Varíation in the Effects of HosË Plant on Ëhe Pea Aphid,

Acyrthosiphon písum (Harris) (Homoptera: Aphididae)

by

S.M. Chandrasíri Subasinghe

A Thesís

Submitted to Èhe Faculty of Graduate Studies of

the Uníversity of Manítoba ín Partial

Fulfíll-ment of the Requirements

for the Degree of

Doctor of Philosophy

DeparËment of Entomology

The Uníversity of Manitoba

Winnipeg, ManíËoba

Canada

l-982

VAR]ATION IN THE EFFECTS OF HOST PLANT ON THE PEA APHID,

ACYRTHOSIPHON PISUM (HARRTS) (HOt'roptnRe: ApHTDTDAE)

BY

S.M. CHANDRASIRI SUtsASINGHE

A thesis subnritted to trre Faculty of Graduate' studies ofthe u¡riversity of Ma¡ritoba i' partial fulfillnrent of the require'rerrtsof the degree of

DOCTOR OF PHILOSOPTTY'/o 1983

Per'issior has beer grarrted to the LIBRARY oF THE uNIVEIì_slrY oF MANIToBA ro re'd or seil co¡rics of'this rhesis. rothe NATIONAL LIBRARy oF CANADA ro nricrofilnr thisthesis ard to rend or seil copies of the firm, and UNIVERSITYMICROFILMS to publish an abstract of this thesis.

The author reserves other publicatio' rights, and neither thethesis nor extensive extracts fronl it may be printed or other-wise reproduced without the author's written pennission.

ABSTRACT

BY

S.M.C. Subasinghe

Variatíon in the effects of host plant on the pea aphid, Acyrthosí phon

písum (Harrís) (HomopËera: Aphididae)

Field and laboratory studies vlere carríed out on the variation ín

hosË planË responses of Acyrthosiphon pisum. The relationshíp between

aphíd response on previous host plant and responses to new host plants

was also examíned. Field transfers were made among plots of alfalfa,

saínfoín, trefoil, s\^/eet clover, fíeld peas and fababeans. parameters

estímated hTere mean survival- and mean fecundíty. Detaí1ed studies r^7ere

carríed ouÈ ín the laboratory with field collected samples of clones

from differenË hosts. rn thÍs case, nymphal survíval and adulÈ dry

weight I^lere measured in addítion to the parameters mentíoned above.

Among aphíds ín any single field, great variatíon in response r4ras

observed when aphíds were exposed to dífferent host plants. This vari-

aËion \^7as as great as that reported between bíotypes havíng díverse geo-

graphic origín. Moreover, characterístics of aphid populatíons on

different hosts ürere not dístínct and persistent. Clones present on

one partícular host plant show some shorË term selectíon during summer

when reproducËíon ís parthenogeneËic, presuflr¿tbly through dífferential

survival reproduction, and/or mígration. Thís is follor,¡ed by genetic

recombination duríng sexual reproductíon ín the fa1l resuJ_tíng in a

111

different set of aphid genotypes. There is no relatíonship between re-

sponses of clones to different host plants in one year and their re-

sponses to the same host plants in anoÈher year. Therefore, biotypes

are annual phenomena.

Samples of cl-ones from older, geographically separated populations

showed sorne differences. These differences nay be attríbuted to spacial

separation, the high selectíon pressures exerted by insecticides on one

of the populaËíons or to the different varíetíes of Èhe host. Relative

status of thís varíatÍon of clones available from widely dífferent geo-

graphic areas, particularly where anholocycle prevail-s, remaíns to be

es tablÍshed.

Clones exhibiting variable characterístics are not mutually ex-

clusíve. Therefore, the system of nomenclature currently beíng employed

seens inappropríate. rt appears that the sympatríc biotypes of A. pisum

prevailÍ-ng ín any population represent fairly símple genetíc varíants.

Therefore, identifyíng and naming or otherwise l-abelling of clones of

A. písun could lead to confusíon as ít may gíve a false impression of

the biologícal status of the ínsect.

ACKNOI^ILEDGEMENTS

Thís study r¡ras undertaken at the suggestion of Dr. P.A. MacKay,

Department of EnËomology, the University of Manitoba, Inlínnipeg, Manítoba,

Canada. I wísh, therefore, to express rny deep sense of gratitude to

Dr. MacKay for advice, constant encouragement, and helpful critícísms

at all staËes whÍch enabled me to,carry out the study successfully.

My sincere gratlÈude ís extended to Dr. N.J. Holliday, Department

of Entomology, UniversÍty of Manitoba, for advice ín statistícal- analysís

and helpful cormnents on the manuscript. A sírnílar gratíÈude ís extended

to Dr. R.A. Brust, Department of Entomology, ancl to Dr. A.K. SËorgaard,

DepartmenÈ of Plant Scíence, for servíng on my advísory commíttee and

giving me help whenever needed.

I am thankful to Dr. B.D. Frazer, Agriculture Canada, Research

SËation, Vancouver, B.C., for acting as the External Examiner and also

for taking the trouble in comíng all the way Èo attend the oral

examination.

Tt is my pleasure to express my great índebtedness to

Dr. A.G. Robínson, Professor Emeritus and Former Head, and to

Dr. S.C. Jay, Professor and Head, Department of Entomology, Uníversíty

of Manitoba, for the Ínterest they showed in my academic program and the

help they extended to me. Great gratitude is also owed to Dr. R.J. Larnb

and Dr. P.S. Barker of AgriculÈure Canada, Research Statíon, I^Iínnipeg,

for their help and cormnents at varíous stages of the study.

I am grateful Ëo Ëhe Department of Agriculture, Government of the

Republic of Sri Lanka, for grantíng me three yearst study leave and to

the International Development Research Centre (IDRC) for the fellowship.

v

The research projecË was funded by grants from Natural sciences and

Engineering Research Council of Canada and from Agriculture Canada made

available to Dr. MacKay.

I am thankful to Mrs. Lynda Klymochko and to Mr. Glen Cartwríght

for theÍr technícal- assístance both in Ëhe fíeld and laboratory. Assis-

tance gíven by Mr. John Serger, Head TechnÍcían, Department of Entomology,

is also gratefully acknowledged. Thanks are also due to the Farm Manager,

Research Station, Glenlea, and his sÈaff for theÍr kind co-operation and

to Mr. Ho¡+ard snÍth at Dugald for allowíng free access to his forage

fields. I am thankful to Mrs. M. Iunk for typing the manuscrÍpt.

My deepest thanks Ëo my wífe, SumÍthra, and son, Suchanna, for their

patience and encouragement, and to my parents back in Sri Lanka for their

sacrifices and best r¡íshes which enabled me to achieve thís goa1.

TABLE OF CONTENTS

ABSTRACT

Page

1l_-11a

iv-v

vi-viii

íx-x

xi

xíi

L-6

1

3

5

7 -29

7

ACKNOIIILEDGEMENTS

TABLE OF CONTENTS

LIST OF TABLES

LIST OF FTGI]RES

LIST OF APPENDICES

CHAPTER I. INTRODUCTION

1. DístrÍbutÍon and EconomÍc Importance ofAcyrthosíphon písum

2. Purpose of the study

3. DefiníÈions of terms used

CHAPTER II. LITEMTURE REVIEW

1. Food Selection by Phytophagous Insectsí. Physical characterístÍcs

ii. Biochemical characteristícsiií. Nutrítional requirements

2, Life Hístory and Bíology of A. pisum

3. Effects of Host Plants on Aphids

4. Variation and Insect Biotypes

CHAPTER III. MATERIALS AND METHODS

1. Laboratory Studies

í. Aphid cul-tures

íi. Plant culËures

ííi. Growth-chamber condítionsiv. Experimental procedures

a. Fecundity experiments

b. Survival experíments

15

20

22

30-39

31

CHAPTER TV. RESI]LTS

v Clones testeda. 1980

b. 1981

c. L9B2

2. Field Studíes

i. 1980 and 1981

íí. L9B2

Effects of Caging and RearÍng Techniques

Laboratory Studies

i. 1980 clones

a. Survívalb. Fecundity

c. Alata productíon ....ií. 1981 clones

a. Survivalb. Fecundíty .

c. Alata production .......iíÍ. 1982 clones

a. Fecundity ..b. Alata production

3. Field Studíes

v1l_

Page

37

40-82

40

43

¡+J

4B

4B

53

57

62

1

2

CHAPTER V. DISCUSSION

64

70

73

83-9s

B3

B3

B4

B6

B8

93

1. Introductíon2. BÍotypíc Phenomenon and Variabílity wiËhin

Po pulations3. Seasonal Changes

Annual Changes

Variability between Populations

4

5

6 Concept of BíoËypes and Agrícultural pests

CHAPTER VI. SI]MMARY AND CONCLUSIONS

REFERENCES CITED

APPENDICES

v]-11

Page

96-98

9 9-11 3

114-115

LIST OF TASLES

Table

I Effects of different cages on fecundsurvÍval on al_falfa (Clone:- At-80)

ity and nymphal

2 Suitabílity of excísed leaves and whole plants offababeans as hosts (Clone:-AL-80)

3 ProductÍon of alatae by lll clones on differenthos ts

4 Fecundity and longevíty of the three 19BO clonesreared on different hosts (t S.E.)

Alata production by the three 1980 clones followinga crowding stimulus on excised fababean leaves ... ...

Survival and mean adult dry weight (mg t S.D.) ofclones from various populaÈions when reared ondifferenË hosts (Early season-1981)

Survíval and mean adult dry weight (mg t S.D.) ofclones from varíous populations when reared ondÍfferent hosts (Late season-l981)

B Fecundity of clones from various populations ondífferenr hosrs (t S.E.) (Early season-1981)

9 Fecundíty of clones from various populations ondÍfferent hosrs (t S.E.) (Late season-l_981)

Progeny productíon by clones from differentpopul-ations during early and late seasons-l981

Production of alatae by clones frorn differentpopulatíons sampled in 1981 (t S.E.)

Fecundity of clones from varÍous popul_atíons ondifferenr hosrs (t S.E.) (Early season-l982)

Fecundity of clones from varÍous populatíonson dífferenr hosts (t S.E.) (tate season-1982)

Progeny productíon by clones from differenÈpopulations duríng earl_y and late seasons-1982

42

Page

4T

44

50

52

s4

55

5B

6L

63

66

5

6

7

59

10

11

L2

13

L4

6s

68

X

15

Table

Variabílity of clones from the alfalfa (var.Algonquín) populatíon during early and lateseasons (L982)

16 Production of alatae by cl-ones frorn differentpopulations sampled in l9B2 (t S.E.)

1B ANOVA table for fecundity data of aphids sarnpledfrom populations on alfalfa, trefoÍl, and s\,üeetclover tested on dífferent hosts at varíableintervals over the season in the fÍeld (19S1)

Page

7I

72

82

x1

LIST OF FIGIIRES

Fígure

1 Life cycle of the pea aphid, Acyrthosiphon písum(Harris) in Manítoba

2 Aphid cultures in petrí-dÍshes

Clip-on cages

htrole plant cages

Sleeve cages

Percent survivaL of clone AL-80 on different hosts

PercenË survival- of clone TR-80 on dífferent hosts

Percent survival of clone SA-80 on different hosÈs

Adult dry weíghts (me) of the three 1980 clones ondífferent hosrs (t S.D.)

3

4

5

6

7

B

9

39

Page

t7

32

34

35

45

46

47

49

74

77

7B

B1

10 Fíeld populations in 1981 (June through Augusr).(Nurnber of aphíds/sweep; Average of 50 sweep/host)

Feeundity of aphids sampled from different popu-lations on perennials and when reared on dífferenthosts in Èhe field

Survival to reproduction of aphíds sampled frompopulatiolìs on perennials and when caged ondífferent hosts Ín the field

Fecundity of aphids sampled from populatÍons onannuals and when reared on dífferent hosÈs inËhe field

Fecundity of aphids sampled from different popu-latíons and when reared on different hosts in thefield aË variable íntervals over the season(1981)

i1

T2

13

T4

76

xll-

Appendix

LIST OF APPENDICES

The meterological data duríng Ëhe period offíe1d studíes.(The Research Station, Glenlea, Manitoba)

2 Hydroponic solutíon: contents

Page

]-I4

t-

115

CHAPTER I

INTRODUCT]ON

1. Dístributíon and Economic rmportance of Acyrthosiphon pisum.

Acvrthosiphon pisum (Harrís), whích is found on every continent of

the world (Hi1l 1975), is often called the pea aphíd. This conmon rrame

does not reflect the real síËuaÈíon because only a small proportion of

the forms and sub-specÍes uníted under thÍs name colonÍze the pea p1ant,

especíally in Europe (Mu1ler l_981).

A. písum, first descríbed in Great BrÍtaín in L776 (Harper et al.

1978)' I47as ÍnÈroduced into North Ameríca from Europe in infesËed clover

and peas (Fo1-som 1909). It was unkno¡vn ín North America before 1B7B and

appeared as a crop pest for rhe fírst time ín lB99 (Davis 1915). rnaddítíon to the usual green form, red and yel-low aphids are also known

to occur. The aphid may seríously damage peas, alfalfa, vetch, and

clovers (Harper and Kaldy L9B2). Parch (1938) and EasËop (L97r) lísr

the known hosts.

The economíc importance of aphids was outlined by Palmer (1952) and

ís expressed ín several ways:

a. robbing of plant sap,

b. toxic actíon of sal-ivary secretíons, injected during feeding,

and causing stunted growth, deformatíon of leaves or fruits,galls on leaves, stems or roots,

c. vectoring of virus diseases of plants,

d. deposition of honey-dew on plant surfaces.

2

The pea aphíd usuall-y infests the growing tips of plants. Both

adult and young aphÍds pierce the plant tissue and suck juice from leaves,

petioles' stems, and flor¡er buds. Heavíly infested plants becorne stunted

and wi1-t.ed, the top leaves turn light green, and the 1or¿er ones turn

ye11ow and dÍe. As a result, the yíe1d and quality of Ëhe crop may be

greaÈIy reduced. rn the unlted states, infestations of the pea aphíd

have been responsible for losses ín alfalfa production of about $60

rnillíon a year (Carnahan et al. 1963). Control of pea aphids with Ín-

secticídes has Íncreased alfaLfa hay yields up to 152% (Franklín 1953).

A. pisurn is also reporÈed to reduce wínter hardíness of alfalfa (Harper

and Freyman 1979). The pea aphid has affected yíeld by signíficantly

reducing the mean heighrs of alfalfaby 457", the green weight by 387",

the dry weight by 44%, and the fiber by r37" (Harper and Kaldy rg}z).

Feedíng by A. pisum on young pea plants ín the laboratory reduced the

relative growth rate and efficiency of productíon of new tíssue relative

to the amount of l-eaf area by as much as L1-B% (Barlow and Messmer 1982).

Although Lhe figures in the above two references are based on l-aboratory

experiments, ít illustrates the potentíal of A. písum as a pest on

cultivated legumes.

There are some 170 plant víruses transmitted by 102 species of aphids

but some aphid specíes can tïansmít a large number of different víruses.

For example, Myzus persr_cae (Su1z.¡ can transrnít 108 dífferent planË

víruses (Lamb 1974). The pea aphíd ís also known to be a vector of plant

diseases. The príncipal viruses it. transmits are alfalfa mosaic, alsike

clover mosaíc, bean yel-Iow mosaicr pêâ enatíon mosaic, pêa mosaic, peâ

3

streak, and red clover vein mosaíc (Harper et a1. 1978). on fababeans,

vírus diseases caused 59-96% reduction in yield (Frowd and Bernier 7977).

The pea aphid, A. pisum, occurs in synonyrny in the líterature under

various scíentific names including: Acyrthosíphon onobrychís, A. písi,

A. pisi destructer, A. písi pisí, A. pisi turanícum, A. písi ussurensis;

Anuraphis (Macchíatíe1la) omed n1s ; Aphis pisi, A. lathyrí,DT

A. onobrychis ,4. ulmariae Illínoia pisi; Macchíatíella trífo1ií;

Macrosiphum genistae, M. onobrychis, M. ononis, M. pisi, M. písum,

M. theobaldi M. trífollíí, M. ulmariae; Nectarophora pisi, N. destructor,

N. pisi desËructor; SÍphonophofa corydal_Ís, S. ononís, S. pisi,

S. spartii, and S. ulmariae (Eastop L97I).

2. Purpose of the Study

There is some evidence that indivídual aphíds are more restricËed

in theír host-plant relatíonship than the species as a whole (e.g.

Cartier L959; Cartíer et al. L965; Frazer L972). Thís resrricËion has

1ed to the adoptÍon of the concept of fbiotypesr in aphíd bíology.

Although many studíes have documented such varíations among different

clones of A. pisum, in most sLudles Èhe varíatíon among indivídual_s

within a population and thaË among populaÈions has noË been examined ín

detail-. It also appears that some workers have used only a single clone

and drawn conclusions made by ecologist.s ín studyíng entire populatíons.

Documentation of any íntra-popu1-ation as well as inter-population vari-

atíon in hosË plant preferences would assíst in describíng the exact nature

of this intra-specific variation and of resource utilizatíon patterns,

and would also be expected to provide some indicatíon on shífts to ner47

4

host plants.

A feature of the 1ífe cycle of A. pisum ín Manitoba is cyclical

parthenogenesís ín which a series of parthenogenetic generatíons in

spring and summer are combined wíth a single annual sexual generation

which enÈaíls genetÍc recombination. During the course of the season

some of these new parthenogenetic clones r¿ill survive, whí-le others may

be elímínated. Those survivíng clones wíl1 contribute to the gene pool

for the next yearrs aphids. A knowledge of such íntra-specific varíatíon

Ís of importance because tbiotypest r"y be of very different economic

ímportance as pests or as vectors of vírus diseases and theír existence

renders the breeding of resístant plant varieËíes more dífficult. In

addition, the study of íntra-specífic varíatíon is relevant to studies

of mechanísms of host accepÈabilíty and host avoídance. Such research

appears essentíal for the undersLanding of evolutíonary processes,

especially the evolution of resístance in insecËs (Bush f975b).

The purpose of thís project \.ras to examíne the varíatíon in hosË-

plant preferences of A. pisum. The experíments were desígned in such

a r¡ray as to achíeve the following experímental objectÍves:

a. To determíne the extent of variatíon in host-plant

preferences among aphids available from popul-atíons

ínfesting a single crop,

b. To determíne the extent of variatíon in host-pIant

preferences between crops,

c. To examíne changes over the season ín the extent

of variation in host-plant preferences on a crop.

5

Achievement of Ëhe above objecËíves might be expected to provide

data to dístinguísh whether biotypes aïe dÍstínct and persistent genetic

strains adapted to a given host plant (perenníal), or seasonal phenomena

caused by annual cycles of sexual reproducÈion (annual).

