause boll weevil control: a comparison of two meth-

ods. Texas Agricultural Experiment Station, Bulletin No. 1054, 11 p.

Brazzel, J. R. 1961. Destruction of diapause boll weevils as a means of boll weevil control. Texas Agricultural Experiment Station, Miscel- laneous Publication No. 511, 22 p.

T. B. Davich, and L. D. Harris. 1961. A new approach to boll weevil control. Journal of Eco- nomic Entomology 54:723-730.

and L. D. Newsom. 1959. Diapause in Anthonomus grandis. Journal of Economic Entomology 52:603-611.

Eden, W. G. 1976. Report of Entomological Society of America Review Com- mittee on the Pilot Boll Weevil Eradication Experiment. In Proceedings, Conference on Boll Weevil Suppression, Manage ment, and Elimination Technology, Memphis, TN, February 13-15, 1974. U.S. Department of Agriculture, ARS-S-71, 126 p.

Fye, R. E., C. L. Cole, F. C. Tingle, A. Stoner, D. F. Martin, and L. F. Curl.

1968. A reproduction-diapause control program for the boll weevil in the Presidio, Texas - Ojinaga, Chihuahua area, 1965- 67. Journal of Economic Entomology 61:1660-1666.

Knipling, E. F. 1960. Use of insects for their own destruction. Journal of Economic Entomology 53:415-420.

1968. Technically feasible approaches to boll weevil eradication. Ln Proceedings, Beltwide Cotton Production-Mechanization Conference, Hot Springs, AR, January 11-12, 1968. National Cotton Council of America, Memphis, TN.

1976a. Biomathematical basis for suppression and elimination of boll weevil populations. In Proceedings, Conference on Boll Weevil Suppression, Management, and Elimination Technology, Memphis, TN, February 13-15, 1974. U.S. Department of Agricul- ture, ARS-S-71, p. 130-148.


Knipling, E. F. 1976b. Report of Technical Guidance Committee for the Pilot Boll Weevil Eradication Experiment. _In Proceedings, Conference on Boll Weevil Suppression, Management, and Elimination Tech- nology, Memphis, TN, February 13-15, 1974. U.S. Department of Agriculture, ARS-S-71, p. 122-125.

1979. The basic principles of insect population suppression and management. U.S. Department of Agriculture, Agriculture Hand- book No. 512, 623 p.

_^ and J. U. McGuire, Jr. 1966. Population models to test theoretical effects of sex

attractants used for insect control. U.S. Department of Agri- culture, Agriculture Information Bulletin No. 308, 20 p.

Lloyd, E. P., G. H. McKibben, E. F. Knipling, J. A. Witz, A. W. Hartstack, J. E. Leggett, and D. F. Lockwood.

1980. Mass trapping for detection, suppression, and integration with other suppression measures against the boll weevil. Pre- sented at an international colloquium on the management of insect pests with semio-chemicals, Gainesville, FL.

M. E. Merkl, F. C. Tingle, W. P. Scott, D. D. Hardee, and T. B. Davich.

1972. Evaluation of male-baited traps for control of boll weevils following a reproduction-diapause program in Monroe County, MS. Journal of Economic Entomology 65:552-555.

437

Chapter 17

COTTON AND INSECT MANAGEMENT SIMULATION MODEL

L. G. Brown Department of Industrial Engineering Mississippi State University Mississippi State, MS 39762

R. W. McClendon Department of Agricultural and

Biological Engineering Mississippi State University Mississippi State, MS 39762

J. W. Jones Department of Agricultural Engineering University of Florida Gainesville, FL 32611

ABSTRACT The cotton crop model COTCROP was interfaced with the boll weevil model CIM-BW and the Heliothis spp. model CIM-HEL to form the Cotton and Insect Management (CIM) model. The effects of beneficial insects and insecticides were also included. The CIM model was structured to aid in the development and evaluation of insect pest management strategies.

Simulated results with selected populations of boll weevils (Anthonomus grandis Boheman), Heliothis spp., and predators, with and without insecticide applications, are presented.

The CIM model starts on the day of emergence of the cotton plant and advances through the season. The status of the crop and that of the insect populations are updated each day.

INTRODUCTION

Current approaches to cotton insect pest management, like past ones, rely heavily on insecticides to prevent pests from reducing yield and economic value of the crop. This type of management has allowed producers to satisfy the demand and to realize profits, but new methods are needed today. Insecticides have harmful side effects on nontarget organisms, and extended use of an insecticide

438 L. G. BROWN ET AL.

may produce resistance in the target species. As an example, Heliothis virescens (F.) has evolved as a major cotton pest in some areas because of its increased resistance to organophosphate insecticides (Harris 1972). In addition, costs of the fossil fuels used in the production of many insecticides are increasing rapidly.

Two pest management systems (see chapters 15 and 16 of this handbook).have been proposed as alternatives to current methods of controlling insects in cotton. One was tested in the Boll Weevil Eradication Trial (BWET) and the other in the Optimum Pest Manage- ment Trial (OPMT). Both Trials were regional because the mobility of the target insects is such that traditional field plot experiments would not provide sufficient information. Results of the two approaches were then evaluated to determine the advantages and disadvantages of each, and, in particular, the impacts on yield, insecticide usage, and net return above insect management costs.

Three methods of determining the effects of the Trials on yield and insecticide usage were studied: direct experimental method, regression analysis, and simulation. Replicated experiments, of course, can be designed to produce a direct comparison of yield for a range of soils, weather, and insect and management practices. However, the variations in climate and soil, the differences in time of development and in the magnitude of insect populations, and the differences in management practices in the two Trial areas were so great that the required degree of experimental control was difficult to achieve. Regression analysis involves use of historical data to explain the factors that produce variations in yield of a crop and thus requires a large amount of historical data; however, such a data base was unavailable.

For simulation, a model is developed that is capable of mimick- ing the behavior of the real system. First, the objective is defined; then the system is divided into relevant components. Next, the experimental method is used to study the components and to quantify the effects of important variables on each. Mathematical descriptions of the processes that change the state of the components are developed. These mathematical relationships are then combined and solved by computer simulation so as to study the behavior of the entire system.

In this case, the objective was to determine the effects of insect management strategies on insecticide usage and yield of cotton grown on different soil types and exposed to different weather and levels of insect populations. The system was therefore the cotton field, and the components were the crop and the populations of boll weevils (Anthonomus grandis Boheman), Heliothis zea (Bod- die), H. virescens, and predators. Each component would be affected by weather conditions and by management strategies and tactics. The crop integrates, through time, the effects of weather, insects, and management tactics on growth and yield. Simulation appeared feasible because of earlier efforts to develop and interface cotton and insect models (Jones et al. 1974, 1977; McKinion et al. 1975;

COTTON INSECT MANAGEMENT SIMULATION MODEL 439

Brown et al. 1976, 1979; Hartstack et al. 1976; Gutierrez et al. 1977; McClendon et al. 1977).

In this chapter, we describe the Cotton and Insect Management (CIM) simulation model that was developed by interfacing three component models, the crop model (COTCROP), the boll weevil model (CIM-BW), and the Heliothis spp. model (CIM-HEL). A sensitivity analysis of the CIM model is presented to give the reader an idea of the responsiveness of the model to changes in critical factors. Although this model is discussed relative to specific insect management strategies (BWET, OPMT, and the Current Insect Control (CIC)), it has potential for evaluation of other strategies.

COTTON CROP COMPONENT MODEL

The cotton crop component model, COTCROP, was developed by an interdisciplinary research team of engineers, plant physiologists, economists, and entomologists (Jones et al. 1980; Brown et al. 1982) to study insect and other management strategies including irrigation and nitrogen fertilization. Subsequently, COTCROP was modified, integrated into the more comprehensive system model (CIM), and tested for use in insect management studies.

Considerable research and several single (average) plant models were developed prior to COTCROP; and these provided much of the background for the current model. Two such models were developed in the late 1960*s and early 1970's: SIMCOT (Duncan 1972; Hesketh et al. 1972a, 1972b) for southeastern conditions, and COTTON (Sta- pleton et al. 1973) for western production under irrigation. SIM- COT was later revised and became SIMCOT II (Jones et al. 1974; McKinion et al. 1975). These models simulated single plants by maintaining a carbohydrate balance, and later a nitrogen balance was included. They predicted the production of discrete numbers of fruit by an average plant; therefore, to estimate production by plant populations, they multiplied numbers of fruit by the plant population. However, to include insect feeding on fruit and floral buds, one must vary the number of fruit and floral buds per area in a continuous manner rather than discretely with large increments. Brown et al. (1976) and Gutierrez et al. (1977) therefore restructured SIMCOT II for interfacing with insect models in studies of insect management strategies.

In COTCROP, crop growth is calculated for plants growing on 1 m of ground area. It maintains carbohydrate and nitrogen balances for the plants and water and nitrogen balances for the soil. Each day's demands (or sink strengths) for carbohydrates and nitrogen are calculated on the basis of organogénesis and growth rates of the plants and organs. The available carbohydrate is then determined on the basis of carbohydrate reserves in the plant and photosynthate produced. Available nitrogen is determined from plant uptake on the basis of depth of roots and distribution of nitrogen in the soil. If there is insufficient carbohydrate or

440 L G. BROWN ET AL.

nitrogen to meet daily demands, the rate of organ initiation and the growth rates of existing organs are reduced until the demand for nutrients is equal to the amount available. A surplus of either nitrogen or carbohydrate is stored in the crop for later use; a shortage of either nitrogen or carbohydrate causes fruit of different ages to be abscised after a certain period. Water stress also causes the abscission of fruit and retards the development of new organs for several days.

Model Structure

The mathematical structure of the model is described by vectors of continuous state variables plus a discrete time transition matrix as,

\ ' \ \-i * \ til

where

X = a state variable vector; A = the transition matrix for day t; and b = the growth and organogénesis rate vector for day t.

The vector x represents several column vectors describing the state of the crop on day t, and each of these has m elements, where m is the maximum number of days of the simulation. For example, FR is the (mxl) vector of fruit densities and fr (i) is the vector element representing the fruit density on day t for fruit "t-i" days old since they were initiated on day i. In addition, on day t the mass of the fruit that are "t-i" days old is maintained in the ith element of vector FRW . Likewise, the nitrogen content of the fruit is maintained in the vector NFR . Similar variables are maintained for leaves and stems although root mass is a scalar quantity.

Growth rates of existing organs of the plant depend on potential growth rates (which vary with temperature and the age of the organs) and supplies of carbohydrate and nitrogen. Insect damage to fruit reduces the number and mass of growing fruit and therefore reduces total boll growth or fruit sink strength on a given day. The balance between the supply of and demand for carbohydrate and nitrogen throughout the season alters the initiation of crop organs and the growth rates and thus affects both the fruit density and yield. Therefore, insect damage to fruit will have different magnitudes of effect, depending on the time of the year and growing conditions.

Because of the physiological detail in COTCROP, simulation is required to solve the model and describe the growth response of the


cotton crop to variations in temperature, insect damage, rainfall, solar radiation, soil characteristics, and nitrogen fertilization. Focus is on processes; for example, organ initiation, organ growth, photosynthesis, respiration, and nitrogen uptake. A schematic of the subroutines that are structured around the processes included in COTCROP is presented in Figure 1. For a description of each subroutine, see Jones et al. (1980) and Brown et al. (1982).

Soil Model

The soil model in COTCROP maintains water and nitrogen balances. The soil is divided into L homogeneous 10-cm deep layers, each having distinct volumes of water and concentrations of nitrogen. Availability of water and nitrogen to the plant depends on root depth. Root depth increases in time to a maximum depth, which is an input to the model. The emphasis of this soil water balance is on the overall soil volume; thus, all boundary values are calculated first.

The overall soil water balance is

W, = W^_^ 'h-\- E,t - ^t " \ [2]

where

W = water volume in the root zone on day t;

I = the irrigation volume on day t;

D = the drainage volume on day t;

E = the soil evaporation on day t;

E = the plant transpiration on day t; and

\ the rainfall infiltration on day t (all in cm water per cm soil area).

Redistribution of water in the one dimensional soil profile is calculated on the basis of an approximate finite difference (x 10 cm) solution to the water flow equation

a0(x,t) = ^[D(0) 9e(x,t) + k ] -S [3] 3t 8x 3x ® ^

where

0(x,t) = volumetric soil water content on day t at depth x;

D( 0) = the soil water diffusivity;

k = the unsaturated hydraulic conductivity; and

S = the rate of uptake by roots.

442 L G. BROWN ET AL

o 6

u O

u u w I I

60


The equation is solved with boundary conditions of (1) drainage as calculated by the method of Jackson and Whisler (1970) or (2) an upward flow from a wetter zone. The boundary conditions depend on the soil conditions and on soil evaporation and plant transpiration as calculated by the model of Ritchie (1972). _!_/ Rainfall infiltration is calculated by the Soil Conservation Service method (Schwab et al. 1966). The model, excluding redistribution, was tested by Jones et al. (1976) for Leeper sandy loam soil in Mississippi.

Nitrogen in the soil is assumed to be nitrate in solution. Nitrogen uptake by the plants is proportional to the mass flow of the transpiration stream. Redistribution of nitrogen in the soil is by mass flow; for this, a dispersion coefficient as outlined by Gardner (1965) is used.

Crop Growth Model

Considerable data on crop growth were available for arriving at estimates for rates of photosynthesis (Baker et al. 1972), organ initiation (Jones et al. 1974), and growth rates (Hesketh et al. 1972a, 1972b). However, several relationships such as the effects of carbohydrate, nitrogen, and water stresses on fruit abscission and organ initiation were not available. Therefore, carbohydrate and nitrogen stresses were defined as the ratios of supply to demand of carbohydrate and nitrogen, respectively. Water stress was considered a nonlinear function of average soil-water potential (H. D. Bowen unpublished data).

The fraction of fruit of each age that would abort given the severity of predicted stresses was based on data of Bruce and Romkens (1965). In their 1961 experiments on Leeper sandy loam, one of the treatments, AAA, consisted of frequent irrigations that maintained soil water potential above -0.3 bar throughout the season. Another treatment, ADD, consisted of maintaining the same water level until plants reached the small boll stage; then when soil dried to a water potential of -2.4 bar, the plots were irrigated. (Rainfall was excluded by rainfall shelters.) The resulting data on soil-water status, plant development, and weather provided an excellent data set for model calibration. (Nitrogen stress probably did not occur because of the high rate of nitrogen fertilization (300 pounds per acre).)

A trial and error procedure was therefore used to calibrate the abscission parameters. Three comparisons of simulated results with experimental data were used in the calibration: number of fruiting sites, number of fruit, and final yield. Both AAA and ADD treatments were simulated. Actual yields were 3.18 and 2.46 bales

\J Appreciation is expressed to L. A. Smith, ARS, U.S. Depart- ment of Agriculture, Mississippi State, MS, for assistance in improving the solution of soil-water redistribution in the soil profile.


per acre for treatments AAA and ADD, respectively. Corresponding simulated yields (after calibration) were 3.22 and 2.69 bales per acre.

The percentages of fruit assumed to abscise per day were 11, 2.5, and 2.5 for young, medium age, and old squares, respectively, and 13 and 9 for bolls less than 10 days old and bolls between 10 and 20 days old, respectively. These percentages are the maximum per day; they occur only with severe stress conditions such as zero supply of either carbohydrate or nitrogen. It was assumed that older bolls do not abscise. Most fruit abscission occurs when the fruit are young squares and young bolls according to experimental data of Jones (1975).

Discussion

A subsequent experiment was conducted in 1977 at the site of the Bruce and Romkens experiments (J. D. Hesketh unpublished data 1977). However, there were two major differences between the two experiments. First, in 1977, the rate of nitrogen application was 100 pounds per acre. Second, water stress was allowed to occur earlier during the season. Also, four water treatments (0, 3, 5, and 8 irrigations) were established for each of four varieties of cotton. The results with two varieties, Stoneville 213 and Delta- pine 16, were averaged for comparison with simulated results.

Comparisons of the results of zero and three irrigations in the 1977 experiments and in the simulation showed that the plants responded differently if water stress occurred after flowering. Despite early water stress, organ initiation proceeded at a normal rate; however, if water stress occurred for the first time after flowering, organ initiation was sharply curtailed. Therefore, the effect of stress on organ initiation before the boll period was modified in the model. The abscission parameters were not further modified.

The simulated versus actual yield data are shown in Figure 2 for both experiments. The results demonstrate the responsiveness of COTCROP to both nitrogen and water variables. In 1977, the eight-irrigation treatments resulted in approximately 55% of the yield produced with the frequent irrigation treatment of 1961. The nitrogen application rates were 100 and 300 pounds per acre for 1977 and 1961 experiments, respectively. In addition, simulated yields compared well with the actual yields for the different water stress treatments. In 1977, the simulated yield for five irrigations was the same as that for eight irrigations, which was similar to the observed field response.

The COTCROP model was designed for interfacing with insect models. The age distribution of the fruit is included because of the preference for fruit of different ages by boll weevils (Lloyd et al. 1961; Jones et al. 1975) and Heliothis spp. (Nicholson


Simulated yield, bales/acre

5

Í 2 3

Actual yield, bales/acre

Figure 2.—Comparison or simulated and actual yields for 1961 and 1977 irrigation treatments, and the 1978 Panola County, MS, field data (from Brown et al. 1982).

1975). In addition, the crop response to fruit damage depends on the age of fruit damaged.

BOLL WEEVIL COMPONENT MODEL

The boll weevil component model used is the population dynamics Cotton and Insect Management-Boll Weevil (CIM-BW) model, which is a modification of the Boll Weevil Simulation (BWSIM) model developed by Jones et al. (1977). For our purposes, BWSIM was

446 L. G. BROWN ET AL

simplified to reduce the computer run time and was restructured to facilitate coupling with the cotton crop model (Brown et al. 1979).

The boll weevil population is closely related to the growth dynamics of the cotton crop as shown in Figure 3. The model is initiated with emergence of overwintering adult weevils into the cotton field. »This may occur when the crop is young and has no fruit (bolls or squares). Since the boll weevil must have cotton fruit for reproduction, no reproduction occurs until the crop begins to produce squares. As the female adult encounters fruit, she oviposits"into them. As the larvae develop, the fruit are abscised from the plants. This fruit loss causes a response in the growth and development processes of the plants. Both the development and survival of the larvae depend on temperature and quality of food.

Many of the relationships used in the model to describe feeding, oviposit ion, development, and mortality have been reported (Bacheler et al. 1975a, 1975b; Jones 1975; Jones et al. 1975, and Jones et al. 1977). Following is a summary of the structure and processes used in the CIM-BW model.

Model Structure

The state variables in the model consist of vectors of population densities for cohorts of each life stage (egg, larva, pupa, adult). Thus, age structure of each life form is explicitly considered. The vectors EGG (a), LARV^(a), PüPA^(a), and ADULT (a) represent the densities of boll weevils on day t of age a in days. A discrete time step of one day is used to solve the following population dynamics equations for each stage

Nj.(a) = N^_j(a-1) (1-6^) (l-P^(a)) I^ (4]

where

N (a) = the density of one boll weevil life stage on day t, age a;

6 = the probability of insect death on day t;

P (a) = the probability that an insect of age "a" will make a transition to the next stage of development on day t; and

I = the survival of insects on the day of an insecticide application.

Initial and boundary conditions for solving these equations consist of initial population influx and transitions between life stages. Figure 4 is a schematic that shows the subroutines and the calling sequence of the CIM-BW model.


no Q) U Cu CO

CO

no O B S M

C

O

o

c o

o o

»TO c CO

o 43

CO

§ O

CO

m

3 ON &0.-H


ININ

DEV — Calculates elapsed Developmental Units (DU's) each stage. DU's stored in COUNT (250x5).

LIFE — Determines the number of incoming overwintered weevils.

—Ages weevils and causes stage changes according to elapsed DU's.

— Removes weevils due to natural mortality.

DP -Finds number of weevils that should be in diapause and removes them from adult arrays and preoviposition arrays.

-Calculates diapause mortality.

WDMG —Calculates maximum number of eggs laid by females (based on temperature).

— Reduces egg-rate due to age and diet.

— Distributes eggs among squares and bolls.

— Damages fruit according to age f of fruit.

WSPRAY —Calculates spray mortality for adults, preoviposition, and diapause weevils.

Figure 4.—Subroutine calling sequence for the CIM-BW model.


Development Times and Variances

Development, described by P (a) in equation 4, is a nonlinear function of temperature. It was derived from developmental data for the various stages (egg, larva, and egg to adult) from several sources (see Figure 5). For example, data of Bacheler et al. (1975b) were used to estimate the coefficients for describing the average development time for egg, larva, and pupa; and coefficients for adult longevity were based on data from Isley (1932). The form of the equation is

L((t)) = C^ exp (C^/cl)) for (|)>14.4'C [5]

where

L((1)) = the length of a stage for a given temperature; and C,, C« = the parameters given in Table 1.

Since rate of development is the reciprocal of L((|)), the developmental rate for variable temperatures is integrated through time to calculate developmental units. Transitions from one stage to the next are initiated when the development unit value reaches 0.83 and are completed when it reaches 1.17. Half of the stage transitions occur as developmental units increase from 0.83 to 1.0. P (a) describes the proportion of insects of age a that makes a transition on day t based on a Gaussian distribution (Jones et al. 1977).

Table 1.—Development time parameters (Jones et al. 1977)

Stage n (r^)

Egg Larva Pupa Adult

45.9 39.8 40.1 58.0

0.55 1.80 1.63 3.46

(0.97) (0.98) (0.94)

Fecundity and Feeding

Damage to the cotton crop due to boll weevil feeding and oviposition is calculated by subroutine WDMG (see Figure 4). It is assumed that damage done by the female weevil during oviposition is affected by the average daily temperature, insect age, and diet. (Boll weevils prefer squares for feeding and oviposition, but young bolls (less than 19 days old) can be substituted if squares are scarce.) Oviposition is reduced 80% when the diet consists solely of small bolls, but there is no reduction if the diet consists only of squares provided the square density is adequate. The fecundity reduction factor due to square availability is given by


Temperature, °C

34 ^

30-

26-

i' Temperature, °C

34

30-

> Larva

22- i 26- Í

18- \

22- V

♦ T? XT

\

I 1 1 1 1 0 2 4 6 8

Days

18 -ö ^

I 1 1 1 1 1 1 I 0 4 8 12 16 20 24 28

Days

O Bacheler et al. (1975a) X Isley (1932) > Cole (1970) ^ Hunter and Pierce (1912)

Temperature, °C

34 *«^^

Y Egg to Adult

30 yp^

18- -xo-

1 10

1 15

1 20

1 25

r 30

Days

1 35

1 40 45

Figure 5.—Developmental time for boll weevil eggs, larva, and egg to adult (from Jones 1975).


g^ = 0.25 I ?.. + 0.05 I (1-Pi.) [6] ^ i = t-3 ^^ i = t-3 ^^

where

P,. = fraction of potential eggs that are laid in squares.

In the more detailed BWSIM (Jones 1975), selection of sites for oviposit ion and feeding are based on detailed models of searching and egg laying or feeding processes. For the CIM-BW model, results from that work were used to generate a family of curves based on densities of bolls and squares. Figure 6 is an example of the type of curves used to partition eggs to squares and bolls, thus defining P-. according to densities of squares and bolls on day i.

It is also assumed that female weevils oviposit one egg per fruit form before moving to another fruit. No discrimination is made against fruit with previous boll weevil damage (Jenkins et al. 1975). Density of new eggs on day t is calculated by

EGG (1) = 0.5g q I ADULT, (j) E.((t)) tj = 1 t J

[7]

where

g = reduction in egg production on day t due to the insect diet during the last 4 days;

q = probability that an egg will be viable if it is in an optimum environment; and

E.((|>) = potential number of eggs produced per day by females of age j at temperature (j). J

In the CIM-BW model, the maximum number of eggs laid per day per female is assumed to range from 3 (at an average temperature of IS'^C) to 12 (at 30'*C). After the female is 8 days old, the rate is allowed to decline with age (Jones 1975). The feeding damage by males, preoviposition females, and diapausing weevils is calculated as one fruit per insect every 2 days.

Mortality

In CIM-BW, daily mortality of each boll weevil stage is assumed to be constant (0.28, 0.074, 0.028, and 0.001 for egg, larva, pupa, and adult, respectively). Adult mortality due to longevity is included in the transition probabilities. Insecticide-induced mortality for treatment with EPN-methyl parathion was assumed to be 0.90 for adults (i.e., I = 0.10) and 0.0 for all immature stages (i.e., I = 1.0) on days when insecticide was applied (Jones et al. 1977).


Fraction of potential eggs laid in squares

1.0

X10' Squares/acre

Figure 6.—Proportion of boll weevil oviposit ion in squares as affected by square density and boll density.

Discussion

The simulation of the boll weevil population (see Figure 4) is initiated by the introduction of overwintered adult weevils into the model through a "table look-up" function. The rate of emergence can be set to predetermined levels. The developmental rate of the boll weevil and the development units for each day are then calculated by subroutine DEV. In subroutine LIFE, the boll weevils progress through the various life stages according to the number of developmental units to which they have been exposed. Boll weevils of each life stage are removed as a result of natural mortality. Finally, the number of weevils to be placed in diapause and the diapause mortality are calculated by subroutine DP.


Simulated results from the original BWSIM model were compared with experimental results for three North Carolina cotton fields (Jones et al. 1977). The simulated and actual fruit damage due to populations of adult boll weevils is presented in Figure 7a, b, and c.

Also, simulations obtained with the CIM-BW model were compared with those obtained with BWSIM to ensure that the modifications had not significantly changed the results. In this case, CIM-BW was used to simulate boll weevil population dynamics in two producer fields in North Carolina, and the results were compared with simulated results for the same two fields from BWSIM (Figure 8a and b). Results were in close agreement though computer time and memory were reduced by factors of 10 and 3, respectively, for CIM-BW. The effects of the detailed oviposit ion and feeding behavior submodels were incorporated by using simulated results to establish curves for fruit selection for the simplified model.

Damaged squares/acre on plants (xlO^)

250

No Insecticide ^\ o Observed Simulated (BWSIM)

T 205 215 225

Time, Julian day number

Figure 7a—Comparison of simulated and observed damaged squares for an assumed initial population of 1,977 weevils per ha, Raleigh, NC, 1973 (Jones et al. 1977).


Insecticide Spray Dates

iU i i Ui \ Damaged squares/acre on plants (XIO^)

100

o Observed — Simulated

(BWSIM)

160 I

200 220 Time, Julian day number

Figure 7b.—Comparison of simulated and observed damaged squares in producer's field 1, Rich Square, NC, 1973 (Jones et al. 1977).

Insecticide Spray Dates ^^

11 i li il 11 Damaged squares/acre (XI0^)

75

O Observed •— Simulated

(BWSIM)

200 220 Time, Julian day number

260

Figure 7c.—Comparison of simulated and observed damaged squares in producer's field 2, Rich Square, NC, 1973 (Jones et al. 1977).


Boll weevils/acre 15000

BWSIM (from Jones, 1975)

CIM-BW

10000

5000

180 200' 220 Time, Julian day number

260

Figure 8a.—Comparison of simulated boll weevil populations from CIM-BW and BWSIM for producer's field 1, Rich Square, NC, 1973.

Boll weevils/acre

7500

BWSIM (from Jones 1975)

CIM-BW

5000

2500

140 T 160

1 r 180 200 220

Time, Julian day number 240 260

Figure 8b.—Comparison of simulated boll weevil populations from CIM-BW and BWSIM for producer's field 2, Rich Square, NC, 1973,

HELIOTHIS SPP. COMPONENT MODEL

"^^^ Helíothís spp. component model CIM-HEL was developed by L. G. Brown and D. B. Hogg (unpublished, Mississippi State Uni- versity) specifically for interfacing with the cotton model COT- CROP and the boll weevil model CIM-BW. The model advances time during the season in one-day increments and updates the status of populations each day. The subroutines of the CIM-HEL component model, their purposes, and the calling sequence are shown in Figure 9.

Since H. zea and E. virescens have different rates of development and oviposit ion and react differently to insecticide, they are kept separate in the model. Each species is also separated in the model by cohorts. The following eight arrays are used to maintain the number in each cohort: ZEGGS, ZLARV, ZPUPAE, ZADULT, VEGGS VLARV, VPUPAE, and VADULT.

Degree days above 12.6^*0 (Hartstack et al. 1973) are used to calculate physiological time. Hourly temperatures are used to calculate the degree days; that is,

25 Degree days = I Max (0, (i).-12.6)/24 [8]

i = 2 ^

where the <t>^ is hourly temperature. The temperature at midnight the previous day is represented by (|)- .

Since the number of degree days that have accumulated from the start of the simulation is calculated and stored each day as PT(t), calendar age and physiological age of each cohort can be determined. Then as the model moves through the season in daily increments, cohorts age (in degree days) until they make the transition to the next life stage. However, it is necessary to account for the variation in developmental times within a cohort. Therefore, the transition of the members of a cohort to the next life stage is distributed over several days. Each day, the percentage of the insects within each cohort that advances to the next life stage is a function of the physiological age of the cohort and the degree days accumulated that day.

Developmental Times

The time required for eggs to hatch is estimated to be 50 degree days from data reported by Butler and Hamilton (1976). In fact, the variation reported in early studies has been sufficiently small so that all eggs are assumed to hatch (move to the ZLARV or VLARV array) on the day that 50 degree days have been accumulated.


ININ

HELADV Accumulates the degree days above 12.6°

Sums the number of Heliothis zea and H. virescens in each life stage.

ZEA Advance Heliothis zea through the life stages.

\ Calculates the number of eggs laid by H. zea adults.

\ VIR Advances Heliothis virescens through the

'V^ life stages.

Calculates the number of eggs laid by H. virescens adults. x\

EGGFAC Calculates the temperature and temperature/age effects on fecundity.

|HMORT Reduces the numbers in each life stage due to mortality caused by predators and other natural causes.

HDMG Schedules fruit for abscission later due to Heliothis spp. feeding damage.

HSPRAY Reduces the numbers in each life stage due to insecticide mortality.

Figure 9.—CIM-HEL subroutine calling sequence.

Thus, the number of eggs hatching on day t is calculated from

t-1 ZLARV(t) = I ZEGGS(i) ô^(i,t) [9]

i = 1 ^ t-1

and VLARV(t) = I VEGGS(i) 5^(i,t) [10] i = 1 ^

where

to.O if T(i,t)< 50 degree days ÖE(i,t) =

(l.O ifT(i,t)>^50 degree days and

T(i,t) = elapsed degree days from day i (the day the cohorts were established) to the current day t.

Thus T(i,t) represents physiological age of cohorts established on day i, that is, PT(t)-PT(i).

Developmental times assumed for the larvae and pupae in CIM- HEL are based on field data collected by Hogg and Calderón (1981). They reported that the developmental time for the larval stage of Ü* ^^^ ^^s significantly longer than for that of _H. virescens. They also found that developmental times of female pupae of both species were shorter than those of males. Since the developmental rates of the females control the rates of population growth (Hogg and Gutierrez 1981), they are used in the model rather than developmental rates for males. The developmental times for H. zea and JH. virescens pupae are separated in the model (though the means are not significantly different) because JI. virescens took slightly longer to develop.

Developmental times for Heliothis spp. larvae are shown in Figure 10. The number of larvae pupating on day t is calculated from

t-1 ZPüPAE(t) = I ZLARV(i)ô (i,t) [11]

i = 1 ^

t-1 and VPUPAE(t) = I VLARV(i)ô (i,t) [12]

i = 1 ^

where

ô^(i,t) = (P^(i,t) - P^(i,t-1))/ (1.0 - P^(i,t-1)) and

P_(i,t) = fraction of larvae that will have pupated by physiological age T(i,t).

Fraction of larvae that have pupated— PL(T)

1.0

190 210 230 T

250 270 Physiological age—r

330

Figure 10.—Cumulative developmental times of Heliothis spp. larvae (Hogg and Calderón 1981).

When larvae are moved into pupal arrays, they are removed from the larval arrays.

Developmental times for Heliothis spp. pupae are shown in Fig- ure 11. The number of adults emerging on day t is calculated from

t-1 ZADULT(t) = I ZPUPAE(i) ô (i,t)

i = 1

[13]

t-1 and VADULT(t) = I VPUPAE(i) <S (i,t)

i = 1

[14]

where

Ô (i,t) = (P (i,t)-P (i,t-l)/(1.0-P (i,t-l)) and p P P P

P (i,t) = fraction of pupae that will have emerged by physiological age T(i,t).


Fraction of pupea that have emerged —Pp (r)

1.0

210 230 Physiological age—r

250 270

Figure 11.—Cumulative developmental times of Heliothis spp. pupae (Hogg and Calderón 1981).

