Entomol. exp. appl. 66: 59-74, 1993. �9 1993 Kluwer Academic Publishers. Printed in Belgium. 59

Development and application of an integrated pest management programme for the psyllid, Ctenarytaina thysanura on Boronia megastigma in Tasmania

R. K. Mensah 1 & J. L. Madden Department of Agricultural Science, University of Tasmania, G. P. O. 252C, Hobart, Tasmania, Australia Present address 1 N S W Agriculture, Agricultural Research Station, Myall Vale, Narrabri, NSW 2390, Australia

Accepted: July 6, 1992

Key words: Boronia megastigma, Ctenarytaina thysanura, integrated pest management (IPM), organophosphate, parasitoids

Abstract

An integrated pest management programme for control of the psyllid, Ctenarytaina thysanura (Ferris & Klyver) (Hemiptera: Psyllidae) in commercial boronia plantations was developed and implemented from 1986-1989. The programme involved spraying boronia stems only with the systemic organophosphate mevinphos at peak incidence of late stage nymphs. At this time, the majority of parasitoids were pu- pating within mummified hosts. Consequently, actively feeding nymphs were potentially susceptible to mevinphos but the parasitoids were not. Stem application negated any contact effect on parasitoids and predators. The conservation of natural enemies subsequently reduced psyllid numbers and no insecti- cide has been required since 1989. In economic terms the benefit to cost ratio of the IPM programme was $22.40: $1.0 and this was 40 times greater than the conventional 10 demeton-S-methyl sprays used by growers prior to the study.

Introduction

Boronia megastigma (Nees) (Rutaceae) is predom- inantly grown in Tasmania as an essential oil crop for the flavour and perfumery industry. The major pest is C. thysanura which is capable of causing severe yield losses (Mensah & Madden, 1992). Heavily infested plants lost turgor, growth ceased, leaves abscissed and plants died. Less severe in- festations reduced vegetative growth and the ini- tiation and formation of flower buds resulting in fewer flowers and reduced yields of oil (Mensah & Madden, 1992). The psyllid has three genera- tions annually. There are five nymphal stages and they feed from the phloem of young actively grow- ing boronia shoots by inserting the stylets through

the stomata to reach their food supply. Adults gain access to food in the same way as nymphs but do not significantly damage plants.

Prior to this study, growers in Tasmania were applying demeton-S-methyl 10-12 times a year but were not achieving control. This was due to a lack of understanding of the psyllid pest and its natural enemy system, poor choice of chemical, improper timing of sprays and an inappropriate method of application. Thus the growers, in an attempt to control the psyllid, were modifying the environment and unknowingly making it more unfavourable to natural enemies viz. encyrtid par- asitoids, Psyllaephagus spp. and coccinellid, spi- der and syrphid fly larvae predators which are potential biological control agents. This indis-

60

criminate application of insecticides resulted in instability with subsequent damage to plants. As a result many growers considered leaving the in- dustry. Integrated pest management of the psyl- lid could be a solution but to develop such a programme required the understanding of the pest insect and its natural enemy system and how it operates in the agroecosystem.

Mensah (1990) studied C. thysanura popula- tions and concluded that natural enemies had the potential to reduce host/prey densities to sub- economic levels. However when natural enemies were destroyed by spraying, C. thysanura out- breaks occurred, resulting in considerable plant damage. Psyllid numbers declined through host plant deterioration leading to emigration and re- duced size and fecundity of adults, events induced by intraspecific competition for space and food. The decline in psyllid numbers reduced feeding pressure on the plant resulting in the regrowth of shoots. These new shoots were rapidly invaded and resident psyllid numbers increased to the fur- ther detriment of the plant.

Based on simple graphical analyses, Mensah (1990) demonstrated that the more predators and parasitoids there are per prey individual, the higher the relative mortality of prey, so that ef- fective biological control of C. thysanura requires a high natural enemy to prey ratio. Therefore a selective form of control was required that had minimal effect on natural enemies in order that pest numbers could be effectively reduced and sustained at sub-economic levels.

This paper reports the development and appli- cation of an IPM programme for C. thysanura based on fewer applications of a systemic insec- ticide, using an efficient method of application and timed to conserve beneficial insects. The con- trol economics of commercial boronia crops re- ceiving conventional chemical and IPM pro- grammes are also compared.