3. Defínítíons of Terms Used

AnholocyclÍc

Clone

Fundatríx (sËem mother)

Holocyclic

Monophagous

Nymphal development

Oligophagous

Popyphagous

- Not capable of reproducíng via híber-

natíng eBBs, Ëherefore not capable of

producing sexuals or viable eggs.

- the indíviduals of successíve partheno-

genetíc generat.íons which are the

offspring of a single fundatrix and

therefore possess the same genotype as

theír stem mother which developed from

a fertilízed egg.

- víviparous parthenogeneËic fernale

developing from a fertilized egg.

- capable of producíng sexuparae, sexuals

and fertilLzed eggs and therefore there

is an ínterruption of the thelytokous

parthenogenetíc reproduc tion.

- aphíds f-ivíng on one host specíes only.

- the time taken for progeny to develop

from bírÈh to the adult stage.

- aphids livíng on few host specíes.

- aphids lívíng on many host species.

6

Population

Primary host

Secondary host

Sexuals

Sexuparae

Thelytoky

Virgínopara

aphíds exísting on a particular host

in a partícular 1oca1Íty.

a host on whích the sexual cycle takes

place.

a host on which only parthenogenetíc

reproduction Èakes p1ace.

males and gamic females. The females

mate \,rith the males and lay fertilízed

eggs.

indivíduals whích give birth to both

sexes of the gamic stage ín the cycle.

parthenogenetic development ín which

only females are produced.

víviparous parthenogenetic female pro-

ducíng other parthenogenetic vivíparae.

CHAPTER II

LITERATI]RE REVIEI^I

Much has been written coneerníng Èhe íntraspecífic varíatíon ín

host plant relaËionship of insects which leads to the concept of bíotypes

in insect bíology. An aËtempt wíll be made Ëo bring together major

references to such inÈraspecífic varíaËíon with specÍal reference to

aphids so as Ëo Íllustrate the extenL of varíatíon e>dribited by such ín-

divíduals havÍng diverse geographíc origins. In addition, a bríef review

wíll be presented on food selection by phytophagous ínsects with regard

to dífferent theoríes proposed and varíous factors that govern insect-

plant relatíonships. LiteraËure pertaíning to life hístory and bíology

of A. pisum will also be dealt with.

1. Food Selectíon by Phytophagous Insects

Phytophagous ínsects show various degrees of specíficÍty to pl-ants

(Dethier L947, 1966i Beck 1974). They are polyphagous, o1-ígophagous,

or monophagous, dependíng on whether they feed on many, a few, or a

síngle specÍes of plant respectívely.

The chemÍcal composition of plants is of fundamenLal importance in

their acceptance or rejectíon as food by insects. This probably is

true with regard both to selectíon beËween different plant species

(Nayar and Thorsteinson L963; Hsiao and Fraenkel 1968), and to selection

betr+een dífferent parts of a p1-ant (Rees L969). A food plant is charac-

terízed not only by the presence of specific chemÍca1 attractants

or feeding stÍmulants called phagostímulants but also by the absence of

B

repellent secondary plant substances (Dethier L954; Fraenkel 1969). The

basíc behavíoural and physiological processes mediated by these compounds

are host fínding by adult females for feeding and oviposítíon, and host

fíndíng by inunature stages for feeding, growth and development.

Two theoríes have been proposed to descríbe host plant selection

by insects. one of the theories (Painter 1951, 1958; Thorsteínson L96o;

Kennedy 1965) claims that the choíce of food plants ís governed by

primary chemicals ín the plant. Primary chemicals are defined as beíng

that set of chemicals whích are índispensable to the metabolíc and

developmental process of the Ínsect (Beck L974). They include various

amino acíds, lipids, carbohydraÈes, vitamíns and mÍnerals.

Ïhe second theory of food selectíon states that secondary plant

chemicals are responsible for host planË selectíon by phytophagous ín-

sects (Dethier 1954, L970; Fraenkel L959, L969; schoonhoven 1972).

Secondary plant chemicals are defined as non-nutríents usually elaborated

as by-products of metabolíc systems ín the plant (Ltlhittaker I97O:

I,rrhittaker and Feeny 197L). They are characteristícal1y toxíc, unpalat-

able, or offensíve to non-adapted insects. They Ínclude glucosíno1ates,

cucurbitacins and essentíal oils. This theory implíes that the majority

of host plants are nutritional-ly adequate for phyÈophagous insects and

that host plant selection Ís based on the presence or absence of secon-

dary plant chemicals.

It has also been recognízed that both primary and secondary plant

chemicals jointly are involved in host plant selection (Hsiao L972;

Beck L974; Dethier L976). Two or more primary chemicals may jointly

9

exert synergist.ic effecËs to incíte an ínsect to feed. The effect of a

secondary plant chemícal as a feeding stimulant may be enhanced in the

presence of a prímary chernical. Both primary and secondary chemicals

can also act joinËly to inhibít feeding. Dethier (L976) concluded that

although a particular compound or category of compounds may be the major

chemícal constítuent of a plant and may contríbute the major sensory cue,

ít is the total chemícal complex of the plant thaË forms the basis of

selectíon.

Studíes of insect-plant ínteractíons have led to some general con-

clusions: (a) insect feeding, development and survival are often ín-

hibíted by host planÈ defenses (Cates 1980; Haukíoja 1980; lfartson 1980),

(b) insect herbivores change plant competítíve relationships through

selective herbivory, (Connell and Slatyer L9773 Schowalter et al-. 1981a),

and (c) insect herbivores ínfluence the rate and direcËíon of nutríent

transfer between vegetation and lítter (Springett I97B; Schowalter et a1.

r_9Blb) .

An acceptable host plant must provide the insect with a suitable

envíronment and a nutriËíona1 substrate that ís adequate, non-Ëoxic,

and utilizable. Beck (L974) pointed out that even the best host plants

may be suboptimal ín some of these characterisÈics and that mortalíty

among larvae tends to be very hígh. The phenols, flavonoids, alkaloíds

and various glycosides contaíned ín plants are deleÈeríous and insects

feedíng on plants contaíning these substances must be able to degrade

Ëhem meÈabo1ícal1y (Beck 1965). The abílíty to metabolize such plant

components consËítutes an important aspect of the adaptation of an

ínsect species to a particular plant as a host (se1f et al. 1964;

L0

Kríeger et al. 1971). Different plant species may differ eíther quali-

tatively or quantÍÈatively ín respect to these substânces. Therefore,

an ínsect that fs metabolically adapted to one type of planÈ rnay not be

able to meet the metabolj-c demands posed by anoËher plant. Consequently,

the ínsect !üi11 not be able to survive on ít.

There are several factors whích govern insect-plant relationshíps.

Among them, physícal characteristics, bío-chemical characteristícs, and

nutrítíonal factors are Ëhe most important. Sínce plants differ in these

basic factors, most insects can only feed on a few selected food plants

which allow optimal development and survival.

i. Physíca1 characteristics

The role of physíca1 characterístícs has been studied rnainly ín

relatíoir to host planË resistance. Characteristics such as pubescence,

spacing of vascular bundles and tissue silíca content have been ín-

vestigated.

Leaves I^Iith haiTy surfaces may reduce feedÍng, increase rnortalíËy

and depress grovüth in some phytophagous insects (Levín L973; I^lellso L973),

but not ín some others (Maxwell and Jenníngs 1980). Hairy surfaces some-

times prevent insects from corning ín contact with the leaf cutícle, thus

acting as a physical obstructíon to feeding. For aphids, a sticky sub-

sËance discharged from g1-andular hairs on Èhe leaves of several Solanum

spp. entraps the insects and prevents theír establishment (Gibson 1971).

Gílbert (I97L) reported that smal1 caterpÍllars of Heliconííne butter-

flies are entrapped and effectively prevented from feeding by hook-like

tríchomes on the leaves of Passíflora adenopoda D.C. Young larvae of

11

Prodenía eridanía (Cramer) are Ërapped and ínjured by fish-hook like

sp ines on Dorsternia contr ajerva L. (Soo Hoo and Fraenkel 1966).

Physícal characteristícs may Èherefore either injure the insecÈ directly

or prevent ít frorn feedíng.

ti. Bio-cheruical characterisËics

It is commonly known that chemical stÍmuli play an important role

in the feedíng behaviour of many phytophagous ínsects. secondary plant

substances guÍde the insectrs choíce of food. A non-food plant is

characÈerized not only by the absence of specífic chemícal attïacËants

or feedj.ng stímulants, but also by the presence of other secondary plant

substances which act as repellents (Dethíer L954; Fraenkel 1969). These

compounds together wíth nutrients account for insect-pl-ant interactíons.

Alfalfa is knornm to contain feedÍng stimulanËs for the alfalfa

weeví1, Hypera postica (Gryllenhull) (Yamamoro L963). Hsíao (1969) re-

port.ed that these compounds are adenine salts and nucleotides. Tannic

acid in altaLfa acts as a repellent for alfalfa weevil larvae (Bennett

1965). The saponíns in alfalfa have been indicated as a possible resis-

tance factor not only to whíte grubs, Melolontha vulgaris F. (Horber

1965) but also to stored product insects in legume seeds (Applebaum

et al-. L969) .

Beans, Phaseolus spp., have been shown to contaín feeding stimu-

1ants, phaseolunatim and lautaustrin, for the Mexican bean beetle,

Epílachna varivesËris (Mulsant) (flíngenburg and Bucher l_960). Sweet

clover, Melitolus officína1ís L. and other clovers contain coumarin,

which is a feedfng attractant for the vegetable weevil-, Lístroderes

l2

costrirustris (Klug), at 1ow concentrat.ions but a deterrent ín higher

concentrations (lufaËsuuroto L962). Chlorogeníc acid and rutin, major

phenolíc constítuents of tomâto folíage, ínhibít growth of the fruít-

r+orm Helíothís zea Boddíe larvae (E11íger et al. 1981; Isman and Duffey

L9B2), but ruËin is reporËed to increase gro\¡rth and fecundity of the

larvae of Acheta domestícus (L .) (McFarlane and Distler f9B2).

Variability ín concentTatíon of secondary substances may influence

the feedíng actÍ.víty and developmental success of the ínsect. Colorado

potato beetle larvae, Leptinotarsa decemlíneata (Say), were observed to

feed more readíly and to grow better when fed young potato foliage than

when given ol-der tíssues, while senescent foliage of either potato or

tomato tended to retard growth (Bongers L970; Cibula er a1. 1967).

Feeny (1968) showed that larvae of the wínter moth, OperophËera brumuta

(L.) consumed oak leaves early in the growing season, but not later,

apparently because of a high concentration of tannins in older leaves.

However, Bernays (1981) reported that though tannÍns do affect the gro\,rth

and survíval of insecÈs, there ís no unequívocal proof of an antidiges-

tive effect of tannic aci.d or condensed tannín ín insects. These results

indicate that synchronization is an ímportant factor ín insect-plant

relationshíps. Other researchers have emphasízed the importance of

proper synchronizaLíon beÈween insect and host phenology for the develop-

ment of rnost phytophagous insects (Embree L965; Eidt and Lírtle 1968).

iiÍ. Nutritíonal- requirements

It is generalJ-y accepted that the nutríent leve1 and nutrient

balance of a food plant wíll determine íts adequacy for an ínsect. House

L3

(L969) reported that for Celerío euphorbiae L., the amount of food

eaten r¡ras greater when there was favourable nutríent balance. .Altering

Ëhe nutríent balance resulted in 1or¿er food consumptíon and a reduced

efficíency of conversíon from 207" on a normal balanced diet Èo 9.57" on

an imbalanced díet.

Banks (1965) states that the fecundÍty of Aphis fabae Scop. seems

to depend primarí1y on the quality of the nutrients it gets from íËs

hosts. Aucl-air et a1. (L957) and Maltais and Auclair (1962) found re-

sistance of varieties of peas to A. pisum to be correlated wíth the

relative concentrations of amíno acids and glucose. The susceptible

varieties generally contaíned a hígher concentraËion of free and total

amíno acíds than Ëhe resistant ones. Accordíng to Äucl-aír (1963),

asparagine, glutamíne and homoserine are the factors determíníng the

resistance of pea varietíes. Some workers (B1aís L952; I^trilde et al .

L969) have reported differences in nutrient content of pl-ant structures

of different ages and their apparent effects on insect growth, survival,

and reproduction. Others (House L969, L970, L97L; Maltaís and Auclair

1962; McGinnís and KasËing 1961) have suggested that díetary proportíons

of requíred nutrients may be of greater importance than theír absolute

quantÍties ín food selectíon. Díets which lack one or more primary

chemicals or have unsatísfacËory ratios of these chemicals may be less

acceptable to an insect.

Íhe concentrations of some elements and minerals have been shor^¡n

to have direct or índírecË effects on the feedíng behavÍour and survíval

of insects. Al1en and Selman (1957) , working wíth Pieris brassícae

L4

(L.), reporËed that defícÍency of nitrogen and iron in a food plant

caused a reductíon ín Èhe relative growth rate of larvae and íncreased

larval rnortalíty.

I,rïater, although not usually classifíed as a nutrient, mây be an

ímportant factor to plant-feedíng insects. Lepidopterous larvae

general-ly maíntain a body \,raËer content of 85-92% (Evans 1939;

Wígglesworth 1975). The possíbl-e effects of plant tíssue \^/ater content

llere consídered by hlaldbuer (L964), who attríbuted some of the dífferences

in the digestibilÍty and conversion of host plants of Manduca sexta

(Johan) to differences Ín their moÍsture content.

Plants vary in their conÈent of nutríents as vle11 as secondary

plant cornpounds. These variatlons are dependenË not only on the taxo-

nomíc differences but also on the plant part, developmental stage, physio-

logical condíËíon of the pJ-ant, to name a few. These factors have been

shown to ínfluence both the behavíour and the development of plant feed-

íng ínsects.

Among the pl-ant species included in Ëhe present study, different

species have shown various degrees of suítab1lity to A. pj-sum. Generally,

field peas and aLfalfa appear Ëo be the most acceptable hosts to A. písurn.

Ho¡vever, there are <iífferent l-evels of suítability among various varietíes/

cultívars wíthín any gíven species. For instance, dífferent pea varieties,

Perfectíon, Príde and onward, have been shown to host A. pisum ín Ëhree

signifícantly dífferent vrays (Harrington L945; cartíer L959; Maltaís

and Auclaír L962). Poor survíval and development of A. pisum on some

hosts may be due to a nutritional deficíency (Maltais and Auclair

L962) or may be due Ëo lower ingestíon or some secondary plant chemicals

15

which inhibit or deter feeding. The factors leading Èo differences ín

the resistance of plants to insects are inadequately known. The clones

of pea aphíd behave in very dífferent ways to the same variety of plant

species and thus to Ëhe same food. Although it ís beyond the scope of

the present study, iÈ would be very ímportant to study why the clones

díverge so greatly ín their reactíons to the same varíeÈy of plant.

rnvestígations of this nature wí1l go a long way in solvíng the problem

of the resístance of plants to aphÍds.

2. Life History and Bío1ogy of A. pisurn

The lífe cycle of aphíds ís a complex sequence of evenÈs ínvolvíng

a series of different forms, the transítÍon from one form to another

beíng triggered by changes in the environment (Lees 1"966; Hille Ris

Lambers L966). A feature of this life cycle which ís found in most

specíes of aphids is cyclical parthenogenesis, in which a series of

thelytokous parthenogenetic generations in spring and summer are combined

Ì,¡iËh a síngle annual sexual generatíon. usual-ly sexual morphs are pro-

duced in late summer or autumn and the aphids overwínter as eggs. Thís

ís a complete cycle or holocycle. Life cycles involving contínuous all-

year-round parthenogenesís (anhol-ocycly) are deríved secondaríl-y from

the holocycle (Blackman L974). Lees (L966) considered that the anholo-

cyclic character most probably aríses as a gene mutatÍon, and Muller

(L977) has come to the same conclusion after rearing holocyclic aphÍds

of seven specíes for up to 15 years without l-oss of the ability to pro-

duce sexual- forms. The pea aphld exhíbíts either holocycly or anholo'-

cycly, or a combinatíon of boËh, according to the environmental condítíons

L6

Ëhey encounter in different regions (Cooke 1963).

Perhaps of more fundamental signífícance are Ëhe genetic írnplica-

tíons of thís life cycle variation, because holocycly and anholocycly

are líkely to have dífferent effects on the genotypÍc composition of

aphíd populaËíons. The sexual phase of the aphid hol-ocycle entaíls

genetic recombinatÍon between genoÈypes. Populatíons of aphids vrhich

have overwínLered parthenogenetícally may consíst of lesser numbers of

oId clones than the popuJ-atíons of aphíds whích have overwíntered as

eBBS, physíologícally and perhaps genetícally adapted to wínter sur-

vival on one host plant. In Manítoba, A. písum is holocycl-ic and over-

wínters as eggs deposíted on perennj-al legumes (Fig. l-).

The bíology of A. pÍsum has been studied princípally ín Europe and

North Ameríca over recent decades. The number of generatíons of pea

aphíds varíes in different parÈs of Ëhe world. Folsom (1909) reported

17 generations ín the first-born line in the state of lllínois.

According to a study by Davis (1915) ín Indíana, between March 3l- and

December 31, there were l-9 generations ín the first-born 1íne, and on

average of 13 generaËíons. SmÍth (1916) reported 2L generatíons ín

Vírgínía, Campbell (L926) L4-28 generations in California, and

HarrÍngton (1941) 15-l-6 generatíons ín the state of Wísconsín ín one

season. Markkula (1963) reported that ín Fínland, the maximum number

of generations produced ín one season was 9-10 in the fírsË-born líne,

thus the average number of generatíons produced was 6-7. There are no

reporÈs of the number of generatíons of the pea aphíd ín Manitoba.

Because of the lower temperatures and shorËer growing seasons ín Manítoba,

L7

- - _ _\ ALATË VIRGINOPARAE I--.\

ll

I1..

FUNDATRIGINAE

FIJNDATRICES

^

SEXLTPARÁN¡

I

I

I

I

,l'vSEXUALES

(males and ovíparousf ernales)Ìs

\ . -'- /,-- - EGGS (Diploíd) ¿=(overwinteríng on perenníal l-egumes)

Figure 1. Lífe cycle of the pea aphíd,in Manítoba.

Acyrthosí phon písum (Harris)

18

the number of generations produced woul-d be expected to be lower than

ín the USA, and íË may be that the siÈuatíon is quíte comparable wíth

Èhat of Finland.

Little Ís known of the comparaËÍve bíology of holo- and anholocyclíc

aphíds. Tamakí et al. (1982a) reported that an anholocyclic strain of

M. persÍcae, which oven^/íntered in the víviparous stâge, exhibited some

degree of cold toLerance compared to the holocyclic straín tested.