When pupae are moved into adult arrays, they are removed from the pupal arrays.

Fecundity

In CIM-HEL, fecundity is a function of temperature and adult age. The functions that reduce fecundity due to temperature and temperature/age effects are from MOTHZV-2 (Hartstack et al.


1976). Thus, total eggs laid by the population on day t is calculated by:

t-1 EGGS(t) = 0.5 I ADULTS(i) PI P2 EP [15]

where

i = 1

EP = potential number of eggs laid per female per day (400 for H. zea; 300 for ii. virescens);

Pi = reductTon in fecundity due to temperature (Hartstack et al. 1976); and

P2 = reduction in fecundity due to temperature/age effect (Hartstack et al. 1976).

Mortality

In the model, mortality can be caused by insecticide, by predators, and by other natural causes. The mathematical relationships for the mortality of eggs and larvae were developed from field data collected by D. B. Hogg in 1978 and 1979 (unpublished data). The coefficients for CIM-HEL were adjusted after the results of a simulation were compared with Hogg's data and with field data collected by G. L. Andrews (unpublished data).

The proportion of eggs that are destroyed daily by predators (PME) is thus given by

PME = (number of predators) 1.325x10 . [16]

The proportion of larvae within each cohort that are destroyed daily by predators (PML) varies with the age of the cohort as

PML = PME EXP(-1.011 AGE ^'^^^) [17]

where

AGE = age of the cohort in degree days.

The proportion of the larvae within each cohort that dies as a result of other natural causes (XML) is given by

XML= 1.0-0.9915(^^(^>-^^^'-^^^ [18]


The mathematical relationships for the survival of adults were developed from data for caged adults collected by D. B. Hogg. The adult survival functions are:

XMAZ = 1.0-EXP((AGEY/118.54)^-^^-(AGE/118.54)^-^^) [19] for ji. zea and

XMAV = l,0-EXP((AGEY/134.93)^-^^-(AGE/134.93)^-^^) [20] for jl. virescens

where

AGEY = age in degree days yesterday (that is, (i,t-l)); XMAZ = proportion of H. zea adult cohorts surviving day t;

and XMAV = proportion of li. virescens adult cohorts surviving

day t.

Figure 12 illustrates these survival functions.

Proportion surviving

0 20 40 60 80 100 120 140 160 180 200 Age in degree days

Figure 12.—Survival of H. zea and H. virescens.


An additional 15% daily mortality was introduced (Hartstack et al. 1976) since the adults in Hogg's study were caged. Natural mortality (other than that caused by predators) is 3% per day for eggs. Also, the daily mortality for pupae is 3% (Hartstack et al. 1976).

Feeding

The number of fruit damaged by a Heliothis spp. larva (Ta- ble 2 _1/) was worked out by using the regression equations developed by Nicholson (1975) to determine the age distribution of fruit damage by the larvae.

Table 2.—Number of fruit in each age class damaged by Heliothis spp. during larval stage

Fruit ages Number of fruit damaged in days per larva _1_/

1-6 2.77 7-12 2.61

13-18 1.03 19-24 2.06 25-30 1.66 31-36 0.57 37-42 0.20 43-48 0.10

Total 11.00

\J These values are for H. zea larvae living 310 degree days and li. virescens larvae living 300 degree days.

The total number of squares and bolls damaged was based on the weighted averages of square and boll damage observed by Quaintance and Brues (1905), Kincade et al. (1967), and Nicholson (1975). If there are insufficient fruit of a particular age to satisfy the feeding demands of larvae of a particular age, then the unsatisfied feeding demand is distributed over fruit of other ages, depending on availability and larval preference (Wilson and Gutierrez 1980). In addition, each larva also destroys 0.714 squares in terminals (Nicholson 1975). (These "pin-head" squares are not normally included in field estimates of square numbers.) It is assumed that Heliothis spp. larvae will feed on fruit that have been damaged by boll weevils; however, boll weevils will not oviposit in fruit already damaged by Heliothis spp.

IJ Appreciation is expressed to E. P. Lloyd, ARS, USDA, Raleigh, NC, for assistance in developing the feeding algorithm.


CIM MODEL

Integration of Component Models

The objective in developing the CIM model was to provide a method of evaluating the effect of insect pest control strategies on yield, insecticide usage, and cost of insect management. As noted, it was formed by using three component models, COTCROP, CIM- HEL, and CIM-BW.

In the CIM model, the interaction, between the cotton crop and the insect pests occurs through the fruit. The crop damage done by the insect pests is calculated each day and transferred to the crop component model. Also, status of the fruit is updated daily and transferred to the component models of the two insect pests.

Insect pest management strategies in the composite CIM model are concerned largely with insecticide applications. These applications are performed either on a predetermined fixed schedule or in response to the percentage of square damage or insect pest densities or both. The interval between simulated scouting reports of damage and density can also be varied to simulate different strategies. The insecticide used in the simulations, EPN-methyl parathion, differs in degree of effectiveness against Heliothis spp., depending on the temperature and the age and species of the insect. The insecticide-induced mortality factors (Tables 3 and 4) are from laboratory data collected by McDaniel (1976). Each insecticide application affects Heliothis spp. for up to 3 days. The same application kills 90% of the adult boll weevils on the day of the application. For boll weevils it is assumed that the insecticide has no residual effect or temperature dependency.

The data required as input to the CIM model are the following: (1) Daily weather information

(a) Maximum and minimum temperatures (b) Rainfall (c) Solar radiation (d) Pan evaporation

(2) Agronomic data (a) Day of crop emergence (b) Day of harvest (c) Soil parameters - sample soil parameters that must be

specified by the user for the particular soil type considered are shown in Table 5

(d) Day and amount of nitrogen fertilizer applications (3) Insect populations

(a) Initial Heliothis spp. population (b) Initial boll weevil population (c) Predator population for the year

(4) Insect control strategies (a) Boll weevil (b) Heliothis spp.


Table 3.—Daily kills of instars of Heliothis spp. larvae due to insecticide 1/

Da ily fraction of each age group kill ed^/ 1st instar 2nd instar 3rd instar

Day TJ H. zea H. virescens H. zea

H. virescens H. zea

H. virescens

0 1 2

0.95 0.32 0.16

0.96 0.48 0.38

0.90 0.59 0.25

0.9: 0.36 0.18

0.70 0.41 0.18

0.72 0.39 0.13

Daily fraction of each age group killed _3/

4th instar 5th instar 6th instar H. vir- H. vir- H. vir-

H. zea escens H. zea escens H. zea escens

0.51 0.46 0.25 0.21 0.06 0.01 0.32 0.33 0.16 0.17 0.05 0.04 0.16 0.20 0.13 0.06 0.06 0.03

]J From McDaniel 1976. Ij Days after insecticide application. _3/ These values are reduced by 30% in the insecticide mortality

calculations in the model to simulate inefficiencies under actual field conditions.

The output from the CIM model includes a daily record of crop status and daily levels of insects in each life stage. At the end of the growing season, a summary report (Table 6) is produced that gives the value of some of the initial parameters as well as final yield, number and cost of insecticide applications, and monetary returns above costs of insect control.

Table 4.—Temperature effect on mortality of Heliothis spp. larvae exposed to insecticide J_/

% effectiveness relative to effectiveness at 25°C

Temperature (*C) H. zea H. virescens

20 95.4 86.1 25 100.0 100.0 30 105.0 103.0

1/ From McDaniel 1976.


Table 5.—Estimated soil parameters for a hypothetical silty loam soil

COTROP soil parameters Description

Texture

THETAS THETAR THETFC

HB ETA

HYDROC XN

U COEFF

PORGAN

QO

RDEP SOILNI

Estimated value

12% sand 75% silt 13% clay

3 3 Saturated water content (cm per cm ) Residual water content (cm per cm ) Field capacity water content (cm per cm ) Bubbling pressure (cm) Brooks & Corey moisture tension constant Hydraulic conductivity (cm per day) Runoff curve number for hydrologie soil

cover complexes Cumulative evaporation (mm) Slope of cumulative evaporation curve

(mm per day * ) Fraction of organic matter content in

the soil Initial drainage rate from bottom of

profile at saturated condition (cm per day) Rooting depth (cm) Residual nitrogen (g per m )

0.3964 0.1019 0.2938

60.0 2.8080 6.0

65.0

9.0 4.04

0.01

4.2

90.0 12.61

Sensitivity Analysis

A sensitivity analysis was undertaken to demonstrate the responsiveness of the CIM model and to show how a simulation might be useful in evaluating cotton insect management strategies. This study is analogous to a field experiment in which certain variables are held constant and others are varied over a range of interest.

The variables selected for study were densities of Heliothis spp., boll weevils, and predators. Two insect control strategies were used for each pest density. Strategy 1 (Sl) consisted of using no insecticide. Strategy 2 (S2) consisted of scouting twice a week (every 4 days in the model) starting on June 1 and continuing through September 15 with insecticide being applied according to the following thresholds:

(1) Boll weevil - treat when oviposit ion-punctured squares reach 5% (does not include feeding punctures).

(2) Heliothis spp. - treat before first bloom whem damaged squares reach 25%; after first bloom and until first treatment, treat at 5% square damage; after first treatment, treat when 4% of the terminals contain larvae and there are eggs present (in the CIM model, 4% terminal infestation is estimated to be 1500 larvae per acre).


Table 6.—Sample CIM model output

COTTON INSECT MANAGEMENT (CIM) MODEL

8/13/80

WEATHER DATA USED - STONEVILLE 1972 DAY OF EMERGENCE - 125 PLANT POPULATION - 40000 PLANTS/ACRE ROOTING DEPTH OF SOIL - 35.4 IN RESIDUAL NITROGEN ON DAY OF EMERGENCE - 112.5 LB/ACRE RESIDUAL WATER ON DAY OF EMERGENCE - .36 IN**3 NITROGEN FERTILIZATION

TOTAL - IRRIGATION

DAY LB/ACRE 125 80.0 145 30.0

110.0 DAY INCHES 0 .0 0 .0 TOTAL

TOTAL RAINFALL - 16.8 IN TOTAL SOLAR RADIATION - 85090.00 LANGLEYS TOTAL PHYSIOLOGICAL DAYS - 164.5 DAY OF HARVEST - 300 REMARKS - INITIALIZE WITH EGGS

GROSS CROP VALUE YIELD - 889.8 LB/ACRE

GROSS LINT VALUE OF $.65 COTTON - GROSS SEED VALUE OF $.06/LB SEED - GROSS CROP VALUE (LINT+SEED VALUE) -

INSECT CONTROL COSTS

NUMBER OF INSECTICIDE APPLICATIONS

578.35 $/ACRE 82.75 $/ACRE

661.10 $/ACRE

COST OF EACH INSECTICIDE APPLICATION - 4.96 $/ACRE TOTAL COST OF INSECTICIDE APPLICATIONS - 29.76 $/ACRE COST OF TWICE WEEKLY SCOUTING - 3.75 $/ACRE TOTAL COST OF INSECT CONTROL - 33.51 $/ACRE

RETURNS ABOVE COST OF INSECT CONTROL

PRICE $/LB .50 .55 .60 .65 .70 .75 .80 RETURNS $/ACRE 494.12 538.61 583.10 627.59 672.08 716.56 761.05

468 I- G. BROWN ET AL.

The soil and crop variables were held constant. The soil is described in Table 5. The plant population was always 40,000 plants per acre, the date of crop emergence was May 5, and the harvest date was October 27. Nitrogen was applied to the crop at planting in the amount of 80 pounds per acre and as side-dressing in the amount of 30 pounds per acre on May 25. Two years of weather data from Stoneville, MS, (1967 and 1972) were used to demonstrate the impact of weather variability on simulated results. Simulations were also performed for both years without insect damage to provide a basis for comparison.

Three populations (low, medium, and high) of predators, Helio- this spp., and boll weevils were used in the analysis. These populations were identified on the basis of consultations with J. W. Smith and E. P. Lloyd (personal communication).

The seasonal progression in the three predator populations is shown in Figure 13. The low, medium, and high populations peaked at 7,400, 11,800 and 15,700 predators per acre, respectively. As mentioned earlier, the predator population is treated as an exog- enous variable. However, this population is reduced by insecticide applications.

The simulated Heliothis spp. populations with the 1972 weather data and the medium predator population are shown in Figure 14a. Heliothis spp. larvae of the third generation (September 1 to Sep- tember 20) reached maximums of 8,500, 16,000, and 63,700 per acre for the low, medium, and high populations, respectively. (To initiate the CIM-HEL model, we enter adults in the model early in the year to mimic adults entering a field. Then, to simulate the different populations, we vary the number and timing of the adults entered in the CIM-HEL model.) These adults were assumed to be 60% Heliothis virescens and 40% Heliothis zea. The number and timing of the adults entered in the CIM-HEL model were identical for 1967 and 1972; however, the resulting populations were different due to differences in weather.

The simulated boll weevil populations with the 1972 weather data and with no Heliothis spp. or predators present are shown in Figure 15a. The low, medium, and high populations reached maximums of 19,800, 33,600, and 60,900 adults per acre, respectively. (These populations are affected by the diet of the adults and number of oviposition sites available. Since the number of Heliothis spp. present alters the crop, the simulated boll weevil populations would be different if Heliothis spp. were present.) The number of adults and the time they entered the field were identical for 1967 and 1972; however, the resulting populations were different because of differences in weather and crop development.

The simulated yield and number of insecticide applications for each scenario in each year are shown in Table 7. The simulated yields with 1967 and 1972 weather with no insects were 501 and 971 pounds, respectively. The rainfall during the growing season was

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14.4 inches for 1967 and 16.8 inches for 1972. Thus the 1967 crop had more water stress than the 1972 crop. The accumulated solar radiation was 3% less for 1967 than the 1972 total.

The numbers of squares and bolls available with the low, medium, and high populations of Heliothis spp. in 1972 with no insecticide (Sl) are shown in Figures 14b and c, respectively. Since the medium population of predators and no boll weevils were used for the simulations, the differences are the results of the three populations of Heliothis spp. Because the Heliothis spp. damaged all of the squares late in the season, the number of bolls became constant. The percentages of reduction in yield for the low, medium, and high Heliothis spp. populations were 1.7, 2.2, and 10.4, respectively, for 1967 and 3.6, 9.2, and 30.5, respectively, for 1972.

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Figure 14.—(a) Simulated low, medium, and high Heliothis spp. larval populations, (b) resulting square populations, and (c) resulting boll populations. (1972 weather, medium predator population, no insecticide application.)


For each Heliothis spp. population, the percentage of reduction in yield was much less in 1967 than in 1972.

In the simulations with insect control strategy S2, there were five applications with the medium H. spp. population and seven applications with the heavy K. spp. population for 1967 and 1972. For the low Heliothis spp. population, three applications were necessary in 1967 and two in 1972. The percentages of reduction in yield with insect control strategy S2 were approximately the same for both years for all three Heliothis spp. populations.

The effects of the boll weevil populations on the numbers of squares and bolls are shown in Figures 15b and c. With insect control strategy SI, the percentages of reduction in yield for the low, medium, and high boll weevil populations were 6.3, 11.3, and 40.1, respectively, for 1967 and 15.3, 21.7, and 46.9 for 1972. Also, with insect control strategy S2, the number of insecticide applications was less in 1967 for the low and medium populations of boll weevils. For the high population, the number of insecticide applications was equal in 1967 and 1972.

The effects of the predator populations on the medium population of Heliothis spp. in 1972 with insect control strategy SI are shown in Figure 16a. With the low, medium, and high predator populations, the medium Heliothis spp. population reached maximums of 33,300, 16,000, and 4,700 larva per acre, respectively, during the third generation (September 1 to September 20). The effects of these Heliothis spp. populations on the squares and bolls are shown in Figures 16b and c, respectively. With insect control strategy SI, the percentages of reduction in yield for the low, medium, and high predator populations were 5.8, 2.2, and 1.2, respectively, for 1967 and 23.5, 9.2, and 1.0 for 1972.

With S2, the number of insecticide applications was the same for 1967 and 1972 for both the low and the medium predator populations (seven and five, respectively). With the high predator population, one insecticide application was made for 1967 and two for 1972. With S2, the percentage of reduction in yield was less for 1972 than for 1967.

Simulations were also performed with all three insect populations at the medium level. In 1967, the reductions in yield were 14.6% with insect control Si and 12.8% with insect control S2. In 1972, the reductions were 25.6 and 8.3 for SI and S2, respectively.

This sensitivity analysis illustrates how the simulated yield of the CIM model is affected by different levels of three insect populations, when an insecticide is or is not used. The results also indicate the usefulness of the CIM model in evaluating insect pest management strategies. Because the simulated experiments can be run under controlled conditions, the factor of interest can be isolated, and the experiment can be replicated over several years.


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Figure 15.—(a) Simulated low, medium, and high boll weevil populations, (b) resulting square populations, and (c) resulting boll populations. (1972 weather, no insecticide applications.)


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Figure 16.—Simulated effects of low, medium, high predator populations on (a) medium Heliothis spp. larval population, (b) squares, and (c) bolls"! (No insecticide application; (1972

weather.)


In addition, once the model has been developed, the time and cost of each experiment is small compared with that of a field experiment. The simulation of one season with the CIM model requires approximately 2 minutes on the UNIVAC 1100/80 at Mississippi State University.


LITERATURE CITED

Bacheler, J. S., J. W. Jones, and J. R. Bradley. 1975a. The effect of temperature on development and mortality of

boll weevil immature stages. Environmental Entomology 4:808- 810.

J. W. Jones, J. R. Bradley, Jr., and H. D. Bowen. 1975b. Influence of temperature on abscission of cotton squares

infested with boll weevil eggs. Journal of Economic Entomol- ogy 68:298-300.

Baker, D. N., J. D. Hesketh, and W. G. Duncan. 1972. Simulation of growth and yield in cotton. Gross photosyn-

thesis, respiration and growth. Crop Science 12:432-435.

Brown, L. G., J. W. Jones, and F. A. Harris 1976. A simulation study of insect pest management alternatives

by integration of a Heliothis spp. model and a cotton crop model. American Society of Agricultural Engineers, Paper no. 76-5025, St. Joseph, MI.

J. W. Jones, J. D. Hesketh, J. D. Hartsog, F. D. Whis- ler, and F. A. Harris.

1982. COTCROP: Computer simulation of a cotton production system. Users manual. Mississippi Agriculture and Forestry Ex- periment Station, Mississippi State, MS.

R. W. McClendon, and J. W. Jones. 1979. Computer simulation of the interaction between the cotton

crop and insect pes^-s. Transactions of the ASAE 22:771-774.

Bruce, R. R., and J. M. Romkens. 1965. Fruiting and growth characteristics of cotton in relation

to soil moisture tension. Agronomy Journal 57:135-140.

Butler, G. D., Jr., and A. G. Hamilton. 1976. Developmental time of Heliothis virescens in relation to

constant temperature. Environmental Entomology 5:759-760.

Cole, C. L. 1970. Influence of certain seasonal changes on the life history

and diapause of the boll weevil. Anthonomus grandis Boheman. Ph.D. dissertation. Texas A & M University, College Station, TX.

Duncan, W. G. 1972. SIMCOT. A simulation of cotton growth and yield. Pro-

ceedings, Workshop Modeling Tree Growth. C. M. Murphy and J. D. Hesketh, editors Oak Ridge National Laboratory, Oak Ridge, TN.


Gardner, W. R. 1965. Movement of nitrogen in soil, Ln Soil Nitrogen. W. V. Bartholomew, and F. W. Clark, editors. American Society of Agronomy, Madison, WI, 557 p.

Gutierrez, A. P., T. F. Leigh, Y. Wang, and R. D. Cave. 1977. An analysis of cotton production in California: Lygus hesperus injury - an evaluation. Canadian Entomologist 109: 1375-1386.

Harris, F. A. 1972. Resistance to methyl parathion and toxaphene-DDT in bollworm and tobacco budworm from cotton in Mississippi. Journal of Economic Entomology 65:1193-1194.

Hartstack, A. W., Jr., J. P. Hollingsworth, R. L. Ridgway, and J. R. Coppedge.

1973. A population dynamics study of the bollworm and the tobacco budworm with light trays. Environmental Entomology 2:244- 252.

J. A. Witz, J. P. Hollingsworth, R. L. Ridgway, and J. D. Lopez.

1976. MOTHZV-2: a computer simulation of Heliothis zea and Heliothis virescens population dynamics. Users manual. U.S. Department of Agriculture, ARS-S-127, 55 p.

Hesketh, J. D., D. N. Baker, and W. G. Duncan. 1972a. Simulation of growth and yield; respiration and the car-

bon balance. Crop Science 11:394-398.

D. N. Baker, and W. G. Duncan. 1972b. Simulation of growth and yield in cotton. II. Environ- mental control of morphogenesis. Crop Science 12:436-439.

Hogg, D. B., and M. Calderón. 1981. Field developmental times of Heliothis zea and H. vires-

cens (Lepidoptera: Noctuidae) larvae and pupae in cotton. En- vironmental Entomology 10:177-179.

and A. P. Gutierrez. 1981. A model of the flight phenology of the beet armyworm

(Lepidoptera: Noctuidae) in central California. Hilgardia 48:1-36.

Hunter, W. D., and W. D. Pierce. 1912. The Mexican boll weevil: a summary of the investigations

of this insect up to December 31, 1911. U.S. Senate Document 305, 188 p.

478 L. G. EÎROWN ET AL

Isley, D. 1932. Abundance of the boll weevil in relation to summer weather

and food. Arkansas Agriculture Experiment Station, Bulletin No. 271.

Jackson, R. D., and F. D. Whisler. 1970. Equations for approximating the vertical nonsteady-state

drainage of soil columns. Soil Science Society of America, Proceedings 34:715-718.

Jenkins, J. N., W. L. Parrott, and J. W. Jones. 1975. Boll weevil oviposition behavior: multiple punctured

squares. Environmental Entomology 4:861-867.

Jones, J. W. 1975. A simulation model of boll weevil population dynamics as

influenced by the cotton crop status. Ph.D. disseration, North Carolina State University, Raleigh, NC.

H. D. Bowen, R. E. Stinner, J. R. Bradley, Jr., and J. S. Bacheler.

1977. Simulation of boll weevil population as influenced by weather, crop status, and management practices. Transactions of the ASAE 20:121-125, 131.

H. D. Bowen, R. E. Stinner, J. R. Bradley, Jr., R. S. Sowell, and J. S. Bacheler.

1975. Female boll weevil oviposition and feeding process: a simulation model. Environmental Entomology 4:815-821.

L. G. Brown, and J. D. Hesketh. 1980. COTCROP: a computer simulation model for cotton growth

and yield. In Predicting Photosynthesis for Ecosystem Models, Vol. 2, p. 209-241. CRC Press, Boca Raton, FL.

J. D. Hesketh, E. J. Kamprath, and H. D. Bowen. 1974. Development of a nitrogen balance for cotton growth

models: a first approximation. Crop Science 14:541-546.

F. D. Whisler, and J. D. Hartsog. 1976. Soil water model for crop level simulations. In Proceed-

ings, Beltwide Cotton Production Research Conference, p. 116-118.

Kincade, R. T., M. L. Laster, and J. R. Brazzel. 1967. Damage to cotton by the tobacco budworm. Journal of Eco- nomic Entomology 60:1163-1164.

Lloyd, E. P., J. L. McMeans, and M. E. Merkl. 1961. Preferred feeding and egg laying sites of the boll weevil

and the effect of weevil damage on the cotton plant. Journal of Economic Entomology 54:979-984.


McClendon, R. W., L. G. Brown, J. W. Jones, J. D. Hesketh, J. Hartsog, F. A. Harris, and D. W. Parvin.

1977, Modeling crop-insect pest ecosystems for studying conflicting alternatives caused by species interactions. Iri Pro- ceedings, International Federation of Automatic Control~Sympo- sium on Cotton Mechanisms in Bio and Ecosystems, p. 121-131.

McDaniel, S. G. 1976. Rate, temperature, Heliothis spp. and developmental stage

effect on methyl parathion efficacy in cotton. M.S. thesis, Mississippi State University, Mississippi State, MS.

McKinion, J. M., D. N. Baker, J. D. Hesketh, and J. W. Jones. 1975. SIMCOT II: a simulation of cotton growth and yield. In Computer Simulation of a Cotton Production System. Users manual. U.S. Department of Agriculture, ARS-S-52, p. 27-82.

Nicholson, W. F., Jr. 1975. Feeding of Heliothis virescens (F.) and ^. zea (Boddie) on

cotton with emphasis and development of a simulation model of larval feeding. Ph.D. dissertation, Mississippi State Univer- sity, Mississippi State, MS.

Quaintance, A. L., and C. T. Brues. 1905. The cotton bollworm. U.S. Department of Agriculture,

Bureau of Entomology Bulletin No. 50.

Ritchie, J. T. 1972. Model for predicting evaporation from a row crop with in-

complete cover. Water Resources Research 8:1204-1213.

Schwab, G. 0., R. K. Frevert, T. W. Edminster, and K. K. Barnes. 1966. Soil water conservation engineering, 103 p. John Wiley &

Sons, New York.

Stapleton, H. N., D. R. Buxton, F. L. Watson, D. J. Nolting, and D. N. Baker.

1973. Cotton: a computer simulation of cotton growth. Univer- sity of Arizona, Agricultural Experiment Station Technical Bulletin No. 206.

Wilson, L. T., and A. P. Gutierrez. 1980. Fruit prédation submodel: Heliothis larvae feeding upon

cotton fruiting structures. Hilgardia 48:24-36.

481

Chapter 18

IMPACT OF ALTERNATIVE COTTON INSECT MANAGEMENT STRATEGIES ON PRODUCER INCOME IN MISSISSIPPI

E. H. Simpson, III, and D. W. Parvin, Jr. Department of Agricultural Economics Mississippi State University Mississippi State, MS 39762

ABSTRACT A simulation model was used to estimate the biological impacts of each of four alternative management strategies used against cotton insects in Mississippi. The results were then used as input in linear programming models to estimate the economic impacts of each of the alternative strategies on producer income. Soil constraints were found to limit acreage shifts to less than expected levels.

INTRODUCTION

Methods of controlling cotton insects have changed so radi- cally over time that they can be grouped by period; for example, the pre-boll weevil period, the pre-calcium arsenate period, the calcium arsenate period, and the synthetic organic insecticide period (Newsom 1974). We now appear to be entering a period during which new synthetic organic and biological insecticides will be components of integrated management strategies for controlling cotton insects. Since many of these strategies are based on a community or regional approach, a large proportion of the cotton acreage in a given treatment area must be included in a program. There- fore, producers require information about how new or proposed strategies will impact on their incomes and how the impact will differ from that of current methods of control.

THE PROBLEM

Cotton producers in many regions of the Cotton Belt have recently had to pay excessively high costs to control damaging insects. Thus, various strategies have been devised to aid them in reducing these costs. Two major alternatives are presently receiving considerable attention as a result of the trials conducted in North Carolina and Mississippi, the so-called Boll Weevil Eradica- tion Trial (BWET) and the Optimum Pest Management Trial (OPMT). Eradication implies that the boll weevil will be eliminated from

482 E. H. SIMPSON III AND D. W. PARVIN, JR.

the environment. 0PM implies that boll weevil populations will be reduced to levels that do not require in-season treatment.

STRATEGIES TO BE EVALUATED

In this chapter, we report the results obtained wVien we used a simulation model in an attempt to estimate the impact on producer income of four alternative strategies developed from the two major strategies. It was assumed that each of the four had been implemented successfully and that the desired impact on the target pest(s) had been stabilized. These are compared with a fifth strategy, current normal insect control (CIC), that is, the approach currently used by cotton producers. (CIC is not constant within or among regions of the Cotton Belt.) We do not address the transition periods so the massive costs during these periods are not considered. Additionally, these alternatives may impact the ecosystem in different and subtle ways and thereby have economic consequences for producers (a classic example is insecticide resistance), but these are not considered.

The alternative strategies considered are as follows:

(1) CIC—The approach to cotton insect control currently used by producers. CIC is constant neither within nor among regions.

(2) MOPM—Modified Optimum Pest Management. This alternative assumes an increased level of producer education such that most acreage (field by field) is managed by using the best available technology applicable.

(3) 0PM—This alternative is equivalent to MOPM but community or regional activities are included; these are designed to maintain subtreatment levels of boll weevils during most of the growing season.

(4) CIC-BWE—This alternative assumes that boll weevil eradication (BWE) begins with CIC already in place. Then after completion of BWE, producers manage the remaining cotton insects, both those that are beneficial and those that are damaging, by using CIC techniques.

(5) OPM-BWE—This alternative assumes that BWE begins with an 0PM program already in place. Then after completion of BWE, producers manage the remaining cotton insects by using 0PM techniques.

COTTON PRODUCING REGIONS IN MISSISSIPPI

The Mississippi Agricultural and Forestry Experiment Station (MAFES) considers that there are five cotton producing regions in

PRODUCER INCOME AND MANAGEMENT STRATEGIES 483

Mississippi (Cameron 1978, Seale 1979) (Figure 1). However, admin- istratively, the Department of Entomology of the Mississippi Co- operative Extension Service (MCES) considers that there are only four. The difference stems from the MAFES delineation, which is primarily related to soil types and farm size; the MCES delineation is determined on the basis of insect problems. However, MAFES Re- gions IV and V are equivalent to one of the four MCES regions, and the other three MAFES regions are consistent with the other three MCES regions. The size of the five MAFES regions in terms of cropland acreage and the historical relationship among cotton and alternative crops are summarized in Table 1.

METHODOLOGY

The analysis progressed through two distinct phases. The first was concerned with obtaining estimates of the biological impacts of the alternative strategies on per acre yield of cotton lint and the number of insecticide applications. The second phase was concerned with obtaining estimates of the economic impact of the biological changes on producers.

Method of Estimating Biological Impacts

The computer simulation model (CIM) was used in the experiment to determine the specific changes in per acre yield and number of insecticide applications for each alternative strategy and for CIC. Readers interested in the details of this model are referred to earlier publications (Brown et al. 1970, 1976, 1979; McClendon et al. 1977, Escarra 1979; Jones et al. 1979; Murphey 1980).

The experimental simulations were run on the Mississippi State University Univac 1100/80 computer. Each of the five strategies was simulated for four levels of infestation of three insect species. Also, 4 years of weather data were provided for each of the four MCES regions. The three insect groups were boll weevils (Anthonomus grandis Boheman), the bollworm/tobacco budworm complex (Heliothis spp.), and beneficial insects (predators and parasites). The four levels of infestation were zero, light, moderate, and heavy. However, the probability of occurrence of each level varies among these insect groups so the probabilities were provided by the Biological Evaluation Team (BET) of Beltwide Boll Weevil/Cotton In- sect Management Programs. The BET also provided estimates of the numbers of insects associated with each level of infestation.

The experimental design implied the need to execute CIM some 192 times for each strategy (4 infestation levels x 3 insect groups X 4 years x 4 regions = 192). Then since it was intended to simulate five strategies, 960 executions of CIM would have been required. However, CIC, the strategy used as the basis for comparison, consists of as many as four substrategies in some regions


Figure 1.—Major cotton producing regions of Mississippi

I. Delta II. North Central

III. South IV. Northeast Hills V. Northeast Prairie

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(once a week scouting, twice a week scouting, once a week scouting plus an occasional spot check, and a calendar spray program), and each of these would require as many executions of CIM as would a single strategy without substrategies. Consequently, an excessive number of possible executions were projected. Therefore, situations determined to have an extremely low probability of occurrence were not simulated, and a panel of entomologists uniquely familiar with cotton production and insect problems in Mississippi was called upon to adjust the results of the experiment to account for the situations that were not simulated.

Method of Estimating Economic Impacts

Five regional linear programming optimization models were used in the experiment to estimate the impact of the alternative strategies on producer income. The constraint for each of the linear programming models was the soil resource. Yields of cotton and of the alternative crop (soybean) by soil resource for each of the regions are reported in Table 2.

The models were structured in such a way as to select the crop (cotton or soybeans) for a given soil that would maximize returns above specified expenses (direct and fixed costs). Cost estimates (inputs) used are appropriate for 1979 (Hamill et al. 1979a, 1979b, 1979c; Parvin et al. 1979a, 1979b). Output prices (producer returns) selected were the average prices received by Mississippi farmers in 1979 (Mississippi Crop and Livestock Reporting Service, selected issues). The prices were: cotton lint—$0.607 per pound; cotton seed—$0.062 per pound; soybeans—$6.45 per bushel; and rice—$3.60 per bushel. These prices were assumed to be constant because numerous factors such as weather, domestic consumption, and export demand have a far greater impact on commodity prices than does the particular strategy selected for control of insect pests.