Materials and methods

The systemic insecticides evaluated were Meta- systox (demeton-S-methyl) 25 EC (Bayer Austra-

lia Ltd.), Rogor (dimethoate) 30 EC (May and Baker Rural Australia Pty. Ltd.), Nuvacron (monocrotophos) 40 EC (Ceiba Geigy Australia Ltd.) and Phosdrin (mevinphos) 36 EC (Shell Australia Ltd.).

Glasshouse spray test

This experiment was conducted in November 1986, in a glasshouse maintained at 18-20 ~ The experimental plants were mainly one year old and of the HC4 clonal variety. Each insecticide treatment and a control plant were replicated 10 times with 10 plants per replicate. The stem and four basal leaves of each plant were sprayed for 10 seconds on both sides using a knapsack sprayer delivering 420 ml per minute. The control plants were sprayed with water. Following each treatment application, the terminal tips of each plant were infested with five newly emerged 5th stage nymphs selected from a culture cage in the laboratory. All nymphs were starved for 24 h prior to the experiment.

Records were taken daily of the number of dead nymphs on each treated plant until no more deaths occurred. Mortalities for each treatment were calculated on a daily basis.

Field studies

Pilot and large scale experiments were conducted on three boronia farms between 1986-1989 in Tasmania. Unless otherwise stated all the pilot experiments were conducted at Copping (east Tasmania), but in addition large scale experiments were conducted at Huonville and Bakers Beach. The plants of both study sites were 3-4 years old, planted in rows at 0.5 m spacing with 1.0 m be- tween rows.

Experimental plots were arranged in a random- ized complete block design with seven replicates per treatment and untreated controls. Each rep- licate was 3.0 m wide and either 10.0 m long con- taining 20 plants (for pilot experiments) or 60.0 m long with 120 plants (for large scale trials). A

4.0 m wide buffer separated each replicate to min- imize spray drift between treatments and con-

trois. Pre-treatment counts of insects were made 24 h

before treatment application and post- treatment counts on each 3 days and then at weekly inter- vals (pilot trials) or on 7 days and then at monthly intervals (large scale trials). Insect counts were

made by taking a single 'closed' terminal shoot, 15 cm long with 10 nodes, from the outer layer of each of 70 randomly selected plants from each treatment and control plot (i.e. 10 shoots/ replicate). Harvested shoots of each treatment

and control were placed and sealed in individual plastic bags (15 x 16 cm) and transported to the laboratory for dissection. The leaf axils of indi- vidual shoots were opened under a binocular mi- croscope using a pair of forceps and numbers of C. thysanura eggs, live and mummified nymphs

61

and predators (viz. coccinellids, spiders, Syrphus sp. larvae) recorded. The mummies from each

treatment and control plot were held separately to assess parasitoid emergence.

The growth of plants in each experiment was assessed from 14 randomly selected plants (2 plants per replicate) and a dominant shoot from each plant tagged by marking the tips with non-

toxic yellow paint. Records were taken of the number of new nodes formed during 28-day in- tervals until the completion of the study.

Experiment I

Site of insecticide application Each insecticide treatment was applied either as a foliage (FS) or stem (SS) spray using a knap-

sack sprayer. The effect of the treatment was

Table 1. Effect of site of spray application on C. thysanura nymphs on boronia plants sprayed twice on either foliage or stem with four systemic insecticides at Copping, East Tasmania, 1986-87

Time (in days Average no. of live nymphs per terminal shoot Control after treatment)

Demeton-S-methyl D i m e t h o a t e Monocrotophos Mevinphos

*FS *SS FS SS FS SS FS SS

24h Pre-treatment 7.29a 5.60a 6.84a 6.76a 7.54a 8.14a 6.91a 7.34a 6.16a counts (lst spray)

3 0.42a 2.73b 0.14a 2.75b 0.29a 3.84b 0.22a 0.81a 5.48c 7 0.94a 3.26b 0.90a 3.63b 0.83a 5.30b 0.67a 1.31a 6.89c

14 4.69ab 5.36ac 3 . 0 3 a b 5.46ac 2.50b 5 . 3 4 a c 3 . 8 7 a b 4.91ac 7.37c 21 5.10ac 6.74a 3.50b 6.24a 2.97b 6.54a 4.42b 5.01a 7.26a 28 6.01a 7.59ac 5.64ab 8.00ac 3.82b 7.87a 5.04ab 5.66ab 8.79c