There are numerous reports in the líterature on the 1-ength of the

various phases of the life cycle of A. pisum. Temperature data, how-

ever, are sometínes J-ackíng. The pre-reproductíve period has generally

been reported to be 9-12 days (Smíth and Davis L9263 Cartier 1960;

Markkula 1963; Sylvester and Ríchardson L966; Murdie L969; Frazer L972:

Siddique et al . Lg73; MacKay and hrellington fg75). According to the

above mentioned workers, the average length of reproductive period was

approximateLy L5-20 days. However, Markkul-a (1963) reporËed it Èo be

25-3L on red clover. The average length of the post-reproductive period

was reported to be l-0 days by Cartíer (1960), 4-6 days by MacKay and

trniellíngton (1975) and 15-21 days by Markkula (1963). The average

length of lífe is generally around 30 days (CartÍer 1960; MacKay and

I{ellington 1975), at tempeïatuïes around 2OoC. It appears, however,

that the average J-ength of various phases of the f-ife cycl-e depends, to

a great extent, on the host p1-ant, temperature, and other envíronmental

factors.

The pea aphid appears to be fairl-y prolifíc and a great number of

investigators have determined the number of progeny produced by agamic

19

females. Average figures reported for number of progeny generally range

between 60-95. campberL (7926) reported 68 (apterae , 7r.7 and, alarae,

58.3), IlarríngÈon (1943) 68-72, Kenren (1955) 77-86, Siddique er al.(1973) 83,7, MacKay and l,iellington (1975) reporred for 95 for aprerae and

86 for al-atae and Murdie (1969) I]-7. The largest numbers of offspring

noted per femal-e are L76 (Campbell 1926) and L75 (Knowlton and Sorenson

L937). Mean daily fecundíty ranged between B (Siddíque et al. 1973) and

L2 (Murdie L969).

The specíes and varÍety of hosÈ p1-ant have a consíderable effect

on the number of progeny produced by the pea aphid; Reproduction is

very great on certain susceptible pea varíeties such as Perfection

and considerably less so on resistant varieties (e.g. Príde and Onward)

(Harrington 1941; carríer 1959). This facr, as well as the dífferences

Ín reproductíve capacíty of varíous bíological races (Trazer 1972)

explain to some extent, the rather wíde dívergences ín numbers of

progeny found by the above ínvest.igators.

Markkula (1963) studíed the numbers of progeny produced by fundat-

rices of A. pisum and he found that the reproductíve capacíty of the

fundatríces hTas clearly greater (20-40%> than that of the following

generations of agamic females. Ifarkkula (1963) also claíms that this

feature seems to be characterístic of several aphid species including

Brevícoryne brassicae (1,.) .

Very few ínvestígations have been performed on the bíology of sexuals

of A. písum. Thís ís understandabl-e, sínce in tropícal areas thís species

does not produce any sexuals and reproduction is usually partheno-

20

genetic. The sexual females of the pea aphíd are apterous. Among the

males, however, both alate and apterous forms are known. The general

víew is that in North AmerÍca alate males are more prevalent while in

Europe, by contrast, the males are usually apterous. Markkula (1963)

reporÈed that there vras no difference in length of life of sexual fe-

males when reared on red clover and on peas ín Finland. He reported the

average values to be pre-reproductive períod 27 days, reproductive period

35.3 days, post-reproducÈive period 16.3 days and total life span 78.6

days. Markkula (1963) reported that average number of eggs laíd was 23.

He al-so claimed that this T^7as one of the highest fígures known for

aphids.

3. Effects of Host Pl-ants on Aphids

It appears that plants vary in the degree Ëo whích they support the

survival, growth, and devel-opment of aphíds. Likewise the responses of

aphids to host specíes under test may vary not only with dífferences

between aphíd strains but also with prevÍ-ous experience. For ínstance,

Myzus persicae, settl-es more readily on sugar-beet if taken from cultures

on Chinese cabbage than from cultures on other hosts (Russell 1966).

Lowe (1973) also found some evídence on M. persícae to support the

observations made by Russell (1966). Sirnilar preconditíoníng effects

occur in other aphids (Schízaphís gramínum (Rondaní), Macrosiphum avenae

(nU.¡ and FJropalosiphon rnaídís (Fitch))infesting cereals (Apablaza and

Robínson L967). I,rlilson and Starks (1981), however, observed very 1iÈtle

precondítioning effects in the greenbug, S. gramínum, reared on fíve

different plant specíes.

2I

Auclair (1966) took seven straíns of A. písum from alfalfa and reared

them on peas for seven months, but did not observe any kind of condition-

Íng. Markkula and Roukka (1970b) found dístinct conditioning of A. pisum

to red clover over one year ín only one clone out of three tested.

Therefore, it appears that the phenomenon of conditioning of A. pisum is

a clonal characterísËic rather than a specíes characteristic.

The hosÈ plant can also affect the behavíour and physíology of

aphids ín other !üays. For ínstance, it can be responsíble for the deter-

minatíon and development of alates (Markkula L963; Sutherland 1967, 1969;

hloodford Lg6g). Markkula (1963), ín studying two strâins of A. písum,

found that boÈh produced more alatae on pea than on red clover, and con-

cluded that the kind of hosÈ plant had an effecÈ on the productíon of

alates. Cartier and Paínter (1956), in theír study of the corn leaf

aphíd, R. maidis, noted Èhat the ratío of apterous and alate aphids

varied with the hosts and biotypes. They also found that bíotypes of

this species could be dífferentíated on the basis of the number of alate

and apterous adults produced by the orígínal apterous females when reared

on different varíetí"es of host p1ant. Sutherland (1969) observed more

alatae in the progeny of crowded fernales of A. pisum caged on mature

bean leaves than uncrowded females. He also reported that fewer alatae

were produced by females caged on excísed mature pea leaves fed with

glucose and amino acÍds Èhan on leaves fed with a pure glucose solution.

Aphids, Sitobíon avenae (F.) and Rhopalosiphum padí (L.) feedíng on oats

infected with barley yellow dwarf virus produce more alatae than on

unínfected oats and this rnight favour the spread of vírus (Gildow l-9BO).

.22

There !üere no reports on the effects of different host plants on

A. písum populations as a whole ín the field. rt ís likely that when

the season progresses from early to l-ate, a pea aphid population on a

partícular host may show some adaptation to the same host. Iilhen such

populations are tested at dífferent times of the season, íf there is such

an adaptatíon, that coul-d be measured by their dífferential survival,

fecundity, alate productíon etc. on different hosts.

4. Varíation and Insect Biotypes

Inlhen considering any Ëype of íntraspecific variation, a major prob-

lem is determinatíon of the extent to which íÈ ís due to genetic dif-

ferences within the species, and Ehe extent to which ít is ínfluenced

directly by the environment. rn aphids, every fundatríx will díffer

genetically from every oËher fundatrÍx as each has arisen from a dif-

ferent fertLlized egg. Each Ís therefore founder of a dístinct clone.

Anholocycly of aphíds ín the tropics could be due dírectly to lack

of the environmental- stimulus needed for production of sexual morphs.

In Ëemperate climates, Ëhe occurrence of both ho1-ocycJ-y and anholocycly

in the same regions under ídentícal climatic conditj-ons makes ít clear

that genetic dífferences are ínvolved, and experímental work indícates

that these dÍfferences are a feature of the varíatíon \^/ithín as well as

between local populatíons (Blacknan L971).

IntrapopulatÍon variatÍon is exlíibited ín a number of ways. Inlool

and van Emden (l-981) suggested thaÈ dífferent abilities of M. persicae

clones Èo adapt to an artíficíal dÍet ís genetically based. They found

only fíve clones survíved the 10th generatíon on artíficial diet out of

23

Èhe .64 clones tested. Masakí (1961) gave several examples of specíes

with dífferences in diapause duration.

The precise biologícal nature of thís varíatíon, hor^rever, ís sti11

poorly understood. Conflícting suggestions, based on litt1e experímental

evídence, have been made concerníng the degree of genetic dj-fferentiation

some ¡,¡orkers have reported such varíations, among clones of A. písum

having diverse geographic orígíns and have termed them bíotypes (e.g.

cartier eË a1. 1965; Auclair 1978). The scope of the pea aphid bíotypíc

differences with regard to theír geographíc dístribution will- be dis-

cussed below.

The existence of genetíc variability in the capacity to overcome

crop varíetal resisËance ís a well recognized phenomenon among insect

specíes. such genetíc and physíological strains of insects are com-

monly referred to âs bíotypes. Many species of aphíds have been found

to consist of a complex of biotypes (Eastop 1973). A eomplícated genetíc

ínteractíon has been demonstrated between the Hessian f1y, Maye tíola

des truc tor (Say) and wheat varieties (Ca1l-un ]-977 z Sosa 1978, 1931) , and

ín the genus of flíes Rhagoletis (Bush 1969). The case of the brown

plant-hopper, Nilaparvata lugens Stal, and the ríce varíeËíes has been

the subject of study by many workers (Sogawa 1980, 1_981; pathak and

Heinriches 1982 and references thereín).

BioÈypes are usually recognised by a bío1ogícal function rather

than by rnorphol-ogícal characters. These bíotypes have been recognised

by a varieËy of characters, includíng differences ín life cycles, host

plant preferences, susceptíbí1ity to insectícides, virus Ëransmítting

24

abilitíes, feeding behaviour, reactíon to 1íght and susceptíbilíty to

pathogens. Numerous authors have used the words ttracestt, ttstraínstr,

and'rlinesrrínstead of bíotypes. rn thís review, these words will be

used interchangeably, as used by the authors concerned.

Muller (1966) regards the anholocyclíc tropícal populations of

Lipaphis erysími (Kitb.) and Aphfs craccívora Koch as races of their

respective European holocyclic species. Muller (L969) has described a

populaËíon of Aphis nasturtíí (Kltb.) which prefers calla to potato as

a secondary host plant but boLh populatÍonsarternate on Rhamnus.

Cognetti (1965) recognísed different straíns of Brevicoryne

brassicae (L.) by their biologíes and Lar¡rnerink (1968) recorded a strain

of B. brassicae ¡rhích colonísed previously resístant varietíes of crops.

Gíliomee et al. (1968) found populations of the wooly apple aphid,

Eríosoma lanigerum (Hausmo) which can coloníze prevíously resistant

varíeÈies of apples. Blackman (7971) gâve accounts of the bíologÍes of

clones of M. persícae deríved from specimens collected on different

crops and at dífferent localíties, wíÈh special reference to the pro-

portions of different biotypes found on dífferent crops. Tamakí et al.

(1982b) report,ed that a holocycl íc straín of M. pers icae was more suc-

cessful ín ËransmíÈting beet western ye1-low vírus (BI^IYV) to shepherds-

purse, Capsellabursa pastoris (f,.), than the anholocyclíc strain.

Rochow and Eastop (L966) described a populaÈion of Rhopalosiphon

padi (L.) in whích hot weather dwarfs had both an unusual wing venatíon and

an íncreased virus transmittíng abflity. Rochow (1960) reported that strains

of the greenbug, Schízaphis graminum (Rondani), differ in theír abilíty

25

to transmit the Barley ye1low-dwarf virus (BYDV). 0r1ob and Arny (1960)

studíed the transmission of BYDV by different biologícal forms of the

apple grain aphid, Rhopalosiphum fítchíí (Sanderson), and concluded that

vector specifícity resÈs with characters which are genetícally fixed.

Saksena et a1. (L964) reported that various biotypes of R. maidís dif-

fered in transmíssion efficiency of BYDV. Jones (L967) found tvro races

of A. craccivora with dífferent abilíties of transmítËíng groundnut

rosette vírus.

In corn leaf aphíd, R. maídis, the occurrence of two races \¡ras re-

ported by CartÍer and PaÍnter (1956). Pathak and Painter (1959) pro-

víded evídence for the occurrence of two more bíotypes and r,7ent on as-

sígning varÍous populations all over Kansas Ëo the said four biotypes

(KS-l to KS-4), on the basis of their fecundíty. Símílarly, six bio-

types of the spoÈted alfalfa aphíd, Therioaphís maculata (Buckton),

have been reeognízed in the hTestern Uníted States (Níelson et al. 1970).

The first observatíons on the resistance of pea plants to the pea

aphid, A. pisum, r¡/ere publíshed as early as the i-gz}ts (Russe1l and

Morrison 1924). Searls (L932) recorded the occurrence of resistance in

some varíeties of peas to A. pisum. Harrington (1941) fírst demonstrated

the exÍstence of biotypes ín A. písum. Harrington (1945) kept 31- pure

parthenogenetic lines collected from different parts of the USA and

concluded that there Ì¡rere aÈ least five bíotypes ín the United States,

separable on the basis of body síze, feedíng ínjury, and rates of re-

production on peas (varieties - Perfection, Príde and Onward). He

observed, on the vâr. Perfect.íon, among the 31 lines tested for theír

26

fecundíty, a line 441 collected from Alabama whích had Èhe híghest

fecundity fÍgure (97.4 progeny/female) as against the lowest fígure

(48.3 progeny/fernale) exhíbited by a clone collected from Virginia.

Líkewíse on the var. Príde, a clone from Hamílton, Mont., had the

largest fecundíty (89.7) and Ëhe smallest fecundiËy figure was 25.1

progeny/f.emale of a clone from Virginia (V-42). On the var. Onward, a

clone from Alabama had the largest fecundity figure (88"0) whí1e the

Virginía clone Y-42 i¡,ad the smallest (16.0) .

Cartíer (L957, L959 and 1963) investigated 23 separate clones and

recognized three bíotypes in Quebec on the basis of weÍght and rate of

reproduct.íon on three varíeties of pea. Two of these bíotypes (R, and

*Z) orígínated from St. Jean and the third (Rr) was from hlaterloo,

Ontarj,o. On the var. Perfectíon, fecundíty fígures (mean progeny/3

females) were 190, 130 and 100 for the biotypes Rl, R2 and R, respec-

tively. On the var. Príde the figures hTere 170, B0 and B0 while on the

var. Onward, the fígures were 70, 20 and 40 for the bíotypes R' R, and

R, respectively.

CarÈier et al. (1965) tested Ëwo biotypes, one from Quebec (C61-

86) and the other from Kansas, on dífferent varíetíes of alfalfa. On

the var. Buffalo, the Quebec biotype had a mean of 2I"75 progeny/3

fernales while the Kansas biotype had 40.75 progeny/3 females at 7oop.

Likewíse on the var. Ladak 84.25 and 43.0, on the var. Du puits 7.50

and 46.75, and on the var. Atlantic 66.75 and 39,75 for the Quebec

biotype and the Kansas biotype respectíveIy. Frazer (L972) recognized

five bíotypes in Brítish Columbia, collecting one each from the hosts

21

bean, broom, clover and the remaining two from aLf.arfa at thTo dífferent

locatÍons. Their range of net reproductive rate on broad bean varíed

from 91.0 for the bean biotype to 53.3 for the broom bíotype. Auclair

(1978) had síx clones from diverse geographic areas tested on broad bean,

peas and artificial diets. Two of them came from Quebec, one each from

New Mexíco and Kansas ín Ëhe USA, and Èhe remaíníng two from France. On

broad bean, the green biotype from France had 11.5 progeny/female/day

and the Kansas biotype had 9.0 progeny/f.emal.e/day which were the largest

and the smallest figures. Likewíse on peas, Ëhe green bÍotype from

France had 9.9 and the rleaux condres (Quebec) biotype had 4.7 progeny/

female/day, the largest and the srnallest figures. Adult weÍghts varíed

from 4.8 rg. for the Kansas bíotype to 4.1 for the st. Jean (Quebec)

bíotype on broad bean. on peas, the green biotype frorn France had the

heaviest weíght 3.9 mg. as agaínst the líghtest figure 1.8 mg. for the

ïlenux Conderes (Quebec) bíotype.

Muller (7962) separated níne strains cor-lected in rhe field by

observing the maíntenance of populatíons on eíght species of papí11íon-

aceae. He dístínguished the strains on the basís of preferred host

plants. Markkula (1963) observed that the green forms of A. pisum were

more fecund than the red forms and Èhat, although both forms produced

more alatae on pea Èhan on red clover, the proportion of alatae among

progeny did not differ in the two forms írrespectíve of host. Lowe

and Taylor (L964) found green and red lines of A. písurn that also differ

ín alary polymorphism and behaviour patterns and described quantitatíve

evidence of these differences. Neíman (L97L) tested 31 field collected

2B

lÍnes of A. písum and assigned them to eíght biotypes based on signifi-

cant differences as measured by mean adult dry wefght, reproductíon and

survíval on four leguminous hosÈs. Mí1ner (1982) reported two biotypes

of A. pisum occurring in Australia separable in theír susceptíbility to

an isolate of Ëhe fungal pathogen, Erynía neoaphídis Remaudíere and

Hannebert. A dosage whích kí1led an average of 94% of one biotype díd

not kíll a single aphld ín the other.

Muller (1971) reported that ín hybridízatíon experÍments, Ít was

possible to obtain hybrids of several biotypes of A. písum. He further

reported Èhat ít was possible to obtaÍn a víable hybríd between a pea-

attackíng form and one form whích colonÍzes Trifolíurn pratense L. as

its principle host plant and cannot colonize on the pea.

MeÍer (1964) ínvestígated how far morphological differences of A.

pisum could be considered an indicatÍon of biologícal separatíon, but

was unable to discern any differences among the biotypes attacking dif-

ferent host plants. Thotrappílly et a1. (L977) examíned morphological

differences between tI,Io bíotypes of A. písum. They observed dífferences

in pígmentaÈíon as well as other morphologícal differences between the

tI^7o

According to Eastop (1973):k, a biotype

"is a taxonomic concept mostly used by non-taxonomists, and íthas been defÍned as consisting of all índívíduals of equalgenotype. In aphíds at least, and probably elsewhere, equalgenotype means behaving sími1ar1y as far as researchertsímmedíate ínterests are concernedtt.

*EasËop, V.F. (1973), Biotypes of aphids,aphid biologyr Ed. by A.D. Lovre, 8u11. NoDSIR, Auckland, 123 pp.

40, In rPerspectives ín, Ent. Soc. New Zealand,

p.2

29

Maxwell and Jennings (1980)¡k define Ëhe term bíotype as

"an indívídual or populatíon that is distinguished from therest of íts specíes by criterÍa other than morphology,for example, a difference Ín parasite ability".

Bíotypes of A. pisum have been studíed j-n Australía (Milner L9B2),

Canada (Auclair 1978; Cartier L957, 1959; Carrier er al. L965; Frazer

1972), Finland (Markkula and Roukka L97Oa, I97Ob, 197L), France

(BournovilIe L977a, L977b), Germany (Muller L962, L97L, 1980), fraly(Frohlich L962), Switzerland (Meíer L976), and in the USA (Harrington

\94L, L945) over the past decades. Hor¿ever, Ít appears that ín most of

the studies, although rthe bíotypic phenomenont has been clearly docu-

mented, Èhe exact biological nature of such biotypes and theír precise

relationshíp with host plants and/or geographic l-ocation has not been

adequately documented.