Each of the linear programming models was executed once for CIC and once for each of the four alternative strategies. The effect of each alternative strategy was built into the linear programming models by modifying the CIC cotton yield and that portion of the direct cost that would be associated with insect control for that strategy. Each insecticide application was assumed to cost $4.96 per acre (including aerial application charges). This amount reflects the 1979 cost of application of the standard rate of EPN plus methyl parathion.

Since each alternative strategy could impact on producer income by increasing per acre returns for cotton or increasing cotton acreage, the linear programming models were designed to capture both effects, subject to the appropriate constraints. The linear programming models were solved by using the Functional Mathematics Programming System—a standard linear programming solution algorithm (Anonymous 1977, Cameron 1978, Cameron et al. 1981, Seale 1979).


Table 2.—Soil resources, acreage, and per acre cotton and soybean yields, by region, Mississippi

Cotton lint Soybean yield Soil yield (pounds (bushels

resource \J Acreage per acre) per acre)

Delta A 51,445 730 19.6 B 102,891 702 18.7 C 439,724 612 17.0 D 237,270 585 22.1 E 355,904 495 19.9 F 154,535 449 20.4 G 875,701 359 14.5

Total 2,217,470 North Central

A 31,152 640 26.1 B 16,852 640 24.3 C 8,989 600 26.1 D 67,344 600 24.3 E 54,381 560 23.4 F 28,537 525 20.7 G 86,191 520 24.3 H 57,461 510 24.3 I 8,809 510 20.7 J 55,928 440 18.9 K 143,301 400 21.6 L 74,169 400 18.9 M 70,786 360 21.6

Total 703,900 South

A 23,240 630 26.4 B 92,869 690 24.3 C 74,993 570 23.6 D 39,354 500 21.9 E 77,125 460 23.5 F 102,280 400 18.9 G 241,339 380 18.9

Total 651,200 Northeast Hills

A 32,834 585 27.9 B 32,430 540 27.9 C 28,787 535 26.9 D 40,534 500 26.1 E 94,578 427.5 26.1 F 102,285 405 25.2 G 146,039 405 23.4 H 163,783 360 21.6 I 24,268 270 17.1 J 27,662 225 15.3

Total 693,200 (continued)


Table 2 (continued).—Soil resources, acreage, and per acre cotton and soybean yields, by region, Mississippi

Cotton lint Soybean yield Soil yield (pounds (bushels

resource J^/ Acreage per acre) per acre)

Northeast Prairie

A 14,046 550 25.6 B 14,120 530 22.6 C 42,019 505 26.0 D 95,464 470 26.8 E 154,929 445 26.6 F 36,331 400 21.7 G 88,091 380 20.7

Total 445,000

State total 4,710,770

\J A-M represent broad soil classifications identified by Cameron 1978; Collins 1980; Seale 1979; and U.S. Department of Agriculture, selected issues.

RESULTS

Biological Impact

The results of the adjusted CIM simulation of the four alternative strategies and of CIC are presented in Table 3. The major changes in yield and in the number of insecticide applications were related to the level of the boll weevil infestation, and the impact of this level was greatest in the South Region where the level of infestation is highest. Since a large portion of the Delta Region is not infested by boll weevils, estimated impacts of the alternative strategies were not as great in the Delta Region as in other regions.

In the four regions where boll weevils are a problem, MOPM was estimated to result in an 8- to 10-pound increase per acre in yield and a 0.9-1.0 decrease in the number of insecticide applications. 0PM produced an estimated 18- to 22-pound increase in yield and a 2.2-2.4 decrease in the number of insecticide applications. CIC- BWE produced an estimated increase in yield of 19-24 pounds and a 2.4-2.6 decrease in the number of insecticide applications. 0PM- BWE had the largest impact (Table 3).

In the Delta Region, which is relatively free of boll weevils, both MOPM and 0PM slightly outperformed CIC-BWE. This difference is attributed primarily to improved early-season insect control resulting from the increased level of producer education.


Table 3.—Estimated increases per acre in yield of cotton lint and decreases per acre in applications of insecticide by region and by strategy, Mississippi \_l

Region CIC MOPM 0PM CIC-BWE OPM-BWE

Delta Base +6(-0.6) +10("0.9) +4(-0.4) +7(-0.9) North Central Base +10(-0.9) +22(-2.2) +23(-2.4) +29(-2.9) South Base +10(-0.9) +22(-2.4) +24(-2.6) +31(-3.1) Northeast Hills Base +8(-1.0) +18(-2.4) +19(-2.5) +24(-3.0) Northeast Prairie Base +8(-1.0) +18(-2.4) +19(~2.5) +24(-2.0)

1/ Decrease in parentheses.

Note: CIC = Current Insect Control; MOPM = Modified Optimum Pest Management; 0PM = Optimum Pest Management; CIC-BWE = Current Insect Control-Boll Weevil Eradication; OPM-BWE = Optimum Pest Management-Boll Weevil Eradication.

Economic Impact

The results of the attempt to determine economic impacts are presented in Tables 4-8 for each of the regions so each reader can determine how acccurately the linear programming models simulate CIC and can compare the impact of the alternative strategies on the various regions.

In fact, the linear programming models tracked actual acreage extremely well; thus, they can be viewed as providing reasonable estimates of the impacts of alternative strategies relative to CIC. For example, the estimated cotton acreage for CIC in the Delta Re- gion is consistent with the 1974-78 Delta Region average (Table 1).

Table 4.—Impact of alternative cotton insect control strategies on producer returns (above specified costs) and on cotton acreage. Delta Region of Mississippi

Strategy

Total Returns above cotton

specified expenses acreage (million dollars) (acres)

CIC MOPM 0PM CIC-BWE OPM-BWE

133.572 831,330 139.558 831,330 139.558 831,330 137.554 831,330 141.370 831,330


Table 5.—Impact of alternative cotton insect control strategies on producer returns (above specified costs) and on cotton acreage, North Central Region of Mississippi


specified expenses acreage Strategy (million dollars) (acres)

CIC 52.940 207,255 MOPM 55.365 216,064 0PM 58.824 302,255 CIC-BWE 59.036 302,255 OPM-BWE 61.657 359,716

Table 6.—Impact of alternative cotton insect control strategies on producer returns (above specified costs) and on cotton acreage. South Region of Mississippi


specified expenses acreage Strategy (million dollars) (acres)


Table 7.—Impact of alternative cotton insect control strategies on producer returns (above specified costs) and on cotton acreage. Northeast Hills Region of Mississippi

Strategy

CIC MOPM 0PM CIC-BWE OPM-BWE



41.415 94,051 42.410 94,051 44.236 134,585 44.398 134,585 45.204 134,585


Table 8.—Impact of alternative cotton insect control strategies on producer returns (above specified costs) and on cotton acreage, Northeast Prairie Region of Mississippi

Strategy




Also, none of the alternatives caused an increase in cotton acreage there relative to CIC. Likewise, cotton acreage estimated for CIC in the North Central Region was consistent with actual acreage. MOPM increased acreage, OTPM and CIC-BWE increased it more, and OPM- BWE had an even greater impact. In the South Region, CIC cotton acreage was estimated to be 191,102 acres, somewhat lower than the actual average (Table 1). There was no increase in cotton acreage with either MOPM or 0PM, but both CIC-BWE and OPM-BWE increased acreage. Also, in the Northeast Hills Region, cotton acreage estimated for CIC was somewhat lower than the actual acreage, and again MOPM did not result in an increase in acreage. However, 0PM, CIC- BWE, and OPM-BWE all increased cotton acreage. CIC cotton acreage estimated for the Northeast Prairie Region likewise was a little low. MOPM, 0PM, and CIC-BWE did not result in an increase in cotton acreage. However, OPM-BWE essentially doubled the average for 1974-78 and more than doubled the acreage for CIC. The dominant factors that influenced the results were the constraints on acreage and the relative yields of cotton and soybean associated with the various soil groups.

The estimated returns above specified expenses for each region and the State are reported in Table 9.

Table 9.—Estimated total returns (millions of dollars) above specified expenses for five insect control strategies and five regions in Mississippi

Region CIC MOPM 0PM CIC-BWE OPM-BWE ilVtT 133.572 139.558 139.558 137.554 141.370 North Central 52.940 55.365 58.824 59.036 61.657 South 47.309 49.505 52.539 53.008 54.716 Northeast Hills 41.415 42.410 44.236 44.398 45.204 Northeast Prairie 33.835 34.133 34.527 34.561 34.884 State 309.071 320.971 329.684 328.557 337.831


Table 10—Increase in total returns (millions of dollars) above specified expenses by insect control strategy relative to returns from CIC, by region in Mississippi

Region CIC MOPM 0PM CIC-BWE OPM-BWE

Delta Base 5.986 5.986 3.982 7.798 North Central Base 2.425 5.884 6.096 8.717 South Base 2.196 5.230 5.699 7.407 Northeast Hills Base 0.995 2.821 2.983 3.789 Northeast Prairie Base 0.298 0.692 0.726 1.049 State Base 11.900 20.613 19.486 28.760

Plainly, the changes in returns above specified expenses were small so it is easier to examine these results relative to CIC, as in Table 10. OPM-BWE consistently resulted in the largest increase in producer returns relative to those from CIC. However, when the Delta Region is excluded, CIC-BWE resulted in slightly larger producer returns than those resulting from 0PM. In the Delta Region, both MOPM and 0PM resulted in producer returns that were larger than those resulting from CIC-BWE.

The increased returns to all acres above specified expenses relative to CIC are reported in Table 11. These figures show increased returns from all acreage in each of the regions.

Table 11—Increase in returns per acre (millions of dollars) above specified expenses by insect control strategies relative to returns from CIC, by regions in Mississippi

Region CIC MOPM 0PM CIC-BWE OPM-BWE t

Delta Base 2.70 2.70 1.79 3.51 North Central Base 3.44 8.36 8.66 12.38 South Base 3.37 8.03 8.75 11.37 Northeast Hills Base 1.44 4.07 4.31 5.47 Northeast Prairie Base 0.67 1.56 1.63 2.36 State Base 2.53 4.38 4.14 6.11


IMPLICATIONS

The figures presented in Tables 9, 10, and 11 indicate that in some regions, and in the State, the producer returns associated with the various alternative strategies did not differ substantially. Therefore, the "preferred" strategy for Mississippi cotton producers may be related to factors and costs that were not considered in this study, for example, the producer share of the cost of eradication during the transition period and the producer share of the cost of treating diapausing boll weevils after the 0PM program has been implemented and the ecosystem stabilized. Apparently a careful examination of these two items must be undertaken.

LIMITATIONS

In this study, we examined alternative cotton insect management strategies from the producer standpoint assuming no change in product prices. Policy makers who must select the "best" strategy must consider numerous other factors such as public costs, pesticide resistance, impact on the environment, and regional shifts in cotton acreage among States. Also, the results of this analysis are specific for the regions of Mississippi. Extrapolation to other portions of the Cotton Belt would not be appropriate.


LITERATURE CITED

Anonjnnous. 1977. Functional mathematical programming system (FMPS). Pro-

gram reference, Sperry Rand Corporation.

Brown, L. G., J. W. Jones, and F. A. Harris. 1976. A simulation study of insect pest management alternatives

by integration of a Heliothis spp. model and a crop model. Presented at the Annual ASAE Meeting, Lincoln, NE, Paper No. 76-5025.

R. W. McClendon, and J. W. Jones. 1970. Complete simulation of the interactions between the cotton

crop and insect pests. Transactions of the ASAE 22.

R. W. McClendon, and J. W. Jones. 1979. An integrated simulation of cotton and insect pests. Pre-

sented at the Joint National Meeting of the Institute of Man- agement Science and Operations Research Society of America, New Orleans, LA.

Cameron, D. M. 1978. An economic assessment of production alternatives avail-

able to representative farms of the Mississippi Delta. Unpub- lished M.S. thesis, Department of Agricultural Economics, Mississippi State University.

D. W. Parvin, Jr., and F. T. Cooke, Jr. 1981. A survey of farm resources and production activities in the Yazoo-Mississippi Delta. Mississippi Agricultural and Fores-

try Experiment Station, AECR. R. No. 120.

Collins, G. S., III. . 1980. An econometric simulation model for evaluating aggregate

economic impacts of technological change on major U.S. field crops. Unpublished dissertation. Department of Agricultural Economics, Texas A&M University.

Escarra, B. 1979. Estimates of the effects of alternative insect management

programs on cotton yield and insect control cost in the State of Mississippi. Unpublished thesis. Department of Industrial Engineering, Mississippi State University.

Hamill, J. G., D. W. Parvin, Jr., F. T. Cooke, Jr., D. M. Cameron, and R. D. Seale.

1979a. Cost of production estimates for the black belt of northeast Mississippi, 1979. Special Edition of Research High- lights, Mississippi Agricultural and Forestry Experiment Sta- tion, Mississippi State University.


Hamill, J. G., D. W. Parvin, Jr., F. T. Cooke, Jr., R. D. Seale, and G. Simpson.

1979b. Estimated costs and returns, row crops, northern brown loam area of Mississippi, 1979. Special Edition of Research Highlights, Mississippi Agricultural and Forestry Experiment Station, Mississippi State University.

R. D. Seale, D. W. Parvin, Jr., and F. T. Cooke, Jr. 1979c. Estimated costs and returns, row crops, central brown

loam area of Mississippi, 1979. Mississippi Agricultural and Forestry Experiment Station, Mississippi State University, AEG M.R. No. 91.

Jones, J. W., L. G. Brown, and J. D. Hesketh. 1979. COTCROP, a complete model for cotton growth and yield. In Predicting Photosynthesis for Ecosystem Models. CRC Press, West Palm Beach, FL.

McClendon, R. W., L. G. Brown, and J. W. Jones. 1977. Investigation of integrated pest management strategies utilizing computer simulation of the cotton crop insect interactions. Presented at the Annual ASAE Meeting, NC Paper No. .77-5019.

Mississippi Crop and Livestock Reporting Service, selected issues.

Murphey, S. M. 1980. Use of simulation to evaluate alternative cotton insect

pest control strategies. Unpublished M.S. thesis. Department of Industrial Engineering, Mississippi State University.

Newsom, L. D. 1974. Pest management: history, current status and future prog-

ress. In Proceedings, Summer Institute on Biological Control of Plan~Insects and Diseases, Mississippi State University, p. 64.

Parvin, D. W., Jr., J. G. Hamill, F. T. Cooke, Jr., D. M. Cameron, and E. H. Simpson III.

1979a. Cost of production estimates, major crops, sand clay hills of Mississippi, 1979. Special Edition of Research High- lights, Mississippi Agricultural and Forestry Experiment Sta- tion, Mississippi State University.

J. G. Hamill, F. T. Cooke, Jr., S. H. Holder, Jr., and D. M. Cameron.

1979b. Budgets for major crops. Delta of Mississippi, 1979. Special Edition of Research Highlights, Mississippi Agricul- tural and Forestry Experiment Station, Mississippi State Uni- versity.

^^^ E. H. SIMPSON III AND D. W. PARVIN, JR.

Seale, R. D.

1979. The economic impact of optimum pest management on cotton production in Mississippi. Unpublished thesis, Department of Agricultural Economics, Mississippi State University.

U.S. Department of Agriculture. Soil Conservation Service and Mississippi Agricultural and Forestry Experiment Station, Soil Survey, selected issues.

497

Chapter 19

ECONOMIC EVALUATION OF THE BOLL WEEVIL ERADICATION TRIAL IN NORTH CAROLINA, 1978-80

G. A. Carlson and L. F. Suguiyama Department of Economics and Business North Carolina State University Raleigh, NC 27650

ABSTRACT Biological, economic, and environmental variables were monitored in the Boll Weevil Eradication Trial (BWET) after operations began in 1978. The objective of the BWET was to determine the feasibility of its implementation across the boll weevil-infested portion of the Cotton Belt. In this chapter, we tabulate the economic effects of the BWET on the trial zone and on a comparison zone by examining data drawn from a random sample of farmers. The economic evaluation of the Trial centered on measurement of changes in the costs of production, in cotton yields, and in public expenditures. The major economic impact of the program was the reduction in the use of insecticides in the trial zone over time and the even greater reduction in the use of insecticides in comparison with a nontrial zone. There was an indication that the reduction in cotton acreage that occurred in the Trial zone was attributable to farmer eradication fees in the first year of the trial. The direct effects of the trial on yields were difficult to assess; however, there was evidence that small increases in yields were an indirect effect of the trial. In order to insure complete removal of the boll weevil from the trial area, monitoring of the project was very thorough and, therefore, public costs were high.

INTRODUCTION AND METHODS OF ANALYSIS

The major purpose of the Boll Weevil Eradication Trial (BWET) in North Carolina was to determine whether eradication of the boll weevil (Anthonomus grandis Boheman) from a large area is technically feasible. Therefore, the Trial was planned so that biological, environmental, and economic variables might be monitored. Information on these three features is essential to any decision

^9Ö G. A. CARLSON AND L SUGUIYAMA

about the desirability of attempting eradication across the boll weevil-infested portion of the Cotton Belt in the United States.

This economic evaluation of the BWET centers on the measurement of changes in costs of cotton production, in cotton yields, and in public expenditures relative to current insect control (CIC) practices.

Comparisons with CIC in the same years as the BWET (1978-80) were possible by examination of data from a randomly selected set of 60 farmers in three counties outside the trial area (control zone, CZ). The information was also obtained from a random sample of 133 farmers in four counties of the trial area (eradication zone, EZ). It was also possible to compare CIC in the eradication zone itself by examining the costs and yields in the 4-year period prior to the implementation of the Trial (1974-77).

In this chapter we present data for the base period 1974-77 and for the 3 years of the BWET (1978-80). Data on pesticide use, cotton yields, and public expenditures are actual figures obtained in the personal and telephone surveys of about 200 randomly selected farmers. This information has been supplemented by information from the Animal and Plant Health Inspection Service (APHIS), BWET personnel, spray group directors, the Biological Evaluation Team of the State Extension and Crop Reporting Service offices, and a sample of pesticide applicators and pesticide dealers.

The regions covered by the study are the EZ and the CZ. The EZ includes Edgecombe, Halifax, Northampton, and Nash Counties; that is, about 95% of the APHIS evaluation zone. The CZ includes Robeson, Scotland, and Cleveland Counties. A limited amount of cotton (less than 20% of the State acreage) is grown in other counties of North Carolina, but these areas were not included in the analysis.

There are known differences and similarities in cotton production between the CZ and the EZ. Table 1 gives a summary of differences and similarities of characteristics for cotton farms in the CZ and EZ (Grube and Carlson 1978). Major differences include smaller cotton acreages, lower yields, lower scouting costs, more use of spray groups, and a larger share of pest control efforts for boll weevils in the EZ than in the CZ. Similarities include the number of trips across the fields, years of farming experience, farmer age, boll weevil and bollworm (Heliothis zea (Boddie)) treatment thresholds, number of treatments with boll weevil as the primary target, number of diapause treatments per season (1974-76), and average length (days) of the pest control season. The historical differences in pest control between the two zones are well known, so comparisons during the eradication period can be made.

Cotton acreages and yields for the EZ and the CZ for 1970-80 are shown in Figures 1 and 2. Cotton acreages for both zones show a distinct declining trend over the 10-year period. Cotton yields

ECONOMIC EVALUATION OF CONTROL OPTIONS 499

in the two zones are quite similar, and subject to variation from year to year. The possible effects of eradication and program fees charged to cotton producers on acreages and yields are examined in later portions of this chapter.

Table 1.—Comparison of characteristics of cotton farms in eradication (EZ) and control (CZ) zones J^/

Data means Eradication Control Significant

Farm characteristic zone (EZ) zone (CZ) difference Ij

Years of farmer schooling 11.6 12.8 S 1974-76 cotton acreage per farm 89 456 S 1974-76 cotton yield per acre

(pounds) 454 520 S Hours scouting per acre per

season 0.35 0.54 S Bollwotm application interval

(no. of days) 6.2 4.8 S Boll weevil application interval

(no. of days) 6.3 5.4 S Share of in-season applications

for boll weevils (%) 25.3 19.4 S Member of spray group (%) 71 23 S Total cost of scouting per

acre (dollars) 1.40 2.10 S Average farmer age 49 47 N Boll weevil treatment threshold

(%) 8.0 8.2 N Bollworm treatment threshold

(%) 5.4 5.5 N Number of applications with boll

weevil as a target 2.55 2.46 N Average length of application

season (no. of days) 57 48 N No. of diapause treatments per

season, 1974-76 0.99 0.83 N Trips across field 11 11 N Years of farming experience 24 23 N

\j Figures are for 1976 unless otherwise noted. The EZ statistics are based on responses of 133 farmers in the four-county test area; the CZ statistics are based on responses of 60 farmers in Robeson and Scotland Counties. The area surveyed represents 78% of the 1976 acreage in the State. See Grube and Carlson (1978) for details on variable description, sampling procedures, and other characteristics.

2/ N = no significant difference by "t" test; S = significant.

500 G. A. CARLSON AND L SUGUIYAMA

• Eradication zone Acreage

60,000

20,000 u-O^ 10,000-

0 t 1 1 1 1 1 1 1 1 \ 1 1970 71 72 73 74 75 76 77 78 79 '80

Figure 1.—Acreage in the eradication and control zones, 1970-80.

Comparisons in the EZ before and during the eradication effort were used to determine how eradication changes pest control practices and yields in a given area. This method of comparing areas with and without a given pest control program by adjusting yields and costs for historical differences is commonly used (Von Rumker et al. 1975). These comparisons must also be modified for changes in pest populations, in weather, and in available pest control chemicals. For example, the introduction of synthetic pyrethroids for bollworm control has changed the costs and amounts of chemicals used independent of the changes brought about by eradication.

In the following discussion, all prices and costs have been reported in 1979 dollars unless otherwise noted. Production costs and yields have not been adjusted for variations in pest levels, in weather, or in other factors unless specifically noted. The effects of such factors on yield will be discussed in the section on yield changes.


Average yield per acre (in lbs. of lint)

V-. //'^v^-.../! 400 ^ ^^.^^ ^

300 —

200- ^ Eradication zone

•-----* Control zone 100-

'I 1 1 1 1 1 1 1 1 1 1 1970 71 72 73 74 75 76 77 78 79 '80

Figure 2.—Average yield per acre in the eradication and control zones, 1970-80.

Source: North Carolina Crop Reporting service.

CURRENT INSECT CONTROL

Current insect control is defined as those practices that the average grower uses to control cotton insects. This is the base set of conditions to which eradication is compared for each of the two zones.

Some of the features of historical insect control in the EZ and the CZ are shown in Table 2 and Figure 3. County averages and the acreage-weighted zone averages for yield, numbers of insecticide applications, and total insect control cost are given. This information is based on grower surveys asking for recall back to 1974. Items (2) and (4) in Table 2 are zone averages for only those growers who continued to grow cotton in 1978 or 1979. These averages are computed since there is a considerable change in growers between these two periods. Historically, in-season treatments have numbered ca. 2.1 treatments per season more in the CZ than in the EZ (11.13 treatments per acre in the CZ and 9.03 in the EZ). The number of diapause treatments has been slightly less than one treatment per season in both zones (0.92 in the EZ and 0.82 in the CZ). Total insect control costs have been slightly higher in the CZ than in the EZ, about 12% higher for all growers ($56.83 in the CZ and $50.81 in the EZ). These costs include scouting costs at


$2.50 per acre since the Grube-Carlson survey (1978) showed that all cotton growers in North Carolina use some type of scouting. Those growers who continued to grow cotton in 1978 or 1979 applied more insecticide treatments than did all growers. Yields of cotton per acre were about 4.47% higher in the EZ than in the CZ for all growers during the 1974-77 period.

Table 2.—Average yields, number of insecticide applications, and costs for the eradication and control zones, 1974-77

Yield Control (pounds Number of insecticide costs 1/

per applica tions per acre (dollars Zone and county acre) In-season Diapause per acre)

(1) Eradication 429.7 9.03 0.92 $ 50.81 Edgecombe 499.5 9.75 1.53 54.61 Halifax 434.5 9.80 0.77 55.01 Nash 319.0 7.88 0.68 41.62 Northampton 433.0 8.19 0.81 47.07

(2) Eradication (only farmers who grew cotton in 1978 or 1979) 497.0 9.13 1.02 52.47

(3) Control 411.3 11.13 0.82 56.83 Cleveland 292.0 5.83 0.74 32.06 Robeson 412.5 11.70 0.82 58.07 Scotland 443.0 11.65 0.84 59.99

(4) Control (only farmers who grew cotton in 1978 or 1979) 480.0 11.51 0.88 58.52

1/Includes cost of chemicals, aerial application, and scouting.

Source: Farmer survey conducted by the Department of Econom- ics and Business, North Carolina State University.


Average number of in-season applications per acre

Total private Insect control cost per acre ($)

▲

Eradication zone

Controi zone

-60

1974 1975 1976 1977 I

1978 1979 1980

Figure 3.—Average number of in-season applications and total private insect control cost per acre in the eradication and control zones, 1974-80.

Source: Farmer survey conducted by the Department of Eco- nomics and Business, North Carolina State University, Raleigh.

An additional set of historical information for CIC is reported in Table 3. These data were collected from experimental trials at Rocky Mount, which is located in the EZ. These trials showed an average of 8.36 insecticide treatments per acre beginning on July 27 and ending September 5 for the period 1967-80. The 1974-77 average was 8.75 treatments per acre.


Table 3.—Cotton insecticide trials, North Carolina State Univer- sity, Rocky Mount, NC, 1967-78

Number of insecticide Dates of % check plot damaged

Year applications insecticide applications 1/ Boll Boll- per acre First Last weevi 1 worm

1967 13 195 251 47 5 1968 10 205 247 23 51 1969 8 210 244 52 30 1970 7 212 253 37 12 1971 12 195 257 23 25 1972 10 32 1973 10 208 254 24 55 1974 6 208 240 1975 13 183 253 44 22 1976 8 220 257 14 37 1977 8 223 266 13 73 1978 4 226 243 0 36 1979 5 214 241 0 17 1980 3 213 227 0 17

Means for 1967-80 8.36 209 249 23.08 31.69

9.54

8.75

Means for 1967-77 208 253

Means for 1974-77 209 254

30.78 34.20

23.66 44.00

1/ Julian dates of first and last insecticide applications.

Source: J. R. Bradley, North Carolina State University, Ra- leigh (unpublished data).

Estimates of the number of insecticide applications for the various target insects are given in Table 4 for the two zones. For the 1974-77 period, there were more applications for boll weevils alone in the EZ than in the CZ (1.25 in the EZ and 0.15 in the CZ). We will return to the 1978-80 period shortly, but it is important to note that there appears to have been a very distinct reduction in numbers of treatments and costs of insect control per acre for both zones over the 1974-80 period (Figure 3).


Table 4.—Insecticide applications by target insect

Target Average no. appl ications insect 1974-77 1978 1979 1980

Eradication zone Boll weevil 1.25 0.00 0.00 0.00 Bollworm-boll

weevil 1/ 7.66 0.00 0.00 0.00 Bollworm 0.10 4.40 2.43 1.13 Boll weevil-

diapause 0.92 5.70

Control zone

0.00 0.00

Boll weevil 0.15 0.00 0.09 0.65 Bollworm-boll

weevil 1/ 9.40 0.15 0.52 2.73 Bollworm 0.76 8.91 5.42 2.87 Boll weevil-

diapause 0.82 0.05 0.59 0.37 Other:

Spider mites 0.00 0.21 0.11 0.20 Thrips 0.00 0.06 0.05 0.00

1/ The bollworm-boll weevil category refers to bollworms as the major pest and boll weevils as the secondary pest.

Source: Farmer survey conducted by the Department of Econom- ics and Business, North Carolina State University, Raleigh.

Table 5 gives estimates for CIC during 1978-80 for the CZ and the EZ. 1/ Farmer surveys provided information on CIC practices in the CZ. These estimates are given in the final three columns of Table 5 for each of the 3 years of the BWET (1978-80). The most direct comparison over time for CIC is for the CZ. For example. Table 2 shows annual insect control costs for 1974-77 of $56.83 per acre; the comparable figures for total private costs per acre (item 6 in Table 5) are $57.53 in 1978, $46.68 in 1979, and $43.92 in 1980. Numbers of in-season treatments declined from 11.13 in the base period (Table 2) to 9.33 in 1978, 6.19 in 1979, and 6.45 in 1980 (Table 5). These figures reflect both the relatively low pest infestations of 1978 and 1979 and the slight increase in boll weevil pressure in 1980 (Table 4). In addition, the dry August weather of 1978 and 1979 and the sharp increase in the use of synthetic pyrethroid insecticides tended to reduce the need to make as many applications.

j_/ The CZ as defined in this chapter is not directly analogous to any particular Delphi Region. Adjustments have been made by using weighted averages of appropriate Delphi Regions. (U.S. De- partment of Agriculture, 1981.)

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Current insect control practices were not used in the EZ since all cotton acreage there was involved in the eradication effort. However, experts were able to estimate the number of insecticide applications, rates, and costs per acre for both zones (Table 5). These estimates are based on 10-year mean insect populations and 1979 chemicals assumed available. The expert estimate of insecticide costs of $53.42 per acre for the CZ is very close to the 1978 estimate obtained by the survey but about 22% higher than the 1980 estimate.

The same experts estimated that assuming long-run pest infestations, total private insect control costs per acre were $5.97 (or 12.50%) per acre higher in the CZ than in the EZ. This estimated difference is very similar to the historical 11.85% difference in insect control costs during the base period 1974-77 ($56.83 to $50.81) shown in Table 2.

Finally, the public expenditures shown in Table 5 were computed by allocating extension budgets to the two zones based on the proportion of extension time and effort spent in each zone and di- viding them by the respective cotton acreages. The cost of scouting was estimated by contacting commercial scouts in the CZ and using extension estimates for the EZ.

ERADICATION

A description of the cost of eradication in the EZ and the cost of a hypothetical eradication program for the CV based on the same technology used in the EZ for 1978-80 is shown in Table 6. Most of the information was obtained directly from the eradication program personnel. (Target pests are listed in Table 4.) Only the insecticides actually used in Nash, Edgecombe, Northampton, and Halifax Counties are included and used in the calculation of the cost of control by chemicals. (This excludes the insecticides used in the buffer zone and about 1000 acres in other counties in the APHIS evaluation zone. A complete description of the insecticides used in the EZ in 1978-80 is available.)

In 1978, the eradication program included the chemical control of the boll weevil and also of other pests. Cost of this program (both insecticides and application) in the four eradication counties was $42.25 per acre. Though this expenditure varied by area, the cost was evenly shared by all producers in the BWET area; that is, a charge of $46.61 per acre was assessed each producer, which was 50% of all APHIS costs. Total public (APHIS) plus private costs were $93.22; there was another $1.03 expended by the Exten- sion Service for a total of $94.25. The APHIS budget included some additional costs for research and capital items which were necessary for the program but were not charged to the producers. Total costs decreased considerably to $67.03 in 1979 and $40.63 in 1980.

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In 1979 and 1980, APHIS expended eradication money only for boll weevil suppression and eradication. Scouting services for bollworm control were provided to farmers, and an additional Exten- sion Service employee was hired to assist farmers in their decisions regarding bollworm treatment, but EZ producers paid the costs of controlling bollworms. These expenditures averaged $17.63 per acre in 1979 and $8.30 in 1980, considerably less than the historical insect control cost (1974-77) of $50.91 per acre (Table 2). The APHIS assessment to each EZ cotton farmer for boll weevil control was $23.47 per acre in 1979 and $15.29 in 1980. The Extension Service expended $2.21 per acre in the EZ in 1979 and $1.47 in 1980. Thus public plus private costs for eradication of the boll weevil plus bollworm control totaled $94.25 in 1978, $67.03 in 1979, and $40.63 in 1980. These amounts include the cost of private scouting since all spray groups did not charge for private provision of this service.

The costs of insecticides plus application for a hypothetical eradication program for the CZ were estimated at $53.09 per acre. Total private costs per acre (including 50% of total APHIS eradication costs) were estimated to be $53.09 in 1978, $51.90 in 1979, and $38.71 in 1980. The CZ costs were higher than the EZ costs because of the estimated 2.1 additional bollworm treatments per acre (Tables 2 and 6) (11.13-9.03 = 2.1). Total costs per acre were estimated to be $107.09 in 1978, $76.99 in 1979, and $55.63 in 1980. These estimates are higher than the actual costs in the EZ and also higher than the most recent APHIS eradication estimates of $75.55 per acre for a 2-year eradication program (Brazzel 1980).