(2nd spray after counts) 31 0.42a 3.70b 0.20a 3.25b 0.04a 4.17b 0.05a 0.51a 7.82c 35 0.62a 4.29b 0.10a 4.79b 0.04a 5.73b 0.09a 0.61a 7.71b 42 1.40a 5.56bc 0.29a 5.26b 0.06a 6.61bc 0.21a 1.02a 8.29c 49 1.67a 5.94b 0.49a 5.64b 0.10a 6.60b 0.27a 1.26a 6.39b 56 2.26a 6.54b 0.79a 6.20b 0.14a 7.30b 0.31a 2.07a 5.83b Survival 56 days

after treatment 23.53 51.73 15.08 51.22 10.77 59.30 15.15 23.17 71.83 Mean % mortality

after 3 days 93.6 51.3 97.2 59.4 97.6 49.9 97.9 90.0 - 11.0 (lst & 2nd spray)

Means between treatments within rows followed by the same letter are not significantly different (P > 0.05), Duncan's multiple range test. Each of the insecticides was sprayed at 0.02% a.i. Per cent treatment mortalities were corrected by means of Abbott (1925) formula. * FS = Foliage spray; SS = Stem spray.

62

assessed by percentage kill and the accumulated sum of surviving nymphs in time. For stem sprayed plots both sides of the green stems were sprayed for 10 seconds ensuring minimal contam- ination of foliage. For foliage spray plots all foli- age of a plant was sprayed for 10 seconds.

Experiment 2

Optimum timing of insecticidal application Mevinphos SS and monocrotophos FS were each, in two separate experiments, sprayed at peak densities of (i) early (lst and 2nd) and (ii- ) late (3rd-5th) stage nymphs. Each experiment received an initial application of the respective chemical on November 23, 1987 (for early stage nymphs) and December 20, 1987 (for late stage nymphs followed by a second application on Feb- ruary 16, and March 16, 1988 respectively. Records were taken of C. thysanura eggs, nymphs, parasitoids and predator population and also the growth of boronia plants.

Experiment 3

Number of applications for effective control Two separate experiments were conducted with mevinphos SS and monocrotophos FS. In each experiment, the insecticides were applied three times to the late spring (December 23, 1987), summer (January 20, 1988) and autumn (April 21, 1988) generations and twice to the late spring and autumn (December 23, 1987 and April 21, 1988) generations. The December and January applications were carried out 28 days apart just before newly emerged adults had commenced oviposition and parasitoids had not yet emerged. Plots of unsprayed plants provided controls for each experiment.

Experiment 4

Large scale evaluation of stem and foliage sprays In this experiment flower yield assessments were taken at Copping and Huonville in addition to

Table 2. Average number of C. thysanura predators per terminal shoot on boronia plants sprayed twice on either foliage or stem with four systemic insecticides at Copping, East Tasmania, 1986-87

Time (in days after treatment)

Average no. of *predators per terminal shoot

Demeton-S-methyl Dimethoate Monocrotophos Mevinphos

FS SS FS SS FS SS FS SS

Control

24h Pre-treatment counts 0.035a 0.035a 0.023a 0.025a 0.027a 0.031a 0.032a 0.029a 0.027a (1st spray after counts)

7 0.001a 0.034b 0.0a 0.022b 0.0a 0.032b 0.0a 0.027b 0.029b 14 0.001a 0.031b 0.0a 0.024b 0.0a 0.029b 0.0a 0.028b 0.031b 21 0.0a 0.036b 0.001a 0.027b 0.0a 0.029b 0.0a 0.032b 0.036b 28 0.002a 0.041b 0.001a 0.031b 0.001a 0.032b 0.001a 0.037b 0.040b

(2nd spray after counts) 35 0.0a 0.037b 0.0a 0.027b 0.0a 0.029b 0.0a 0.034b 0.036b 42 0.0a 0.035a 0.0a 0.029b 0.001a 0.024b 0.001a 0.032b 0.036b 49 0.003a 0.049b 0.0a 0.036c 0.006a 0.034c 0.002a 0.046b 0.051b 56 0.010a 0.047b 0.002a 0.038b 0.012a 0.036b 0.005a 0.042b 0.046b

Means between treatments within rows followed by the same letter are not significantly different (P > 0.05), Duncan's multiple range test. Each of the insecticides was sprayed at 0.02% a.i. FS = Foliage spray; SS = Stem spray. * Predators assessed were coccinellids (adults and larvae), spiders, Syrphus sp. larvae.

population census of the psyllid and its parasi- toids and plant growth. The numbers of flowers on each tagged shoot from the different treatment and unsprayed control plots were recorded in Au- gust when all flowers were fully opened. In Sep- tember, flowers were harvested and the total yields (in kg) of flowers from each treatment and con- trol plots were recorded separately.