*Maxwell, F.G. and Jenníngs, P.R. (Eds.) (l-980). Breeding planrsresistant to insects, p. 618, John l,liley, New York, 683 pp.

CHAPTER TII

MATERIALS AND METHODS

This study was conducted ín the fíeld as well as Ín the laboraÈory

and the methods for the ÈI^ro areas of work differed somewhat. Hosts in-

cluded ín the field studies r^7ere: alfalfa (Medicago sativa L. var.

Beaver), Sainfoin (OnobrychÍs viciaefolia Scop. var. Melrose), birdsfoot

trefoil (Lo.!gF rniculatus L. var. Leo), sweetclover (Melítotus offíci-co

nalis L. var. Yukon Yellow blossom), fíe1d peas (I¿Egg satívum L. var.

Trapper) and fababeans (vicía faba mipor L. cv. Diana). rn the labora-

tory alfalfa (varíeties Beaver and Algonquín), sainfoin (var. Melrose),

trefoil (var. Leo Birdsfoot), and fababeans (cv. Díana) were used.

Experiments hrere designed so as to documenÈ the responses of aphids

to different host p1-ants, sampled from various populations. Field

transfers of aphids were made among plots of dífferent hosts wíth the

prinary objectíve of estimatíng mean survíval to reproduction and mean

fecundity. However, ín the fíe1d experiments, replication wíthin any

clone \n/as not possíble, although this was done in the laboratory experÍ-

ments. Laboratory e)<Periments were of two types. Survíval experiments

were prímarily íntended to estÍmate mean nymphal survival and adult dry

weíghts whíle fecundÍÈy experímenËs rnrere conducted to estimate mean

fecundity and alata production.

31

1 Laboratory Studies

i. Aphid cultures

Aphíds were collected using sweep nets. To assure thaË Ëhe aphíds

and theír resultanÈ clones v/ere repr"".rrJrtí.res of the population in

each fíe1d, sweep samples were Laken from different parts of the fie1d,

excludíng a 2 m band around the edge where recent immígrants \,rere most

likely to be present (Lewís L969).

Cultures of a single clone r^rere started from one wíngless virgino-

parous female whích was pJ-aced on excised leaves of fababeans on moistened

paper towel ín 60 x 15 rmr size petrí dish (Fig. 2), Undamaged l-eaves

of fababeans r¡/ere sel-ected from pJ-ants ín the eíght-leaf stage. Neíther

the top nor the bottom paír of leaves were used. Pl-ants were grovm ín

a perlite-vermiculite mixEure and watered with a nutrient solutíon

(Appendíx 2). All aphid cultures were mainËained ín a growth-chamber

where temperatures r¡/ere set at 20oct1oc and the photoperiod was L7Lz7D,

The relatíve humidity ranged between 50-707".

ii. Plant cultures

The plants to be tested Ìrere gro\¡rn ín a non-sterilízed soíl mixture

(1 soil: I sand: 1 peat) in plastic pots 12.5 cm Ín díameter and 10 cm

in height. PoËs were seeded with an unknown number of certífíed seeds

in each case, and after germinatíon the planËs were thinned to one per

pot. Plants were fírst used for tesÈs about !14-2 months after seeding.

For subsequent experíments, Ëhe top growth \Áras removed by cuttíng at

ground level, and the planËs \^7ere allowed about ten days for re-growth

32

Figure 2. Aphíd cultures in petrí-dÍshes.

33

before use in experiments. Plants r¡reTe \,ratered as necessaTy.

iii. GrowÈh-chamber conditíons

All laboratory experiments \,üere conducted in a walk-in plant growth

chamber ín ¡¿hích temperature v/as maíntained 20octloC and photoperiod set

at L7L:7D with light intensity of approxirnately 2300 lux at cage 1eve1.

The relative hr:mídity ranged between 50-707".

iv. E:cperimenËal procedures

(a) Fecundity experíments

Fourth instar apterous aphids \¡Iere caged indivídual-ly on hosts

using clíp-on cages (Fí9. 3). Early-born progeny (fírsr 5-7) of a

mother were used. The cages r^7ere examined at leasË every other day and

counts of progeny of each aphid were made. AË each inspection, Lhe new

nymphs r^rere removed using a camel-haír brush and wíthout dísturbíng the

mother. Nymphs \^Iere reared on excísed fababean leaves in petri díshes

ín order to determine theír morph.

At least ten replicates for each clone-host combínation lr7ere car-

ríed out unless oËherwíse stated. Excísed fababean leaves ín petrí

díshes were included as a treatment in all the experíments.

(b) Survival experiments

Fírst instar nymphs born within the previous 12 hrs were placed

on hosËs and the plants úrere caged using whole pl-ant cages (Fíg. 4).

Mortalíty was recorded at least every other day and the tíme taken to

become adult (nymphal devel-opment period) was recorded. As soon as they

34

Fígure 3. Clíp-on cages.

\

3s

Figure 4. InthoLe plant cages.

36

became adults, before they began reproductíon, aphíds were placed singly

in 12 x 75 rnm culture tubes and dried aË BOoC. After 48 hours dry

weights were taken using an auÈomatic electrobalance (Cahn Model 25).

v. Clones tested

(a) 1980

Three aphid clones were collected, one each from fields of

alÍ.aLfa, trefoil , and sainfoín at the Research StaËion, Glenlea,

Manítoba, duríng míd-season (20 July l-980). These fields had been seeded

Ëo theír respective crops Ín earl-y May, 1980. These three clones were

tested ín the laboraÈory throughout 1980/81, and experiments were re-

peaÈed several months apart. Ihe three clones were coded as AL-8C (col--

lecÈed from alfalfa), TR-80 (col-lected from trefoil), and SA-80 (collec-

ted from saínfoin).

These three clones, partÍcul-arly AL-80, \^rere used as standard checks

in experíments conducted in 1981- and L982.

(b) r_eBr_

During Èhe crop season of 1981, síxty clones collected from

the same fields of aLfaLfa, trefoil and sainfoin at the Research Statíon,

Gl-enlea, ManÍtoba, ürere tested in the 1-aboratory. Two collections were

made: the first consistÍng of thírty clones, Èen each from a1fa1fa,

trefoíl and sainfoín, coll-ecÈed early in the season (09 June 1981), whíle

the second consisted of thírty clones, ten from each host, collected

later ín the season (29 JuLy 1981).

In fecundity experiments, the fecundity of each female durÍng the

37

firsÈ seven days of reproducËion was measured as facil-iËies prevented

l-ife-long counts such as was done in the case of l-980 clones. Sinilarly,

only the firsË 20 progeny of each female hrere reared to monítor the morph.

In 1980 and l-981 experfments, only one varíety of aLfalf.a (var. Beaver)

was used.

(c) L982

In 1982, Ít was decided to test the populations existing on

older stands of hosts and also to test two varÍeËies wíthín a host.

AccordÍngLy, a six year old al-falfa fÍeld (var. Algonquin) at Dugal-d,

Manitoba, and a four year old alfalfa fÍeld (var. Beaver) at Ëhe Research

Station, Glenlea, rirere selected. The dístance between these fíelds was

approximetely 50 kn.

T\.relve clones were collected on 30 May J-982, from Dugald, a¡d L2

clones from Gl-enlea on 28 l(ay LgBz. The second collection was made later

in the season: 12 clones from DugaLd on 16 JuJ-y L982, and 12 clones from

Glenlea on 30 Jul-y 1-982. These clones \^'ere tesÈed in the l-aboratory

using procedures símíl-ar to those of l-981, except that survíval experi-

menÈs were not. carried out Ín thi,s case.

2. Field Studies

i. 1980 and 1-981

FÍeld transfers were made duríng the crop seasons of 1980 and 1-981,

among the plots of alfalfa, sainfoín, trefoíl, sweet clover, fieLd peas,

and fababeans, especlally gror4rn for the purpose at the Research Station,

Glenlea. Fiel-ds were seeded Èo the crops Ín early May 1980, and the

38

recon¡mended agronomíc practÍces laid dovrn by Èhe Manitoba Department of

Agriculture r¡/ere followed (Anonymous. 1980) .

Fourth ínstar apterous nymphs were caged singly using sleeve cages

(Fig. 5), and the branch of the plant along wíth the cage r47as removed

after 160 day-degrees above base 4oC and brought ín the laboratory for

examination. Parameters estimated rnrere mean survívaI to reproduction,

mean fecundity, and mean proportÍon of alatae ín the progeny. This work

was carried out throughout the growíng season at varÍable intervals to

examine whether there rras any change over the season ín extent of varí-

atíon in Ëhe effects of host plant on the aphid populations.

ii. L9B2

Because of the easíer and more precíse handling possible ínsíde the

laboratory, it was decided to test the field-collected aphícls in the

laboratory. Thus fíeld-collected fourth instars were placed directly on

different host plants in clip-on cages and placed ín the growth chamber

where other l-aboratory experfm"rrt" r.r" conducted. After about 160 day-

degrees above base 4oC, their survival to reproduction and total fecundíty

I^7ere recorded.

Analysis of variance and tests of signífícance r¡rere carried out as

outlined by Steel and Torríe (1980). Chí-squâre tests and orthogonal

comparísons T¡rere done as outlíned by Snedecor and Cochran (1980).

39

Figure 5. Sleeve cages.

CHAPTER IV

RESULTS

1. Effects of Cagíng and Rearing Techníques

In order to ensure that different experiments could be compared an

investígatíon was carried out Ëo determíne if results would differ íf

aphids LTere caged usíng different Èypes of cages. Fourth i-nstar apterous

nymphs vÍere caged Índívídually using different types of cages. Experi-

ments \,lere terminated on the sevenÈh day of reproduction and the total

progeny and the number of dead nymphs r¿ere counted. Table 1 shows the

results. ClÍp-on cages had drastic effects on the fecundíty and nymphal

survíval. However, it was found that íf the progeny produced were re-

moved at least every other day, progeny productíon in clíp-on cages could

be raísed as hígh as that in whole plant cages and accordíngly n}'rnphal

morÈality could be mínírnízed. Therefore, in fecundity experiments clip-

on cages were used whíle ín nymphal survÍva1 experíments, whole-plant

cages were used. All the field experiments !üere done wíth sleeve cages.

During the study the questíons arose as to whether 1ivíng plants

and excísed leaves of fababeans differ signíficantly as hosts of A.

pisum. Robinson (1961) found that there hTas no sÍgnificant dífference

ín fecundiÈy of A. pisurn when caged on upper and lower surfaces of the

broad bean leaves. There r¡ras no information available on excised

leaves versus whole plants as hosts for A. pisum and, therefore, an

experiment was conducËed. The results obtained are represented in

Table 2. There r'¡as no signíficant dífference in fecundíty per female

4T

Table 1. Effects of differenË cages on fecundity and nymphal survivalon alfalfa. (Clone:-AL-80 ).

I,rÏhole plantcaees

Sleevecages

C1-ip-onClíp-on cages(when progenyremoved dailv)caqes

Progeny/ fe*"le /*seven days (t S.E ) sz.6!4,64 46.3!4.54 22.5!7.8 48.9!4 BA

B

% Nynrphal rrortality?t(t s.E.) I 4A ro . Bt2 .24 48 .g ú .78 6 .3!r.7A

*Mean of eight replicates.

A'BM.rn" havíng different superscrípts in each row are signíficantlydífferent at 17. level. (One way analysís of varíance andDuncants multíple range tesË).

' I i¡,,. i.;l.:i

8Ë 3*rl?f¡'tcr;l,q

r.' .,': l/_ l:t ,'}

Table 2

42

Suítability of excísed leaves and whole plants of fababeans ashosts. (Clone:-AL-80).

hlhole plants Excised leaves

Progeny / female/*seven days (t S.E.)

7. ALatae*(t s.E.)

A A5 7.113.6

0 OA

63,4!2 .6

27 .0!2.8 B

*Mean of eight replícates.

A'U*"rrr" having different superscrípts in each row are signífícantlydífferent at L7. Level. (One way analysis of varíance and Duncanfsmultíple ïange test).

43

beEween whole plants and excísed leaves (P>.01). However, percent alatae

in the progeny differed signifícantly (p<.01). rn addirion, out of rhe

111 clones tested ín the laboratory in 1980, 1981, and LgB2, 100 clones

produced alatae on excísed fababean leaves (Tab1e 3). Questions musË

now be raísed about the suitabí1íty of excísed fababean leaves and cautíon

ensured ín theír use as a host ín laboraLory experíments r¡ith A. pisum.

During the present studies, it appeared that for perenníals and

partícularly for aLfarf.a, even seed certified to be a single variety

gíves rise to p1-anËs of dífferent suitabilities for a given aphid clone.

Therefore, ít is suggested that in the laboratory experiments, allperenníals used may be vegetatively propagated if other resources do

not límít this process.

2, Laboratory Studíes

i. 1980 clones

(a) Survíval

Four hosts (alfalfa, sainfoin, trefoíl, and excísed leaves of

fababeans) were compared for survival and attainment of adulthood forthe three clones. Fírst instar nymphs were placed on Èhe hosts and theirdaíly mortaliÈy was recorded. As soon as they became adults and before

reproductíon, their dry weíghts vrere taken.

Figures 6, 7 and 8 are graphical representatíons of percent nymphal

survival of AL-80, TR-80, and sA-80 clones respectívely. poínts at the

ninth day also represent the percent attainment of adulthood for atlhosts except saínfoin where some n)¡mphal Ínstars were prolonged beyond

44

Table 3. Production of alatae by 111 clones on different hosts

Hos ts

No. of clonesproducíng alataeout of 111 tested

Average 7" alataeproduced by thoseclones responding

(with S.E. and rance)

Fababeans(Excísed leaves)

Trefoí1(who1e plants)

Alfalfa (var. Beaver)(whole plants)

100 21.80 r 3.00(0.6 - 83.0)

10.15 ! 7 .27(o.B - 66.6)

4.75 ! 2.70(o.e - 33.3)

56

25

45

Figure 6. Percent survival of clone AL-80 on different hosts

(N = 45).

100 x-x_x_x4x_x_ ¡æX - t ÉXÉ x-x æXs¡- x -^-À-x-t

ALFALFA AND

FABA BEANS

TREFOIL

SAINFOIN

90

80

70

60

5.0

40

'J- 2 3

FI

H

gCN

ñ

30

\20

10

456 7 B 9 10

DAYS

46

Figure /. Percent survíval of cLone TR-80 on dífferenÈ hosËs

(N = 45).

100

90

80

70

60

50

40

I -t-/

FABA BEANS

TREFOTL

- _ SATNFOTN

1

\Ë

Hdritn

ñ

\¿_ l_r _,_ r__/\

30 ¡__la\20

10

\oruo*o

I234s67891-0

DAYS

47

FÍgure 8. Percent survival of clone sA-80 on different hosts

(N = 45).

100 -{t -{t

90

BO

70

60

50

40

30

10

å bx-x _x _ \ -x-x-x x-x-x-x-x FABA BEANS

\, \/ t-r-.\ '-'-

J4H

Év)

ñ

,{-t-r-ìS¡\INFOINALFALFATREFOTL

9 10

20

L2345678

DAYS

48

Èhe tenth day. These fígures reveal that all three clones did well on

fababeans hIÍth 1002 attainment of adulthood. on alfalfa, the three clones

represent Èhree dífferent patÈerns (roo7i for Ar,-80 , BoT. for sA-80, and

L4% fot TR-80). These were signíficantly different at p<.05 according

Ëo Chí-square Ëests done on contíngency tabl-es (Snedecor and Cochran

1980). sainfoín proved to be a poor host for AL-SO and TR-SO, although

most of the nymphs of sA-80 survived beyond the tenth day but did not

become adults.

Fígure 9 represents the adult dry weights of the three clones on

different hosts. Analysis of varíance índícaÈes Èhat on alfalfa the

three clones were sígníficantJ-y different whereas on fababeans they were

not (P<.05). rn additíon, on sainfoin and trefoil, Èhere was no si.g-

nificant difference.

(b) FecundíËy

Fourth ínstar nymphs were caged singly on the four hosts (a1-

faLfa, sainfoín, trefoil, and excised leaves of fababeans), and theírfecundity l,¡as recorded daily til1 the death of the adult. Table 4 shows

the data on fecundity, longevity and alate production of the three cl-ones.

Both fecundity and longevity of the three clones on alfalfa were síg-

nificantly dífferent (P<.05), while on fababeans longevÍty was not síg-

níficanËly different. However, clone sA-80 had signíficantly more

progeny (P<.05) on fababeans than had AL-80 and TR-80.

(c) Alata production

The three clones appeared to behave sirnilarly wíth regard to

49

Figure 9. Adult dry weights (mg) of rhe rhree l9g0

clones on dífferent hosÈs ( + S.l.¡,

ME

AN

AD

IILT

DR

Y }

ÍEIG

ITT

(m

g)

H (Jlù ()

\o O@ Õ

{ oo\ o

tjl oF

' o(, o

o Þ r r-d Þ r trl Þ o z U) Þ H a o H z

AL-

80

TR

-BO

SA

-80

AL-

80

TR

-80

SA

-80

AL-

80

TR

-80

SA

-80

AL.

80

TR

-80

SA

.8O

z F] '^) llI r-d o H F o Ll Þ H tq Þ z lt)

t-_

}--

t_-

Table 4, Fecundlty and Èy of Èhe three 1980 clones reared

Hos ts

Clones

Alfalfa SainfoinAL-BO TR-80 SA-80 AL-80 rR-80 sA-80

Mean progeny/f ernale

Mean adult1i fe(days)

Mean alatae(z) 0.0 10.015.7 0.0 0.0 5.0!4.2

Analysís of variance and comparfson of means were done on transformed log (x + 1) dataare signifícanÈ1y dlfferenÈ (p<.05) according to Duncanrs multiple range-test.

on dlfferent hosrs (t S.E.)

AL-80 TR-80 SA-BO

Trefoil

0.0

AL-BO

Fababeans

TR-80 SA-80

70.2110.0 0-0t - 34-7!8.6 7.4!2.3 0.51 - g.g!2.4 1.11 .6 1.911 .7 5.Ot2.6 78.g!7.6 80.0t5.6 108.118.0

22'2!2.2 3-2!2-o 12.2!2.4 6.2!2.8 4.3!2.3 9.113.1 3.7!2.3 5.0r2.5 7.013.0 23.4!2.4 22.o!2.3 22.7!.2.2

2.013.8 28.116.3 2.0t4.3 42.L!9.7

l4eans wlthln any given host, NOT jotntly underlíned

(.¡lO

51

one measure' but behaved dÍfferently with regard to another measure on

Èhe same host. For instance, Èheir dry weights r¡rere not signifícantly

dífferent on fababeans (Figure 9) but the clone SA-80 differed sígnifi-

cantly from the other two in fecundíty on fababeans (Table 4).

l,Ihen nymphs from fecundíty experiments Ì"rere reared to determíne

theír morph, it was found thât the three clones had three signifícantly

different patterns of wíng production on alfalfa and on excísed leaves

of fababeans (Table 4). Therefore, an experÍment was conducted to check

whether the three clones respond dífferently or not to a crowding

stÍmulus (sutherland 1970). Groups of 10 young adults were confined

within 5x2.5 run g]-ass specimen tubes for a period of 24 h. Each aphid

was subsequenÈly placed on an excised leaf of fababean ín a petrí dish.