ACREAGE ADJUSTMENTS TO ERADICATION

One important feature that complicates comparisons over time and space is the movement of land in and out of cotton production as a result of implementation of an eradication program. Cotton producers have production inputs and profitable alternative crops to cotton. They therefore may elect not to participate in eradication by switching their land out of cotton production. Rodriguez (1980) showed that 42.3% of all cotton farmers in the EZ stopped producing cotton between 1977 and 1978, the first year of eradication. The comparable figure for the CZ was only 17.7%.

Analysis of cotton acreage in the EZ from 1956 to 1980 was conducted in an attempt to refine and further quantify the effect of eradication on acreage. A statistical and economic model was designed to reflect the options of the farmers to switch crops and thus avoid paying fees for boll weevil control. The fees per acre of cotton planted were $50.50 in 1978, $24.00 in 1979, and $20.00 in 1980. 2/ The fee in 1978 covered both boll weevil and bollworm control; it did not include bollworm control in 1979 and 1980.

2_/ These were fees charged at the time of planting decision. Re- bates were given at the end of each crop year. A separate analysis in which fees less rebates were used produced very similar results.


The model for the eight major cotton counties in North Caro-

lina was: _3/

A. = a + X.d. + a,P^. + a«P^. + ^-{^4*- It o .11 1 et 2 st J It 1

where A. = natural logarithm of county cotton acreage in

year t, in county i,

d. = dummy variable, 1 for county i and 0 for other counties,

P = expected cotton price or deflated futures price at cotton planting time in year t.

St expected soybean price as a competing crop or deflated futures price at planting time.

Y. = average cotton yield for county i in previous 4 years,

RPC = price risk as reflected by percent deviation of futures price from actual cotton price.

It = rainfall index in planting season (rain days,

inches of rainfall).

E. = eradication payment in county i and year t as given, and

e. = random disturbance term It

The model was evaluated by ordinary-least-squares and by generalized-least-squares by using the Fuller-Battese method. The model was also evaluated for the period 1956-78 so as to measure only the effect of the first year of eradication.

The result of this analysis showed that the direct fee for eradication was statistically significant (1% level) in reducing the acreage of cotton over the 3-year period. The effect in the first year of eradication was especially large: about half the acreage reduction occurring between 1977 and 1978 was associated with eradication. The other half reflected the effects of yields, prices, rainfall, and other factors. Consequently, if eradication fees were raised by $10 per acre, each county in the EZ would reduce acreage by about 15% (from the geometric mean of 12,600 acres) for the 3-year period. In fact, without the large negative effect

3/ A complete justification of the model and statistical methods is^given in Rodriguez (1980). However, his estimates were for 1978

only.


of the first year of eradication, the fee still had a negative effect in the last 2 years of the eradication trial. The temporary effect of eradication fees on acreage can be seen in a general way in the time trends of Figure 1.

Further analysis was conducted to determine what characteristics were associated with farmers who participated in eradication. It was found that farmers with more cotton pickers, farmers who had been members of community cotton insect control groups, and farmers with higher cotton yields were most likely to participate in eradication (Rodriguez 1980).

There are two major policy implications of the acreage shifts due to eradication fees. First, charging farmers directly for the program can reduce the number of acres requiring eradication, thereby reducing variable costs of eradication below those based on average cotton acreage. Second, the potential for temporarily adjusting acreage out of cotton will differ among farmers and lead to lower private costs of insect control during the eradication implementation period. This is a temporary gain that probably would not have any considerable effect on long-run costs and returns of eradication.

YIELD CHANGES

Yield effects of the eradication option relative to CIC were difficult to assess. Cotton yields vary greatly from year to year in North Carolina (Table 7; Figure 2). For example, the standard deviations of yields for 1970-80 were 91.20 and 73.80 pounds per acre for the EZ and CZ, respectively. Yields per acre in the period 1974-77 were higher in the EZ, though they were higher in the CZ for 1965-75. Weather, particularly rainfall and frost, affects yields. Also, in recent years, there appears to be a sizable effect of farmers with lower yields who discontinue cotton production. This discontinuance is shown as a 15.6% yield advantage (1974-77) for those farmers in the EZ who continued cotton production in 1978 or 1979 (Table 2). The equivalent figure for the control zone is 16.7%.

Biologically, one could expect a gain in yield from boll weevil eradication from: (1) reduced use of organophosphate insecticides to control early-season boll weevils; this leads to earlier maturity of cotton, permitting avoidance of frost and late-season rain effects; (2) reduced boll damage from bollworms that are controlled by populations of natural enemies which are not reduced by early-season boll weevil treatments; and (3) reduced direct damage to bolls from boll weevils.

Analyses of various data sets have not provided any direct measure of effects of reduced early-season boll weevil populations on yields. One indirect measure has been the effect of delayed applications of insecticide on yields. Table 8 shows the results

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Table 8.—Effects of biological and economic variables on per acre cotton yields, Rocky Mount, NC, experimental data, 1967-78

Independent variables Coefficient ^/ t-Statistic Mean

Intercept 8776.63 2.35 Pounds of insecticides 18.18 4.03 13.97 Julian date of first

treatment 21.33 3.61 210.00 Julian date of last

treatment -46.32 -3.76 252.00

Chlordimeform use 512.66 2.92 0.24

August rainfall (inches) (August rainfall)

325.47 1.95 4.37 -29.55 -1.75 22.40

Check plot % damage ^ (Check plot % damage)

-53.99 -2.81 40.50 0.42 1.82 1922.00

Dependent variable: Seed R^ = 0.75

cotton yield per acre 1328.00

Sample size = 38 plots

1/ The pounds of lint cotton change per unit change in each independent variable.

Source: Data in Table 3 plus experimental plot data provided by J. R. Bradley, North Carolina State University, Raleigh.

obtained by analyzing 38 experiments at Rocky Mount, NC, during the period 1967-78 (Table 3). In this case, the data for the experimental plots were adjusted for five other factors by multiple regression.

The analyses showed that each additional day of delay in insecticide treatment, from a mean date of July 26 (Table 3), added about 21.3 pounds of seed cotton to yield; that is, yield was increased by about 1.6% per day (mean yield per acre 1328). There- fore, a 10-day delay in the initiation of treatment would increase yields by about 70 pounds of lint. The Delphi panel estimated a gain of 21 pounds of lint due to eradication for northern North Carolina (U.S. Department of Agriculture 1981); therefore, this would require a delay in the initiation of bollworm treatments of only 3 days on the average.

However, it has not been shown in a statistically valid manner that boll weevil eradication will delay the date when the population of bollworms reaches a treatable level in North Carolina. The best indirect information seems to be the approximately 15-day delay in bollworm treatments for about 50% of the EZ cotton fields in 1978-80. This is further complicated by the fact that most bollworm populations arrive in North Carolina cotton fields by mass migration from other crops.


The use of new types of insecticides in recent years has also complicated yield assessments. For example, in the Rocky Mount plots, the use of chlordimeform was associated with increases in yield of 513 seed pounds of cotton. However, it is very possible that the use of chlordimeform may have been correlated with un- observed variables in the experimental data. Pyrethroid insecticides have probably had similar unidentified effects.

Actual yields in the EZ were 611 pounds per acre in 1978, 371 in 1979, and 359 in 1980 (Table 7). Producers who grew cotton in 1978 or 1979 had a 1974-77 average yield of 497 pounds (Table 2). Only the 1978 yield in the EZ figure is statistically higher than the base year mean yield. However, the weather was especially favorable for cotton production in 1978. Also, insect scouting was especially good, and chemical selections for bollworm control were especially effective in the EZ in 1978. These factors were not specifically a part of the eradication program. In any case, when one compares the 1978 yields in the EZ and the CZ, it is clear that cotton yields can be increased by effective bollworm control. The 1978 yields were 114 pounds per acre above the 1974-77 yields for farmers growing cotton in 1978 or 1979 in the EZ, but in the CZ they were 16 pounds per acre less.

SUMMARY AND POLICY IMPLICATIONS

Some of the major characteristics of the two North Carolina cotton zones are listed in Table 9, which reports the economic impact of the BWET on cotton producers in 1978-80. Both zones showed a trend to reduced producer insect control cost; however, the reduction was larger in the EZ than in the CZ. Both zones also showed lower insect control costs in these 3 years than in the previous period (Table 2).

Public insect control costs were much higher in the EZ than in the CZ. This is the nature of an investment in which early costs are high and future costs are low. For example, if the average 1979 and 1980 insecticide (and application) cost saving between the EZ and the CZ is a permanent benefit, this is a $30.70 saving per acre of production costs. Even if there was a $5 per acre maintenance cost (for buffer zone, monitoring, and boll weevil suppression), there would be a net gain of about $25 per acre iñ perpetuity. A $25 net gain per acre would return the investment cost of $127.62 expended for eradication in 1978-80, plus a return on the investment of about 20%. If the costs of eradication were only $75 per acre as estimated by Brazzel for a 2-year program (Brazzel 1980), then the rate of return would be 33%. These estimates assume no changes in yield, acreage, or price from the eradication program.

The yields for both zones are compared in Tables 7 and 9. Yields were highly variable in both zones, and it was not possible to detect any changes due to the eradication program.

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^"•^ G. A. CARLSON AND L SUGUIYAMA

In the EZ, the presence of eradication personnel and the absence of need to treat for boll weevils reduced insecticide use relative to use in earlier periods and to use in the CZ. Also, eradication personnel tried to keep eradication costs and farmer insect control costs low. Partly as a result, few bollworm treatments were necessary compared with those seen as necessary in previous years (Table 4). In addition, farmers in the EZ became more aware of the need for scouting and prescriptive treatment. This awareness is growing in other parts of North Carolina but at a slower rate.

Finally, the tabulations and comparisons of cotton insect control costs discussed in this chapter relate to a particular region of the Cotton Belt. They must be viewed cautiously in respect to other areas. Then, too, the farmers who participated in the BWET normally have higher yields and more specialized cotton equipment than the average northern North Carolina farmer. The insecticide use changes were applicable to particular weather and insect population situations. Economic evaluation must thus be supplemented by environmental and biological evaluations.


LITERATURE CITED

Brazzel, J. 1980. Boll weevil eradication plan, third draft. U.S. Depart- ment of Agriculture, Animal and Plant Health Inspection Ser- vice, Raleigh, NC, November 1980.

Grube, A., and G. Carlson. 1978. Economic analysis of cotton insect control in North Caro-

lina. North Carolina State University, Department of Economics and Business, Economics Information Report No. 52, 54 p.

Rodriguez, R. 1980. Acreage response to government pest control programs: the

case of boll weevil eradication. Unpublished Ph.D. dissertation. Department of Economics and Business, North Carolina State University, Raleigh.

U.S. Department of Agriculture. 1981. The Delphi: insecticide use and lint yields. Beltwide boll weevil/cotton insect management programs. USDA Economics and Statistics Service Staff Report, March, 142 p.

Von Rumker, R., G. A. Carlson, R. D. Lacewell, R. B. Norgaard, and D. W. Parvin, Jr.

1975. Evaluation of pest management programs for cotton, pea- nuts, and tobacco in the United States. Contract Report for Environmental Protection Agency and Council on Environmental Quality, 589 p.

SECTION V FUTURE PROSPECTS

521

Chapter 20

OPPORTUNITIES FOR IMPROVING COTTON INSECT MANAGEMENT PROGRAMS AND SOME CONSTRAINTS ON BELTWIDE IMPLEMENTATION

R. E. Frisbie Integrated Pest Management Coordinator Texas A&M University College Station, TX 77843

J. R. Phillips Entomology Department University of Arkansas Fayetteville, AR 72701

W. R. A. Lambert Entomology Department University of Georgia Tifton, GA 31794

H. B. Jackson Plant Pest Regulatory Services Clemson University Clemson, SC 29631

ABSTRACT Cotton pest management programs that have been demonstrated as effective in Texas, Arkansas, and the Southeast include, respectively: (1) a short-season management system for cotton production, (2) community-wide bollworm management, and (3) improved cotton insect management. Regional strategies developed for each of these geographic areas consist of combinations of techniques that have proved to be economically and environmentally sound. An updated review of these three systems is presented.

Specific tactics for suppression of boll weevils (Anthonomus grandis Boheman) such as early-season insecticidal control of spring emerging weevils, fall diapause control programs, the role and efficacy of diflubenzuron (Dimilin), the role of alternate hosts, and the impact of in-season application of phosphate-type insecticides on beneficial

522 R. E. FRISBIEETAL

arthropods are reviewed. The merits of these individual tactics are compared with those of tactics employed in the Boll Weevil Eradi- cation Trial conducted in North Carolina and Virginia, 1978-80.

Logistical constraints to beltwide implementation of a boll weevil eradication or management program are discussed. Constraints considered are cost of implementation, personnel needs, the role of independent consulting entomologists, conduct of an areawide insecticide spray program, maintenance of weevil-free areas and containment zones, and Federal and State regulatory requirements for such programs.

INTRODUCTION

In this chapter, pest management programs that differ slightly from the programs of the Boll Weevil Eradication Trial (BWET) and Optimum Pest Management Trial (OPMT) of 1978-80 or that are alternatives to those programs are discussed. The emphasis is placed on three: (1) a short-season management system for cotton production that has been tried in Texas, (2) a community-wide bollworm management system for cotton production that was tested in Arkansas, and (3) an improved cotton insect management system for cotton production that could be used in the Southeast. All are considered to be improvements on insect management programs currently available in these areas. In addition, discussion of these systems makes it possible to formulate other possible alternatives. Many of the tactics set forth in the three systems were used in the OPMT conducted in Panola County, MS, and in the BWET conducted in North Carolina and Virginia. It is not assumed that all are applicable to all regions of the United States where cotton is produced. How- ever, review of the tactics broadens one's perspective on other candidate management systems designed for optimal pest suppression.

The second section consists of certain biological inquiries relative to beltwide implementation of the programs used in the BWET and OPMT. These inquiries are not meant in any way to indicate criticism or to supersede observations and conclusions of the agencies and personnel involved in these trials nor the report of the Biological Evaluation Team, the Environment Evaluation Team, and the Economic Evaluation Team. All are to be heartily congrat- ulated for the insight and thoroughness with which they carried out their tasks, sometimes under difficult conditions. However, it is of utmost importance that an indepth evaluation be made of the techniques developed, particularly those that would be used for eradication, as they relate to the various cotton production areas that are infested with boll weevils (Anthonomus grandis Boheman).

MANAGEMENT PROGRAMS AND IMPLEMENTATION 523

For example, optimum pest management is essentially defined by research, extension, and farmers within a certain State or region, and each such group must assess cotton growth conditions and pest situations so an optimum combination of management techniques can be developed. In other words, optimum pest management must vary State by State. In contrast, the techniques used for eradication as in the BWET would have to function as well in all cotton producing areas. Comments and discussion are therefore provided concerning earlier experiences encountered beltwide in testing the various tactics tested in the BWET for beltwide boll weevil eradication. It is recognized that such research tests did not expose boll weevil populations to the areawide suppression achieved in the BWET. Nevertheless, studies of the strengths and weaknesses of the various tactics in the several cotton producing areas are still helpful in gaining more complete knowledge of the suppressive values. The fact that these tactics were not employed sequentially and over a large geographic area is not in itself sufficient reason to reject the information. For example, it is necessary to establish a complete profile of all studies of such tactics as early- season insecticidal control of spring emerging weevils, fall diapause control, the role and efficacy of diflubenzuron (Dimilin), and the role of alternate hosts. (Since many of these studies are discussed in previous chapters of this handbook, efforts have been made to minimize duplication.)

Finally, a section on the logistical constraints on implementation of a beltwide program is provided as a means of reviewing the strengths and shortcomings of the draft plan for boll weevil eradication prepared by Plant Protection and Quarantine, Animal and Plant Health Inspection Service (APHIS), U.S. Department of Agri- culture (USDA), in September 1980. It is recognized at the outset that this plan is in the draft stage and subject to alteration. It is hoped that the discussions will provide insight and direction regarding the proposed use and outcome of the boll weevil eradication plan and needs for improved cotton insect management.

ALTERNATE MANAGEMENT SYSTEMS

Short-Season Management System for Texas Cotton Production

Although the role of breeding for insect resistance, modified cotton culture, and the value of short-season cotton production were discussed in a previous chapter (Chapter 4 of this handbook), pertinent literature and evaluations of short-season production systems in Texas are highlighted in this chapter.

The decade of the 1970's is notable as the period when the mystery of the importance of the "short-season effect" of cotton production relative to boll weevil suppression was described and


finally resolved (Parker et al. 1980). Only after a painstakingly careful review of past research inquiries, trial and error, and an exhaustive study of the intricate relationship between the fruiting pattern of cotton and the population dynamics of the boll weevil were principles set forth that define and elucidate the breeding of cotton cultivars to enhance escape from boll weevil populations. The basic information concerning this relationship arose out of studies by Walker and Niles (1971). These scientists, who were working in recent times, had an advantage that only history can provide re the confrontation of U.S. cotton producers with the boll weevil since the turn of the 19th century. Although Howard (1896) provided early information on the biology, ecology, and control of the boll weevil, Mally (1901), the first entomologist of the Agri- cultural and Mechanical College of Texas, was assigned the task of solving the boll weevil problem after the boll weevil invaded Texas and devastated the cotton plantings in that State. This scientist reasoned quite correctly that it was the cotton plant itself and its growth characteristics that made the crop vulnerable to the attack of the boll weevil. Cottons of this period fruited in a slow and prolonged fashion that allowed a progressive increase in the numbers of boll weevils in succeeding generations and extended the period of plant susceptibility to weevil damage. After studying the matter during several production seasons, Mally noted that the plant and its fruiting characteristics were the keys to man's successful cohabitation with the boll weevil. He stressed a need for early maturing cotton varieties and for areawide destruction of cotton stalks at the end of the season so as to disrupt the normal behavior of boll weevils preparing for winter. Mally's recommendations were considered radical in view of the relative unavailabil- ity of early maturing cotton varieties. Also, mechanical equipment capable of dealing with the large numbers of acres requiring stalk destruction was then in a primitive state. In addition, several months were required then to hand harvest the cotton crop.

Mally's sage advice was ignored at the time; only after some years did cotton breeders finally begin to select cotton genotypes that possessed an early fruiting characteristic (Ware 1925). In fact, it was the development of cotton varieties that possessed this unique ability to commence fruiting earlier and to develop larger numbers of fruit in a shorter time that allowed cotton production to survive in the weevil-infested areas of thé Cotton Belt. Growers could stay in business though production was limited to the first few weeks of fruiting before the large increase in numbers of weevils.

Still, something else was needed because the effective production period was limited to early fruit set. The chlorinated hydrocarbon insecticides that came into use after World War II seemed to be the answer. With them cotton now could be produced by planting long-season indeterminate varieties and could be protected from boll weevil attack by using these broad-spectrum insecticides. This alteration in the type of varieties grown plus increased fertility plus irrigation dramatically increased yields. Cotton


production throughout the rain belt was therefore limited only by the length of the growing season and not by how much could be produced before boll weevil populations reached damaging numbers.

The respite was nevertheless short-lived. By the 1950's, the boll weevil had developed resistance to chlorinated hydrocarbons (Roussel and Glower 1955). Growers responded by using the newer organophosphate insecticides, sometimes mixed with organochlorines. Again, the weevils were neatly controlled. However, the tobacco budworm (Heliothis virescens (F.)) developed resistance to these compounds in the I960's (Adkisson and Nemec 1966). It was also during this time that the cost of insect control and the uncertainty concerning effectiveness of compounds created great concern among Texas cotton producers. As a result, the stage was set for a reordering of the management of insect pests in Texas cottons.

At this point Walker and Niles (1971) elucidated the value of rapidly fruiting short-season cottons for managing the boll weevil since use of these cottons precludes the necessity of treating season long, which enhances the potential for population increase of the bollworm (Heliothis zea (Boddie)) and the tobacco budworm by virtue of the insecticidal destruction of beneficial arthropods. The principles set forward were essentially two and are as follows: "1. Precocity and rapidity of fruiting increases the probability for setting an acceptable fruit load before weevil infestations reach a level that will reduce yield. 2. Early and rapid crop maturity permits early disposal of crop residue, thereby reducing host plant support for diapausing weevils and contributing to a reduction in overwintering populations of the pest. The crop may be harvested and stalks destroyed before the environment forces the weevil to diapause. This would be disastrous to the boll weevil and might relegate the insect to the role of a minor pest."

Although these principles were developed around an experimental cotton genotype, it was only a short time before commercial varieties were available that possessed a rapidly fruiting, short- season characteristic. In fact, the Texas A&M University-Multiple Adversity Resistant (TAM-MAR) cottons were released as commercial varieties in the early 1970's. Subsequently other commercial cottons were developed and released that possessed a rapidly increased fruiting characteristic. These cottons provided a distinct advantage in the management of the boll weevil. The question was why. The stage was set for a study of the reasons for this advantage.

Although it was generally accepted that the newly termed "short-season cotton production system" was economically advanta- geous, factors other than cotton genotype entered into this management system. Parker et al. (1980), from work in the late 1970's, finally pieced together the last part of the puzzle as to why the early, rapid fruiting of cotton served to limit damage by the boll weevil. In a detailed set of experiments in Falls, Frio, and Uvalde Counties of Texas in 1975 and 1976, Parker et al. (1980) studied the relationship between the fruiting pattern of short-season


cotton varieties or indeterminate types and susceptibility to boll weevil damage. The objective of this study was to develop a description of cotton production in the presence of the boll weevil and to achieve an acceptable lint yield (500-750 pounds per acre) without the necessity for late-season application of insecticides. Their results showed clearly that if damaging populations of boll weevils were suppressed long enough to allow for 30 days of blooming, acceptable yields could be expected. Also, study of the susceptibility of bolls to boll weevil damage revealed that a population of 10-day-old and older bolls had a high probability of escap- ing damage. Parker et al. (1980) demonstrated that where numbers of boll weevil punctured squares were kept below 1000-1500 per acre during the period the cotton was in the prebloom stage, a significant delay in subsequent population buildup could be achieved, thereby allowing the critical 30 days of blooming to occur and assuring an adequate yield. The salient point here is that if a fast fruiting cotton is allowed to fruit without encountering an unrea- sonable level of damage from boll weevils through about 30 days of blooming, bolls will have developed to the point (10 days or older) where they are relatively- safe from the attack of later developing weevil generations. In this experiment, treatments with one and three insecticide applications were applied near the time of appearance of the first one-third grown square to keep populations of overwintering boll weevils low during the critical blooming period.

There are several earlier examples of elaborations of short- season cotton production systems in various parts of Texas (Namken and Heilman 1973, Sprott et al. 1976, Heilman et al. 1977). These also involved alterations in plant varieties and row configuration, reduced fertility, and reduced irrigation rates to minimize vegetative growth and prolong the fruiting cycle, all of which served to expand the short-season effect and make the system more robust.

Today, short-season cotton production, as it relates to integrated pest management (IPM) in Texas, consists of two major strategies. The first, the suggested and commonly used practice in the Central Blacklands, Central Texas Coastal Plains, Winter Garden, and Lower Rio Grande Valley, includes: (1) early and uniform plant- -ing of a short-season cotton variety for optimum yield; (2) reduced application of nitrogen and irrigation where appropriate; (3) intensive field sampling (scouting, pheromone trapping, Heliothis spp. M0TH-ZV3 forecasting) for early-season pests such as the cotton fleahopper (Pseudatomoscelis seriatus (Reuter)) and overwintering boll weevils so they can be controlled if damaging levels are anticipated; (4) continued intensive field scouting of key insects and application of insecticides based upon appropriate action levels; (5) use of a harvest aid chemical for desiccation or de- foliation; (6) early harvest; and (7) complete and areawide stalk destruction soon after harvest. This system of short-season cotton production has, in effect, eliminated the need for midseason and late-season insect control in most areas.


The second major strategy involves a cotton production system used primarily in the Rolling Plains of Texas. The spring emergence profile of the boll weevil in this region is predictable from year to year (White and Rummel 1978). Thus uniform delay of planting means that cotton is only marginally suitable for feeding and is not suitable for reproduction for the majority of weevils emerging from diapause and overwintering habitats in the spring. As a result, a high degree of suicidal emergence results. The procedure has received wide acceptance in the Rolling Plains (Boring 1974, Slosser 1978). As a result, uniformly delayed planting, intensive field sampling, selective use of insecticides on small acreages when one-third grown squares first appear, and occasional use of a fall boll weevil suppression program in areas of intense weevil activity generally constitute the short-season cotton production system used in the Rolling Plains. Thus the uniformly delayed planting, in effect, acts as a cultural early-season control measure comparable to the early-season insecticide control used in the southern regions of the State.

Extensive economic and environmental evaluations have been conducted to determine the impact of the strategy of the sh.ort- season cotton production system used in the southern part of the State (Namken and Heilman 1973, Sprott et al. 1976, Heilman et al. 1977, Lacewell et al. 1977, Frisbie et al. 1978, Masud et al. 1981). All have shown common threads of consistency. For example, insecticide use has diminished greatly, and yields have increased. A basic philosophy of the management of cotton insects has therefore emerged from this short-season production system. Essential- ly, insect control relies on varietal and cultural control measures as primary inputs, intensive field sampling, and selective application of insecticides (primarily in the early fruiting stage), and areawide, postharvest stalk destruction. For the most part, farmers generally make a maximum effort not to engage in midseason to late-season insecticide applications for the suppression of insect pests.

Perhaps the best example of areawide implementation of the short-season production system is found in the Coastal Bend of Tex- as. A decline in cotton acreage in San Patricio and Nueces Count- ies that was observed beginning in 1970 (104,900 harvested acres) bottomed out in 1975 (50,400 harvested acres) (Masud et al. 1981). Then with the introduction of rapidly fruiting and early maturing cotton varieties (TAMCOT-SP37, TAMC0T-SP21, and others) in the mid- 1970 's, a turnabout in harvested acreage was observed (236,500 harvested acres in 1979). Presently, in excess of 80% of the cotton varieties planted in the Coastal Bend are the short-season type. Today, the use of short-season varieties in combination with the IPM program previously described has produced a current areawide annual benefit of $29 million with a potential increase of $41 million for the Coastal Bend area (Masud et al. 1981), in part because of decreased costs of production and increased yields.

Ö28 R. E. FRISBIE ET AL

In the case of the second strategy, delayed uniform planting,, the reasoning once again is sound. Weevils that emerge from overwintering in the spring must find a suitable food source and oviposition sites. When the cotton plant has not begun to fruit, nutrition is generally poor, and reproduction is not possible; thus, the boll weevil population declines dramatically. The few .weevils that survive do not increase their numbers until late in the season after the crop is substantially made.

Results from a Fisher County, TX, uniform delayed planting demonstration were quite revealing (Finley and Boring 1978). Prior to the initiation of the study, that is, from 1974 to 1976, an average of 2.1 more applications of insecticide were required in 10 fields with a history of heavy boll weevil infestation than in 10 fields with a history of light boll weevil infestation. However, immediately after the study began in 1977, only 0.3 more applications were required in the fields with a history of heavy weevil occurrence (1.3 application) than in the fields with normally light infestations (1.0 applications). Then in 1978 only 0.2 more applications were needed in the heavily infested fields (0.2 compared with 0). No insecticide applications were required in 1979 for either category of field. Yield comparisons indicated that before implementations of the program, boll weevils reduced yields by an average of 170 pounds of lint per acre (29% in 1974, 32% in 1975, and 31% in 1976) (Boring and Fuchs 1980). After the implementation of uniform planting, the cotton fields in the heavily infested areas eventually experienced increased yields over the lightly infested area of 6.4% (697 pounds lint per acre-heavy v. 655 pounds per acre-light) in 1977 and 72% in 1978 (387 pounds lint per acre-heavy v. 225 pounds per acre-light).

Since uniform delayed planting presumably impacts on about 25% of the Rolling Plains acreage heavily infested with boll weevils, producer savings in yield and insecticide costs were estimated to range from $3.38 to $5.45 million. In addition, producers have increased acreage 51.1%, from 703,700 harvested acres in 1976 to 1,051,250 in 1979 (Boring and Fuchs 1980). In sum, uniform delayed planting plus a short-season management system has been a major factor in acreage increase at a time when other regions of the Cot- ton Belt are going through an acreage stabilization or decline.

The two short-season cotton production systems that have been discussed are well suited to Texas. For example, several short- season varieties (CAMD, Cascot, G&P, Lankart, and Paymaster) are available for commercial use in Texas. The majority of cotton in Texas is grown on upland soils, not on highly fertile delta or river bottom soils. Low rainfall (20-35 inches) restricts the length of the cotton production season. Finally, with approximate average yields of 340 pounds lint cotton per acre, production inputs must be kept at a minimum. As a result, integrated pest management systems have been developed to control insect pests without increasing production cost because the vast majority of Texas farmers cannot afford to engage in a season-long insect control


program involving multiple insecticide applications. However, the two short-season cotton production systems that were designed primarily to control the boll weevil have a spin-off of major importance. Consistent insecticide applications for bollworm and tobacco budworm control are needed on less than 7% of the acreage grown on fertile river bottom or on irrigated production systems (Parker et al. 1980). Natural outbreaks of these pests, that is, outbreaks not induced by insecticidal destruction of beneficial arthropods, now occur only occasionally.

The broad implementation of short-season cotton production systems and other factors have caused a dramatic reduction in in-^ secticide use in Texas (Thomas 1979). Insecticide use on cotton in Texas was at its highest, nearly 20 million pounds, in 1964, de-^ clined to 11.5 million pounds in 1966 and to 9.6 million pounds in 1971, and was estimated at just under 2.5 million pounds in 1976 (Thomas 1979). During this time the total pounds of insecticide applied to cotton (and the percentage of total use on U.S. cotton) remained relatively constant (1964-76) in the Southeast, increased sharply in the Delta, and decreased sharply in the Southern Plains. Thus, insecticide use during these years was reduced 88.2% in Texas with near constant acreage, decreased 13.4% in the Southeast with decreasing acreage, and increased 38.8% in the Delta with only a minimum increase in acreage (Thomas 1979). Cooke and Parvin (Chap- ter 2 in this handbook) provide more extensive and recent information on reduced insecticide costs in Texas as compared with costs in other regions in the United States.

It should be clearly understood that cotton producers in Texas utilize insecticides as the last alternative for control of insect pests. Their primary inputs into insect control are varietal and cultural. As a result of the short-season cotton production systems used on the majority (95%) of the acres in Texas, an ecological stability has been created in a relatively insecticide-independent environment. The greatest spin-off of this system, with a few isolated exceptions, has been that the bollworm and tobacco budworm, which are presently considered the key pests of U.S. cotton, have been reduced to occasional pests in Texas.

Community-Wide Bollworm Management in Arkansas

The concept of insect population management within a cotton ecosystem is not recent in Arkansas. As early as 1924, Isely and Baerg (1924) discussed the value of population surveillance and spot dusting in managing the boll weevil. They found that automatic early-season applications of calcium arsenate failed to effectively control weevils or increase yields, whereas scouting and treating as needed proved quite effective. From this early work, an insect pest management system was developed. Its components were scouting, spot dusting, and an early maturing cotton crop. Later, Lincoln and his coworkers (Lincoln et al. 1963), though following the Isely concept, incorporated changes dictated by the


availability of more versatile insecticides, changes in mechanization, land clearing and cleaning, and further quantification and simplification of the scouting system.

The availability of more versatile insecticides that were often relatively inexpensive provided a means of economically producing a "top crop" of cotton. These tactics added a month to the production season, thereby sacrificing earliness for yield.

Mechanization made it possible to clean out small overwintering sites for boll weevils and led also to more nearly uniform planting dates, which usually obviated the need for spot dusting. The dispersed population of boll weevils, changed cultural practices, and improved mechanization thus diluted the weevil population to the extent that it was below treatment thresholds until late in the season.

As noted, the dilution of the boll weevil populations meant that scouting had to be substituted for spot dusting. However, quantification and simplification of scouting procedures was necessary before the procedure was generally accepted. The modified system is referred to as "Point Sample" (Lincoln et al. 1963). It was adopted because the individual farm was basic to the Arkansas system. Thus the weevil emerged from diapause and infested only a few fields initially. However, as the season progressed, additional fields were infested until all or most all fields within an area were infested. As a result, boll weevil control was practiced on a field-by-field basis.

Still, by 1949, the bollworm had become an annually occurring pest. The scouting system was therefore modified slightly and used to monitor bollworm populations, and insecticide use was recommended on a similar basis, i.e., field by field. Population studies by Arkansas cotton entomologists during the 1950*s and I960's indicated that populations of the bollworm increased steadily during the season with infestations becoming quite heavy by August and September. It was also observed that bollworm populations were different in different seasons and in different regions of the State.

Under the auspices of a multistate IPM research project (Huf- faker Project), an effort was begun in Arkansas to determine why such population increases occur and to develop an improved system of managing the bollworm. The area chosen for the initial study is 25 miles east of Little Rock, has an excellent cotton production record, and is among the most threatened by the bollworm. Research conducted in the area included sampling techniques, surveillance techniques, damage threshold studies, modified life table studies, and a short-range bollworm forecasting program.

By the end of the third year of the study, data had been obtained that indicated the following: (1) long-range bollworm migration did not contribute to bollworm outbreaks during the


3 years of the program; (2) the June populations of bollworms in cotton were sufficient to produce the population levels that were subsequently measured; (3) treatment thresholds could be adjusted upward; (4) considerable progress had been made in developing a bollworm forecasting network; and (5) it was possible to utilize as much as 12,000 acres of cotton as a single field for a bollworm suppression system. Conclusions from the data were that the community, through mismanagement of insect control procedures, had been largely responsible for the bollworm problems encountered.

The data also seemed to indicate that the July population of bollworms might be tolerated without treatment, thus reducing the risk of a damaging bollworm infestation in August. Although there was an element of risk in not treating the July population, it was decided that such a tactic should be proposed to the producers and that with their concurrence the community-wide program should be undertaken. It should be pointed out that from the point of view of researchers, there was considerable reservation about the undertaking. No replication of a 12,000-acre experiment was possible; so data analysis, reporting to the scientific community, and assur- ance that cause and effect were being measured were of concern. The experiment was completely vulnerable to the public eye.

Nevertheless, local farm leaders and Cooperative Extension Service personnel arranged for a meeting with the growers in Febru- ary 1976. The proposed control program was outlined, and a poll was taken to determine grower interest in starting a community-wide program. The response was much better than expected: over 90% of the producers contacted were in favor of the community-wide program.

The principal tactic employed in 1976 was that of treating the entire community of cotton fields as a single field. Scouting procedures were changed to support the tactic as were treatment thresholds. For example, the scouting procedure included a whole plant search for eggs and larvae (which were categorized by size) and a total fruit damage count. The treatment threshold was based on community-wide averages for eggs, larvae, and damage. A predetermined threshold was used that will be refined before publishing the results.

When the predetermined treatment threshold was reached, the community growers were so advised at a meeting arranged by the Ex- tension Service. There the growers were appraised of the situation and told which treatments were recommended though they had the option of using conventional materials Treatment was to begin as quickly as possible. The assessment of results would be made as soon as reentry regulations permitted. In short, a "hard" insecticide was applied very quickly over a rather extensive acreage that was infested by the target pest (Phillips et al. 1980).

The program in 1976 was very successful. Insecticide usage for bollworm control was reduced by 80% (a 10-year average of nine

532 R. E. FRISBIE ET AL

applications reduced to 2). Control was excellent, and no unex- pected insect control problems were encountered. Treatments were made on August 6 and August 27. It required approximately 3 days for the community to be treated. Check fields subsequently showed that failure to treat at the recommended times resulted in populations of at least 16,000 large bollworm larvae per acre, which caused economic loss (Phillips et al. 1979).

Sampling data taken during the course of the study indicated that the magnitude of the July bollworm population depended largely on the density of the June population and how well it was synchronized with the phenological stage of the cotton plant. When cotton had reached a fruiting level of approximately 50,000 flower buds per acre and the larval population was in synchrony, larval establishment was good. If the population was large enough (usually > 1500 larvae per acre), treatments were required in July. Thus, the June population was adequate to produce a subsequent population within the community that would warrant action by the growers. In other words, there are times when a suppressive treatment is necessary in June.

It was concluded that if the June population could be reduced by as much as 50%, it might be possible to avoid any further control program against the bollworm until late August. Obviously, when the June population was quite low, as has sometimes been the case, control action would be delayed until the July population reached a preset treatment level.

Materials that are suitable for a June treatment must be specific so as to protect the beneficial insects that provide natural control of the Heliothis spp. complex. Of the materials currently registered for use on cotton, those that most nearly meet the requirement for an environmentally nondisruptive substance are Bacil- lus thuringiensis (Bactur, Dipel, Thurcide) and Baculovirus heliothis (Elcar). Neither directly affects the naturally occurring control components in the cotton ecosystem. The efficacy of these materials against the Heliothis spp. complex in cotton is poorly understood despite some years of research. However, they clearly do not measure up to an effective conventional insecticide in regard to immediate crop protection. Indeed, neither material provides sufficient levels of protection to warrant serious consideration for use against moderate to heavy Heliothis spp. infestations (Yearian et al. 1980).

On the other hand, the key to an early-season Heliothis spp. control program is population suppression. Action is usually taken at a stage of crop phenology when the need for Heliothis spp. protection, if any, is considerably less than in midseason or late season. Thus, some of the disadvantages of B^. thuringiensis and B^. heliothis are not important in early season. For example, the extended time required for mortality to occur is not as critical because the objective is to remove insects from the population, not

to produce immediate kill. Although improved efficacy would be desirable, 40-50% kill plus the action of the natural enemy complex might be adequate to produce the desired level of suppression.

The program in 1977 therefore included the use of a virus against the second generation of the bollworm (the first-generation population in cotton was too low, < 500 per acre). The virus was applied July 12 on approximately 10,000 acres of cotton in the community at the rate of 2 ounces of the formulated product per acre.

By August 12, the bollworm population had increased to a level that required treatment with a broad-spectrum material. As a result, the community was treated with EPN-methyl parathion or with methomyl. This was the only such application needed except that a second treatment was needed on approximately 1500 acres of late planted, irrigated cotton.

Generally, the data obtained in 1977 support the premise that the use of a material with characteristics similar to those of Elcar will have a sufficient impact on the bollworm population so that a much reduced level of insecticide will be required for the balance of the season. For example, data taken during 1973-75 showed an approximate 15-fold increase in the population from July to late August. In 1977 when the virus was used, the increase was only fourfold (Phillips et al. 1979). Obviously other factors could have been involved, and the effects of the virus were still not known with certainty. It was felt, however, that there was a solid basis for trying a "nondisruptive" material early in the season as part of an areawide bollworm management program (Phillips et al. 1979).

The early-season suppression concept was carried out again in 1978. By late June (June 20), the bollworm population had reached an average of approximately 1200 larvae per acre community-wide. The decision was made to apply the virus against the June population, and 2 ounces per acre of formulated virus were again used. Following treatment, larvae were collected from the fields within the community and held for mortality studies. On the basis of these collections, about 25% of the larvae died from a virus.

Subsequent weather conditions in 1978 precluded the taking of data that would be comparable with those taken in 1977. A severe drought began in early July. Obviously, in such a situation, there was considerable disparity of moisture in different locations and attendant disparity in plant growth and fruiting characteristics. By August 1, community integrity had been lost, and a return had to be made to a field-by-field control program. Also, irrigated cotton required more application of insecticides than did unirrigated cotton. However, the community averaged only five applications of insecticide for the season, and the July to August increase in the population of the bollworm was only fivefold, considerably less than the 15-fold reported for 1973-75.


In spite of the adverse conditions encountered in 1978, the results of the community program were superior to the results of the field-by-field program in a neighboring area. The community averaged five applications of insecticides; the check area averaged 11 applications. Weather conditions and yields were comparable in the two areas.

Unquestionably, the experiment in Arkansas demonstrated the value of the community-wide approach to bollworm management of rain-grown cotton. Insecticide usage was reduced, and yields were maintained or improved. The concept of community control has spread and the procedure is now used on over 75,000 acres of cotton in four areas of the State of Arkansas.

Improved Cotton Insect Management in the Southeast

In the Southeast where the average annual rainfall is approximately 50 inches, high yields of quality cotton are a realistic ex- pectation. However, little cotton acreage in this region can be irrigated, so growers must depend on the vagaries of the rainfall pattern. This dependence means that a full-season production system must be used to achieve high yields and desired quality.

A full-season approach to cotton production puts heavy demands on management resources, and management of insect pests is particularly important. Cotton begins fruiting in May and continues to fruit until harvest, which provides pests an extended opportunity to cause economic damage.

The Heliothis spp. complex, i.e., tobacco budworm and bollworm, poses the greatest threat to cotton in the Southeast. Either H. zea or E. virescens is present throughout the cotton fruiting season, often in large numbers. Populations increase on alternate hosts and move to cotton. The boll weevil too is a major pest of southeastern cotton, especially in more southern areas where winters are often mild. Small field size and abundant overwintering habitat enhance the potential for economic boll weevil infestations.

The tarnished plant bug (Lygus lineolaris (Palisot de Beau- vois)), although only an occasional pest, can be devastating to insect management programs when conditions favor its movement into cotton. Other occasional pests include thrips (Thysanoptera), aphids (Aphididae), cutworms (Noctuidae), beet and fall armyworms (Spodoptera exigua (HÜbner) and S. frugipera (J. E. Smith)), whitefly (Aleyrodidae), spider mites TXetranychidae), European corn borer (Ostrinia nubilalis (Hubner)), loopers (Geometridae), cotton fleahoppers, and others.

Cotton insect management in the Southeast can be divided into two categories: preventive measures and corrective actions. Pre- ventive measures include such procedures as variety selection.


rotation, and fertility management; corrective actions include detection of outbreaks through field scouting, setting of action thresholds, and judicious use of insecticides. Areawide pest monitoring with traps and other survey techniques facilitates selection and implementation of both preventive and corrective management techniques.

Insect Pest Surveys

Blacklight traps have previously been used extensively for monitoring the activity of adult bollworms. A promising alternative is the pheromone-baited trap, which is effective in capturing both bollworm and budworm moths. As trap design and pheromone formulations improve, this survey method should be incorporated into all organized cotton pest management programs in the Southeast.

The "sugar line" survey is another method of determining activity. It involves applying a sugar-water solution to cotton plants in late evening to arrest moths and make identification and counting possible. This procedure is simple and inexpensive, but must be done several nights each week of the fruiting season by someone capable of identifying the various species that are collected.

Grandlure-baited boll weevil traps have been used primarily to monitor movement of overwintered boll weevils into cotton fields in the spring and, to a lesser extent, late-season migration and emi- gration to hibernation sites in the fall. Because of time constraints in late spring, pheromone trapping of boll weevils is the preferred method of timing the pinhead square applications of insecticide.

Other survey techniques are being developed for cotton insect pests including plant bugs, fall armyworms, and others. These techniques will not replace field-by-field inspections, but will alert growers and scouts to potential outbreaks.

Preventive Insect Management

Total crop management is the term used to describe a production system that includes insect pest management. The goal of current cotton production systems is to maximize profits by obtaining optimum yields and quality with minimum essential inputs. There- fore, insect control costs are reduced by incorporating certain management practices into the production system. Since production systems vary in different States and even within States, insect management strategies vary similarly.

Cotton varieties are being developed that incorporate insect resistant characters; for example, frego bract, glabrous stems and leaves, red color, and nectariless leaves and fruit.


Currently, only the nectariless character has been used in a commercially grown variety, and it is widely planted in areas where plant bugs may be damaging. Determinate and semideterminate varieties are gaining acceptance because they can reduce the fruiting period and thereby reduce the length of time that cotton is susceptible to insect pests. However, the need for the flexibility of a full-season cotton limits the use of the more determinate varieties to situations involving double-cropping systems and irrigated fields.

Fertility management is used to minimize the attractiveness of cotton to pests and to reduce the fruiting period. Excessive nutrients (especially nitrogen) produce rank growth, poor fruiting, and increased insect pest problems. Yet cotton producers are inclined to apply more fertilizer than necessary to insure an adequate supply under extreme environmental conditions. Nitrate monitoring through leaf petiole sampling and analysis enables growers to apply minimal rates of nitrogen to the soil and to supplement nitrate requirements with foliar applications of urea according to test results.

Planting dates for cotton in the Southeast depend on several factors including weather, alternate crops, and anticipated insect problems. Uniform, early planting reduces the threat from increasing late-season populations of boll weevils and Heliothis spp. Later planting can be used in an insect management program based on a shortened fruiting period, but then fertility and water management are critical.

Stand density and row pattern can be adjusted to reduce pest pressure according to the anticipated pest pressures and climate. Where thrips and other seedling pests are easily managed but plant bugs are a potential threat, lower seeding rates can be used to discourage Lygus spp. infestations. Higher rainfall areas that experience excessive vegetative growth can utilize modified skip-row patterns. Since the plant canopy tends to remain open later in the season when skip-row patterns are used, competition for light and other requisites slows growth, thereby reducing boll rot and increasing penetration of insecticide sprays.

Trap crops have also proved effective in managing the boll weevil but have met limited acceptance by growers. Such strips of cotton are planted several weeks before the remainder of the field. As a result, emerging overwintered boll weevils are concentrated in the strips, and only a small portion of the field must be sprayed, thereby sparing the majority of the population of beneficial insects.

Use of pinhead square sprays is another effective way to reduce populations of overwintered boll weevils. These consist of low rates of organophosphate insecticide applied to cotton prior to


the initiation of fruiting to prevent the oviposition that would produce subsequent generations during the fruiting period. Pinhead square sprays are most effective when peak emergence of overwintered boll weevils occurs prior to fruiting.

Diapause boll weevil control involves reducing the number of boll weevils that enter hibernation by applying insecticides after cotton matures and regular sprays are terminated. The diapause control method is not successful when practiced on an areawide basis. The primary obstacle to this management tool is grower uncertainty concerning planting intentions the following spring.

Corrective Actions

Despite preventive management, pest outbreaks regularly occur in southeastern cotton. However, the severity of outbreaks varies considerably, and the necessity for corrective actions must be determined for each situation. The decisions are based on the knowledge of pest conditions gained through field scouting and a familiarity with natural mortality factors and applied controls.

Biological control of cotton insect pests in the Southeast depends largely on conserving natural enemies. Parasites and predators play a significant role in suppressing infestations of major pests such as tobacco budworm and bollworm when insecticides are used judiciously.

Action thresholds (economic thresholds) have been developed for most cotton insect pests. These thresholds serve as a starting point for decisions on the need for insecticide applications. Thresholds must be adjusted by considering plant growth stage, weather, beneficial insect populations, pest species, value of crop, and cost of control.

The use of chemical insecticides is the primary method of correcting pest outbreaks. Since chemical applications often cause secondary pest problems, sprays should only be applied as needed to prevent certain economic loss. The use of selective insecticides and of minimum rates that are adequate against specific pests and infestation levels reduces costs and is less likely to disrupt natural control systems.

Regular inspection of fields is the only proven method of determining the need for corrective actions for all the potential insect pests of cotton. Field scouting is best done by specially trained individuals employed by cotton producers. Scouting services are offered by individuals, private consulting firms, and grower-owned organizations. The southeastern land-grant universities provide training and technical support through the Cooperative Extension Services and Experiment Stations.


BIOLOGICAL INQUIRIES AND CONSTRAINTS TO BELTWIDE IMPLEMENTATION OF BOLL WEEVIL ERADICATION AND OPTIMUM PEST MANAGEMENT

Biological Evaluation of Techniques

A discussion of the techniques employed in the implementation of beltwide boll weevil eradication and optimum pest management is presented here. However, the mass rearing, release, and efficacy of sterile boll weevils as a control component are reviewed in Chapter 11 of this handbook and consequently will not be discussed. It is very important that the biological strengths and weaknesses of the various techniques used in the BWET and OPMT and in other relevant studies be evaluated on the basis of the experience gained. Eradication assumes elimination; i.e., reduction to zero of the boll weevil in the infested portion of the Cotton Belt. Anything less would simply allow the problems of the past to recur. Eradi- cation places an unusual responsibility on one who might chart such a course, a responsibility not met by achieving 95% or 98% population suppression. Therefore, it is important that any weak- ness in the proposed technology for eradication be discussed. For our basis of reference we will use the specific control techniques proposed in the preliminary draft of the boll weevil eradication plan prepared by Plant Protection and Quarantine, APHIS, USDA, Sep- tember 1980. Again, it is recognized that this is a draft and that alterations can be made, but the point of the following discussion is to comment on the biological impact and feasibility of the fundamental suppression techniques suggested. In addition, the strengths and limitations of optimum pest management will be discussed with the view that this strategy is designed to suppress and maintain boll weevils below economically damaging levels.

Fall Diapause Insecticide Program

The application of insecticides in the fall for the control of prehibernating weevils (diapause control) has proved effective in suppressing weevil populations in the subsequent season, thus minimizing the necessity for in-season insect control. This method of boll weevil suppression has been most widely used in west Texas and was refined there as a result of the largest diapause boll weevil control program undertaken in the United States, the High Plains Boll Weevil Suppression Program. In 1964, an areawide fall boll weevil control program was initiated in eight counties on the southern and eastern edge of the High Plains. The objective was to prevent the westward spread of the boll weevil into the single largest cotton growing area in the United States, the High Plains of Texas. Excellent program organization, coordination, and cost sharing between Plains Cotton Growers, Inc., the Texas A&M Univer- sity, the USDA, the Texas Department of Agriculture, and the Texas Technological University provided an organizational framework and financial base for the implementation of this large-scale program. In addition, there was somewhat restricted availability of


favorable overwintering habitats and high boll weevil mortality resulting from low winter temperatures along the western edge of the test area. Approximately 295,000 acres of cotton were treated an average of 3.9 times at 10-14 day intervals with 16 fluid ounces of ultra-low-volume malathion in 1964. (Rummel et al. 1975).

In 1965, the program was revised into a two-phase program that was continued in 1966 and 1967. Due to budgetary restrictions, fields with light or moderate populations received limited treatment and in some instances no treatment, and fields were not treated until the survey indicated that a certain infestation level had been reached (Rummel et al. 1975). This selective treatment was continued until 1974 when it was realized that adequate suppression was not being achieved. Since that time, all infested acreage within the suppression zone has been receiving insecticide applications. Meanwhile it has been shown that the boll weevil is capable of surviving on the High Plains. Nevertheless, the large-scale application of boll weevil diapause control has successfully pre- empted establishment of the boll weevil in the High Plains of Tex- as, and as a result, substantial losses of High Plains cotton have been prevented.

Also, in the St. Lawrence Valley area of West Texas, which is well isolated from other infested cotton, a fall boll weevil control program has been used effectively since 1968 (Neeb and Cole 1973). This program was designed to be responsive to the fluctuations in boll weevil populations between the various production seasons. One hundred percent of 20,000 acres was treated for diapause control in 1968-70. As a result, the boll weevil was successfully controlled, the number of acres requiring fall treatment dropped to 1200 in 1971, and in-season control could be virtually eliminated (the overall goal of the program). However, the boll weevil possesses the unique ability to resurge and increase in abundance. The weevil resurged in 1973-75, and the entire acreage had to be treated in 1975 and 1976.

This occurrence, like similar occurrences in the High Plains Boll Weevil Suppression Program, was thought to be primarily the result of successive mild winters in 1974 and 1975. Still, the St. Lawrence Valley program has demonstrated that despite fluctuations in weevil populations from year to year and the tremendous potential of the population to rebound, a technically well designed program with 100% grower participation can effectively manage the boll weevil by utilizing this technique.

An important factor in both of the Texas diapause control programs was their cost-sharing features. The High Plains program was cost-shared by growers and USDA-APHIS. The St. Lawrence program was cost-shared by growers and the Texas Department of Agriculture. Such cost-sharing provided a strong incentive for program implementation and continued maintenance.


In contrast, the several fall boll weevil control programs conducted in south Texas have been relatively limited in success. In the programs conducted in 10 counties in 1969, 5 counties in 1970, 4 counties in 1971, and 1 county in 1976-80, nearly all had a cost-sharing incentive. However, the environmental parameters of south Texas, i.e., mild winters and abundant overwintering habitat, are more favorable to successful overwintering by weevils than the harsh conditions of west Texas. In addition, the warm spring and summer temperatures mean that the weevil has a higher biotic potential in this area than in other cotton producing areas of Texas (Rummel and Frisbie 1978). Indeed, the south Texas conditions seem to be somewhat similar to the conditions in the more southern cotton producing areas in the United States. For example, freezes in south Texas and generally throughout the South do not occur until well into winter, so it is necessary to supplement a fall diapause control program with complete and areawide postharvest stalk destruction. Also, inclement fall weather disrupted several diapause control programs in south Texas.

Fall boll weevil control has received limited acceptance beltwide to date. Producer acceptance in Texas has been far greater than in other States, though this control method has been used in some areas outside of Texas. Lloyd et al. (1972) reported on a successful grower-sponsored program conducted in Monroe County, MS, in 1969. By utilizing a "reproduction diapause" control technique as the major component of the program in this Midsouth area, the growers achieved a high level of population suppression. However, the greatest use of the fall diapause technique occurred in the early 1970's when an estimated 1,754,739 acres of cotton in several southern States received fall treatments of insecticide (Thomas 1974). The treatment was used mostly in Arkansas, Louisiana, and Texas though there was limited use in Alabama, North Carolina, South Carolina, and Tennessee, but most programs except those in Texas and South Carolina consisted of a single treatment of insecticide applied with a defoliant. Cooperative Extension Service entomologists reported (personal communication) that little benefit was realized from a single application of insecticide applied with a defoliant. Since then, the number of fall programs for the suppression of the boll weevil has, by and large, decreased. However, a well-coordinated fall program was conducted in the south Missis- sippi Pilot Boll Weevil Eradication Experiment in the early 1970's, and in the BWET, the fall program was a suppression component.

It is suggested, the experience gained with this method of boll weevil management shows its strength. However, in milder and more moist areas of the South, this control technique has limitations, even under highly organized pest management programs.

Insecticidal Control of Boll Weevils Emerging in the Spring

The use of insecticides to suppress the population of overwintering boll weevils that enters cotton when plants are in the


squaring stage was first suggested by Ewing and Parencia (1949). Such treatment of a 10 -mile area in North Carolina did, in fact, delay the development of the boll weevil population (Mistric and Covington 1968, Mistric and Mitchell 1968). Sprott et al. (1976), in a review of Walker's short-season, narrow-row cotton production system, subsequently discussed the use of spring insecticide applications to delay the development of subsequent boll weevil populations. Parker et al. (1980) utilized this system in a short-season production scenario to delay boll weevil increase and to allow sufficient time for the safe development and maturation of fruit. The use of insecticide applications directed at overwintering adults entering cotton has proved to be an effective tool in Texas and in other areas of the Cotton Belt that are infested with boll weevils (personal communication. Extension entomologists 1980). Also, this so-called "pinhead" square application had limited use in the 0PM Trial. Rummel et al. (1981) have now developed an index whereby grandlure-baited pheromone traps are used to obtain an indication of which fields require treatment. By utilizing the catches in these traps as an index, Rummel suggests that it may not be necessary to treat an entire area; only selected fields need be treated as indicated by the trapping index.

The suppression of overwintering and spring emerging adults has proved to be beneficial in both short-season and long-season cotton production. However, care should be taken in applying early-season insecticide to avoid eliminating beneficial arthropods that subsequently suppress bollworm/tobacco budworm populations. If insecticides are applied within 10-14 days of the bloom stage, there is a high probability that beneficial insects will be destroyed, and cotton will be left vulnerable to bollworm/tobacco budworm attack. The draft of the boll weevil eradication plan suggests that four applications of diflubenzuron (Dimilin) be made (7- day intervals) to fields infested as indicated by trap catches. These applications would then be followed, if necessary, by a single application of azinphosmethyl (Guthion) as a cleanup treatment, but this treatment would occur during the bloom period. Although the plan states that the diflubenzuron and azinphosmethyl treatments will be applied in an effort to reduce, "insofar as possible," the probability of destroying beneficial insects and inducing a bollworm outbreak, such a procedure would still be extremely hazardous. It might have less impact in those cotton producing areas that normally treat for bollworm/tobacco budworm infestations; however, those areas that routinely do not apply insecticides for bollworm and tobacco budworm, but rely primarily on beneficial arthropods for control, would be placed in jeopardy. For example, throughout most of Texas where the short-season, low insecticide input systems are used, a serious problem could be created that could force farmers to apply additional insecticide to control the Heliothis spp. complex. The economic situation in these production areas is not sufficiently robust to allow for this additional expenditure, a fact well understood by farmers of the area.


Role and Efficacy of Diflubenzuron

The role and efficacy of diflubenzuron is discussed in Chapter 9 of this handbook. However, a brief summary of pertinent literature is presented here along with a discussion of the utility of this compound in weevil control programs. This insect growth regulator has shown activity against the boll weevil; for example, it has been reported to be effective in suppressing boll weevil populations in tests conducted in North Carolina, South Carolina, and Arkansas (Taft and Hopkins 1975, Ganyard et al. 1977, Lloyd et al. 1977, Ganyard and Bradley 1978). Also, studies by Abies et al. (1980b) and Keever et al. (1977) indicated that Dimilin is generally less detrimental to beneficial arthropods than conventional insecticides.

However, tests of the effectiveness of Dimilin in suppressing boll weevil populations conducted by Rummel (1980) in the Rolling Plains, Abies (1980b) in the Central Texas River Bottoms, Cole (1980) in the Upper Gulf Coast, and Harding and Wolfenbarger (1980) in the Lower Rio Grande Valley showed varying degrees of effectiveness. Generally, the highest level of reproductive suppression occurred with higher application levels directed against light weevil populations. The poorest results were reported in the Lower Rio Grande Valley study: there was no significant difference in reproduction suppression between treated and untreated plots having moderate to heavy populations (Harding and Wolfenbarger 1980). Later in the season after 35% of the squares were damaged, migration may have accounted for the poor results; however, results were not significantly better before the onset of migration. Likewise, in the Upper Gulf Coast study, average adult emergence in the treated fields never fell below 43% under light boll weevil population pressure (Cole 1980). On the other hand, under heavy boll weevil infestations in west Texas and with rates of 1.0 and 2.0 ounces active ingredient (Al) per acre, average adult emergence in treated plots was about 40% compared with an average emergence of 73% in untreated plots (Rummel 1980). Under a light infestation in the same area, the average adult emergence reported was only 13.4% for the 10 ounce AI rate per acre and 9.2% for the 2.0 ounce AI rate. Also, in the test conducted in the Central Texas River Bot- tom, substantial suppression of reproduction in treated fields was noted (Abies et al. 1980b): weevil mortality in fields treated with Dimilin at rates of 0.5, 1.0, and 2.0 ounces AI per acre averaged 46.4, 67.4, and 77.3%, respectively.

Thus suppression of reproduction was obtained with diflubenzuron in the Texas studies, but the degree of suppression achieved generally did not approach the degree reported from tests in other States. In general, the heavier boll weevil infestations encountered in Texas could have accounted for the difference in suppression (Rummel 1980). However, the results of the Texas studies indicate that one might have difficulty in controlling even light to moderate infestations of boll weevils with diflubenzuron. Therefore, special management practices are indicated for the


effective use of this material. It is suggested that diflubenzuron is best applied at the pinhead square stage of cotton, or earlier, before weevil oviposit ion begins. Also, diflubenzuron would have to be applied at regular intervals, every 5-7 days, for an extended period to maintain control. In years of moderate to heavy boll weevil population pressure, it would be necessary to supplement diflubenzuron applications with applications of a conventional insecticide.

Because of erratic results obtained with diflubenzuron in the several multiple-year studies that have been made, the material is not recommended for use in pest management systems at present (Ex- tension entomologists, personal communication). (An optimistic but speculative view of its use is presented in Chapter 9 where the authors suggest the utility of diflubenzuron as a multiple application, early-season boll weevil suppressor in a short-season cotton production system.) Even if diflubenzuron were effective, it is questionable whether producers would be willing to pay the excessive costs of material and application in view of the lower costs of conventional materials applied fewer times. Further refinement and study are necessary to determine the role of diflubenzuron in a pest management program (Extension entomologists, personal communication).

In-Season Application of Phosphate-type Insecticides for Boll Weevil Control

The preservation of entomophagous arthropods is central to a balanced IPM program. Therefore, the use of phosphate-type insecticides directed at the boll weevil in-season, that is, beginning near the bloom period, imposes an element of risk. As noted in Chapter 5 in this handbook, the risk of destruction of beneficial arthropods that play a key role in the suppression of Heliothis spp. and other pests is ever present. The point here is that the risk entailed in artificially releasing Heliothis spp. from the biological control of beneficial arthropods must be carefully assessed. We thus come again to the risk involved, particularly in large acreages of Texas cotton, where great care is taken to minimize the use of phosphate-type and other insecticides just prior to and around the bloom period. Indeed, one of the special advantages of short-season cotton production systems is that they are basically geared not to become involved in insecticide treatments for Heliothis spp. populations; thus insecticide applications are carefully applied so as to vastly minimize risk of Heliothis spp. outbreak. A question arises: What is the risk and how detrimental will it be if an application of azinphosmethyl is required after diflubenzuron in applied near the bloom period? The matter is serious since it impacts greatly on approximately 3.75 million acres of cotton produced in Texas and on additional acreage in other cotton producing States where efforts to conserve natural enemies of the bollworm are a high priority.


Impact of Alternate Hosts on Eradication

Cross et al. (1975) provided an extensive review of the literature on host plants of the boll weevil. Malvaceous species that have been implicated as possible hosts of the boll weevil in south Florida (Gossypium hirsutum L. var. punctatum (Shum. and Thonn.) Roberty, Thespesia populnea (L.) Soland.x Correa, Cienfuegosia yucatanensis Mills p., and Malvaviscus drummondii Torr. & Gray) are presumed to be sufficiently isolated from present populations of boll weevil so they have low probability of becoming infested and sustaining an incipient boll weevil population. Thespesia populnea was found by Luke fahr (1956) to be infested in Browns- ville, but this ornamental tree may be only a sporatic host of the boll weevil. Cross et al. (1975) concluded that Sphaeralcea angustifolia (Cav.) G. Don. and other related species of the genus may only occasionally serve as boll weevil hosts in desert and semi- desert areas of Texas and the western States. Hibiscus syriacus L., a frequent and popular dooryard planting in the South and Southeast, has only been recorded as being infested when grown adjacent to infested cotton (Parrot et al. 1966). The boll weevil has been reported as feeding on, but not reproducing on, the flowers of yellow woolywhite (H3mienopappus flavescens Gray) during May and June in the Rolling Plains of Texas (Rummel et al. 1978).

It appears that the most important persistent alternate host for the boll weevil in the United States is Cienfuegosia drummondii (Gray) Lewton, which is distributed throughout the Coastal Bend region of Texas. This plant apparently has the ability to sustain low level, incipient boll weevil populations at some distance from cotton. Therefore, it would be wise to consider suppressing the boll weevil in this alternate host if eradication is attempted.

LOGISTICAL CONSTRAINTS ON BELTWIDE IMPLEMENTATION OF BWE AND 0PM

Logistical problems frequently create the most nagging constraints on the implementation of large-scale projects. One such problem, cost of eradication, should therefore be seriously considered. Although the draft plan for boll weevil eradication contains a carefully considered analysis of the costs involved in the eradication of the boll weevil, special care should be taken so that cost estimates (particularly in personnel, production of mass- reared sterile weevils, maintenance of weevil-free areas, and the maintenance of a containment zone to prevent boll weevil reentry) are calculated as precisely as possible.

Cost of Implementation

Cost estimates in the draft boll weevil eradication plan are based on the 1979 cost of the BWET. However, boll weevil infestations in both the BWET and OPMT areas were considered very light in 1977 and 1978, and light in 1979 (Science and Education Adminis- tration 1981). This biological occurrence is favored in the


evaluation zones in regard to costs. A question then arises: would there be a cost increase in eradication if weevil populations were moderate or heavy? More specifically, are costs underestimated for beltwide implementation because they are based on cost estimates for a situation characterized by very light weevil populations?

Cost for rearing and sterilizing weevils has been estimated at $2 per thousand with additional dispersal costs of $2 per acre. Sterile boll weevils used for release in the BWET were reared at the USDA-ARS Gast Rearing Laboratory at Mississippi State, MS. A question arises concerning the increase in demand for sterile weevils needed for an areawide eradication plan. Will the Boll Weevil Laboratory be able to rear a sufficient number of weevils to accommodate the eradication? If not, will an additional facility(ies) be required, and what additional cost and time will be involved in constructing this new facility(ies)?

Reference must be made to the establishment of a containment zone at the Mexico-United States border or running north-south along the western boundaries of Arkansas and Louisiana and the eastern edge of Oklahoma and Texas in a relatively cotton-free area. If technology is available to develop an effective barrier zone to prevent spread of the boll weevil into uninfested cotton, careful consideration must be given to the cost of the establishment and maintenance of this area. Costs of a containment program would continue, essentially, into perpetuity. The agencies and others responsible for encumbering these costs must be identified.