The data (fa¡te S) reveal that the clones AL-80 and SA-80 are simílar

but are sígnificantly different (P<.05) fron TR-80 ín response to the

crowdíng stínulus although all three had consístentl-y dífferent patterns

of alata productíon throughout the early experiments (ta¡te 4).

Survival, fecundíty, longevity and alata production measurements

\¡rere repeated three tímes several months apart duríng IgBo/8I, and the

Èhree clones responded consísÈent1-y wÍth regard to parameters estímated

on different hosts, showing no signíficant differences among repetítions

(P>.01). These clones had been selected for theír survival orr* fababeans

at the time of the initiatíon of aphid culÈures. Similarly in case of

L981 and l-982 clones, selecÈion to fababeans occurred at the tíme of

culture initÍatíon. This may be part of the reason why all the clones

Ëested throughout the present l-aboraÈory studies generally díd well on

52

Table 5. Alate productíon by the three 1980 clones followíng acrowdÍng stimul-us on excÍsed fababean 1eaves

percent al_atae* (t S . E. )

Clone Crowded Nof cro\,üde ,1

AL-80

TR-80

SA-80

53,4!rL.2a

12.4!4 .6b

59.9tB.Ba

20.g!8.24

4.0!4.9 b

45 .2Ì10. 8c

*Mean of síx replícates.

a'b'c'lleans having same superscripts in each column are notsignifícantly different (P<.05). (Two way analysís ofvariance and Duncants multíple range test).

53

fababeans.

ii. L9BI Clones

(a) Survíval

Clones col-l-ected from the fiel-d plots of alfalfa, sainfoín and

trefoil I47ere tested on alfalfa, sai.nfoin, trefoil and excísed leaves of

fababeans. First insËar nymphs were placed on Èhe hosts and rnortality

I^Ias recorded every oÈher day. Twenty nymphs were used in each clone-host

combínation. As soon as they became adults, before reproduction, their

dry weíghts were recorded.

Survival and adult dry weíghËs of different cl-ones from populaËíons

sampled duríng the early season are presented in Table 6 while Table 7

consísts of data on clones from populatíons sampled later ín the season.

Sainfoín proved to be a very poor host. For most of the clones tested,

very few nyrnphs attained adulthood on saínfoin while ín some cases there

were none at al-l-. Therefore adult dry weíght data on sainfoin has been

excluded. The data ín Tables 6 and 7 show that wíthÍn any given popu-

laËíon-host combination, there is great. varíation. chi-square tests

(contíngency tables) conducted on survíval data showed that the popu-

lations are not sígnifícantly different (P<.05). There was no relation-

shíp between the response of clones to one host pJ-ant and their response

to another host plant. For example, on alfalfa (Table 6), aphids of

clone 2 ftom the early season sample of the alfalfa population were the

heaviest aphids (0.861.20 mg) whí1e those of clone 9 r¿ere the lÍghtest

(0.541.07 mg). But aphids of the same tvro clones vüere equal in weíght

on trefoíl, weíghíng 0.39!.07 and 0.381.13 respectívely. on fababeans,

Table 6. Survlval and uean adult dry welght (ne I S.D.) of clones from varl-ous populatlons when reared on dlfferent hosts. (Early season - 1981")

Source of clones andhosts tested

I. Clones from alfalfapopulatlon on hosts:

AlfalfaTrefoflFababeans

II. Clones fron trefoLlpopulatlon on hosts:

AlfalfaTrefollFababeans

III. Clones fron safnfolnpopulatlon on hosts:

AlfalfaÎrefo11Fababeans

184

t75

181

0.81!.100 . 51r. 14

0.611.14

169

L75

181

No.*survived** No. I No. 2 No. 3 No" 4 No. 5 No. 6 No. 7 No. 8

L76

158

190

0.26!.050 . 51r. 20

0 .511 .09

0 . 71r.10

0.39r.11o.72!.t2

0.861.20

0.391.07

0.46t.04

L.O7 !.220. 78r.14

0.57r.11

0.69r.090.33r.100.491.19

0 .6 2t .10

0.31!.060.431.06

0 .59r . 12

0 . 37r .09

0 . 55t .10

0 .811 . L4

0 .28!.O7

0.531.07

o.79!.2I0 . 44! .10

0 .601 . 17

0.491.11

0 . 61-t .15

0 . 611. 14

o.5v!.!20 . 39 1.08

0 . 48r .10

0.57r.10

0.471.10

0 . 70r .15

0 .64!.20o.25!.I2o.47!.o7

o .47 !.I40 . 34t .09

0.52r.13

0.651.13

0.39r.15

0 .77 ! .I5

0 . 381. 12

0 .40r . 10

0.46!.O9

0.781.19

0.151.04

0 .611.14

0.69!.L70 . 46t .11

0.621.15

0 . 40r .1_3

0.311.06

0.45r.06

0.77!.160. 36J.13

0 . 61r. 14

o.82!.240.481.14

o .66!.74

0 . 95t .10

0. 351.07

0.60r.17

0.76!.I20.49!.100.531.10

No. 9

0.54t.07

0.381.13

0 .58r . 11

0.57!.720.461.10

0 .60r.17

o.77!.220 . 31r. 10

0.671.08

No. 10

0.76!.140 .44t. 11

0 .641 . 11

0.631.12

0.281.06

0.57r.07

o.66!.23o.27!.O3

0.491.05

*Number of nyrnphs that survlved to the adult stage out of a total of 200 nyrnphs, 20 each from each clone, at the start of the experfment foreach host.

**Number of nymphs that survived on salnfoln rrere 55, 37 and 52 for categorles I, II and III respectlvely.(JrF.

Table 7. va1 and me adult È 1S D. of clones from va¡ious tions when reared on dlfferent hosËs. (Late season - 1981

Source of clones and No, *hosts tes d

I. Clones from alfalfapopulatlon on hosÈs:

AlfalfaTrefollFababeans

II. Clones from trefoLlpopulation on hosts

AlfalfaTrefollFababeans

III Clones from salnfolnpopulation on hosts:

AlfalfaTrefoilFababeans

survl.ved** No.2 No1 No. 4 No. 5 No. 6 No. 7 No. 8 No. 9 No. 10

1,7 3

158

190

o.72t.270 . 31t.08

0.49!.07

0.631.16

0.291.05

0.6 31.07

o.29!.060.411.08

0. 731.18

0 . 331.08

o.56!.L2

0.861.18

o .t7 t .o2

0 .55 r.06

0. 31r.07

0.401.08

0.681.14

o .27 !.050.531.13

O .28!.O4

o.24!.060.541.09

0.44!.06O.42!.06

0 . 581. 15

0.641.31

o.47!.I2

0 .60r. 12

0.191.02

0.43r.06

o.46!

0 . 911. 07

0 . 341 .09

o.62t.15

0.53r.07

0.42!.O80.591.10

0.561.09

0.23!.040.52t.11

o.42!.I3o.28!.070.561.08

o .37 !.O7

0 .47!.090.581.16

0.301.06

o.7I!.O4

0.631.16

o.29!.o20 . 681. 11

0.84r.130 . 30r. 15

o.52!.O7

o.36!.720.20r.09

o .47 !.O2

0.651. 19

0 .28!.070.551.11

0.54r.130 . 21r. 09

o.47!.73

o.67!.I20 . 25 r.04o .67 ! .74

0.631.11

0.35t.060.561.09

0.271.08

0.261.08

0.401.02

0 . 681. 15

0.321.03

0.501.04

0 . 68r. 16

0. 37t . 10

0.581.13

0 . 81r. 19

0.22!.o40 . 41r. 11

0 . 641. 19

0.13r.02

0.451.06

752

L64

180

t26

157

r82 0.451.07

*Number of nynphs that survlved to the adulÈ stage out of a total of 2oo nymphs, 20 each from each c1one, at the start of the experiment foreach host.

**Numbe¡ of nymphs Èhat survived on sainfoín were 44,42 and 38 for categories r, ll and rrï respective.l_y. (Jr|Jr

56

theír weights rrere noÈ significantl-y dífferenÈ (0.46t.04 and 0.581.11).

Síníl-arly on alfalfa, aphids of cl-one 2 of the earl-y season sampLe of

Èrefoil populatÍon úrere the heavíesÈ (1.071.22) whíLe those of cl-one 1

were the lightest (0.26!.05), buË on trefoil- and fababeans the same Èulo

cl-ones performed equal-l-y well. Clones l and 4 of the early seâson sample

of the sainfoin population did not show any sÍgnifícant difference on

hosts of alfalfa and trefoil while on fababeans their weíghts were sig-

nificantly dÍfferenr (0 .72!.L2 and 0.481.10 respecrively). símí1-arly,

clones 6 and I of the early season sample of the saÍnfoín popul-atíon did

not díffer sígnifícantly on alfalfa and fababeans but on trefoil theír

weighÈs were significantly different (0.1-51.04 and 0.49!.10 respectively).

Líkewise late season data (Table 7) show that within any gíven popu-

lation-host combination there is great variaÈion. trrlhen Èwo particular

clones are compared they perform equally on some hosts, buÈ signífícant1-y

dífferently on some other. Chi-square tests (contíngency tables) show

that survival of the clones from the alfalfa populaÈion on alfalfa (173)

was signifÍcantl-y different fron the cLones of the sainfoin populatíon

(L26) on alfalfa (P<.05). However, survíval of the cl-ones from the

trefoÍ1 population on al-faLfa (L52) was not sÍgnificantly dífferent from

those of the aLfalfa populaËion on alfal-fa. Sirnílarly on trefoíl, sur-

vival- of Èhe clones from al-l- three populations \¡rere not sígnífícantly

different (P>.05). ThÍs suggests that the clones.present on al-fal-fa

l-ater ín the season are better adapted to al-falfa than the clones presenÈ

on saÍnfoin are to alfalfa.

Based on Èhe consístency exhíbited by the 1980 cl-ones over an

57

exËended period of tíme, ít seems líkely that such measurements on clones

are repeatable and hence are rea1.

(b) Fecundíry

Fourth instar nymphs r/ere caged on the four hosts (alfalfa,

sainfoÍn, trefoil, and excised leaves of fababeans) and their fectrnclity

vlas recorded every other day till the seventh day of reproductíon. At

each inspection the nymphs r"tere removed and reared on excised fababean

leaves in order to determine theír rnorph. Tables g and 9 consist of

data on fecundity of clones from populaËíons sampled ín early and late

seasons respectÍvely. Analysis of varíance showed that samples from

populatíons are not signÍfícantly different (P>.05) ín fecundity. F ratio

comparisons made between populatíons and beÈween clones show that díf-

ferences among clones between popul-atioïrs are no greâter than differences

among clones r¡íthín any gíven populatÍon (p>.01). Fecundity data í1-

lustrate the fact that the host p1-ant responses of one clone are un-

related to those of other cl-ones. For lnstance, fecundíties of aphíds

from clones I and B from the early season sample of the trefoil popu-

lation (Table B) on safnfoin and on fababeans are not sígnificantly

different while on trefoíl and alfalfa fecunditÍes aïe signíficantl_y

different (P<.05). Thís type of clonal variatíon ís apparent from Table

B and 9 íf two or three clones are compared together r¿ith regard to

theÍr fecundity on different hosts.

Late season data (Table 9) liker¿ise índicate that there is a greât

deal of variation wíthin any populatíon-host combínatíon, and. two clones

that perform similarly on one host can díffer sígnificantly ín Ëheir per-

Source of clones and

Table 8. Fecundl of clones from varlous

Mean

tlons on dlf t hosts +qË earl season - 9

/fer¡a1e/seven (t S.E.) (avera of 10 reollcated

I. Clones frou alfalfapopulaÈfon on hosts:

AlfalfaSalnfolnTrefollFababeans

II. Clones from Ërefol_lpopulatlon on hosts:

AlfalfaSalnfoinTrefollFababeans

No. 1

35.gt|.2ab7.7!3.24

L^9.418.8"'

43.3!5 .74

49.6t7 .Bb"

3.7r3.0422.2!5.74

36.8t4.0c

53.313.4c

6 . 7t3.04

7. 3t4.lb"47.3!5.Lab

46.515.9ab

3.611.04

7 .5t7 .7b"49 .2!.5.Lab

35 . 3r8 .54

4.5t8.447.3xh.gb"

63.7ú.24

26.g!5.zeb

o. 3to. ob

1.512.1d

25 .5!3.7c

No

52. 315.04b

1 . 2r1. 0b

6 .5t6.5b"44.7 t4 .|ab

2 No. 3 No. 4 No. 6

59 .114. 3ab

o.oto.ob:'4.Bx4.gab

52.2!3.3ab

No. 7 o No 9

45.4t5.14 49 .3!4.gc5.6tll. la 6.1t4.9a

10.8t2.1 "b 27.4*6.0^

50.6tlo.5ab 54,2!4.5ab

6.5+6.7c

0.0+0.04

7.8!3.2c51. 7t6.14

55.2!5.54

o . gr0 .0e

19.9t5.4b"29 .8t6.6b

25.016.5b

3.5!2.647 .3!4.O4

42.7!7 .ga

2L.6t4 .tc1 . 3t0 .04

t5.l!2.3453.618.34

38.517.04

0.0r0.046.916.obc

5B.1rB.2a

28.1*.4b0 . 8t0 .04

6.2t5.1b"55 .2!6 -74

26.2!7.0b

o.7ro.oa12 .8t2.3b"52.4!5 -ga

30.614.9b

0 .oto.oa25.r!5.2ab59.6ú.74

35.1t5.8b

3.0 t6 . 0a

7 .2t3.7b"33.3!2.84

34.2!IO.4a

0,4t¡.g a

2.2t0..0 d

4r.3!2.g a

IÏI. Clones from salnfolnpopulaÈion on hosts:

AlfalfaSainfolnTrefollFababeans

36.916.9c 52.I!4.La0.0i0.04 0 ,110 .0a

23.8t5.4btd 7.4!5.rcd49 .2!6 .Ia 32.r!6.2a

49.2!5.44

0.010.04

1g.5t6.l"b"5 3.0J4. Oa

42.2!71.r4 39.4!5.f0.110.0 ^ 2.8t3.O^

:..2.g!2.1tb" 18.o*3. 5tb59.1r4.oab 29.7lr.gc

36.3!4.34 43.3!4.4a

o.gt2.5a 0.0t0.0":-.3,6!4.obtd 17.013.8'36.5t6.74b 60.611.6b

45.1t5.64

5 .4!4 .54

19 . gt3.2"b"d

39 .zt3.zb"

44 .7 lL .gb

0.010.04

17. Bt2.5ab

36.6!4.44

44.6!4.2b

o.oto.045 .9 !2 .5d

30 -6t2.7ab

Analysis of variance and comparison of means were done on transformed JT- data.Means followed by the same letter' r¿ithin any given row, are not signlficantly different according to Duncan's mulciple range test at the 5% 1eve1(¡(,

Table

Source of clones andhosts tested

I. Clones fron alfalfapopulation on hosLs

AlfalfaSafnfoln

TrefollFababeans

II. Clones frorn trefoilpopulation on hosts:

AlfalfaSaínfoin

ïre foí1Fababeans

III. Clones from sainfoinpopulation on hosts:

AlfalfaSalnfoinTrefoilFababeans

9. Fecundity of clones from

No,1 No. 2

atlons on di

female/seven

No. 4

fferent hosts (t

No. 5

40.7 !6 .2

0.3r0.09 .2!3.4

55.8t2.04b

37.2!7.|ab0.010.0b

1. 1t0.5ab

45 .2t2.obc

Mean p

No. 3

22.4t8.74

0.5t0.0b4.gt3.4cd

34.815 .5ab

No. 9

48.116.5c

8. 1t3.5426.7fi.6d43.2!6 .3c

No 10

39 .4!5.74

0.010.0b

10.4t2.5cd28.8t3.4ab

bc

b

bc

43.7 !5.8"b" 52.7t3. 3b.2.rtL.3a o.6to.ob7 .otz.sb"d 2.4!r.fd

37 .7!5.6ab 33.5!4.7a

S.E.) (1ate season - 1981

s.E.) ( of 10 repllca tes)No. 6 No. 7 No. 8

46.gt5.0a 53.619.8"bt 32.2!g.gabo.olo.ob o.oto.ob o.8to.ob7.1*1.7ob" 1.9r3.5"bt 4.513.la

35.215.94b 34.815.3ub. 40.0t3.9ab

11.6J7.4d

0.2*o.oa

10 .615. Bcd

47.1t3.oab

2.oto.ob"0.0t0 .04g.7+2.34

34 .gxz.5c

10.7r3.3b" 54.6x4.2bc 48.316.4ab1.8r3.54 1.9i5.0a o.oro.oa

30.5t2.3b"d 28.Bt4. 7"b" 15.1t6.2cd45.7t11.54b 54.0t9.64b 46.5!4.6a

37.9t9.8tb" 21. 7t5.Bcd

0. Bt0 .04 1.1t0.049.5t2.1b"d 73.0!2.7ab47.g!4.5a 43.0!4.2at)

33.7 !6.2abc 25 .7 tg .8^b"3.6!2.44 0.0t0.04

14.911.9a 12.012.8b"d

32.5!3.9a 28.2r5.9b.

1.6to. ob.d

0.oro.oa

0.0r0.0d

6. 3t1. 3b"

1.516.5b o.1to.obo. oro.ob o .2Jo .ob

7.6!3.7a 3.¿rtl.zb56 . 6 *7 . 9ub" 49 .2!.6 .sc

40.913.64b

0. 310.5bg.o!2.r4

15 .g tz .4b"

11.317.6

0.010.0

14 . 8r3. 5

54.7!7.0

49 .2!2.7ab1.2r1.Oab

:-4.O!2.7ab

30.6!2.7ab

68.6t5.04

5.8!2.r48.4t3.5ab

35.817.0c

21.011.54

40.816. 3a

38 .2!4 . 3ab

0.010.0b

8.311.24

19. 8t5. B"b"

ab

b

a

bc

15 .6tr2. 2ab 5L. 6!2. |ab'o.oio.ob o.tto.obl4.g!2.ga 4.413.8b51.017.9c 34.015.6c

55.7!4.340. 3r0.5b

Analysis of varlance and comparison of means r¡ere done on transformed 1og (x + 1) data.Means followed by the same letter' within any given ror'r' are not significantly different according to Duncan's rnulliple range test at the 5z leveI.

\.n\o

60

formance on another host. Similarly, r\^¡o clones whích behave equally

on one host ü7ith regard Ëo one measure can differ on the same host wÍth

regard Èo another measure. For Ínstance, dry weíghts of aphíds frorn

clones 3 (0.441,06) and clone 5 (0.23!,04) from rhe late season sample

of the sainfoin populatíon tested on trefoil (Tab1e 7) are significantly

dífferenÈ whereas their fecundity on the same host (9.0 and 14.0 re-

spectively) are nor sígníficanrly differenr (p>.05) (Tab1e 9). sími-

larly, mean fecundity of aphíds from clones 3 (15.9) and clone 9 (40.g)

from the late season sample of sainfoín population tested on fababeans

differ signíficanrly (Table 9) whíle rheír dry weíghts (0,42!.06 and

0.501.04) are nor sÍgnificantly different (Table 7). This phenomenon

was clearly exTríbited by the three 1980 clones with regard to their

fecundity and dry weighÈs on fababeans as well as theír responses to a

crowding stimulus (Table 4, 5 and Figure 9).

Analysís of variance comparing early and late season fecundíty data

índicates that the responses of clones collected during the two seasons

differ sígnificantly (P<.005). Table 10 represents progeny production

on alfalfa by clones sampled from different populations duríng early and

late seasons. f Ë reveal-s that total fecundity of cl-ones samplecl f rom

the alfalfa population on alfalfa declíned from early to late season

by 8.L7" as agaÍnst L6.97, for clones sampled from the trefoil population

on alfalfa and 23.3% for clones sampled from the saínfoín populatíon on

alfalfa. Orthogonal comparísons made on these data indicate that the

reductionsof total fecundity of clones sampled from the alfalfa popu-

latíon on alfalfa (8.77") is not sÍgnifícant vrhereas reductionsin progeny

of clones sarnpled from the Ërefoil populatíon (L6.9%) and that of clones

Table 10. Pro roductÍon b clones from different tions d

Early season Late season

tl47 752

1108 1431

]-547 1058

earl and late seasons - 1981

Clones sampled frompopulations on:

Alfalfa

Trefoil

Saínfoin

Total progeny on alfalfa by10 clones with 10 replicates

Total progeny on trefoíl by10 clones with 10 replicates

Z íncrease ordecrease fromearly to late

8. t_ IL6.9 ,t

n.3 I

% increase ordecrease fromearly to lateEarly season Late season

4536 4L68

2932 2478

4338 3327

34.4 tr

2e.1 I31.6 J

o\F

62

sampled from the sainfoin population (23,3%) are sígnificant (p..OS).

Simílarly, Tabl-e 10 also represents toÈa1 progeny of clones sampled from

dífferent populatíons, early and late, on trefoil. cl-ones sarnpled from

the alfalfa population show a reductíon of progeny from early to late

season by 34.4% wii,Íl-e the number of progeny of clones sampled from the

trefoil populatíon increased by 29.2%. Clones sampled from the saínfoin

populatíon record.ed a decrease on trefoil of 31 .6% from early to late

season. Orthogonal comparísons made on Èhese data indicate that this

íncrease Ín fecundity by 29.2% is significanr (P<.01). Thís índicares

that the cl-ones sampled from the trefoíl- populatíon show some improved

performance over the season when tested on Èrefoil, whíle the clones

sampled from the other two populations show reduced perforrnance when

ÈesÈed on Ërefoil-.

Out of the 63 clones tested ín 1980 and 1981-, only one clone was

found to perform well on saínfoín. Thís clone had been eollected on

alfalfa duríng the latteï part of the season ín 1981, and was retained

and tested further. These daËa revealed that thís clone produced

an average of 39.4 progeny/female on saínfoin during its fírst 10 days

of reproductíon. This was the highest fecundity fígure recorded

on saínfoin by any clone during the present study. It produced B.B%

alatae on salnfofn.

(c) Alata Production

Pooled data on aLata production by different cl-ones measured

duríng the 1981 studíes are presented in Table 1l-. In the early season,

clones sampled from the alfalfa and trefoíl populatíons e>rhibited no

63

Table 11. Production of alsampled ín 1981

atae(ts by clones frorn different populations

.E. )

I. On alfalfaClones sampl-ed

fromEarly season*

7" aLaLael,¿fg ss¿ssnlt:t

7" aLatae

Alfalfa

Trefoil

Alfalfa

Trefoí1

0.0(N: - L724)

0.55(N: - II49)

I.49!L.23(N: - 659)

L.96!L.29(N: - 728)

0.0(N: - 1598)

8.35!2.37(N: - 1098)

15.6510.97

(N: - 555)

L42tI.23(N: - 936)

II. On trefoíl

*Based on ten clones from each fÍerd col-lected on 09 June 19g1.

**Based on Èen clones from each fíeld colLected on 29 July 1981.

N is the total índivÍdual_s monitored.

64

alata productíon on either al-falfa or trefoíl. However, later in the

season' cl-ones sampled from the trefoil populatíon showed increased

productíon of alata on alfalfa buÈ not on trefoil. The clones sampled

from the alfalfa population produced Íncreased numbers of alatae on tre-

foí1 but not on alfalfa. chí-squaïe tests (contÍngency tables) con-

ducted on these data show signíficant dífferences (p<.05). These data

suggest, that these populatíons show some differential selection on theÍr

respective hosts towards the latter part of the season.

ííí. 1982 clones

(a) Fecundíty

Procedures followed were the same as in the 1981 experíments

except thaÈ in addítíon to alfalfa (var. Beaver), ai-fal-fa (var. Algonquin)

was included as a host whíle saínfoin was excluded. Saínfoín appeared

Ëo be a very poor hosË on whích most of the clones díd not reproduce at

all. Samples of clones to be tested were collected only from Èhe fíelds

of two alfalfa varíetíes mentioned above but the alÍal-Ía (var. Beaver)

field herá was dífferent from that of 1981 collection. Table 12 consi-sts

of fecundíty data for clones sampled from the populatíons early in the

season while Table 13 incl-udes for those clones sampled from the popu-

lations later in the season. As in 1981, two clones whích behave

similarly on one host may behave differently on another. For ínstance,

clones 3 and 4 collected in the early season from the al-falfa (var.

Al-gonquin) populatíon tested on alfalfa (var. Algonquin) (Table 12)

differed significanËly ar P<.05 (18.8 and 57.1 progeny/female respec-

Tab

Source of clones and

le 12. Fecundi on dlfferent hosts t S-E-) (eer1vfv of clones from various DoDulâtíons ( season - 1qÂ? ì

/ç seven 1S E of 10 re lfcaÈs t.ested

I. Clones frorn alfalfa(var. Algonquin)populatlon on hosts:

Alfalfa (var.Algonquln)

Alfalfa (var.Beaver)

TrefoÍ1

Fababeans

II. Clonee fron alfalfa(var. Beaver)population on hosts:

Alfalfa (var.Algonqufn)

Alfalfa (var.Beaver)

Trefoll

Fababeane

No. I No 2 No.3 No.4 No.5 No 6 7 No.8 No 9 No. 10 No. 11 No

26!638t1

61

åo.

58. 5!2.2438. 7

13 .54

54.4tl.ga

44cd 45.9.11.7b

57-r.r3. 1ab

56.312.04

6.6t3. 3c

60 .8!2.34

s9 .5!3.2431.1-13. 3d

34-7_13. 3bc

3t-2t4.lcd

7 .3.t3. 3bc

31-. 6 -!2.2d

18.8 -

t8.3d

:å0.

52!4

34.r10 1ro"

5-gab

.5, 30.7 46.r. 35.7-

.6D t5.7cd tg.6þ t2.9b"5t+.5 3716.04 !4

L8.2 . 14*2.6ab !232-O -

16.3d46.7- 4L.2_*4. gbc *4.lbtd

38 .6!4.zcd

4L.9!4.64

22.2.t3. gbc

37 .2*5. 7cd

l-6.1!2.7cde

"to'.1"u*

46.O-13.3Þ

24.2 -

!4.2d

40.5-t3. 6Þc

14.1-!3.7(Ie

?\'."u",

46.6!3.213 .0x4.3

ab 39r6

2L!2ahc

57.8!4.34

r3

47.8.!4.7ab

16!4

36!4

ab

cd

50t3

3^o29t9

39.6+6.24

1-0ab

15c

l^a"

1+0

48+2

13. 5+3 .5c

7

7a

51.5 -

t3.7ab

18.414 .9cd

35.4.+4.3Þc

ef

39!5

2Lt6

11

Ir.a

3'o22.Ot2.La

53.8 -+1.Oab |*.

a.9.0

.9

.8

11.+7

47.15.

c .6.5

.9

.5

14 .1!2.4abc 18.4.

+3-2aÞ

ab56 .l+1. la

3"032!7

14.0+5. gc ab

44.8 -

!1 . gab

!"a40!4

8. 24.6 - -2Þ" lz.gd.et

!u"a33.011.5

30 .6tl .9

24.5 - _

t3. gdet

L4.7*1. gd"

34.9-*3. 2Þccl

25r6

I!2

fu.

.5

.4e !2.LL2.Lr1.5?!t'.tt^*

26.3t3. 8

33.8 -+3.3aÞ

35.6 -

!2.6aÞ

15 .1.+4.3'

L5.2 -

t4.4d'14.1 _+1 - 7et

36+q

22!6

44

0

31.0t4.3cdet9 '>if i.t.27 -2t4 - 3cde

36+<

4!1

24r3

cd47

ab

cde

de

f

47e

fcaer

Means followed by the aaæ letter' r¡lthfn any gLven rort, are not slgnlflcantly dffferent accordlng to Duncanrs uultlple range test at the 52 level.

o\I-r¡

Tat¡le 13 Fccuntll iw of clones from various oooulatlons on different hosts + S.E.) llate season - L982

/feruale/sèven days (1 S.E.) (averase of 10 reolicaMeanSource of clones andhosts tested

I. Clones fron alfalfa(var. Algonqutn)populatlon on hogts:

Alfalfa (var.Algonquin)

Alfalfa (var.Beaver)

Trefoll

Fababeane

II. Clonee fron alfalfa(var. Beaver)population on hosts:

Alfalfa (var.AJ-gooquln)

Alfalfa (var.Beaver)

lrefoll

No. 1 No. 2 No. 3 No. 4 No. 5 No. 6 No. 7 No. I No. 9 No. 10 No. L1 No. 12

4L!6

24x2

50 .4.13. 3Dcd

41.4+1 , de 51.

!4- f,r"a56.014.0

32r5

4L.2.tl-lb

6ge

44.9 43.9 -

t5.gc(le t5.9cdeI2

II

44.9 -

t6.3ab

15.7*2.lc(I

46-4 -

tl. 3ab

47

I4

cde

ab

52a

cde

29+1

ab

abc

L2!2

37x4

16.6 -!2.zab

"7r'.'u"u

46.7tl. ga

64.7+r.74

43a

54!2

3

2c20r5

7.7-tl.4(l45-1.*1.lab

cd

43r3

24+7

50 .9+L.74

ab

L3.4 -*2.4ab

27.L .,4.2co

L4!9

46!6

20.t3.64!3

abc 33.0t7 .5e

50.1+3. la

43.4!2.3ab

33.6r10. 3e

4r.91g.0{l

34.8t3. 3a

"tr'.1'"u

ah 13:å"u Xi.'ro. 1l:?"u"' iä:3*'

1.gab

4I

84c

32-5.!4.zbc23.O -

tl. 7aÞc

l"o0-2aÞc

40.1 -

15.Ode

45.3 -!2.2eÞ

2L.3 -

t2. 3abc

46.2 _

t3.2ab

61.1 -+6.4aÞ

47.O!4.2429.9 -

!2 -gaÞ

40.1.t3. 7Þ

12.6+', t

46.711 -5

11. lu"u5t.2 -*1.74b

I

46.Or0.9

38.8-13 .9Þ

54.611 .54

a

ab

21.8.t4 -6Þc

21 .311. 9

ef

49.3 -,2.2ab

I0c

11.6-t2.2Þ

33. 1t5.6cc

31!424+3

35!462r5

2615

55!2

21.0.t4 .9bc

16.8 -*3. 3ab

50.0 .*1. gaÞ

415!4

39!2

1813

40!4

06c

lu.

16c

4

5a

32.2!7 .6ab

ab

40.0 19.9- L4t6.5a t5 .3Þc !4

28.7. 34.4 -

tl.Bca *4-gcd

15.1t4. gc ab0

4

grt

la25!4

39.t+!7.3 lu.

å"0

58.615.6

24.3!3.450 .0!2.9

cdef

a14 .113 .1ab

23.7!4.zab

Fababeans

Means followed by the eaæ letter, wtthin any glven row, are not slgnlffcantly dffferent accordfng to Duncante nultlple range test at the 52 1evel

10.8-tl.8b25.4 -

tl .9d

34a

9_a)

10.8.r1. gÞ

OrOr

67

tively), but their performance !üas not dífferent on fababeans (52.9 and

60.8 progeny/female respectively). However, on trefoil, the same cl-ones

3 and 4 had 2L.9 and 6.6 progeny/fernale respectÍvely and also on aLfa¡Ía

(var. Beaver) they had 39.1 and 53.3 progeny/female respectívely. These

figures díffer significanÈly (p<.05). Late season dara (Table 13) also

extríbít the same phenomenon. For ínstance, clones 5 and 7 which were

sarnpled from the alfalfa (var. Beaver) populatíon, when tested on

alfalfa (var. Algonquin) had mean progeny/fernale of 14.1 and 40.0 re-

spectively. These fígures differ significantly (P<.05). But on alfalfa(Beaver) and trefoil their differences vreïe not signífícant. On fababeans

they differed sígnifÍcantl-y wíth 64.4 progeny/Íemare being produced by

cl-one 5 and only 28.7 progeny/femaLe by clone 7.

An analysis of variance done on early and late season samples, com-

paring fecunditíes índícates that early and late clones sampled from

different populations díffer signífícanÈ1y (p<.005). Table 14 shows

progeny production on alfalfa (var. Algonquin) by clones sampled from

different populations during early and l-ate seasons. This indicates that

clones sampled from the aLfaLfa (var. Beaver) exhíbited decrease ín

total- progeny production of 23.6% on alfal-fa (var. Al-gonquin) from earl_y

Ëo late season, while clones sampled from alfalfa (var. Algonquin) on

the host alfalfa (var. Algonquín) íncreased by L5.3"/.. These two figures

are signifícantly different (P<.01). similarly, clones sampled from

the alfalfa (var. Beaver) population tested on the host alfalfa (var.

Beaver) (Table 14) had an increase in pïogeny production of 20 .rT" as

compared wiÈh only 2.0% increase by clones sampled from the a]'falfa

Table 14. Pro

Clones sampled frompopulations on:

roduction clones from different ations durin earl and late seasons - 1982

Total progeny on alfalfa (var. Algonquin) Total progeny on alfalfa (var. Beaver)by L2 clones \.üith 10 replicates by L2 clones \^rith 10 replicates

% increase ordecrease from

% increase ordecrease from

Earl season Late season earl to late Earl season Late season earl to late

Al-falfa(var. Beaver)

Alfalfa(var. Algonquin)

3578

4797

2735

5531

n.6I Á.20.L I

,l\2.0 I

4L75

5L47

5013

5252ls.3 I

o\æ

69

(var. Algonquin) population tesÈed on al-falfa (Beaver). This indícates

that the clones from the alfalfa (var. Beaver) populatÍon show better

adaptatíon on alfal-fa (var. Beaver) over the season than Èhe clones from

the other varíety. Simílarly, the cl-ones from the alfalfa (var. Algonquín)

population tesÈed on alfalfa (var. Algonquín) show better adaptatíon to

that host than the set of clones sampled from the alfal-fa (var. Beaver)

population.

The 1982 studies conducted Ied to other findings. The sample of

12 clones collected in early season from the aLfalfa (var. Algonquin)

populat.ion dÍffered from the sample of L2 clones collecÈed early season

from the alfalfa (var. Beaver) population with regard to theír fecundíty

on the two varieties of alfalfa (p..OS). Thís was Ehe only case ín which

populations l¡/ere sígnificantly different. The late season sample of 12

clones from each population r¡/ere also sígnificantly different (p<.05) from

each other with regard to their fecundity. There rrere several differences

bet¡,¡een these populatíons. The alfalfa (var. Algonquín) fíel_d was 6

years old while Ëhe alfalfa (var. Beaver) fíeld was four years old. The

alfalfa (var. Beaver) fíeld was situated south of the city of trriínnipeg

and had been used for hay. The al-faLta (var. Algonquin) field was located

Northeast of Èhe city and had been used for seed productíon. The distance

between the fields vlas about 50 kn. In addÍtion, insecticides had been

used every year on the alfalfa (var. Algonquín) field. This might have

acted as â strong selectíon pressure on the aphid populations. The

artaLfa (var. Beaver) fÍel-d had received no ínsecticides at all.

The clones from the alfalfa (var. Algonquín) popul-ation showed

increased fecundity compared ¡¿ith those from alfalfa (var. Beaver).

70

For instance, L2 clones sampled in the early season from the alfaLfa

(var. Algonquin) populatíon produced 4797 progeny on alfalfa (var.

Algonquin) as againsË 3578 progeny by the 12 clones from the alfalfa

(var. Beaver) population on the same host. Líkewise, the same 12 clones

from the aLfaLÍa (var. Algonquín) populatíon produced 5L47 progeny on

alfalfa (var. Beaver) as against 4775 progeny by the corresponding 12

clones from the al-falfa (var. Beaver) populatíon (Table 14). Late col-

lected samples showed even greater differences. In late collected samples

of. L2 clones from the aLfal-fa (var. Algonquin) populatíon had 5531 progeny

on alfalfa (var. Algonquin) as against 2735 progeny by Ëhe 12 clones

sampled from the alfalfa (var. Beaver) population on the same host

(Table 14). Thís increased fecundity in alfalfa (var. Algonquin) clones

could be due to several factors. Hígher average fítness caused by the

selecËion pressure of the insecticidal Ëreatment could be one factor.

However, the effects of variety, fÍe1d age, and l-ocations cannot be

excluded at Èhís tíme.

Table l-5 consisÈs of data on mean progeny of early and late collected

clones from the alfalfa (var. Algonquin) population on all the four hosts

tested ín the laboratory. Thís shows that the twelve clones collected

l-ater in the season in L9B2 díd not extribit sígníficant clonal vari-

abílity (P>.05), whereas early col-lected clones díd so.

(b) Al-ata Production

Table 16 shows the pooled data on alata productíon. Here

again, early sampled clones from dífferent populatíons show no marked

difference ín theír aLata producEion on any host. However, the clones

Table 15.