Should an eradication plan be implemented, the question arises as to the benefits that would be realized by the farmers involved in the program as it is implemented, presumably from east to west. Those farmers who have been involved in an eradication phase will have a distinct economic advantage over those who are still required to control the boll weevil by conventional means. This will place farmers in the weevil-free area at a distinct advantage over those in infested areas (L. D. Anderson, past President, Texas Asso- ciation of Cotton Producers Organizations, Lubbock, TX, personal communication). It is anticipated that after eradication and in the absence of the boll weevil, production costs for insect control would be decreased. However, the time frame for beltwide eradication is estimated at approximately 9 years during which a favorable economic position would be enjoyed by a certain percentage of the U.S. farmers in the weevil-free area.

Second, and possibly of greater significance, an increase in acreage could come about as a result of government cost-sharing of control costs during the implementation phase. Increased planted acreage resulting in an increase in supply of cotton, depending on market conditions, could drive the market price of cotton down (W. Hart, Executive Officer, Southern Texas Cotton and Grain Producers Association, Victoria, TX, personal communication). Further, if the containment zone should be established along the eastern edge


of Texas and Oklahoma instead of on the United States-Mexico border, farmers in Texas and Oklahoma could be placed at a long-range economic disadvantage because of the need to deal independently with weevil control costs.

Indeed, it is not clear how a containment zone in Texas and Oklahoma would function. If it is assumed that eradication is to take place over the entire weevil-infested area, why would this area be selected? What would be the cost associated with controlling the weevil over the large acreages of Texas and Oklahoma if reinfestation occurred? Biologically, what would prevent reinfestation of the weevil from Mexico into Texas and Oklahoma, a buildup there in numbers, and an overrun of the containment zone? The only reasonable location for a containment zone would be along the United States-Mexico border.

Then there is the matter of utilizing available Cooperative Extension Service personnel and others from land-grant universities to provide technical and supervisory support for an eradication program. Costs associated with involvement of the time and facilities of universities cooperating with beltwide implementation should be calculated as part of the total cost of the program. Frequently, similar hidden costs that are not included, but assumed, do not appear in an overall cost estimate. These should be identified and included as legitimate costs of implementation.

Beltwide boll weevil eradication costs have been estimated by USDA-APHIS. The most recent estimate is $483 million though costs are increased to $569 million if an optimum pest management program precedes the beginning of eradication. It is interesting that a Stanford Research Institute study contracted for by Cotton Incor- porated to estimate costs of beltwide boll weevil eradication in the early 1970*s, that is, following the south Mississippi Boll Weevil Eradication Trial, gave a high cost of $2.46 billion and a low cost of $1.11 billion when the figures were corrected for in- flation and undiscounted (Peter Stent and Andrew Korsack. Refined Cost Estimate for Beltwide Eradication of the Boll Weevil. Stan- ford Research Institute Project No. 2372. Unpublished report, August 31, 1973).

This discrepancy between the cost projected by an independent study group and by USDA-APHIS gives rise to several questions. USDA-APHIS responds by saying that technology for eradication has improved and that diflubenzuron is now available. However, cost estimates were higher about 1.5 years ago before it was shown that diflubenzuron was not as effective as originally assumed. Since then, cost estimates have decreased. This discrepancy leads one to question the origin and accuracy of the USDA-APHIS figures. They appear to be alarmingly low, and if so, are misleading relative to the cost of this massive proposed program.


Personnel Needs

The need for qualified professional and paraprofessional personnel is always a problem when one is implementing large-scale management programs. As an example, there has always been a need for well-trained and qualified supervisory and scouting personnel in the ongoing pest management programs that have been underway throughout the boll weevil infested area of the Cotton Belt. In personal communications with Cooperative Extension Service entomologists, it was found that the number of available scouts frequently limited the number of acres that could be included in the particular State's pest management program. Particularly in Texas, implementation of a beltwide program would require excessively large numbers of scouts. The identification, training, and supervision of these scouts by qualified personnel is viewed quite real- istically as an identifiable constraint. Further, even if such paraprofessionals (scouts) could be identified, the Cooperative Extension Services frequently have a problem because of the difficulty of retaining scouts long enough to participate in the entire program. In any beltwide effort, a minimum of 4-6 months would be required to cover the spring, in-season, and fall activities. The most reliable scouts have been found to be college age students (Extension entomologists, personal communication), but because of conflicting schedules, students oftentimes have to return to class before the end of the production season; and in the southern lati- tudes, the ability of college students to participate in a scouting program in the spring is hampered by their need to complete spring semester classes. Nothing is more important to an areawide program than highly qualified paraprofessionals who can collect the pertinent field information season long. Without this vital ingredient, any program is severely handicapped.

Role of Independent Consulting Entomologists

The role of the independent consulting entomologist should be considered in any beltwide implementation plan. Consulting entomologists who participate in pest management programs in their capacity as business consultants should have a clearly defined role in the plan. It has been estimated that approximately 1000 independent consulting entomologists are in business within the boll weevil infested area of the Cotton Belt (E. S. Raun, personal communication). These consultants have been valuable in the dissemi- nation of vital, high quality information to farming clientele. No other private group has had more impact on the implementation of IPM than the independent consulting entomologist. High priority should be placed on developing an agreement with independent consultants, possibly a contractual agreement for their services, as an integral part of any plan.


Conduct of an Areawide Insecticide Spray Program

Perhaps the most experience in an areawide, intensive insecticide spray program was gained in the High Plains Boll Weevil Sup- pression Program (Rummel et al. 1975). The earlier discussion of the fall diapause insecticide program explained how this large- scale program effectively stopped the westward spread of the boll weevil into the High Plains of Texas. In this program, the primary technical component was the areawide application of insecticides to reduce the numbers of potentially overwintering weevils in several hundred thousand acres of cotton. The intensive organization and administration of this project by USDA-APHIS, Plains Cotton Grow- ers, Inc., and Texas A&M University clearly showed the logistical magnitude of such an operation. However, the perennial constraints. . .problems with intensive field mapping, trapping, field inspection, contracting for chemicals and aerial application, and precise application of insecticide on target fields...were overcome in this project. Much is to be learned from this experience as it relates to any areawide insecticide spray program.

A matter of critical importance when an insect species is to be eliminated from identified target fields is application of the appropriate rate of chemical at the appropriate time with a guarantee of adequate coverage of the target area. Wind speed, aircraft height, nozzle pressure and arrangement, and working conditions are all factors that must be considered. Excellent experience in this was gained in the High Plains Boll Weevil Suppression Program and in the North Carolina BWET. As a result, a prototype of coordination and logistics has been worked out.

Maintenance of Weevil-Free Areas and Containment Zones

The very rapid extension of the range of the boll weevil during the first years of its invasion of the United States is strong testimony to the dispersal ability of this insect. Long-range, late-season dispersal, frequently termed migration, has been the major reason for the expansion of the boll weevil into previously uninfested cotton (Bottrell et al. 1972). This behavorial. phenomenon is cited as probably the most powerful weapon that the boll weevil possesses. Certainly the ability to migrate comparatively long distances has allowed the insect to continually invade new territories and to reinvade old territories that have been temporarily cleared of this pest (Bottrell et al. 1972). Some evidence of the long-range mobility of the insect was provided by a catch in male-baited wing traps located between Juarez and Chihuahua, Mexi- co, in 1968: 15 boll weevils were captured on 49 of these traps though the traps were 25-45 miles distant from cultivated cotton (Davich et al. 1970). Also, after weevils were released in South Carolina during midseason, the F, through succeeding generations were trapped at least 19 miles away from the point of release (Roach and Ray 1972). In addition, a weevil marked and released at McBee, SC, in late June 1980 was captured in Candor, NC, a distance


of approximately 65 miles (W. A. Dickerson, USDA-ARS, personal communication). Such late-season dispersal of the boll weevil represents a potential constraint on the establishment and maintenance of weevil-free areas and containment zones.

Finally, relatively little attention has been focused on the requirements for the development and maintenance of boll weevil containment zones though experience gained from previously discussed boll weevil suppression programs should provide some clues. Presently, it is suggested that in a containment zone there should be a fall diapause program supplemented by intensive trapping and survey. These procedures would then be followed by a regulatory program to prevent movement of potentially infested items, as in the program in effect against the pink bollworm (Pectinophora gossypiella (Saunders)). These tactics may quite adequately keep the weevil from moving into uninfested cotton; however, if elimination of the weevil is the goal, consideration should be given to gaining a greater understanding of requirements of the containment zone. It is assumed that the weevil will be substantially suppressed through the implementation of the eradication strategies and that procedures in the containment zone should suffice to suppress the weevils to such low numbers that reinfestation will be unlikely. However, historically, fall boll weevil suppression programs used in conjunction with survey traps have not been sufficient to eliminate or contain the weevil from season to season (Rummel et al. 1975).

In view of the reproductive potential of the boll weevil and its long-range migrating ability, consideration should also be given to other suppressive techniques that could be utilized within a containmment zone. These include uniform planting and postharvest destruction dates, use of short-season cotton varieties, and early-season suppression of spring emerging adults. The question arises: how effective will these tactics be singly and cumula- tively in the maintenance of a containment zone? Except for past experience with a limited number of these tactics, little information exists on the cumulative effect of such strategies in containing boll weevil populations. Probably additional information should be developed to more clearly define the needs and limitations of a boll weevil containment zone. These comments reflect no intention to minimize any past efforts at boll weevil suppression; they are only meant to assist in a better description of the technical components necessary to maintain a containment zone.

But there is still another matter. Assuming elimination of the boll weevil, the maintenance of weevil-free areas will pose a problem. The plan for implementation suggests that should spot infestations occur directly after implementation within a particular zone, populations will be eliminated immediately by a special group of personnel involved in the implementation effort. However, if spot infestations occur after the completion of the implementation phase, individual States will presumably be responsible for eliminating these infestations. It is therefore recommended that a


series of techniques should be developed to deal with this potential problem and the associated costs. This has not been done. It is of critical importance that weevil-free areas be maintained and spot infestations be identified before weevil populations can build and expand into uninfested cotton. A great deal of attention should be placed on contingency plans for dealing with such an occurrence.

Federal and State Regulatory Requirements for Boll Weevil Eradication

The first basic regulatory requirement for any suppression, containment, or eradication program involving an economic pest is to enact legislation that establishes authority for conducting the program. Such legislation is essential at the Federal and State level for the enhancement of cooperative efforts. The secondary requirement is passage of a referendum specific to the boll weevil program.

Legislation already exists at the Federal level and in some States, namely, North Carolina, South Carolina, Texas, and Vir- ginia, regarding the boll weevil beltwide program. All other States in the weevil-infested areas of the Cotton Belt must enact similar legislation before a program can be initiated. These States are Alabama, Arkansas, Georgia, Louisiana, Mississippi, Missouri, Oklahoma, and Tennessee.

Special regulatory requirements, previously outlined in the respective action plans for the BWET and the OPMT, and the necessity for them prior to and during the 3-year life of the program in a given area, were explained as follows (National Cotton Council Technical Subcommittee 1973):

"(1) Authority to establish suppression and elimination zones for the boll weevil. Because of the complexity and size of the area involved, costs, logistics, etc., it is more feasible and practical to implement the program in sections rather than covering the entire infested acreage simultaneously. As the program progresses, certain sections will encompass acreage in more than one state.

"(2) Access and entry authority. During normal program operations such as treatment applications, monitoring, trapping, etc., it will be necessary for Federal, State, and sometimes contractural personnel, to enter cotton fields and adjoining properties in suppression and elimination zones.

"(3) Authority to execute the program on 100% of the cotton acreage. Cooperation and participation by all cotton producers in the treatment zones are essential


ingredients to the success of the boll weevil program.

This authority would insure that necessary activities could be be conducted effectively and efficiently.

"(4) Authority to require reporting of cotton acreage by the grower to insure all acreage is included in

the program. Accurate information on the size and location of all cotton fields, including small patches grown as ornamentals for aesthetic purposes, is paramount in

an eradication program.

"(5) Authority to purchase and destroy cotton which may pose an undue hazard to program objectives because of difficulty in program execution. Field location, size, accessibility and other factors may prevent certain program functions from being conducted. In these instances, it would be better to destroy the cotton and/or indemnify the landowner than risk the possibilities of reinfestation of adjacent areas and ultimate program.failure.

"(6) Authority to prohibit planting of noncommercial

cotton, and prevent volunteer cotton and alternate host plants from jeopardizing program objectives. Strict authority is needed to prohibit ornamental and other noncommercial cotton from being planted. The same holds true for volunteer cotton or alternate host plants to maintain program objectives and continuity."

These same requirements are essential for the conduct of any other boll weevil program. Authority must be provided for in the basic act and set forth in quarantines or regulations promul- gated thereunder. A previous report covers the necessity of each requirement in more detail (National Cotton Council Technical

Subcommittee 1973).

Additional requirements that must be considered are: (1) the interstate and intrastate movement of regulated articles; i.e., the boll weevil, cotton, used harvesting equipment, and alternate host plants, (2) authorization for compliance agreements, (3) authoriza-

tion for penalties for violations, and so forth, that are usually standard conditions and requirements under any quarantine invoked for an economic pest. These requirements are also essential at the onset of the boll weevil program, but would have greater influence once elimination of the weevil from a given sector is imminent.

Those States that have enabling legislation must approve, by referendum, a program authorized by the legislation specific to the eradication requirements. Those States that do not have enabling legislation must both adopt such legislation and pass à referendum. Most State legislatures meet biennially. There must therefore be considerable advance preparation for the development and implemen-

tation of the appropriate necessary legislation.


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271.

INDEX

559

Abdul Matin, A. S. M., 164, 170

Abies, J. R., 103, 114, 120, 121, 144, 207, 215, 216, 217, 223, 229, 231, 349, 552

Acala, M., 552 Acariña, 62 ACNPV (nuclear polyhedrosis

virus of alfalfa looper) has shown promise for control of Heliothis spp., 138-141

Adams, C. H., 105, 121 Adams, J. R., 146 Adelberg, E. A., 298 Adkisson, P. L., 4, 19, 24; 25,

117, 121, 124, 176, 229, 249, 258, 341, 343, 346, 378, 417, 434, 525, 552, 555

Agricultural and Mechanical College of Texas, now Texas A&M Univ., 524

Alabama argillacea, cotton leafworm, 4, 5, 6, 65, 237, 253, 330, 332

Aldicarb, 190, 191 Alfalfa looper, Autographa

californica, 137, 138 Alkylating agents, apholate,

aphomide, and aphoxide, 154-155

All, J. N., 357 Allen, G. E., 138, 139, 143 Anderson, F. S., 306, 324 Anderson, R. E., 100 Anderson, T. W., 51, 259 Andow, D., 124 Andres, V., Jr., 171 Andrews, G. L., 4, 19, 148, 385 Andrilenas, P. A., 32, 34,

37, 48, 49, 51, 259

Angus, T. A., 133, 143, 145 Animal and Plant Health

Inspection Service (APHIS), 4, 185, 321, 498, 507, 508, 509, 515, 523

Anonymous, 8, 12, 19, 30, 31, 32, 51, 208, 229, 238, 239, 246, 249, 252, 258, 486, 494

Anthicidae, 63 Anthocoridae (minute pirate

bugs), 106 Anthonomus grandis, boll

weevil, see Boll weevil

Apanteles marginiventris, 216

Aphididae, 62 Aphids, Aphis spp., 64, 329

estimated cotton yield losses from, 339

Aphis gossypii, cotton aphid, 6, 244

cotton losses due to, 329, 332

diflubenzuron ineffective against, 211

insecticide control, 246, 252

Apholate, 154-155 Aphomide, 154 Aphoxide, 154 Apis mellifera, honey bee,

63, 129 Araneida (spiders), 62, 64 Araneidae (orb weavers), 106 Arant, F. S., 346 Arle, H. F., 150 Armyworm, Spodoptera spp.,

105 ARS Metabolism and Radiation

Research Laboratory, Fargo, N. D., 428

Arthropods (cotton): beneficial, 7, 62, 63, 66,

67, 103-108, 110, HI, 115, 120, 216, 314, 315, 318-320

boll weevil, Anthonomus grandis, see Boll weevil

bollworm, Heliothis zea, see Heliothis spp.

cabbage looper, Trichoplusia ni, 105, T4r,~l:08,' 329, 332, 339, 361

560 INDEX

cotton aphid. Aphis gossypii, 6, 211, 244, 246, 252, 329, 332

cotton fleahopper, Pseuda- tomoscelis seriatus, 8, 85, 208, 211, 238, 252, 314, 329, 332, 333, 339, 342, 375, 526

cotton leafperforator, Bucculatrix thurberiella, 142, 209, 253, 332

cotton leafworm, Alabama argillacea, 4, 5, 6, 65, 237, 253, 330, 332

entomophagous: 7, 62, 63, 66, 67, 103-108, 110- 111, 115

approaches to use of, in integrated pest management, 118-120

conservation of, 119 efficacy of predators in

suppression of Heliothis spp., 109- 111

factors affecting predator efficacy, 111-114

modeling populations of, and Heliothis spp., for IPM decision making, 114-118

populations of key predators of Heliothis spp., 106-111

fall armyworm, Spodoptera frugiperda, 210, 246

major groups in cotton fields, 62

pink bollworm, Pectinoph- ora gossypiella, 3, 4, 5, 7, 15, 104, 105, 119, 120, 136, 137, 138, 208, 210, 227, 238, 246, 247, 329, 332, 333, 339, 341, 342, 361, 549

predators, 7, 62, 63, 66, 67, 103-108, 110-111, 115

sampling: beneficial arthropods,

318-320

comparison of efficacy of techniques, D-Vac, field observations, sweep method, and unit area 312-315

for pests: major:

boll weevils, 316- 317 Heliothis spp,, 314-316 plant bugs, Lygus, 317

secondary, 317 population densities:

absolute methods, 307 relative methods, 308-

311 variables, sampling

duration, locations, size, and others, 303-307

scouting, 6, 64, 68, 225, 385, 392, 397, 398, 399, 400, 486

spider mites, Tetranychus spp., 329, 340

tarnished plant bug, Lygus lineolaris, 63, 74, 208, 211, 314, 317, 343, 534

tobacco budworm, Heliothis virescens, see Heliothis spp.

Ascher, K. R. S., 211, 229 Aspergillus niger, bacterial

contaminant in boll weevil rearing facility, 286

Autographa californica, alfalfa looper virus (ACNPV) infects pink bollworm larvae, 137, 138

Azinphosmethyl, 48, 49, 82, 92, 94, 192, 217, 224, 252, 256

Azodrin, 119

Bacheler, J. C., 349, 379, 446, 449, 450, 476, 478

Bacillus sphaericus, 286

INDEX 561

jB. thuringiensis, 129, 130, 133, 136, 137, 139, 141, 532

registered for use against Heliothis spp., 138

Bacterial blight, a seedling disease caused by Xanthomonas malvacearum, 77

Baculovirus heliothis, a nuclear polyhedrosis virus (NPV) from Heliothis zea, infects only Heliothis spp., 129, 130, 131, 132, 139, 532

registered for use against Heliothis spp., 138

Baerg, W. J., 23, 553 Bailey, C. F., 121, 346 Bailey, J. C., 86, 96, 98,

336, 343, 346 Baker, D. N., 259, 361, 378,

380, 443, 476, 477, 479

Baker, S., 100 Baker, T. C, 204 Baldwin, J. L., 370, 372, 378 Ballmer, G. R., 126 Bandedwinged whitefly,

Trialeurodes abutilonea, 62, 64, 246

Barber, G. W., 318, 324 Bariola, L. A., 96, 150, 353 Barker, C. H., 26 Barnes, G., 387, 406 Barnes, K. K., 479 Bartlett, A. C., 155, 162,

170, 272, 295 Batzer, 0. F., 146 Baumhover, A. H., 204, 288,

295 BAY SIR 8514 (insect growth

regulator), a benzoylphenyl urea that has been as effective as diflubenzuron against boll weevil, 209-210

Beard, R. L., 288, 295 Beauveria bassiana, boll

weevil susceptible to, 136

Beavers, J. B., 232, 234 Becnel, I. J., 349, 356 Bee, M. J., 229 Beet armyworm, Spodoptera

exigua, a secondary pest of cotton, 141, 209, 361

Bell, A. A., 100 Bell, J. v., 134, 143 Bell, K. 0., Jr., 70, 110

121, 126, 235, 328 Bell, M. R., 129, 137, 138,

139, 140, 143, 148, 150, 301, 349

Benedict, J. H., 554 Beneficial insects, 7, 62, 63,

66, 67, 103-108, 110, HI, 115, 120, 216, 314, 315, 318-320

Benskin, J., 227, 229 Benzene hexachloride, 6, 244 Benzoylphenyl ureas (insect

growth regulators), 207-226, 228

BAY SIR 8514, as effective as diflubenzuron against boll weevil, 210

diflubenzuron, only benzoylphenyl urea approved for use on cotton, 207, 209

penfluron, was more active than diflubenzuron in inhibiting the hatch of boll weevil eggs, 210

structures and activity of BAY SIR 8514, diflubenzuron, and penfluron, 210

Berger, R. S., 180, 199 Beroza, M., 232 Bibow, W. R., 172 Bielarski, R. V., 261 Bierl-Leonhardt, B. A., 201,

202, 380 Biever, K. D., 235 Bigeyed bug, Geocoris

punctipes, 62, 114, 216

Biological Evaluation Team, 402, 483, 498, 522

Bird, L. S., 12, 19

562 INDEX

Bisazir (chemosterilant), 157 Black fly, Simulíum vittatum,

210 Black, J. H., 387, 406 Blake, H., 51 Bogel, D., 356 Bohmfalk, G. T., 149 Boling, J. C, 125, 327 Boll weevil, Anthonomus

grandis, 3 alternative cotton insect

management strategies, impact on prodüber income in Mississippi, 481-493

alternative host plants in the United States, 53

bacterial control of, 133, 135-136

biology, behavior, and ecology, 54-61

Boll Weevil Eradication Trial (BWET), see under main entry

Boll Weevil Research Lab- oratory, 164, 272, 292

BWSIM (boll weevil simulation model), 445

BWSIM model compared with CIM-BW model, 453, 455

simulated results from BWSIM compared with experimental results, 453-454

cause of substantial damage to cotton in Southeast Region, 76

CIM (cotton and insect management simulation model), integration of component models, boll weevil model (CIM-BW), cotton crop model (COTCROP), and Heliothis spp. model (CIM-HEL), into CIM, 464, 466, 469, 472- 473, 475

CIM-BW (cotton and insect management-boll weevil simulation model):

model compared with earlier boll weevil simulation model (BWSIM), 453, 455

schematic of boll weevil and cotton interactions, in CIM model, 447

structure, 446 weevil development,

fecundity, feeding, and mortality, 449- 452

subroutine calling sequence, 448

community-wide bollworm management system in Arkansas, an alternate to BWET and OPMT, 529-534

control, new directions and technologies for, 7-18

cotton culture in weevil- infested areas, 74, 76, 78

cotton production regions for boll weevil evaluation in 1979, 41

diflubenzuron, effect on, 156-157, 165-166, 209-213, 218-224, 225-226, 411

distribution of, in United States, 55

entomophagous arthropods for control, 104

eradication: biological inquiries and

constraints to beltwide implementation:

cost, 544-545 federal and state regulatory requirements, 550-551

maintenance of weevil- free areas and containment areas, 548-549

personnel needs, 547 role of independent

consulting entomologists, 547

INDEX 563

Boll weevil (eradication) components of suppression:

attractant, sex and aggregating, 424-425

diflubenzuron, 427 insecticide, 416-421 pheromone trapping, 423-424

sterile boll weevil release, 159, 425-427

suppression of overwintering generations, 421-423

economic evaluation of BWET in North Carolina, 497-516

improvements in, 428-430 movement of boll weevil

and its effect on, 415

population suppression, fundamental principles of, 412

simulation models, use of to evaluate suppression measures, 413-414

technology: employed in BWET, 409 for maintaining boll weevil-free areas, 430-433

High Plains Boll Weevil Suppression Program, 539, 548

initial years of infestation in United States, 5

insecticides: an appraisal of cotton

insect control with, 250-251

beginning of use of synthetic organic insecticides against, 6-7

cost of insecticides used on cotton, 29-50

for control in Optimum Pest Management Trial (OPMT), Current Insect Control (CIC), and Boll Weevil Eradica- tion Trial (BWET), 256

inorganic, 4, 5, 7, 239

organic, 244 as dusts, 244-245 as sprays, 245

recommended dosages for control of major cotton insects, 252-253

reproduction-diapause control with methyl parathion, 248, 249

resistance to, 246 systemic, 246

juvenile hormone mimics, not effective against, 227

mass rearing: adult emergence, 281-283 as component of weevil

eradication, 265 control of microbial

contamination, 266 development room, 281 diets :

artificial, first suitable formulation, 266

Gast diet used for sterile weevils reared for BWET and OPMT, 162

larval and adult, 270 egg harvest and prepara-

tion, 276-277 egg production, 272 emergence cubicles, 282 Gast rearing facility,

266-269 production data for,

293 microbial contamination,

283-292 amino or fatty acid

content, effect on, 287

cell tissues, effect on, 287

control of, 266 detection of, methods

for, 289-290 of insectary-reared weevils, with diverse aerobic and anaerobic bacteria, 286

564 INDEX

mass rearing (contamination) pheromone production,

effect on, 287 production problems

caused by, 292 sanitary measures

against, 288-289, 291-292

sources of contamination, 284

weevil development, effect on, 286

oviposition: cage, shaker, and

conveyor for, 275 oviposition equipment

and procedures, management of, 274

oviposition room, environment of, 275

pellet-making equipment, 275

pellet-making of adult diet, 273

rackveyor for stacking and conveying planted trays, 280

sterilization of prepared diets, 272

tray processing and egg planting, equipment for, 279

microbials for control of, 133

olfactory and visual stimuli, response to, 57

Optimum Pest Management Trial (OPMT), see under main entry

pheromone: components, isolation,

identification, and synthesis of, 184

dispensing systems, 184- 185

production of, 165 seasonal response of boll

weevil to, 183 pheromone traps:

daylight fluorescent paint (lemon yellow) color on traps attracts the greatest number of weevils, 61

infield traps and insecticides for detection and suppression, 191-194

weevil capture in infield traps: in Arkansas, 194 in North Carolina, 196

male-baited traps around cotton fields for boll weevil suppression, 187-188

pheromone-baited traps for capturing overwintered weevils, 188-191

Pilot Boll Weevil Eradica- tion Experiment (PBWEE), see under main entry

rapid fruiting of cotton, impact on boll weevil populations, 91

resistance in cotton: frego bract, 81-83 primitive cottons, 84 red leaf, 84-85

sampling for, 316-317 sampling procedures

identical for OPMT and BWET, 321

sterilization: chemosterilants, 154-155,

156 gamma irradiation,

154-157, 425-427 irradiation source,

164 new methods of,

156-157 sterile males:

competitiveness of sterilized weevils, 158

evaluation of sterile weevils released in BWET in 1979, 165- 168

release of sterile males in BWET, 159

requirements for using sterile insects for eradication, 168

INDEX 565

Boll weevil (continued) yield losses in cotton due

to: calculated from field

studies, 335-345 estimated, 329-334

Boll Weevil Eradication Trial (BWET) in North Carolina: 3, 13, 15, 53, 61-62, 110, 154, 162, 164, 185, 249, 432-433, 438, 481, 522-523, 538, 540, 544, 545

area: control zone - Robeson,

Scotland, and Cleve- land counties, 498

eradication zone - Edge- combe, Halifax, Northampton, and Nash counties, 498

components of BWET: areawide diapause boll

weevil control with insecticides, 11, 256, 416-417

education and technical assistance to growers, 11

field scouting, 11, 225 insect growth regulator

(diflubenzuron), selective use of, 225, 427

mandatory participation based on grower referendum, 11

pheromone traps, monitoring and suppression of boll weevils with, 11, 423-425

quarantine procedures, 11, 413

sterile boll weevils, release of, 11, 159, 425-427

evaluation of: economic : changes in cotton pro-

duction, 498-501, 509-511

changes in cotton yields, 498-501, 511-514

insecticide applications, 501-506

producer income, 514- 516

public expenditures, 507-509

released sterile boll weevils in eradication trial in 1979, 165-168

purpose of trial, designed to test new methods for insect control, 12

sampling techniques, four compared: field observations by entomologist, D-Vac, sweep net, and unit area sampler, 312-323

Bollworm, Heliothis zea, see Heliothis spp.