Clonescollectedearlyseason

1ab(3s.s)

2a(40 .4)

3ab(33.2)

4ab(33. r)

5ab(37 .7)

6ab(36. s)

7ab(32.s)

Bab(37 .7)

9ab(33.6)

10ab(36.s)

1lb(26.2)

L2ab(31.8)

Variabilítyx of clones from the alfalfaseesons (L982)

(var. Algonquin) population during early and late

Clonescollectedlateseason

1a(3e.1)

2a(32.7)

3a(44.6)

4a(3e.6)

5a(38.e)

6a(40.3)

7a(32.3)

Ba(3e.8)

9a(40.2)

10a( 3B .2)

11a(44.2)

L2a(41.3)

*Based on mean progeny on all the four hosts (fababeans, trefoil, alfalfa (var. Algonquin) and a11fa1.fa(var. Beaver) tested in the laboratory.Numbers with the same letters wíthin any given ro\^/ are not sígnificantly different (p<.05) accordíngto Duncan's multiple range test.Figures within parenthesis are mean progeny/female/seven d.ays, average of ten replícates.

{H

72

Table 16. Productíon of alatae by clones from different populationssampled Ín 1982 (r s.E. )

I. On alfalfa (var. Algonquin)

Clones sampledfrom

Early season*7" alatae

¡r¡" ""r"gnrr*% alatae

Alfalfa (var.A lgonquín)

Alfalfa (var.

B eaver)

Alfalfa (var.

A lgonquin)

Alfalfa (var.

B eaver)

0.35

(N: - 1413)

0.0(N: - 1218)

II. 0n a1f al_f a

0.18

(n: - L667)

0.0

(N: - 1519)

6 .57 lL .9I(N: - 928)

(var. Beaver)

4.5011.91

(N: - 1378)

0.0(N: - 1091)

0.06

(N: - 1570)

*Based on 12 clones each collected from alfalfaon 30 YIay L982, and from alfalfa (var. B eaver)

**Based on 12 clones each collected from alfalfaon 16 July 1982,

"trq from alfalfa (var. Beaver)

N is the total índívidual_s monitored.

(var. A 1-gonquín)on 28 'Ilay 1982.

(var. Algonquín)on 30 July 1982.

73

sampled later in the season from the alfal-fa (var. Beaver) populatíon

shor¡ed increased production of alata (6.57%) on aLfaLfa (var. Algonquin)

but not on (var. Beaver), while the clones sampled from the alfalfa

(var. Algonquin) produced alata on alfalfa (var. Beaver) but not on

alfalfa (var. Algonquin). õhi-square tests (contingency tables) done

on these data show significant differences (P<.05). These data indícate

that these populations show some dífferenÈial selection towards the

later part of the season.

3. Fiel-d SÈudies

In 1980, Ëhere \,rere no aphids availabl-e on crops duríng the early

part of the field season at the Research Station, Glenlea. The 1980

drought had adverse effects on all crop productíon in Manitoba (Phillíps

1980). On the síx crops (alfalfa, sainfoin, trefoil, sr,reet clover, peas

and fababeans) seeded in early May, 1980, aphíds did not appear until

early July, after which time there rras a sudden íncrease ín aphid popu-

lations. Therefore fíe1d studies could not be ínítiated untíl- Ju1y,

1980.

In 1981, aphids appeared on crops in late May and \^rere consistently

present until míd-August, after whích they declined to 1ow levels

(Figure 10). In additíon to the laboratory studies, fiel-d studies

r¡lere carried out throughout this períod. Tn 1982, fÍe1d-collected samples

of aphids r^rere tested in the laboratory because of the easíer and more

precíse handling possíble ín the laboraËory compared with the fíe1d.

Based on the work conducËed in 1980 and 1981, saínfoín r^r¿rs found

to be a'very poor host on which most of the aphids showed high mortal-ity.

74

Figure 10. Field popul-ations in 1981 (June through August)

(Number of aphids/sweep; Average of 5C sweep/host).

Ê1t¡ltrl(/)

tn

HÈdÊ{

F

ÉcôH

b2

6

1

2T

2L

ON ALFALFA ON SAINFOIN ON TREFOIL

6

1

2T

2L

L

6

I

6

ON SI^ÍEET CLOVERON PEAS

ON FABA BEANS

June July Aug. June July Aug. June July Aug.

75

Therefore, sainfoÍn üras excluded as a host ín 1982 experiments. Field

transfers r¿ere made (l-980 and 1981) among fields of alfalfa, saínfoin,

trefoil, sweet cLover, peas and fababeans. These were replicated 12

tímes ín 1-980, 20 tímes ín 1981- at variable ÍnËervals over the season,

and eight times in 1982.

Data on fecundiÈy are presented in Fígure 11 for aphids sampled

from popul-atÍons on perenniaLs durÍng Ëhe three years. FÍgure 12

repïesents the data on survival- to reproductíon whÍle Fígure 13 repre-

sents the fecundity data for aphids sampled from populations on annuals

over the three years.

Data on fieLd populatÍons on different hosts from June through August,

1981, (Figure 10) show thaË fiel-d populatíon data followed the same trend

of preference as exhíbited by the data for fÍeld experíments, í.e. peas,

aLf.aLfa, sweet clover, fababeans, trefoil- and sainfoin Ín descendíng

order.

Anal-ysÍs of variance r^ras done separately on the data from each

year. There were no signíficant differences (P>.01) among sampl-es of

populations tested wíth regard to theiT fecundity. Chi-square tests

(contÍngency tables) conducted wÍth data on survíval to reproducÈion

(Figure 1-2) also confirns that the popuLaÈíons are not sígnifícantly

different (P>.01-). Analysis of variance aleo indicates that the re-

sponses to various hosts by aphids dÍffer signíficantly (P<.01) while

host-popul-atÍon interactíon is signífícanÈ (P<.01). As shovrn Ín the

laboratory studíes, this al-so shows that the characteristics of díf-

ferent popul-ations are not distinct as they are made up of wideLy

76

Fígure L1. Fecundity of aphíds sampled from different popula-

tíons on perennials and when reared oa differenthosts Ín the field.

Analysis of variance and comparison of means r¡rere done on

transformed JT data in 1980, x'28 dut" in 1981, and x'ldata ín 1982.

The same letters above the bars, wíthin any given population-host combination índicate no sígnificant differences among thehosËs accordÍng to Duncanrs multÍple rarge test at the 5% Level.

HOST PLANTS

- Alf¡lfa- S¡infoin- Trefoil- Sweef -clover- Pe¡s- F¡b¡be¿ns

1980a

34. aaFa 26.5b.t 2g.g Han

d

b

bb

cb

bb

1981 a

aa a

b b ab

1982

a

abb

b

ffi

H

aâ31 .0 26.3

Itll

20

11,UJ]UÉ,ol¡¡ê

oo(o|F

tuJ

=l¡J¡!

zulooÉ,o.

1

t2

t2

t2

aa^4

4b

a

20

a'ûaab

a

bc

4

FROM ALFALFA FROM TREFOIL FROM STVEET CLOVER

77

Figure 12. Survival to reproduction of aphids sampled frompopulations on perennials and when caged on

dífferent hosts in the field.

FI

H

gv)

ñ

100

60

100

60

100

60

FROM

ALFALFA

1980

1981

1982

FROM

TREFOTL

HOST PLANIS

FROM

SIIIEET-CLOVER

- Alfalfa- Sainfoin- Trefoil- Sweet-cl-over- Pea:;- Fababeans

20

Þl

H

g(n

È€

20

J

H

ÉU)

ñ20

o

o

ti¡¡

Etr

Efrl.t Ál:fl

78

Figure 1-3. Fecundity of aphÍds sampled from populatíons on

annuals and when reared on dífferent hosts inthe fieId.

Analysís of variance and comparísolt of means ¡¡ere done

on transformed 1og(X + 1) data.

The same letËers above the bars, within airy given popu-

lation-host combination índicate no sígníficant differe-nces according to Duncanr s multiple range test at the

5% 1eveI.

HOST PI,ANIS

ab

t9a80

bc bc

- Al-fal-fa- SaÍnfoín- Trefoíl- SweeÈ-cl-over- Peas- Faba'lr:airs

49.6

20

L0

2-0

10

20

1_0

aA n20

10

20

L0

20

1_0

b

Jd

bc

U)Þlf¡lÉ,(JþlÊ

òc\\or+

FIÈ

ËFr

2f¡lPõl

t¡-i'-t

mLø

F

o

oô

-aab Gt

tuJ,ffili

a

1981

abcc b

aa

tuÆll

a

f 982

aa

b c

FR.OM PEAS F-R.OM FABABEANS

79

different genotypes, with no relationship between the responses of clones

within any gÍven population to one host plant and their responses to

anoÈher host plant.

Aphids from all- the populations generally did well on the two

annual-s (peas and fababeans) wíÈh the exception that aphids from the

fababeans popul-ation did poorly on peas ín 1980 (Figure 1-3), and aphids

from the sr,,reet clover populatÍon did poorly on peas in l-981 (FÍgure 1-1-) .

But these differences rrere not found in other years.

In 1980, aphÍds from the alfalfa populatíon had signifícanrly

different (P<,05) fecundíty on alfalfa versus sr,reet clover. However,

their differences \^rere not signifÍcant in 1981 whíle 1n 1-982 they were

again found to be signifícant (P<.05). Aphids from the trefoíl popu-

latíon díd equally well on trefoíl and al-fal-fa in 1980, but in 1981 and

1982 were signifÍcantly differerit (P<.05). Likewíse, íf any other rwo

populatíon-host cornbinaÈions are compared, it is found that there is

great variabil-ity from year to year. All these clearl-y show that host

plant preference of any gíven populatíon is noË fíxed and that there

is no fixed rel-ationshÍp between the responses of aphids to one host

and theír response to another. Conbined analysís of variance done wíth

the fecundíty data fron dífferent years Índicates that the years are

sígnificantly dÍfferent (P<.01). It is cl-ear from the daÈa that varíous

popul-atíons exhibiÈ a great variation ín their host plant preferences

from year to year Ín a most unpredictable manner. Therefore, one year's

attríbutes of aphid sampJ-es from populatíons can not be used to dif-

ferent.íate and recognÍze aphid popui-atÍons ín succeeding years.

BO

FecundíËy of aphíds sampled from various populations on perennial

hosts at variable Ínterval-s over the season in 1981 is presented in

tr'igure 1-4. Analysis of variance shows (Table 17) that tíme intervals,

response to different hosts and populaËion versus host Ínteractíon are

signifÍcant (P<,01). These illustrate Ëhat when Ëhe season progresses,

responses of Ëhe populations to the hosts also change. This may pre-

sumably be through differential- survíval reproductÍon and/or díspersal.

Sinilarly, there is no relationship between the responses of cl-ones

within any given population to one host pJ-ant and thefr responses to

another host planÈ.

B1

Fígure 14. Fecundity of aphíds sampl-ed from different popu-

lations and when reared on dífferent hosts ín the

fíe1d at variable intervals over Ëhe season (1981).

Analysis of varíance $ras done on transformed X'28 d.a".

2

HOST PLANTS

- Alfa lfa- Sa infoin- Trefoil- Sweet -cloyer- Peas

- F¡babeans

FROM ALFAL FA

FROM TREFOIL

FROM SWEET CLOVER

c,u¡l¡JÉ(,ulo

oo(o

IJJJ

=l¡llr

zl¡JooÉ,o-

4

t2

l2

4

20

t2

4

Late June Early july Mid July Late Jul¡' Early August

82

Table 17. Anova table for fecundity data of aphids sampled from alfalfa,trefoíl, and sweet-clover Lested on different hosts atvaríable intervals over the season ín the fíeld (le81)

Source of variaËionDegrees of

freedomSums ofsquares

Meansquare F - ratio

Tíme

Population

HoStS

Time x population

Time x hosts

Population x hosts

Time x population xhosts

Replicates

Error

TOTAL

4

2

5

8

4.82

0.05

5.72

5,7L

15 .98

11.58

20.64

0. 86

L24.L9

189 . s5

r.20

0 .03

r.74

o.7I

0. B0

T.16

l.J) xx

0.06 NS

2 .46 'k),

1.54 NS

L.72 x

2.49 xx

1.11 NS

0.61 NS

20

10

40

3

267

0.52

0,29

0 .47

Data transformation Z, - X0'28

** Sígnifícant at L% level.

* Significant at 5% level.

NS Not sígnificant.

CHAPTER V

DISCUSSION

1. IntroducËion

The Èerm biotype in Ínsect bíology has been used in the broad con-

texts of species, populations and índividuals. It appears that there

are t\,ro usages of which one is a general concept that applies to both

índíviduals and populations of a species whích share certaín biologícal

characteristics, wíth little or no knowledge of theír geneËic bases.

The second concept ís rather specific in which a particul-ar gene for a

certain characterístic of an insect ís known to correspond with a

partícular gene in a host. For instance, vírulence on the part of a

pest and resistance on the part of a host and the genes responsibl-e

for that phenomenon.

2. Biotypic Phenomenon and Variability wíthín Populations

In Ëhe case of the pea aphíd, it is currently assumed, though seldom

stated, that the bíotypes are separable by cl-ear-cut patterns of responses

to certain p1-anË species or varÍeties of a specíes (Auclaír L97B; Cartier

et al. Lg65; Harrington 1945; Markkula and Roukka L970a, 7g7L), wíthout

much knov¡ledge of theír genetíc bases. In the present studíes when the

Ëhree 1980 clones whích were collected from three different hosts, r,Jere

ËesËed they responded consístently and dífferently on <1ífferent host

plants (Table 4). These three clones might be assumed to belong to

three different bíotypes. I^Ihen field populations on different hosts at

the Research Station, Glenlea, vrere studíed in 1981, they clearly

84

exhibíted great variation r¡ithin any given populatíon, while populations

were not signífícantly dífferent in their responses to different host

plants (Tables 6, 7 , B arrd 9) . Based on the performance of the three

1980 clones, íf the sixty clones tested ín 1981 are to be assigned to

three dífferent bíotypes (Neiman r97L; Pathak and painËer 1959), some

clones are found Èo share the characteristícs of more than one biotype.

Pathak and Painter (1959) tesËed varíous populatÍons from distant

locatíons by caging a known nurnber of aphids on a partícular host an¿

then on Èhe basís of fecundity, they assigned the populations to various

biotypes. Thís method tends to mask any individual variaÈíon present

within the aphíd populatíon. The extent of variatíon exhíbited by

various biotypes originatíng from diverse geographíc locatíons (Auclair

1978; Cartier 1959, L963; Carríer er at. L965; HarríngËon 1945 in

chapter rr, 4) was exhíbíted by different clones sampled from any

particular population on any given host in both 1981 and 1982 studíes.

Therefore, ít appears that field populatíons of the pea aphíd are

normally variable in biologícal characteristícs as shov¡n in the present

studies. Under these circumstances, identífying and naming or other\¡/íse

labellíng such bioÈypes (cartíer L959; Harrington 1945; Neírnan r97L;

Pathak and Painter l-959) ís necessarily arbítrary and could lead to

confus ion.

3. Seasonal Changes

The present studies have documented that the clones present on one

partícular plant species shor¿ some short term selecËion. This is

expressed in terms of differential- survÍval- (Table 7), differential

B5

fecundíty (Tables 10 and 14) and dÍfferential alara producrion (tables 11

and 15). This Ís followed by genetíc recombínatíon during sexual re-

productíon in the fal1. There are no sígnifÍcant differences betr¿een

populations in Ëheir biological characteristics in the spring. This is

probably a selectíon process not unlíke competítion among dífferent

genotypes. Darwin (1859) * stated that competítíon \,ras a primary force

ín natural selection, and he also stressed that competítÍon or

"the struggle wíll al-most invariably be most severe betweenthe individuals of the same specles, for they frequentthe same dístricts, requíre the same food, and are exposedto the same dangerstt.

Loaríng and Hebert (1981) reported results of competitíon experimenËs on

clones of Daphnia pulex Leydig in whích they found that out of 12 experí-

ments, in most cases only a síngle clone remained aÈ the end of the study.

SímiIarly, ín studies on Aspl-anchina (Phylum:Aschelminthes), Snell (L979)

observed the compeÈítíve replacement of one clone by another in as few

as 5 generatíons. This occurrence of competítíve exclusíon míght be

expected as nany experiments have shor,¡n, when Èwo specíes compete for

identícal food in the sarne habÍtats, one species dísp1-aces the oËher

in a few generaËíons (Allan L973; Neí1l 1975; snell Lg77). The number

of clones may be high ín the spring, but thís varíabílíty is reduced ín

the course of the parthenogenetic generaËíons presunnbly through

dífferential survival, reproductíon andfor migration. conseguently, a

a majority of autumn individuals wíthin a fíel-d may be much more

*Darwín,London,

c.R. 1859.488 pp.

The orígín of specíes pp.7I (L928 ed.), Denr.,

86

homogenous in terms of their responses to different host plants. This

ís suggesÈed ín the present studies (Table 15) where twelve clones

sampled from a population on al-falfa (var. Algonquin) l-ate in the

season in 1982 did not extribit signíficant clonal variabilíty with

regard to their mean fecundity on all the four hosts tested (P>.05).

Aphids are knovm to be carríed for hundreds of miles by prevaíling

wÍnds (Johnson L957; Medler and SnLith 1960) . As a result Ëhere ís

every possibility Èhat 1aÈe season sampling on any population míght also

include recenË immigrants. Thís ruight add to the heterogeneity of the

sample of clones in terms of theír responses to different host plants.

Thís fact and the short field season ín Manitoba rnight be responsible

for the difference stil-1 found among the clones sampled from most fields

ín the later parÈ of the season Ín the present studíes.

4. Annual- Changes

The sexual gearat.ion in aphids represents the offspring of the

parthenogenetíc generations. The allele frequencies of the sexual

generatíon represent the end result of selection, which has operaËed

upon the parthenogeneÈic generations. The sexual phase of the aphid

holocycle entails genetíc recombination beh,Jeen genotypes. The resultant

offsprÍng in the following spring show some genetic varíatíon among

themselves whích Ís accounted for by using such terms as bÍotypes, races,

sÈraíns etc. Intra-specific varíatíon may occur either wíthin popu-

l-ations or groups of neíghbouring populatÍons, or between geographícally

separated groups of populations. I,iíÈhín a populatíon, the range of

B7

variation may be greaË or small, but it ís subjected to environmental-ly

induced selection pressures. As a result c1ona1 varíabÍl-íty Ís reduced

(Table 15) Ín the course of parthenogenetíc generatíons. Consequently,

autumn fndíviduals withín populatíons are much more homogenous as com-

pared to spring individual-s. The present studies have shown that the

bíological variat.ion among clones recognized represented the síÈuation

as it occurred Ín the year or time of the season when the clones \^rere

sampled and tested (Figures 11, 72, L3 and 14). These data show that

Ëhere is no relatíonshíp between the responses of aphids to dífferent

host plants ín one year and Ëheír responses to the same host plants

in another year. Therefore, the attributes extríbited by clones cannot

be used to separate and. recogníze similar clones ín succeeding years.