Bondy, F. F., 351 Bonell, N. P., 21 Booth, G. D., 326 Boring, E. P., 527, 528, 552,

553 Borkovec, A. B., 154, 156,

157, 170, 173, 175, 176, 230

Bottger, G. T., 349 Bottrell, D. G., 4, 19, 20,

70, 105, 121, 208, 229, 378, 548, 552, 555

Bourland, F. M., 19 Bowen, H. D., 379, 476, 478 Bowlus, S., 233 Boyd, F. J., Jr., 187, 199,

230, 553 Boyer, W. P., 406, 554 Boyette, J. D., 355 Bracon kirkpatricki, a poten-

tial parasite of boll weevil, 104

J.* mellitor, has parasitized boll weevil larvae, 83, 105

Braconidae, 62, 64 Bradley, J. R., Jr., 21, 190,

199, 230, 231, 232, 328, 379, 380, 476, 478, 553

Bradshaw, R. D., 100

566 INDEX

Brazzel, J. R., 7, 19, 21, 24, 121, 123, 137, 143, 199, 230, 231, 248, 258, 343, 346, 353, 406, 416, 434, 478, 514, 517, 553

Brennan, M. M., 204, 205, 381 Bridge, R. R., 99 Briggs, R. W., 174 Brown, L. G., 12, 19, 21, 362,

378, 380, 437, 439, 441, 445, 446, 476, 478, 479, 483, 494, 495

Brown, R. G., 99 Brown, R. T., 233 Bruce, R. R., 443, 476 Brues, C. T., 124, 326, 380,

479 Bryson, J. 0., 204 Bucculatrix thurberiella,

cotton leafperforator, 142, 209, 253, 332

Buck, D. R., 201, 379, 406 Buford, W. T., 84, 96, 97 BUGNET, a computerized pest

management system developed for use in Texas utilizing computer models such as MOTHZV in making decisions about pest control, especially for Heliothis spp., 372-377

Bull, D. L., 131, 139, 144, 146, 157, 166, 170, 185, 199, 207, 211, 212, 213, 214, 215, 220, 223, 228, 229, 230, 231, 232, 235, 349, 552

Bullock, H. R., 131, 137, 144, 232

Burgerjon. A., 134, 144 Burke, H. R., 69, 552 Burks, M. L., 171 Burton, V. E., 406 Bush, D. L., 19 Busulfan, a chemosterilant,

155, 158 Butler, G. D., Jr., 378, 456,

476 Buxkemper, W. E., 230, 553

Buxton, D. R., 380, 479 BWSIM (boll weevil simula-

tion model), see also Models, 445, 453-455

Byerly, K. F., 304, 308, 324

Cabbage looper, Trichoplusia ni, 105, 141, 208, 329, 332, 339, 361

Caillavet, D. F., 52 Calcium arsenate, 4, 5-7, 239 Calco oil red N1700 dye, used

in boll weevil larval diet as marker for released sterile adults, 163-165

Calderón, M., 477 Calhoun, S. L., 349, 351, 356 Callahan, R. A., 311, 324 Cameron, D. M., 483, 486,

488, 494, 495 Cameron, J. W. M., 133, 144 Canerday, T. D., 341, 342,

346 Cántelo, W. W., 295 Carabidae, 111 Carde, R. T., 204 Carlson, G. A., 497, 517 Carmine spider mite,

Tetranychus cinnabarinus, 211

earner, G. R., 149 Carpenter, J. E., 204, 205 Carrillo, J. L., 124 Carroll, S. C., 556 Carruth, L. A., 387, 406 Carson, A. D., 149 Carson, R., 8, 19 Casey, J. E., 554 Casida, J. E., 231 Cassidy, T. P., 20 Cate, J. R., 378 Catolaccus grandis, 104 Cave, R. D., 378, 477 Cawich, A., 227, 230 Chaetocnema sp., 62, 313 Chalcidoidea, 62, 64 Chamberlain, W. F., 232 Chambers, H., 163, 170 Chan, B. G., 100 Chang, S. C., 176, 210, 212,

230 Chapman, A. J., 23, 140, 144,

146, 349, 354

INDEX 567

Chapman, O. L., 201, 202, 380 Chemosterilants, 153

apholate, 154 aphomide, 154 aphoxide, 154 bisazir, 156, 157 busulfan, 155 hempa, 155, 156

Cheraosterilization, 153-159 Chesnut, T. L., 121 Chiang, H. C., 171 Childress, D., 172, 292, 295 Chlordimeform, 48, 49, 222 Chloropidae, 62 Chrysopa carnea, common green

lacewing, both adults and larvae are effective predators of Heliothis spp., 106, 110, 120, 216, 320

jC. oculata, goldeneye lacewing, a known predator of Heliothis spp., 106

—' rufilabris, predator of Heliothis spp., 106

Chrysopa spp., 111 Chrysopidae, 106 Cicadellidae, 62 Cienfuegosia drummondii,

most persistent of the alternate hosts for boll weevil in United States occurs in Coastal Bend region of Texas, 54, 544

C^. yucatanensis, implicated as possible host of boll weevil in Florida, 544

CIM (cotton and insect management simulation model), see also Models, 437-475, 481- 493

CIM-BW (cotton and insect management-boll weevil simulation model), see also Models, 445

calling sequence for, 448 compared with BWSIM, 454-

455 schematic interactions in,

447 structure, 446

insect development, feeding, fecundity, and mortality, 449-452

CIM-HEL (cotton and insect management-Heliothis^ spp. simulation model), see also Models, 456-463, 468

calling sequence for, 457 structure, 456 Heliothis virescens and

_H. zea separated in model because of different rates of development, 456

insect development, feeding, fecundity, and mortality, 456-463

Clark, L. R., 307, 324 Cleveland, T. C, 148, 245,

258 Clower, D. F., 26, 261, 347,

357, 555 Coad, B. R., 5, 6, 19, 20,

22, 239, 258 Coccinellidae, 62, 64, 111 Cody, C. P., 173 Cole, A. W., 555 Cole, C. L., 221, 224, 230,

259, 434, 450, 476, 542, 552

Coleomegilla maculata, 106 Coleomegilla spp.. Ill Coleóptera, 111 Collembola, 63 Collins, H. L., 387, 406, 407 Collins, S. G., Ill, 488,

494 Collops spp., 107, 111 Colorado potato beetle,

Leptinotarsa decemlineata, 211

Common green lacewing, Chrysopa carnea, 106, 110, 120, 216, 320

Comstock, J. H., 5, 20, 237, 258

Cone trap, for control of Heliothis spp., 182

Conoderus vespertinus, tobacco wireworm, 63

Cooke, F. T., Jr., 29, 32, 33, 34, 35, 37, 42, 47, 49, 51, 180, 199, 494, 495

568 INDEX

Cooksey, K. E., 134, 144 Copeland, W. W., 204 Coppedge, J. R., 12, 20, 199,

204, 379, 477 Com (Zea mays) :

constitutes the largest single crop pesticide market in the world and the United States, 31-32

MOTHZV-2 simulation model includes simple crop model for corn, 362- 365

Corylophidae, 62 Corynebacterium humiferum, 286 COTCROP (cotton crop compo-

nent model), see also Models, 440-444

Cotton: aphid, see also Arthropods Belt, 4, 33, 34, 35, 36,

37, 43, 73, 111, 191, 208, 222, 238, 250, 386-387, 481, 482, 493, 524

constitutes the second largest single crop pesticide market in the world and the United States, 31-32

cultivars: bloom patterns for several

cotton strains and cultivars, 87-88

characteristics of those grown in boll weevil- infested areas, 80

current cultivars in boll weevil-infested areas of Southeast, Midsouth, and South- west, 76-79

fruiting and fiber characteristics of more recently released cultivars, 86-91

lint yields of selected lines, 90

rapid fruiting, effect on boll weevil population, 91-92

field animal community of, 61-65

fleahopper, see Arthropods insect management: alternatives to boll

weevil eradication: community-wide bollworm management, Arkansas, 529-534

improved cotton insect management for South- east, 534-535

short-season system, Texas, 92-94, 521- 529

beltwide constraints on implementation of BWE and 0PM, 538-551

beneficial insects, 7, 62, 63, 66, 67, 106, 107, 110, 111, 120, 216, 314, 315, 318- 320

Boll Weevil Eradication Trial (BWET) in North Carolina, see under main entry

economic evaluation of BWET in North Carolina, production cost changes, cotton yield, and public expenditures, 497- 516

evolution of, in the United States, from two divergent paradigms:

integrated pest management , 9

total population management, 9

insect growth regulators (IGR) for, the benzoylphenyl ureas, especially diflubenzuron, 156-157, 159, 165-167, 207-228, 411, 427

insecticides: 3, 5, 6, 32, 34, 36, 48, 49, 50, 82, 92, 119, 192, 217, 224, 237, 238, 239, 244, 245, 246, 247, 250, 252, 253, 254, 255, 256

INDEX 569

Cotton (insecticides) microbial, 130-131 resistance to, 3, 7,

238, Ik^-lkl, 251 integrated pest management,

9-18, 82, 103, 111, 114, 116, 118-120, 208, 226, 359

mismanagement of cotton ecology, a case history, 65-68

Optimum Pest Management Trial (OPMT) in Mississippi, see under main entry

pathogens for control, general characteristics:

bacteria, 134 fungi, 144 protozoa, 135 viruses, 130-132

Pilot Boll Weevil Eradi- cation Experiment (PBWEE) in Mississippi, see under main entry

producer income, impact of alternative insect management strategies on, in Mississippi, 481-493

leafperforator, see Arthropods leafworm, see Arthropods losses due to: arthropod pests, 180, 238,

319-332, 339 calculated by experts,

330-334 calculated from field

studies, 335-338 boll weevil from 1909-

1954, 240-241 insects other than boll

weevil from 1909-1954, 242-243

loss models (simulation), see also Models:

CIM, 439, 442, 447, 464-475, 483-493

COTCROP, 439-445 COTTON, 439 cotton-Heliothis spp.

model, MOTHZV, MOTHZV- 2, and MOTHZV-3, 362-376

GOSSYM, 361 SIMCOT, 361, 439 SIMCOT II, 361, 439 SIMPLECOT, 365-369,

372, 374 production:

acreage average by state, 1974-1978, 75

regions: cotton producing areas

in Mississippi, 483-485

Delphi Region and cotton production subregion, estimated harvested acres for selected years, 42-43

for boll weevil evaluation, 40

for cotton cost surveys, 39

for pesticide use survey, 38

resistance: to boll weevils:

in frego bract, 81-83 in primitive cottons,

84 other potential sources

of, 83-84 to Heliothis spp. com-

plex, 84-85 to tarnished plant bugs,

85-86 Courtney, K. D., 171 Covington, B. M., 554 Cowan, C. B., Jr., 25, 125,

261, 324, 327, 347, 349, 350, 351, 354

Cramer, H. H., 330, 340, 346 Cross, W. H., 53, 54, 57, 69,

70, 98, 99, 104, 121, 123, 165, 170, 175, 183, 185, 186, 190, 199, 200, 202, 203, 249, 406, 407, 544, 552

Crowder, L. A., 230 Crowe, B. G., 347 Curculionidae, 54 Curl, L. F., 259, 434 Current Insect Control (CIC),

the approach to cotton insect

570 INDEX

control currently used by producers compared with approach used in BWET and OPMT areas:

control zone (CZ) for BWET- North Carolina compared with eradication zone (EZ):

changes in cotton production, 498-501, 509- 511

changes in cotton yields, 498-501, 511-514

number of insecticide applications, 501-506

producer income, 514-516 public expenditures, 507-

509 control zone for OPMT-

Mississippi compared with test area:

changes in cotton production, 491

changes in per acre yield, 488-489

number of insecticide applications, 488- 489

producer income, 489-492 Curry, G. L., 21, 362, 378 Cushman, R. A., 124 Cycloneda, 111

Darden, E., 173 da Silva, R. F. P., 234 Daum, R. J., 136, 144, 148 Davich, T. B., 69, 154, 155,

158, 170, 171, 172, 173, 175, 176, 200, 201, 202, 203, 204, 258, 260, 295, 301, 407, 434, 435, 548, 552, 554

David, W. A. L., 130, 131, 144

Davis, J. W., 25, 101, 125, 261, 311, 324, 327, 349, 350, 351, 354

Davis, R. L., 200 Dawson, E. M., 99 Dawson, J. R., 173, 174, 177,

298 DDT, 6, 7, 8, 48, 49 Dean, H. A., 21, 351, 352

DeBord, D. V., 239, 259, 330, 331, 333, 334, 346

DeJong, B. J., 233 Delong, D. M., 310, 324 DeMichele, D. W., 12, 20, 21,

360, 378 Demilo, A. B., 230, 233 Dempster, J, P., 123 Diabrotica undecimpunetata

howardi, a minor pest of cotton, 63

Diapause control, 11, 249, 256, 391, 394, 401, 416, 417

Dickerson, W. A., 186, 200, 303, 326, 394, 406

Dicrotophos, 48, 49 Dietrick, E. J., 311, 324 Diflubenzuron, an insect

growth regulator and insecticide:

analysis of, in treated boll weevils released in BWET, 166

approved for control: of gypsy moth, 209 only benzoylphenyl urea

approved for use on cotton, 207, 209

boll weevil is only major cotton pest significantly affected by, 211

component of integrated pest management system, 208

effect on: environment, posttreat-

ment, 213-214 field populations of boll

weevils, 218-224 natural enemies, 215-217 treated sterile males

released in BWET, 165, 411, 427

irradiation plus diflubenzuron to sterilize boll weevils, 153, 156-157, 159

mixed with invert sugar- molasses baits or oil, 218

INDEX 571

mode of action in boll weevil, 211-213

reduced parasitism of tobacco budworm eggs by Trichogramma after eggs treated with, 216-217

structure of, 210 Dilday, R. H., 101 Dillier, J. H., 21 Dimethoate, 48, 49 Dimilin, see Diflubenzuron Dinkins, R. L., 108, 121,

398, 406 Dolichopodidae, 62 Donahoe, M. C, 113, 122, 124 Doolittle, R. E., 205, 381 Dorough, W. H., 176 Dowell, G. C, 554 DuBose, W. P., 346 Dulmage, H. T., 12, 20, 133,

140, 144, 145, 147, 354

Duncan, W. G., 361, 378, 439, 476, 477

Dunlap, T. R., 8, 20 Dunn, H. A., 54, 69 Dunnam, E. W., 349, 351 Dupnik, T. D., 325 DuRant, J. A., 336, 343, 346 Dyson-Hudson, R., 124

Earhart, R. W., 356 Earle, N. W., 12, 20, 156,

157, 159, 160, 165, 166, 171, 173, 176, 177, 266, 295

Earnheart, A. T., 97 Eaton, J., 172 Ebony marker, a genetic semi-

dominant trait in boll weevil which by crossing and backcrossing, provided 99% identifiable weevils for the sterile releases in the BWET, 162-163, 165

Ecology, of cotton insects, 53-68

Economic Evaluation Team, 522 Economics and Statistics

Service, 20

Ectatomma tuberculatum, potential parasite of boll weevil, 104

Eden, W. G., 13, 20, 168, 171, 410, 434

Edminster, T. W., 479 Edwards, R. R., 199, 203 Ehler, L. E., 105, 122 Eichers, T. R., 32, 34, 35,

37, 48, 49, 51, 238, 259

Ekbom, B. S., 122 Elcar, see Heliothis nuclear

polyhedrosis virus Elliger, C. A., 100 Ellman, G. L., 163, 171 Endrin, 48, 49 Enkerlin, S. D., 351 Enterobacter aerogenes, found

on insectary-reared weevils, 286

amino and fatty acids reduced in contaminated weevils, 286, 287

Entomophagous arthropods, see Arthropods

Environment Evaluation Team, 522

Environmental Protection Agency, 130

EPN, 46, 48, 49, 464 EPN-methyl parathion, 464 Eradication, see Boll weevil

eradication Escarra, B., 483, 494 Eveleens, K. G., 122 Ewing, K. P., 6, 20, 21, 23,

244, 245, 247, 259, 351, 353, 355, 541, 553

Falcon, L. A., 27, 126, 134, 140, 141, 145, 324, 378

Fall armyworm, Spodoptera frugiperda, 210, 246

Favero, M. S., 284, 295 Fawcett, D., 52 Featherstone, R. M., 171 Fenton, J. A., 351 Fenvalerate, a synthetic

pyrethroid insecticide effective against Heliothis spp., 46, 48, 49

572 INDEX

Ferrell, C. D., 234 Ferron, P., 134, 145 Field surveys, see Scouting Fife, L. C., 351 Finley, M. D., 528, 553 Flake, H. W., Jr., 298 Fletcher, R. K., 110, 122 Flint, H. M., 154, 158, 164,

172, 181, 200, 210, 211, 230

Forey, D., 230 Formicidae, minor secondary

pests of cotton, 63

Foster, G. G., 177 Fox, A., 51 Frear, D. S., 232 French, B. L., 26 Frevert, R. K., 479 Fricke, H., 159, 172 Fried, M. , 158, 172 Frisbie, R. E., 22, 261, 372,

378, 379, 394, 406, 521, 527, 553, 554, 556

Fryxell, P. A., 69, 552 Fuchs, T. W., 311, 324, 552 Fulgoridea, minor primary

cotton pests, 63 Functional Mathematics

Programming System, 486

Furr, R. E., 149, 355 Fusarium oxysporum f.

vasinfectum, the cause of Fusarium wilt in cotton, in Southeast, 76

Fusarium spp., 77 Fye, R. E., 60, 69, 249, 259,

340, 341, 346, 351, 357, 417, 434

Gaines, J. C., 6, 21, 346, 351, 352

Gaines, R. C., 295, 341, 342, 346, 352, 355, 357, 358

Gallahan, D., 124 Gamma irradiation, see

Irradiation Gannaway, J. R., 100, 378,

556 Gantt, C. W., 327

Ganyard, M. C., 4, 12, 21, 203, 218, 219, 222, 223, 225, 230, 231, 232, 542, 553

Garcia, C., 146 Garcia, R. D., 231 Gard, I. E., 352 Gardner, W. R., 443, 477 Garrison, G. L., 358 Garst, G., 52 Gassner, G., 156, 172 Gast, R. T., 69, 136, 145,

160, 163, 171, 172, 260, 266, 273, 279, 284, 288, 291, 292, 295, 296

Gausman, H. N., 24 Geier, P. W., 324 Genetics, of ebony body boll

weevil, 162 Genotypes, and phenotypes of

boll weevil progeny from crosses of ebony characteristic x wild- type, 163

Gentry, C. R., 180, 200 Geocoris punctipes, bigeyed

bug: beneficial insect, 62, 216 first instar feeds almost

exclusively on tobacco budworm eggs, 114

Geocoris spp.: beneficial insect in

eastern parts of Cotton Belt, 64

predator of Heliothis spp. larvae, 111

Gerard, C. J., 86, 96 Gijswijt, M. J., 233 Gilbert, N., 381 Gilliland, F. R. , Jr., 149,

191, 200 Glass, E. H., 171 Glodt, R. E., 100 Glover, T., 237, 259 Glugea gasti, a protozoan

pathogen that infects Heliothis spp. and pink bollworm, 136

Gonzalez, D., 27, 107, 122, 126, 325, 328

Good, J. M., 11, 21

INDEX 573

Goodenough, J. L., 103 Goodwin, R. W., 288, 296 Gorham, D. P., 104, 122 Gorzycki, L. J., 175 Gossypium anomalum, a cotton

with some resistance to boll weevil, 84

G. arboreum, reduced boll ~ weevil oviposition

about 15%, 84 G. barbadense, SI Seaberry "" strain slightly

reduced oviposition of weevils, 84

G. herbaceum, a cotton with "" fewer anthers than

regular type reduced boll weevil oviposition, 84

G'. hirsutum, 54 ~ some lines show low levels

of resistance to boll weevil, 84, 85

G. hirsutum var. punetatum, implicated as a possible host of boll weevil in Florida, 544

Gradwell, G. R., 328 Graham, H. M., 4, 8, 21, 98,

145, 146, 327 Grandlure, the pheromone of

boll weevil, has been isolated, identified, and synthesized as four terpenoid compounds, 184

Grandlure-baited traps: development of, 185-186 dispensing systems for,

184-185 Granulosis virus, one of two

types of viruses that can infect insects, 131

Graves, G. N., 137, 145 Graves, J. B., 7, 21 Graves, T. M., 199, 200 Green, J. M., 81, 96 Greenslade, R. M., 26 Gregory, B. G., 143 Griffin, J. G., 160, 163,

172, 173, 265, 266, 267, 270, 271, 274,

276, 278, 279, 280, 281, 282, 290, 293, 296, 297

Grosscurt, A. C., 211, 231 Grube, A., 498, 499, 517 Gueldner, R. C., 165, 172,

175, 200, 203, 205, 231, 286, 287, 297

Guerra, A. A., 227, 231 Guilavogui, F., 356 Gutierrez, A. P., 12, 21,

25, 308, 324, 361, 378, 439, 477, 479, 555

Gypsy moth, Lymantria dispar, diflubenzuron has been approved for use on, 209

Haemotobia irritans, horn fly, 211

Hagen, K. S., 26, 27, 126 Hajjar, N. P., 211, 231 Halford, W. T., 355 Halictidae, 62 Hall, P. K., 85, 96 Hamel, D. R., 356 Hamer, J. L., 385, 406, 407 Hamill, J. G., 486, 494, 495 Hamilton, A. G., 476 Hammann, I., 235 Hampea sp., a host for the

boll weevil, but not native to the United States, 54

Handy, R. B., 22 Haney, P. L., 15, 22 Hanna, R. L., 27, 121, 346,

352, 356 Hanny, B. W., 96, 98, 346 Harcourt, D. G., 304, 325 Hardee, D. D., 54, 69, 144,

170, 171, 183, 184, 185, 187, 199, 200, 202, 203, 205, 407, 435, 552, 554

Harding, J. A., 221, 224, 231, 311, 324, 325, 327, 542, 553

Harrell, E. A., 278, 283, 293, 297

Harris, F. A., 249, 259, 438, 476, 477, 479, 494

574 INDEX

Harris, L. D., 258, 434 Harris, R. L., 235 Harris, W., 222, 231 Hart, E. J., 172 Hartsog, J. D., 476, 478, 479 Hartstack, A. W., 12, 22, 103,

115, 116, 117, 122, 175, 179, 181, 182, 183, 200, 201, 202, 203, 316, 325, 336, 344, 346, 359, 362, 363, 364, 365, 366, 374, 376, 377, 379, 394, 406, 435, 439, 456, 460, 463, 477

Hassell, M. P., 112, 122 Haynes, D. L., 171, 327 Haynes, J. W., 27, 154, 155,

156, 158, 159, 165, 172, 173, 175, 177

Hazard, E. I., 291, 297 Head, R. B., 385 Healy, M. J. R., 305, 325 Heath, J., 26 Hedin, P. A., 154, 173, 184,

201, 203, 205, 228, 231, 285, 298

Heilman, M. D., 12, 22, 73, 92, 93, 94, 96, 99, 526, 527, 553, 554

Heimpel, A. M., 134, 145 Heinrichs, E. A., 234 Heiser, R. F., 175 Heliothis nuclear polyhedrosis

virus, is host-specific to Heliothis spp,, 129-131, 138, 139

Heliothis spp. (including H. virescens (tobacco budworm) and H. zea (bollworm)): 2'9,~93, 387, 397, 418, 437, 444, 498, 526, 536

as cotton pests: development of several gen-

erations on cotton within growing season, 65

midseason or late season, 108

most important of secondary pests, 63, 64., 208

Bacillus thuringiensis, registered for use against, 129-130, 138-142, 532

Baculovirus heliothis, registered for use against, 129-131, 138-142, 532

Boll Weevil Eradication Trial (BWET) in North Carolina, see under main entry

bollworm and cotton leafworm were the most important pests of cotton before 1885, 237

Chrysopa carnea adults and larvae are effective predators of, 320

CIM (cotton and insect management model, formed from three component models, COTCROP, CIM-HEL, and CIM-BW, 464-475

CIM-HEL, Heliothis spp. component simulation model, 456-463

insect growth regulators for: diflubenzuron, is ineffec-

tive against, 211, 427 juvenile hormone mimics,

reaction to, 227-228 insecticides for control:

frego bract cotton allows delay in use of insecticides, thus protecting beneficial insects that contribute to control of bolIworm/budworm complex, 82-83

insecticides used for boll weevil often kill beneficial insects that control Heliothis spp. and create a serious pest problem beltwide, 68, 104, 105, 238, 412, 541, 543

Paris green more effective than calcium arsenate against bollworm in early years, 239

recommended dosages of principal insecticides for control, 252

INDEX 575

resistance: budworm/bollworm complex

has developed resistance to the comparatively few available effective insecticides, 257

to DDT, 7 to the organochlorine

insecticides in Louisiana, 246-247

role of insecticides in control of, 238-239, 244-246

shift to use of pyrethroid insecticides, 46

toxaphene and endrin effective against bollworms, 244

losses from, in cotton, 329-333, 336, 338-345

capable of being problem in irrigated fields of Lower Rio Grande Valley, 81

management: BUGNET, a computerized

management system, see BUGNET

community-wide bollworm management system in Arkansas, 521-522, 529-534

entomophagous arthropods for, 103, 118-120

insecticides, effect upon, 119

predator and prey density, distribution, and preferences, 112-114

some known predators of, 106

five alternative strategies including current insect control used by cotton producers (CIC), for control of bollworm/tobacco budworm complex and boll weevil, were compared to determine the specific changes in acre yield and

number of insecticide applications for each alternative strategy and for CIC, 483

modified cotton production system for early maturity to escape late season infestation with, 95

Optimum Pest Management Trial (OPMT) in Mississippi, see under main entry

significant advances in control of, 4

modeling populations of entomophagous arthropods and Heliothis spp. with a cotton- Heliothis simulation model (MOTHZV) and also, revised models, 359-377

MOTHZV-2, 114-117 pheromone:

dispensing system for pheromones used as attractants, 181-182

disruption with, for control of, 183

identification of components of pheromone of H. virescens (virelure) and H. zea, 180-181

traps, development of, 182 plant resistance to, in

glabrous and nectariless cottons, 84

sampling: in BWET and OPMT, whole

plant, terminal squares, and bolls, 322

of eggs, larvae, pupae, and adult populations, 314-316

Helms, T. J., 288, 298 Helms, W. F., 199 Hemiptera, 111 Hempa, a chemosterilant, 155,

158 Hendricks, D. E., 180, 181,

201, 205, 325, 374, 379, 381, 406

576 INDEX

Henneberry, T. J., 143, 150 Henson, J. L., 22, 379 Henson, W. R., 328 Hervey, G. E. R., 298 Herzog, D. C., 325 Hesketh, J. D., 380, 439, 443,

476, 477, 478, 479, 495

Hibiscus sp., 54 H. syriacus, 544 High Plains Boll Weevil

Suppression Program, 538, 539, 548

High pressure liquid chromatography, 166

Hightower, B. G., 27, 258 Hill, A. S., 204 Hill, R., 170 Hillhouse, T. L., 124 Hinds, W. E., 6, 22, 23 nines, R. W., 204 Hippodamia convergens, lady

beetle, 106, 215 Hippodamia sp.. Ill Hobgood, J. M., Jr., 295 Hoffman, J. D., 200 Hoffmann, C. H., 12, 22 Hogg, D. B., 458, 459, 460,

477 Holbrook, F. R., 324 Holder, S. H., Jr., 495 Hollier, D. D., 177 Holling, C. S., 114, 122 Hollingsworth, J. P., 22,

122, 182, 201, 374, 379, 394, 406, 477

Hood, C. E., 124 Hood, J. E., 19 Hooker, P.A., 170 Hopkins, A. R., 70, 204, 234,

237, 246, 247, 260, 330, 332, 333, 346, 347, 351, 353, 356, 357, 556

Horn, B., 230 Horn fly, Haemotobia irritans,

211 Hornyak, E. P., 357 Hostetter, D. L., 146 Houghtaling, J. E., 98 House, V. S., 144, 211, 215,

216, 217, 220, 222, 223, 224, 229, 231, 349, 552

House fly. Musca domestica, 210

Howard, L. 0., 5, 22, 524, 553

Howell, J. F., 288, 298 Huddleston, P. M., 69, 170,

171, 199, 200 Huffaker, C. B., 9, 11, 12,

22, 109, 122 Hughes, R. D., 324, 381 Hunt, H. H., 379 Hunter, D. K., 150 Hunter, R. C., 81, 96, 554 Hunter, W. D., 5, 22, 23,

188, 201, 450, 477 Hymenopappus flavescens, 544 Hyslop, J. A., 333, 347

Ignoffo, C. M., 12, 23, 131, 133, 136, 137, 138, 139, 144, 145, 146, 147, 148, 235, 288, 298

Index of prices, the prices paid by farmers for agricultural chemicals, 1961-1979, 36

Insect growth regulator (s): BAY SIR 8514, 209-210, 226 diflubenzuron, 153, 156-157,

159, 165-166, 208-226 juvenile hormone (JH)

mimics, 227-228 penfluron, 156-157, 209-

210, 226 Insecticides :

aldicarb, 190, 191, 246, 252

application of: aerial, 237, 252 as dusts, 5, 6, 239 as low volume sprays,

245, 252-253 quantities applied by

region, 46, 48-50 with infield traps, 192

appraisal of merits and limitations of, in suppressing insect populations, 250-251

azinphosmethyl, 48, 49, 82, 92-94, 192, 217, 224, 252, 256

INDEX 577

insecticide used against diapausing boll weevils in BWET, 256

azodrin, 119 benzene hexachloride, 6, 244 calcium arsenate, 5, 239,

244 chlordimeforra, 222, 247,

252 control of cotton insects

improved with advent of organochlorine, organophosphorus, and carbamate insecticides, and the phasing out of inorganic compounds, 251

cost: of developing and register-

ing, 257 to producer for use on

cotton, 32, 34, 36, 42-50, 238

cotton cultivar-insecticide interaction, 82

DDT, 6, 48, 246 deleterious effect of conven-

tional insecticides to entomophagous arthropods, 108, 119

dosage: of miticides for control

of spider mites, 254-255

recommended dosages of principal insecticides for major cotton insects, 252-253

inorganic, calcium arsenate, lead arsenate, Paris green, and sulfur, 5, 6, 339, 244

insect pest management system, place in, 256

malathion, 224, 252 methyl parathion, 217, 244,

249, 252 insecticide used against

diapausing boll weevils in OPMT, 256

organic: carbamate, carbaryl, 244 organochlorines, develop-

ment of, aldrin,

benzene hexachloride, chlordane, dieldrin, endrin, heptachlor, and toxaphene, 244

organophosphates, development of, azinphosmethyl, demeton, EPN, malathion, methyl parathion, parathion, and sulprofos, 244-247

pyrethroids, permethrin and fenvalerate, 247

systemlos, aldicarb, disulfoton, and phorate can be applied to cotton seed or in the seed furrow, 246

pesticide use survey, 32, 34, 35, 37-40

reproduction-diapause control with, 248-249

resistance to: organochlorines:

in boll weevil, 246 in 25 species of

insects and spider mites, 246

organochlorine and organophosphorus insecticides in Heliothis spp. complex, 238, 247

organophosphorus insecticides in 4 species of spider mites, fall armyworm, and bandedwinged whitefly, 246

Integrated pest management, 9-13, 82, 103, 111, 114, 116, 119, 226, 359

Irish, M. A., 124 Irradiation, for boll weevil

sterilization, 153-159 source, cobalt-60 and

cesium-137, 164 Isley, D., 6, 23, 83, 96,

188, 201, 449, 450, 478, 529, 553

Ivie, G. W., 157, 170, 173, 211, 212, 229, 231, 232

Ivy, E. E., 6, 20, 21, 23, 351, 353, 355

578 INDEX

Jackman, J. A., 22, 379 Jackson, H. B., 521 Jackson, R. D., 443, 478 Jacobson, M., 204, 228, 232 Jacobson, S. N., 124 James, W., 260, 353 Jaques, R. P., 131, 147 Jawetz, E., 284, 298 Jay, D. L., 150 Jenkins, J. N., 73, 81, 82,

84, 85, 86, 96, 97, 98, 99, 100, 162, 173, 451, 478, 555

Jenkins, R., 51 Jenson, R. L., 310, 325 Johnson, E., 20, 97 Johnson, W. L., 104, 123, 200,

202, 203, 219, 222, 232

Jones, J. E., 83, 85, 97 Jones, J. S., 81, 97 Jones, J. W., 19, 362, 378,

379, 380, 437, 438, 439, 441, 443, 444, 445, 446, 447, 449, 450, 451, 453, 454, 455, 476, 478, 479, 483, 494, 495

Jones, R. E., 324 Jones, S. L., 121, 122, 123,

204, 229, 231, 346, 353, 552

Juvenile hormone (JH) mimics, insect growth regulators that can severely disrupt normal insect growth and development, 227-228

Kamprath, E. J., 478 Kanavel, R. F., 143 Karandiros, M. G., 305, 325 Kearney, J. F., 200, 203, 406 Keever, D. W., 215, 216, 222,

232, 542, 553 Keller, J. C, 148, 170, 184,

201 Keller, K. R., 30, 51 Kennett, C. E., 122 Kent, A. D., 300 Khalil, F., 230 Kido, K., 126 Kimbrough, J. J., 406 Kinard, H. C., 124

Kincade, R. T., 463, 478 King, E. G., 124 Kinzer, R. E., 20, 353 Kiritani, K., 109, 123 Kishaba, A. N., 381 Kittock, D. L., 150 Klassen, W., 155, 173, 174,

347 Klun, J. A., 180, 181, 200,

201, 202, 204, 205, 377, 380

Knipling, E. F., 11, 12, 13, 20, 113, 115, 123, 154, 155, 168, 169, 174, 175, 191, 195, 202, 249, 250, 260, 359, 380, 409, 410, 412, 414, 416, 424, 434, 435

Knott, C. M., 295 Kogan, M., 304, 309, 310,

312, 317, 321, 325, 326, 327

Koonce, K. L., 357 Kotter, E., 203 Krenz, R., 32, 37, 45, 46, 52 Kroop, S. F., 124 Kuhn, T. S., 13, 23 Kulash, W. M., 353

LaBrecque, G. G., 154, 174 Lacewell, R. D., 517, 527,

554, 556 Lacey, L. A., 210, 232 Lactobacillus plantarum,

sometimes found contaminating insec tary-reared weevils, 286

Labren, O. K., 172 Lam, J. J., Jr., 200, 295,

406 Lambert, J. R., 378 Lambert, L., 85, 97, 99 Lambert, W. R. A., 200, 521 Laminated plastic baits, as

dispensing systems for Heliothis spp. pheromone, 181

Landin, M., 172, 295 Langsford, E. L., 32, 34, 35,

52 Laster, M. L., 12, 23, 29,

478

INDEX 579

Lathridiidae, 62 Latson, L. N., 85, 98 Lawrence, R. K., 114, 123 Lawson, F. R., 200 Lead arsenate, in early part

of century was one of the principal insecticides used to control cotton leafworm, 5, 239

Lee, G. H., 201, 202 Leggett, J. E., 175, 179, 186,

195, 198, 199, 202, 394, 406, 407, 435

Leigh, T. F., 27, 96, 122, 126, 307, 318, 325, 328, 378, 477

Leipzig, P. A., 324, 378 Lentz, G. L., 353 Leopold, R. A., 171, 175, 233,

234 Lepone, G., 201, 202 Leuconostoc mesenteroides,

isolated from insectary-reared weevils, 286

Liapis, P. S., 105, 123 Lickerish, L. A., 26 Lin, Y. N., 32, 34, 35, 43,

48, 49, 52 Lincoln, C., 81, 96, 98, 247,

248, 260, 529, 530, 554

Lindig, 0. H., 160, 161, 162, 163, 164, 172, 173, 174, 175, 176, 200, 265, 266, 269, 273, 296, 297, 298, 300

Lindquist, A. W., 154, 174, 175

Lindquist, D. A., 170, 171, 204, 324, 351

Lingren, P. D., 25, 110, 123, 124, 125, 205, 233, 327, 350

Linstone, H. A., 44, 52 Lippke, L. A., 554 Litsky, B. Y., 288, 298 Litsky, W., 298 Little, V. A., 64, 69 Lloyd, E. P., 3, 11, 12, 15,

23, 24, 54, 69, 155, 167, 175, 177, 179, 187, 190, 195, 198,

200, 202, 203, 204, 207, 218, 219, 223, 232, 248, 249, 259, 260, 261, 325, 344, 347, 355, 406, 407, 424, 425, 435, 444, 478, 540, 542, 554

Lockwood, D. F., 175, 202, 435

Loden, H. D., 353 Loew, W., 324, 378 Longoria, R. R., 357 Lopez, J. D., Jr., 22, 110,

122, 123, 182, 200, 203, 325, 379, 477

Lovestrand, S. A., 211, 232 Lowe, A, M., 301 Lowry, W. L., 348, 354 Luck, R. F., 324 Lue, P. S., 177 Lukefahr, M. J., 22, 69, 84,

96, 98, 100, 125, 247, 260, 341, 342, 347, 544, 552, 553, 554

Lund, H. 0., 353 Lu Po-yung, 233 Luttrell, R. G., 140, 147,

151, 353, 555, 557 Lygaeidae (big-eyed bugs),

predators known to attack Heliothis spp., 106

Lygus hesperus, lygus bug, a primary pest species of cotton in Western United States, 208, 361

L. lineolaris, tarnished plant bug, 63, 74, 208, 211

collection by D-Vac, 317 insect management programs

can be devastated by, 534

lint yield affected by, in untreated fields, 343

pest of cotton (primary) in Midsouth, 208

Lygus spp., 8, 64, 65, 85- 86, 104, 119, 238, 253, 256, 340, 387, 536

580 INDEX

Lymantría dispar, gypsy moth, diflubenzuron is registered for use against, 209

Lyon, L. R., 288, 298

MacGown, M. W., 286, 287, 299 MacGregor, J. T., 26 MacLeod, J., 306, 325 Madelin, M. F., 134, 148 Magnoler, A., 288, 299 Malathion, 224 Mally, F. W., 188, 203, 524,

554 Malone, 0. L., 174, 297, 298 Malvaviscus drummondii, a

possible alternate host of boll weevil in south Florida, but its isolation makes it unlikely, 544

Mansager, E. R., 214, 232 Marking with calco oil red

N1700 dye for identification of mass- reared sterile adult boll weevils, 163-164

Marlatt, C. L., 330, 333, 347

Marshall, J. H., 295 Marston, N. L., 310, 326 Martignoni, M. E., 150, 301 Martin, D. F., 23, 27, 69, 98,

143, 146, 199, 259, 288, 299, 347, 353, 357, 434

Martinez, A. J., 301 Martinez, E., 145 Martouret, D., 144 Mass rearing of sterile boll

weevils for release in BWET, procedures for, 155-162

Masud, S. M., 527, 554 Mating, of sterile male boll

weevils and native females, theoretical possibilities, 166- 167

Mattesia grandis, a protozoan pathogen that infects Heliothis spp. and pink bo11worm, 136

Mattix, E., 173

Maxwell, F. G., 96, 97, 98, 99, 100, 125, 555

Mayer, M. S., 175 Mayeux, H. S., 349 Mayse, M. A., 307, 309, 326 McCarty, J. C., Jr., 84, 96,

97, 98, 99, 173 McClendon, R. W., 19, 378,

437, 439, 476, 479, 483, 494, 495

McCommas, D. W., Jr., 121 McCoy, C. W., 134, 147 McCoy, J. R., 27, 156, 175,

177, 260, 312, 316, 317, 325

McDaniel, S. G., 105, 110, 118, 123, 215, 232, 464, 465, 479

McDonough, L. M., 200 McEwen, F. L., 288, 298 McGarr, R. L., 139, 147, 148,

349, 354, 357 McGough, J. M., 199 McGovern, T. P., 230, 232 McGovern, W. L., 83, 98, 99,

121, 123, 165, 173, 175, 177, 202, 203

McGuire, J. U., Jr., 123, 202, 435

McHaffey, D. G., 156, 170, 175, 176, 233

Mcintyre, R. C., 204, 555 McKibben, G. H., 163, 165,

170, 171, 173, 175, 179, 184, 185, 200, 201, 202, 203, 394, 406, 407, 435

McKinion, J. M., 361, 378, 380, 438, 439, 479

McLaughlin, J. R., 137, 147 McLaughlin, R. E., 133, 135,

136, 139, 144, 147, 148, 172, 173, 212, 232, 266, 285, 286, 287, 288, 297, 299

McLeod, P. J., 131, 148 McMeans, J. L., 478 McNeil, G. L., 20 Melnick, J. L., 298 Meloidogyne incognita, root-

knot nematode, is prevalent in cotton fields in Southeast Region, 76

INDEX 581

Melville, D. R. , 149 Menn, J. J., 209, 227, 232 Meredith, W. R., Jr., 85, 86,

96, 98, 99, 346 Merkl, M. E., 69, 171, 175,

202, 260, 347, 355, 435, 478, 554

Metarrhizium anisopliae, boll weevils are susceptible to infection by this fungus, 136

Metcalf, R. L., 214, 233 Methomyl, 46, 48, 49, 67 Methyl parathion, 7, 29, 46,

48, 49, 67 for reproduction-diapause

control : in large-scale experiment

in Big Bend area of Texas, 248

insecticide used in OPMT, 401

Meyer, J. R., 98 Michael, C., 52 Microbial agents, 129-142

Heliothis nuclear polyhedrosis virus and Bacillus thuringiensis can both suppress moderate to low populations of Heliothis zea and H. virescens, Î29"

nuclear polyhedrosis virus from alfalfa looper (ACNPV) infects pink bollworm larvae, 137

Serratia marcescens, a bacterium, can kill the boll weevil, 133

two protozoan pathogens, Mattesia grandis and Glugea gasti, infect the bollworm, the tobacco budworm, and pink bollworm, 136

Micrococcus luteus, bacteria infecting boll weevils, 286

M. varians, bacterial con- ~" taminant of boll

weevils, 287 Miles, L. R., 231 Miller, A. E., 21

Miller, E., 301 Miller, P. A., 73 Minyard, J. P., 205 Miridae, 111 Mississippi Cooperative

Extension Service, 4 Mississippi Crop and Live-

stock Reporting Service, 485, 486, 495

Mistric, W. J., Jr., 352, 357, 541, 554

Mitchell, E. B., 24, 69, 158, 170, 171, 172, 175, 183, 186, 192, 199, 200, 201, 203, 232, 394, 407, 554

Mitchell, E. R., 12, 24, 180, 183, 204, 205, 381, 554

Mitchell, H. C, 54, 57, 69, 70, 81, 99, 121, 123, 199, 202, 407

Mitlin, L. L., 54, 70 Mitlin, N., 70, 173 Models (simulation), for

cotton insect pest management:

BWSIM (J>oll weevil simulation model), 445, 453-455

CIM (cotton and insect management simulation model), formed from the boll weevil model (CIM-BW), the Heliothis spp. model (CIM-HEL), and the cotton crop model (COTCROP), was structured to aid in development and evaluation of insect pest control strategies on yield, insecticide usage, and cost of insect management, 464-475, 481-493

CIM-BW, based on BWSIM, 445-455

CIM-HEL, 456-463 COTCROP, based on SIMCOT

and COTTON, 439-445

582 INDEX

cotton growth model, 439-440

soil model, 441-445 CIM-BW (cotton and insect

management-boll weevil simulation model:

model compared with BWSIM, from which it was modified, 453, 455

schematic of boll weevil and cotton interactions, 447

structure, 446 weevil development,

fecundity, feeding, and mortality within CIM-BW model, 449- 452

subroutine calling sequence, 448

CIM-HEL (cotton and insect management-Heliothis spp. simulation model), with 11. virescens and Ü* ^^^ separated because of different rates of development, 456, 458-460

calling sequence for, 457 data on insect development,

fecundity, feeding, and mortality, 456-463

structure, 456 COTCROP (cotton model),

developed to study insect and other management strategies including irrigation and nitrogen fertilization and composed of a crop growth model and soil model, 439-445

COTTON, a cotton model developed for western cotton production under irrigation, 439

GOSSYM, a more recent cotton model than SIMCOT but derived from it with a highly detailed model of soil, water.

and plant-root relationships and plant growth dynamics algorithm, 361

MOTHZV (Heliothis population model), 362

flowchart for, 363 MOTHZV-2, a more detailed

population model than MOTHZV, that included simple crop models for corn, cotton, and sorghum; the FORTRAN computer program for MOTHZV-2 consisted of a main computer program and 16 subroutines, 362, 365

flowchart for, 364 use in BUGNET program in

Texas, 374 MOTHZV-3:

produced by addition of a Heliothis damage submodel, 369-372, 374-377

revision of MOTHZV-2 with replacement of original cotton model with SIMPLECOT, 365-369

MOTHZV-4, a simplified version of MOTHZV-3 which lacked versatility of MOTHZV-3 but could predict timing of Heliothis spp. oviposition, 375

use with BUGNET, 375 SIMCOT, an early cotton

model developed to calculate daily production and distribution of photosynthate of cotton, under southeastern conditions, 361, 439

SIMCOT II, a revision of SIMCOT to interface with insect models to fit California environment and cotton varieties, 361, 439

INDEX 583

SIMPLECOT, was derived from SIMCOT by adding a submodel for cotton fruiting behavior that interfaced with MOTHZV- 3, 365-369

Modified Optimum Pest Manage- ment (MOPM), 482

Monocrotophos, 46, 48, 49 Montoya, E. L., 139, 148 Moody, D. L., 232 Moody, R. J., 387, 406, 407 Moore, G. C., 553 Moore, L. , 406 Moore, R. F., Jr., 27, 156,

157, 175, 177, 211, 212, 228, 233, 297, 347

Moreland, R. W., 353 Moritz, R. J., 199 Morris, R. F., 304, 306, 324,

326 Morrison, R. K., 144, 177,

229, 231, 235, 349 Moss, A. M., 124 Mott, D. G., 304, 326 Mulder, R., 211, 233, 234 Mulkey, J. R., 99, 555 Mulla, M. S., 232 Mullinix, B. G., 204, 205 Mullins, P. W., 355 Murphey, S. M., 483, 495 Musca domestica, house fly,

154, 210 Mjonaridae, 62

Nabidae (damsel bugs), beneficial insects, 63, 64, 106, 111

Nabis spp., 216 Nagasawa, S., 288, 299 Nail, B. J., 173 Namken, L. N., 12, 22, 24,

73, 86, 87, 96, 99, 526, 527, 553, 554

National Academy of Sciences, 168, 176

National Cotton Council, 180, 239, 260, 334, 347

National Cotton Council Technical Subcommittee, 550, 551, 554

Neeb, C. W., 204, 539, 555 Nemec, S. J., 7, 24, 211,

233, 552

Nemny, N. E., 229 Neter, E., 283, 299 Neurocolpus nubilus, clouded

plant bug, can be a pest of cotton, 63-65

Newsom, L. D., 4, 13, 24, 97, 119, 123, 258, 434, 481, 495

Nichols, F., 69, 199 Nicholson, W. F., Jr., 444,

463, 479, 555 Nilakhe, S. S., 20, 165, 171,

176, 177 Niles, G. A., 27, 99, 100,

378, 555, 556 Nishimura, H., 299 Noble, J. M., 230 Noble, L. W., 8, 24 Nolting, D. J., 380, 479 Nomuraea rileyi, a fungus

pathogenic to boll weevils, 136

Norgaard, R. B., 517 Norland, J. F., 173, 174 Norman, J. W., 22, 96, 553 North Carolina Crop Reporting

Service, 501 Nosky, J. B., 357 Notoxus spp., predators of Heli-

othis spp., 107, 111 Nuclear polyhedrosis virus:

ACNP, from alfalfa looper, 141

Baculovirus heliothis, 129- 131, 138, 139

Nucleopolyhedrosis, a disease caused by a nuclear polyhedrosis virus, 131

O'Dell, T. M., 288, 299 Oldacre, S. W., 297 Oliver, B. F., 84, 85, 99 Oliver, J. E., 209, 233 Olsen, C. M., 200 Oman, P., 171 Optimum Pest Management (OPM),

482 Optimum Pest Management-Boll

Weevil Eradication, 482 Optimum Pest Management Trial

(OPMT) in Mississippi, 3, 13, 15, 53, 61-62, 110, 159, 185, 249, 481-482, 522, 538, 544

584 INDEX

components of OPMT: diapause control (with full

reimbursement to producers for costs):

insecticide costs per acre for 1978, 1979, and 1980, 385

insecticide usage, 249, 256-257, 391, 394, 401

inseason control of cotton insects based on scouting reports, 392, 398, 400

pinhead square application of insecticides, 392, 397

planting dates, 392, 397 scouting, 392, 397-399 mapping, 391, 393

stalk destruction, 394, 397

trapping: blacklight tra^s for Heliothis spp., 392

pheromone traps: cone Heliothis spp.

traps, 392-397 Leggett traps, 392-397 modified Mitchell

traps, 392-397 contractual agreements, 391 location of: Panola County, Mississippi,

site of trial, 387 Pontotoc County,

Mississippi, control site where normal procedures were followed (Current Insect Control (CIC)), 387

objectives and goals, 388 Orius insidiosus, most

numerous predator in area, 318

personnel : advisory, 389 for operations, 388-390

public awareness and education, 389, 391

sampling techniques, four compared:

field observations by entomologist, 312-323

D-Vac, 312-323 sweep net, 312-323 unit area sampler, 312-323

support for: Mississippi Department of

Agriculture and Commerce, Division of Plant Industry, 403- 404

research groups, 404-405 yield and insecticide usage

determined by regression analysis, replicated experiments and simulation, 438

Orius insidiosus, predator of Heliothis spp., 106

Orius spp., 62, 64, 111, 114 —' tristicolor, predator of

Heliothis spp., 106 Orthoptera (Saltatoria), 62 Owen, W. L., Jr., 258, 356,

434 Oxborrow, G. S., 295 Oxyopes salticus, a predator

of Heliothis spp., 106

Parathion, 48, 49 Parencia, C. R., Jr., 4, 21,

24, 86, 99, 180, 204, 237, 239, 246, 247, 249, 250, 258, 259, 261, 311, 316, 317, 326, 341, 343, 347, 350, 351, 353, 354, 355, 553

Paris green, 5, 239 Parker, R. D., 91, 95, 99,

524, 525, 526, 529, 541

Parrott, W. L., 83, 85, 96, 97, 98, 99, 100, 173, 478, 544, 555

Parvin, D. W. , Jr., 23, 29, 51, 52, 199, 479, 481, 486, 494, 495, 517

Pate, T. L., 143 Patti, J. H., 139, 149 Pectinophora gossypiella,

pink bollworm, 3, 4, 5, 7, 15, 104, 105, 119, 120, 136, 137

INDEX 585

138, 208, 210, 227, 238, 246, 247, 329, 332, 333, 339, 341, 342, 361, 549

Penfluron, insect growth regu- ator, 156-157, 209-210, 226

Pénicillium spp., 286 Pentatomidae (Asopinae), Heli-

othis predator. 111 Percy, R. G., 19 Perkins, J. H., 4, 9, 11, 13,

24, 168, 176 Perkins, W. D., 297 Permethrin, 46, 48, 49 Pesticide use, see also

Insecticides, 30 survey and results, 37, 38,

40, 44 Pest management strategies,

implementation, 16 Peters, P. K., 177 Pfrimmer, T. R., 139, 149,

204, 237, 355 Phalacridae, 63 Phaltan, 286 Phene, C. J., 378 Phillips, G. B., 300 Phillips, J. R., 4, 15, 21,

25, 325, 521, 532, 533, 555

Ph3miatotrichum omnivorum, causes root rot of cotton, 81

Pickett, A. D., 6, 25 Pierce, W. D., 5, 23, 25, 104,

124, 477 Pieters, E. P., 140, 149, 308,

311, 326, 355, 356 Pilot Boll Weevil Eradica-

tion Experiment, Mississippi, 11, 15, 153, 155, 185, 249, 266, 410, 411, 413, 415, 416, 417, 418, 419, 423, 540

Pilot pest management project, 389

Pimentel, D., 119, 124 Pink bollworm, Pectinophora

gossypiella, see Arthropods

Pinnell, R. E., 123 Pitre, H. N., Jr., 107, 122,

124, 325

Pitts, D. L., 356 Plimmer, J. R., 200, 201,

202, 380 Poinar, G. 0., Jr., 291, 299 Pomonis, G., 172 Ponder, W. W., 326 Pons, W. J., 235 Populations of insects:

boll weevil, effect of short season cottons on, 91-94

differences in predator populations :

by cotton varieties, 107 by location, 107

modeling populations of entomophagous arthropods and Heliothis spp. for IPM decision making, 114-118

suppression, of Heliothis spp., efficacy of predators, 109-120

fundamental principles of, 410-412

Post, G. B., 6, 25 Post, L. C., 211, 233 Predators, of cotton insects,

particularly Heliothis spp., 106- 120

Price, P. W., 105, 112, 114, 124, 326

Price, R. G., 356 Primiani, M., 201, 202 Production indexes, cost of,

36 Protozoa, Mattesia grandis

and Glugea gasti infect Heliothis spp., 136

Pruitt, G. R., 233, 556 Pryor, N. W., 144 Pseudatomoscelis seriatus,

cotton fleahopper, 8, 63, 64, 85, 208, 211, 238, 252, 314, 329, 332, 333, 339, 342, 375, 526

Pseudomonas aeruginosa, 286 Psocoptera, 63 Puleo, J. R., 295 Pythium spp., 77

586 INDEX

Quaintance, A. L., 110, 124, 320, 326, 372, 380, 463, 479

Rabb, R. L., 9, 13, 25, 380 Ramsey, D. A., 122 Ranney, C. D., 99 Raulston, J. R. , 205 Raun, E. S., 288, 298, 299 Ray, L., 70, 204, 327, 555 Reddy, M. S., 100 Redfern, R. E., 232 Red imported fire ant,

Solenopsis invicta, 104

Reduviidae, 111 Reduviolus alternatus,

a predator of Heliothis spp., 106

_R. americoferus, a Heliothis spp. predator, 106

R. roseipennis, 114 Ree, B., 356 ~" Reeves, S. A., 96 Regional Extension Educational

Advisory Committee, 389

Reproduction-diapause control, 188, 247, 249-251, 256-257, 391, 394, 401

Resistance, to boll weevil in cotton, 81-85

Reynolds, H. T., 4, 25, 119, 124, 171, 318, 326

Reynolds, W. T., 126 Rhizoctonia solani, cause of

seedling disease in cotton, 77

Rhizopus spp., 286 Rhyne, C., 98 Rice:

acreage in Mississippi, 485 yield, 487

Richmond, C. A., 311, 327, 349, 356

Ridgway, R. L., 3, 4, 6, 8, 12, 15, 20, 22, 25, 26, 103, 106, 108, 113, 117, 119, 121, 122, 123, 124, 125, 144, 190, 199, 204, 215, 230, 233, 320, 324, 327, 346, 350,

351, 353, 356, 379, 477

Riley, C. v., 104, 125, 237, 261

Ripper, W. E., 6, 26 Ritchie, J. T., 443, 479 Roach, S. H., 54, 70, 188,

204, 307, 316, 327, 3.94, 407, 548, 555

Roberson, J. L., 163, 173, 174, 176, 177, 292, 297, 298, 299, 301

Roberts, D. W., 134, 149 Rodriguez, R., 510, 511,

517 Roelofs, W. L., 180, 204 Rogers, R, L., 357 Rogers, S., 52 Rollinson, W. D., 299 Romine, C. L., 143, 349 Romkens, M. J. M., 476 Root-knot nematode,

Meloidogyne incognita, 76, 215

Root rot, of cotton, caused by Phymatotrichum omnivorum, 81

Rothrock, M. A., 553 Roussel, J. S., 7, 21, 26,

246, 261, 295, 337, 338, 347, 349, 525, 555

Ruesink, W. G., 307, 310, 327 Rummel, D. R., 191, 204, 216,

217, 220, 221, 224, 233, 235, 249, 258, 261, 434, 539, 540, 541, 542, 544, 548, 549, 552, 555, 556

Runkle, R. S., 284, 288, 300

Salter, S. S., 200 Salticidae (jumping spiders),

106 Saltmarsh caterpillar,

Estigmene aerea, 209 Sampling, arthropods in

cotton, 303-323 Sarmiento, R., 230, 232 Sartor, C. R., 406, 407 Scales, A. L., 175, 353 Scelionidae, 62 Schlinger, E. I., 324 Schreiner, I., 124

INDEX 587

Schroeder, W. J., 211, 234 Schuster, M. F., 83, 85, 97,

99, 100, 107, 125, 311, 327

Schwab, G. 0., 443, 479 Schwartz, P. H., 329, 332,

335, 336, 347, 356 Schwarz, M., 230, 232 Scott, H. A., 148 Scott, W. P., 191, 202, 203,

204, 258, 303, 435, 554

Scouting, 6, 68, 385, 386, 392, 397, 399, 486

a key component of present- day pest management strategies, 6

control decisions based on examination of cotton fields for presence of adult boll weevils or damaged fruit, 225

data gathered by scouts include in addition to insect populations, stage of cotton crop, current growing conditions, past history, and potential yield, 398

percentage of cotton squares damaged by bollworms reported by OPMT scouts, 1978-1980, 399

scout training workshops conducted for OPMT, 391

whiteflies, thrips, aphids, Lygus, fleahoppers, Heliothis spp., clouded plant bugs, and boll weevils are the pests the trained scout looks for and records for eastern part of Cotton Belt, 64

Scymnus, 111 Seale, R. D., 483, 486, 488,

494, 495, 496 Seay, R. S., 235 Secondary cotton pests, most

important, 208 Selhime, A. G., 234

Serratia marcescens, a bacterium that sometimes kills boll weevils, 133, 136

Seward, R. W., 385 Shapiro, M., 284, 288, 300 Sharpe, J. H., 378 Shaunak, K. K., 203 Shaver, T. N., 200, 201, 203,

230, 379 Shaw, D., 230 Shaw, F. R., 324 Shepard, H. A., 6, 26 Shepard, M., 107, 108, 124,

125, 311, 327 Shieh, T. R., 133, 139, 149 Shipp, 0. E., 356 Sikorowski, P. P., 160, 171,

176, 177, 265, 267, 272, 273, 277, 280, 283, 284, 285, 286, 287, 288, 290, 291, 292, 297, 298, 299, 300, 301

Simmons, L. A., 20, 171 Simpson, E. H., Ill, 481, 495 Simpson, G., 495 Simulium vittatum, black fly,

BAY SIR 8514 effective against, 210

Sirrenberg, W., 235 Skeith, R., 21 Slatten, B. H., 136, 149 Sloan, C. E., 173 Slosser, J. E., 375, 380,

527, 556 Smith, C. E., 356 Smith, D. B., 100, 146 Smith, G. L., 352, 358 Smith, J. W., 108, 125, 303,

307, 308, 311, 318, 320, 327

Smith, K. M., 131, 149 Smith, R. F., 22, 25, 26,

124, 387, 407 Smith, R. L., 230 Smith, W. R., 349, 356 Snow, J. W., 182, 204 Solenopsis invicta, red

imported fire ant, a potential predator of boll weevil, 104

Solomon, M. E., 112, 125 Sonnet, P. E., 232

588 INDEX

Sorghum bicolor, sorghum, crop model included within MOTHZV-2, 362, 373

Southwood, T. R. E., 304, 305, 307, 316, 328

Sowell, R. S., 478 Soybean:

cropland acreage in Mississippi, 485

soil resources, acreage, and per acre soybean yields, 487-488

Sparks, A. N., 181, 182, 201, 202, 204, 205, 297, 380

Spates, G. E., 177, 235 Sphaeralcea angustifolia,

possibly an occasional host for boll weevil in Texas, 544

Spider mites, Tetranychus spp., secondary pests of cotton, 6, 244, 255, 329, 332, 333, 339, 340

Spiders, 111 Spodoptera exigua, beet army-

worm, a cotton defoliator, 141, 209, 361, 534

-§-• frugiperda, fall army worm, is resistant to organophosphorus insecticides, 210, 246, 534

1' l^ttoralis, 211 Spodoptera spp., 105 Sprott, J. M., 526, 527, 541,

556 Staal, G. B., 209, 227, 228,

234 Stable flies, Stomoxys

calcitrans, 211 Stacey, A. L., 140, 149, 151,

557 Stadelbacher, E. A., 125, 149,

325, 327, 355 Stairs, G. R., 133, 150 Stanley, J. M., 201 Staphylococcus aureus, 286 Stapleton, H. N., 361, 380,

439, 479 Starbird, I. R., 8, 26, 32,

37, 45, 52

Starler, N. E., 26 State Extension and Crop

Reporting Service (North Carolina), 498

Staten, R. T., 150 State Pest Management

Advisory Committee (Mississippi), 389

Stehr, F. W., 109, 125 Steinhaus, E. A., 130,^131,

150, 283, 288, 300, 301 Sterilization, of boll

weevils, 153, 154- 157

Sterling, H. R., 406 Sterling, W. L., 12, 26, 105,

123, 125, 149, 160, 176, 232, 258, 304, 326, 327, 328, 434

Stern, V. M., 7, 26, 27, 126 Stewart, F. D., 288, 301 Still, G. G., 212, 232, 234 Stinner, R. E., 126, 314,

316, 328, 361, 379, 380, 478

Stipanovic, R. D., 85, 100 Stokes, J. B., 230 Stoner, A., 259, 434 Streptococcus spp., 286 Strickland, A. H., 304, 328 Suber, E. F., 348 Suguiyama, L. F., 497 Sulfur, was more effective

than calcium arsenate in control of late- season cotton insects, 6, 239

Surveys, of pesticide use and sales in the world and in the United States in the last decade, 30-50

Sutter, G. R., 288, 301 Sutton, R. A., 234 Systena spp., minor pests of

cotton, 63

Taft, H. M., 70, 175, 211, 218, 219, 232, 233, 234, 260, 353, 356, 542, 556

Tañada, Y., 135, 150

INDEX 589

Tarnished plant bug, Lygus líneolarís, see Arthropods

Taylor, C. R., 554 Tejada, L. 0., 110, 126 Telford, A. D., 126 Terry, P. H., 156, 170, 176 Tetranychus cinnabarinus,

diflubenzuron effective against, 211

Tetranychus spp., 6, 244, 255, 329, 332, 333, 339-340

Texas A&M University, 120, 373, 524, 548

Texas Agricultural Extension Service, development of BUGNET, a computerized pest management delivery system, 372-377

Texas Pest Management Association, 15

TH-6040, see Diflubenzuron Thespesia populnea, possible

host of boll weevil in south Florida, 544

Thespesia sp., 54 Thomas, B. R., 177 Thomas, F. L., 122 Thomas, G. M., 299 Thomas, J. G., 529, 540, 556 Thomisidae (crab spiders), 106 Thompson, A. C., Jr., 173,

205, 231, 286, 287, 300, 301

Thompson, T. E., 124 Thripidae, Thrips, 62, 64, 340 Aeolothrips, bandedwinged

thrips, 64 cotton with high gossypol

has increased susceptibility to thrips, 85

Tifton, K. W., 97 Tingle, F. C, 69, 202, 203,

249, 259, 260, 261, 434, 435, 554

Tinney, J. C., 26 Toba, H. H., 381 Tobacco budworm, Heliothis

virescens, see Heliothis spp.

Todd, J. W., 234, 345, 348 Toscano, N. C, 126

Total population management (TPM), 9-13

Townsend, C. H. T., 5, 26, 237, 261

Townsend, J. R., Jr., 369, 370, 372, 380

Toxaphene, 29, 48, 49, 67 extensive use of this

insecticide diminished with the advent of the pyrethroid insecticides, 46

Trap crops, for suppression of boll weevils, 188, 191

Trialeurodes abutilonea, bandedwinged whitefly, 62, 64, 246

Trichogramma pretiosum, egg parasite of Heliothis spp., 216, 223

Trichogramma spp., 115, 120, 217

Trichoplusia ni, cabbage looper, 105, 141, 208, 329, 332, 339, 361

Tsao, C. H., 341, 342, 343, 348

Tsuchiya, T., 299 Tumlinson, J. H., 69, 180,

184, 199, 200, 201, 204, 205, 374, 381

Turnipseed, S. G., 216, 234 Turoff, M., 52

Ultraviolet radiation, of boll weevils, 131

University of California, Riverside, 120

U.S. Congress, 8, 26 U.S. Department of Agricul-

ture, 4, 12, 15, 27, 32, 36, 37, 44, 45, 52, 330, 331, 333, 334, 340, 348, 488, 496, 505, 513, 517, 523

U.S. Department of Agricul- ture Marketing service office areas, 78

Vail, P. v., 137, 142, 150 Van Daalen, J. J., 234

590 INDEX

van den Bosch, R., 8, 26, 27, 105, 108, 110, 113, 119, 122, 126, 320, 324, 325, 328, 378

Vanderzant, E. S., 160, 176, 266, 301

VanDuyn, J. W., 328 Van Steenwyk, R. A., 105, 113,

119, 126 Vardell, H., 296 Varley, G. C., 304, 328 Veal, S. D., 148 Veech, J. A., 215, 234 Verloop, A., 211, 214, 234 Verticillium dahliae, a prev-

alent fungal pathogen of cotton, in the Midsouth, 76, 77

Villavaso, E. J., 153, 157, 158, 159, 165, 166, 171, 176, 177

Vincent, W. R., 233 Vinson, S. B., 26, 229, 327 Vinzant, B. G., 124 Virelure, synthetic pheromone

of Heliothis virescens, 180-181

Viruses: chilo irridescent virus,

infectious to boll weevil, 138

Heliothis spp. nuclear polyhedrosis virus, is host specific to Heliothis spp,, 131

nuclear polyhedrosis virus, ACNPV, isolated from alfalfa looper, infects pink bollworm larvae, 137

Von Rumker, R., 500, 517

Waddle, B. A., 81, 86, 96, 98, 100

Wade, L. J., 233 Waiss, A. C., Jr., 85, 100 Wakabayashi, N., 232 Walker, A. B., 171 Walker, H. J., 356 Walker, J. K., Jr., 7, 12, 27,

54, 70, 86, 91, 95, 99, 100, 125, 357, 524, 525, 555, 556

Walker, R. L., 351

Wall, M. L., 406 Walter, J. K., 378 Walters, S., 200 Walton, G. S., 295 Wang, Y., 21, 378, 477 Ware, J. 0., 524, 556 Warren, L. 0., 314, 328 Waters, R. M., 232 Waters, W. E., 305, 328 Watkins, W. C., 324, 350, 351 Watson, F. L., 380, 479 Watson, T. F., 123, 145,

230, 357 Watt, K. E. F., 114, 126,

304, 305, 328 Watts, J. G., 357 Weaver, D. B., 357 Weaver, J. B., Jr., 83, 97,

100, 357 Weeks, J. R,, 200 Weiser, J., 135, 150 Wellinga, K., 209, 234 Wellso, S. G., 176 Westphal, D., 378 Whisler, F. D., 476, 478 Whitcomb, W. H., 64, 70,

105, 109, 110, 121, 126, 215, 235, 318, 320, 328

White, J. R., 225, 233, 235, 527, 556

White, W. H., 97 Whitefly, bandedwinged,

Trialeurodes abutilonea, 62, 64, 246

Whitten, C. J., 228, 235 Whitten, M. J., 168, 177 Wilkins, J. S., 349 Wilkinson, J. D., 163, 177,

215, 216, 235 Williams, B. R., 357 Williams, P. P., 295 Wilson, A. G., 361, 365, 381 Wilson, C. A., 121, 406 Wilson, F. D., 150 Wilson, L. T., 463, 479 Wilson, N. M., 203 Wilson, R. J., 6, 27 Wilson, R. L., 150 Wipprecht, R., 21, 352 Witz, J. A., 22, 122, 175,

200, 201, 202, 325, 359, 360, 379, 381, 406, 435, 477

INDEX 591

Wiygul, G., 27, 172, 174, 177, 298, 300

Wolf, W. W., 374, 381 Wolfenbarger, D. A., 86, 101,

147, 231, 354, 357, 553

Wood, R. H., 24, 232, 554 Woods, C. W., 170 Wright, J. E., 12, 27, 153,

156, 157, 158, 163, 165, 166, 170, 173, 174, 175, 176, 177, 211, 232, 235, 298, 299

Wyatt, J. M., 176, 297, 298, 300, 301

Xanthomonas malvacearum, the cause of bacterial blight of cotton, 77

Yearian, W. C, 12, 27, 139, 140, 146, 147, 148, 149, 151, 353, 532, 555, 557

Yendol, W. G., 149 Yield (cotton):

increase with new insecticides, 251

reduction, due to insects, 240-243, 329-345

Yokayama, V. Y., 108, 127 Young, D. F., Jr., 64, 70,

385, 406, 407 Young, J. H., 356 Young, M. T., 352, 357, 358 Young, S. Y., 27, 131, 139,

146, 147, 148, 149, 151, 353, 557

U)-9-tetradecenal (Z;-9-TDAL) and (Z^)-ll-hexadecenal U-11-HDAL) are two components of Heliothis virescens pheromone, 180

Zelus renardii, assassin bug, predator of pests in cotton, 114

Zoebelein, G., 210, 235

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