Frazer (L972) suggested that new biotypes of A. pisum arise annually by

adapËation of parthenogenetic clones to different specíes of hosË plants.

This indicates that the biotypes are annual phenomena.

One yearrs population increase of aphids ís often dífferent from

the prevíous yearrs paÈtern (Figures 11 and 13). The reason may be

that they are greatly affected by environmental condÍtions. It may be

that early spring weather has many indírect effects, including the

selectj-on of some clones at the expense of others. The exÍstence of

such genetic varíatíon wíthín any gíven population nay be one of the

reasorrs why aphíds can be so unpredictable with regard to theír popu-

l-atíon growth.

B8

5. Variability BeËvüeen populaËíons

FÍerd studíes conducted over the three years díd not show any

dífferences among populations. Nor did laboratory sÈudies conducted ín

1981. However, l-aboratory studies conducted ín 1982 with the samples

of clones from ttro older alfalfa fÍelc1s differed from each other with

regard to thefr fecundity (p<.05) (Tables 12,13 and 14). These rwo

fields r¿ere different ín several ways. Geographic separatíon of the

fíelds rnight be responsible for the dífference. Lamb and MacKay (Ig7g)

reported similar differences among natural populatíons of A. pisum

located less than 23 km apart. Thís difference ís based on mígratory

tendency (the nr:rnber of alaÈae produced) of various populations. They

also report.ed that fíe1ds that r¡rere very close had populatíons with

sírn-ilar migratory Ëendencies. Likewíse, Èhe alfal-fa (var. Beaver) field

sarnpled in 1982 and the aLf.aLfa field sampled in 1981 were located cl-ose

to one another at the Research Statíon, Glenlea. An analysis of variance

carried out to compare the data from Èhese tü/o populatíons showed that

the samples are not significantly different (p<.01). High selection

pressures exerted by the applicatÍon of Ínsectícides every year on the

aphid popul-atíon on alfalfa (var. A]-gonquin) at Dugaj-d, míght be re-

sponsible for the vírulent nature of Èhose clones. The aphid populations

at Glenlea r¡/ere never Ëreated with ínsecticídes. However, variation

among different clones between those populatfons \¡ras no greater than

that of clones wíthin populations (p<.01). This rnras true with regard

to populations tested Ín 1981 as well.

89

The data are Èoo limÍted to permít any fírm conclusion on geographíc

relationships ín bíotyplc phenomena. However, ít ís important to

establísh Èhe relaÈíve sËatus of intra-specífíc varíation from widely

dÍfferenË geographic areas, particularly where anholocycle prevaíls.

In such areas, Èhere is no genetic recombination possible. As shown by

the present studíes, selectíon and adaptatíon do occur among populations

present on a particular host. Therefore, it fs hypothesized that the

populatÍons of A. písum Ín areas where anholocycle prevails r¿ould be

relatively homogenous conpared to those ín areas where holocycle occurs.

In tropical regíons where anholocycle is said to occur, distinct agro-

climatologícal areas prevail due to dífferentíaI altitudes. fn such

areas díverse genotypes nay occur Ëhat particularly adapted to local

envÍronments. In additíon, the prevalence of a wide range of host plants

can also contribute to divergences of genotypes. Since geographícal

populations are knor,m to be concerned in the developrnent of a species,

it ís thus irnportant that studíes should be undertaken on such geo-

graphically separaÈed populations.

In apomictic parthenogenesis the effect of selecÈíon ís opposed

only by mutation. For instance, the corn-leaf aphid, R. rnaídis, appears

to be entirely parthenogenetíc ín reproduction, males havíng been re-

ported only a few tímes in the literature and eggs and egg-layíng females

not at all (Painter and Pathak 1960). Therefore, it appears that the

only possible origin of biotypes ín such cases would be through gene or

90

chromosomal alteratÍons. Since the specíes concerned ís parthenogenetíc,

Ëhe genes r¿hich cause these changes musË almost cerLainl-y be domínant.

In tropícs where sexual- reproductíon in A. pisum is not reported to

occur, bíotypes could occur through gene or chromosomal alteratíons and

also by inmigration from other regions. Such mutaËÍons have occurred

under observation in another aphid, Macrosiphum solanifolíi (Ashn.)

(Shull L943). Apparently a símilar start is responsible for the origín

of the spotted alfalfa aphid biotype resÍstant to insecticides (Stern

and Reynolds 1958).

The possíbility of mutatíon leadÍng to bÍotype formatíon could

account for clonal responses to sainfoin in the present study. The high

nymphal mortality and poor fecundity on some host planÈs particularly

on saÍnfoin (Tables B and 9) cannot be accounted for by any possible

parental effect because nymphs fed on other hosÈs in the same experiment

showed norrnal survíval and growth. However, it Ís assumed here that the

maintenance of aphíd cultures on fababeans had no drastíc preconditíoning

effects which make saínfoin unpalatabl-e. This hígh rnortal-íty rnay be

caused by toxíc or repellent substances ín the foliage. Dethíer et a1.

(1960) have suggested that some plants may contaín substances which deter

sustained feeding in addition to those having a Ëoxíc effect. Shaver

(L974) suggested that high mortality can also be caused by rnetabolíc

'inhíbitors ín planËs or by insuffícient quantitíes of specific nutríents

required by the insect for growth. Out of a 1-arge number of clones

tested ín Ëhe present studies, only one clone was found to do well on

sainfoín. Thís partícular clone vras among those that were sampled

91

duríng the later part of the 1981 season. It may be possible that this

clone is a muÈant vühich has a greater ability to feed on sainfoin Ëhan

other clones Ëested.

Muller (I97I) reported that ít was possÍble to obtain hybrids between

several biotypes of A. pisum íncludíng a vÍable hybrid between one green

pea-attackíng form and a red form which colonízes T. praÈense as its

princÍpal host and cannot colonize peas. He also showed that ín-

heriËance of host plant selectíon is, in most cases, wíthout d.ominance

and F, hybrids of such combinaÈions settled on the hosts of both parents.

rf no breedíng barríers exist between bíotypes and matíng occurs at

random, it ís clear that the bíotypes represent fairly símp1e genetíc

varíants of one freely interbreedíng bÍological specíes.

Most aphid specíes are host specífic. This specíficity must have

lasted for long períods of time. Many comron plant specíes seldom develop

colonies on them although they are regularly aËËacked by common aphids.

There ate a number of reasons for the persistance of the resístance.

ResÍstance Ëo ínsect attack is part of the evolutíonary sÈrategy of

plants, just as oveïcoming the protecËíve mechanisms of plants ís part

of the evolution of phytophagous insects.

Theoríes of ínsect-plant co-evolution suggest that there should be

genetic varíation within insect populations in characters which control

host selection and utilization (Feeny L976). oviposítion (or larva-

position by wínged aphids) preference ís one example of such a character,

and genetic variation among indívíduals coul-d cause dífferences among

fernales in oviposition preference. Varíatíon ín ovipositíon preference

92

among the fernales ín a populaÈíon coul-d have ímportant evolutíonary

consequences. Thís type of varíation would make a population more

flexible, íf the primary host(s) \^rere not avaílable. Some indivíduals

night even prefer alternative hosÈs. Therefore, intra-populatíon varí-

ati.on ín host selection characters may play a key role ín host shifts

and insect plant co-evolution. Modes of specíatíon amongst parasític

insects íncluding pJ-ant feeders centres on the suggestion Èhat sympatric

host race formatíon is relatÍvely common ín nature (Price 1980; I,rlhíte

L97B). Some workers (Bush L975a, L975b) have suggested thaË some rela-

tively specific insect herbivores may transfer occasionally to prevíously

unsuitable host plants, and consequently such insects rnight develop

barriers Ëo rnatíng wíÈh the parent.al population. BuË it is noÉ certaín

whether such host races do occur in the fíeld (Futuyma and Mayer 1980;

Jaenike 19Bl-). Thís area is one of considerable current díscussion and

críticísm. Detailed fíeld studies are most desirable to documenË

whether such s1'rnpatric host plant assocíated bíotypes do occur among the

plant feeding ínsects.

Ovipositíon (larviposition) choice is especially important in

insects whích have írnrnature stages that are relatively ímrnobíle.

Hopkinrs host selection prínciple (Hopkíns 1917) states that a female's

oviposítion preference ís biased ín favour of the plant species she.

fed upon as a larva. The presenÈ studies indicate thaÈ the índivíduals

col-lected from crop X did not prefer crop X more sÈrongly than those

collected frorn crop Y partícul-arly during Èhe early part of the season.

The results show that the larviposítíon is not bíased ín favour of the

host plant species they fed on as larvae.

93

6. Concept of Biotype and Agricultural pests

The practical usage of the term bíotype which was used to describe

the responses of ínsecË pests to different crops or cultivars of crops

(Painter 1951) has recently been revÍewed by Russell (1978) more widely

in breeding plants for pest and disease resístance. Pathak (L975) 1ísted

seven species of insect pests including fíve specíes of aphids ín which

biotypes have been indentified. The remainíng two species were the

Ilessían fl-y of q¡heat and Ëhe brown plant hopper of rice. The most sig-

níficanË biological characteristÍc of such biotypes is their ability to

feed on crops resistant to some other bíotypes. This assocíatíon of

virulence ín a pest with resistance in a plant to that pest, is wíde1y

assumed to be characterízed by a gene for gene relatíonshíp (GaLlum and

I(hush 1980; Price 1980). However, such relatíonships are knor,,¡"n ín very

few cases only, and none ín case of A. pisum biotypes. rn the brown

plant hopper, three such biotypes wíth a known gene for resistânce

are said to occur (Pathak and Khush L97g). However, recent studíes

have documented great variatíon wíthin each of the three bíotypes of

Èhe brown plant hopper maintaíned at the InËernatÍonal Ríce Research

rnstítute (rRRr), Phílippines (claridge and Den Holl.ander 1980; sogawa

1981) .

As it has been clearly shown in the present studíes, bíological

varÍatíon in characterístics e:iûíbited by different clones are not

necessarily mutually exclusíve. An índivídual or cl-one may belong to

Ëwo or more biotypes (Tables 6r 7,8,9, L2r 13). Two clones that belong

to one biotype wíth regard to theír abílity to feed on a pest resistant

plant may belong to ÈIÀro dífferent bíotypes if another species of plant

94

or a varíety of species is compared. Likewise, L\^ro clones belongíng to

the same biotype can differ on one and the same host or vice versa wíth

regard to Ëwo different parameters estimated (Table 4 and 5).

As biotypes are temporally unstable, and ofÈen diffícult to detect

norphologícally, the sysÈem of nomencl-aÈure currently beíng employed

seens quite ínappropriate for insects líke A. pisurn. As reported by

Flor (1956), labelling of bíotypes may be useful in the relationshíp

between some fungal pests and theír hosts. However, when biotypes such

as those of A. pÍsum which have a wíde range of varíation and overlap

wíde1y ruith each other, the assígning of populaËions to particular bío-

types ís of very lÍtt1e value.

From the definítion by Maxwell and Jennings (1980) quoted in

chapter rr, ít is clear that the concept of biotypes ís used of both

individual-s and populatíons wíthín one species of insect. However, the

precise nature of this biological variation ín A. pisum is not clear.

Conflictíng suggestíons, based on 1ittle experímental evídence, have been

made concerning the degree of geneËic dífferenËíation between them. But

broadly based investígatíons on the rnorphology, cytology, biochemisLry

and behavíour of the clones in addition to genetíc studies, are needed

ín order to understand the exact nature of these clones exhibiting

diverse geneti.c varíation whi.ch has led to the establíshment of the con-

cept of biotypes. However, untÍl an efficient and reliable method of

hatching of eggs of A. pisum Ín the laboratory ís developed, studíes on

inheritance of resistance and oËher aspects of genetícs appear rather

difficult.

95

Present studíes have elucidated to a great extent the exact bío-

logical signífÍcance of the varíation among clones of A. pisum. Dif-

ferent authors have gíven varÍous definitions to bíotypes since the

inception of Ëhat concepË. Most of those definitions are mÍsleadÍng

rather than enlíghtening, aË least so far as the bíological status of

the insect ís concerned. Among others, the definÍtion gíven by Eastop

(L973) has been wídely used and referred to by varíous authors.

According to Eastop (1973)'k,

'ra bíotype is a Èaxonomic concept mosÈly used by non-taxonomists,and it has been defíned as consisting of all indívidual-s ofequal genotype. In aphíds at least, equal genotype meansbehaving sirnil-arly as far as the researcherfs ímmedíate ín-terests are concernedtt.

But the presenË studíes have clearly índícated that when the researcherrs

immediate inËeresËs are broadened by involving a few host species or

varíeties of a specíes rather Ëhan limited to one or tvüo host plants

in Èhe research, partícul-ar t\,ro or three biotypes whích behave símí-

larly on one host would no longer be similar on different hosts.

Therefore, it appears that Ëhe sympatríc biotypes of A. pisum prevaíling

in populations on any given host represent faírly sirnple genetic varíants

and the term biotype represents no dísÈinct bío1ogíca1 concepË. However,

the relative sÈaÈus of thís intra-specific varíation from wíde1y dífferent

geographical areas , where anholocycl-e prevails, remains to be

es tablished .

t(Eastop, V.F. (L973). Bíotypes of aphíds,Aphid Bíologyr Ed. by A.D. Lowe, 8u11. No.L23 pp.

pp. 40 In rPerspectives in2, Ent. Soc., New Zealand

CHAPTER VI

SI]MMARY AND CONCLUSTONS

The resul-ts of the experiments described above have important con-

clusions and ecological írnplicatÍons. Some of these will be pointed out

below.

The Ëhree 1980 clones responded consistently and differently,sug-

gesting that they belonged to three dífferent biotypes. I^Ihen fÍeld popu-

latÍons on dífferent hosts \,rere tested in 1981 they clearly e>rhíbíted

Èremendous varj,atíon wÍthin any gíven population. But the characteristics

of populations \nlere not signifícantly different. These populatíons \¡rere

also found to include individuals with the characterístics of more than

one bioËype. In addition, dífferent clones,from any population tesËed,

exhibited variation among themselves to the same extent as is exhíbíted

by bíotypes having díverse geographíc origin. Therefore, ít appears that

fíeld populatíons of the pea aphid are normally variable ín biological

charac teris tics .

It was found that the clones present on a partícular plant specíes

show some short term selectíon during sutttrner when reproductíon is par-

thenogenetíc. In the fall, as a result of genetíc recombinatíon during

sexual reproductíon, a differenÈ set of clones is generatecl alcl appears

in the followíng spríng. rt was found thaÈ there is no relatíonshíp

between responses of clones to different host plants in one year and theír

responses to the same host plants ín another year. Therefore, ít appears

that Èhe bíotypes are annual phenomena. The number of clones may be hígh

in the spring, but. thís variability is reduced in the course of partheno-

97

genetic generations, presuaâbly through differential survival reproduction

andfot migratÍon. Consequently, autumn índividuals wíthin a populatíon

are more homogenous wíth regard to theír responses to different host

plants.

Sarnples of clones from the two populations tested ín L9B2 showed

sone differences. This may perhaps be due to the geographíc difference,

high selectíon pressures exerted by ínsectícídes on one of the populations,

or to the differenÈ varieties of the host, more Ëhan mere age of the popu-

lation. These data are too límíted to vüarrant any concl-usions on geo-

graphic relationship. Relatíve status of this intra-specífic variation

of clones available from wídely different geogïaphic areas, partícuLarly

where anholocycle prevails, remaíns to be establ_íshed.

Fíeld studíes indícaËe that the characterístícs of the clones repre-

sent the situaËíon in that parËícular yeaî and should not be used to

separaËe and recogníze clones duríng succeedíng years. Therefore, as sug-

gested by Frazer (L972), Ín assaying plants for resistance to pea aphids,

on1y fundatrices and their inrnedíate offspríngs which have not been

subjected Ëo selecÈíon should be used as tesÈ organisms. Moreover tests

should be carried out over several seasons so as to expose varíetíes to

all possible genotypes.

Clones exhibíting variable characteristícs are not necessaril-y

mutually exclusíve. An indívidual or clone may belong to two or more

biotypes. Therefore, the system of nomenclature currently beÍng enployed

seens ínappropriate as it tends to give a false impression of the bÍo-

logical significance of the pest by masking the inherent varíabí1íty of

98

the pea aphid populatíons.

Absence of an efficient rnethod of hatchíng A. pisum eggs ín the

laboratory has become an obstacl-e in the progress of further work on

genetics of variable clones. Broadly based investígations on the mor-

phology, cytology, biochemistry and behaviour of the clones in addition

to genetic studíes wíll elucidate the exact nature of thís biological

variation in A. pisurn.

Defínitions given by various authors Èo bíotypes seem ínadequate

and misleading with regard Ëo the bíologica1- signifícance of biotypes.

It roay be concluded Ëhat Èhe sympatríc bíotypes of A. pÍsum prevaíling

ín populations on any gíven host represent faírly sírnp1e genetíc varí-

ants. Therefore, Ít ís suggested Èhat the practice of identifying and

numberíng of clones of A. písum should not be contínued as ít may gíve

a false ímpressÍon of the bío1ogíca1 sËatus of the pest.

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Acyrthosiphon

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tL4

AppendÍx 1. The meterol-ogícal data during the perÍod of fíeld studies(The Research Station. Glenlea . Manítoba)

1980

19Bl

L982

1980

19 B1

L982

1980

r9B1

I.

May

15 .0

L2,0

13.1

Temperature (oc)

June

16.s

L6.2

L3.4

monthly mean

July

19 .5

19 .5

19 .5

Augus t

16 .0

19 .9

16 .8

TL7.7

90.0

30.5

88. B

1982

15.70

50.53

ïr. Raín fall nonthly total- (nrn)

64 .2 2L.8

88.7 58.8

64 .L 83.6

45.s

26.0

23.9

III. RelaËive humídity

96.6 76.s

67.2 84.1

(Z) uronthly mean

59 .5

84 .8

IV.

Temperature (oC)

Raín fall (nrn)

Relative hurnidíty

Monthly mean for the crop season (May-August)

1980 1981.

L6 .75 16 .90

62.30 6s.88

(7.) 77 .53 8L.23

1_ 15

KNOJ

KH|PO 4

cu(NOr), .4H

MeSOO.7H20

FeEDTA*

Micro elements

H3BO3

ì4nC12 .4H20

ZnCI,

CuC1r.2H20

MoO,

Apoendíx 2 Hvdroponic So1ution: contents

Stock solutiongrl^/9,

101.11

136.09

236.L6

246.s0

36.71,

20

Nutrient solutionm9"/9'

1**

2

2

3

2

1

2.50

1.50

0.10

0.05

0 .05

*Ethylenediamínetetra - acetíc acid(Ferric monosodium salt). [crr,

.olccr2 . coo) 2] FeNa2

**1 m1 of a stock soluËíon contaíning all the micro nutríentsis used.