In addition the yields of oil from the different treatments and unsprayed control plots were as- sessed for Copping only. In this assessment, fresh flowers (150 g) of each treatment were harvested in September 1989, and solvent extracted by Es- sential Oils of Tasmania (EOT). Comparisons were made of the flower and oil yields for boronia crops receiving monocrotophos FS and mevinphos S S at Copping.

63

Experiment 5

Economic benefit of IPM programme A comparison was made between the growers conventional programme (demeton-S-methyl at 0.04~o a.i.) and the IPM programme (mevinphos SS at 0.02~o a.i.) on a 4 ha commercial boronia farm using four replicates (0.50 ha/replicate) in a randomized complete block design.

For the conventional programme the plant's foliage was sprayed using a tractor drawn boom sprayer. Spraying commenced in October 1986 according to the growers' spraying schedule and repeated at three weekly intervals until June 1987, a total of 10 applications. Control plots of simi- lar size were left unsprayed. In 1987/88 similar plots were used but only the stems were sprayed three times with mevinphos. These non-foliage

Table 3. Effect of site of spray application of 4 systemic insecticides on the survival of C. thysanura parasitoids when boronia plants were sprayed twice on either foliage or stem

Time (in days Average no. of mummified C. thysanura nymphs per terminal shoot Control after treatment)

Demeton-S-methyl Dimethoate Monocrotophos Mevinphos

*FS *SS FS SS FS SS FS SS

24h Pre-treatment 0.13a 0.10a 0.10a 0.07a 0.13a 0.14a 0.13a 0.10a 0.10a counts ( ls t spray)

7 0.11a 0.09a 0.13a 0.11a 0.13a 0.11a 0.16a 0.13a 0.11a 14 0.07a 0.10a 0.06b 0.10a 0.04b 0.20b 0.09a 0.1 la 0.09a 21 0.04a 0.06a 0.01b 0.06a 0.01b 0.03b 0.01b 0.04b 0.04b 28 0.06a 0.16b 0.07a 0.06a 0.01a 0.1% 0,00a 0.17b 0.14b

(2nd spray after counts) 35 0.04a 0.10c 0.00a 0.19b 0.01a 0.19b 0.03a 0.16b 0.16b 42 0.09a 0.21b 0.01a 0.17b 0.01a 0.19b 0.00a 0.25b 0.27b 49 0.01a 0.26b 0.03a 0.24b 0.00a 0.15b 0.03a 0.14b 0.21b 56 0.04a 0.21b 0.03a 0.29b 0.01a 0.17b 0.01a 0,24b 0.24b Cumulative total

of mummified nymphs after treatment 0,46 1.19 0.34 1.22 0.22 1.23 0.33 1.24 1.26

Mean parasitoid emergence from mummified psyllid nymphs (%) 16.4 89.9 0.0 86.3 0.0 85.5 0.0 90.4 91.7

Means between treatments within rows followed by the same letter are not significantly different (P > 0.05), Duncan's multiple range test. Each of the insecticides was sprayed at 0.02% a.i. * FS = Foliage spray; SS = Stem spray.

64

sprays were applied in December, January and April. Control plots were unsprayed.

In September of each season the total weight of flowers harvested from treated and control plots was recorded separately and respective oil yields determined.

Results

Glasshouse spray tests

This study was to determine the minimum effec- tive dosage of the four systemic insecticides to be used in the field trials for C. thysanura control. Each of the four insecticides were evaluated at

0.01, 0.02, 0.03 and 0.04~o v/v (a.i.)respectively. The test showed that all chemicals tested at 0.02, 0.03 and 0.04~o caused more than 85~ mortal- ity within three days after treatment, whereas 0.01 caused less than 55~o. All four chemicals were therefore further tested in the field at a concen- tration of 0.02~o a.i. to determine the most effi- cient method of application.

Field studies

Site of insecticide placement Demeton-S-methyl, dimethoate, monocrotophos and mevinphos were each applied at 0.029/0 a.i. All four insecticides applied as foliage sprays (FS)

12"

~ 1 0 '

r

~ 6

4

2: 2 '

20-

a ] 161

peak of early stage 12"

IXekot'la~s~e '~ ~ 8

4 2:

0

Nc;v. ~ . j & . Fib. ~ . A~r. Post-treatment counts

b ~ ~u01 peak of early stage

�9 ~ - 0 peak of late stage

- �9 - �9 - i - , - = - i

Nov. Dec..l 'an. Feb. Mar. Apr.

Post - treatment c o u n t s

.. 0.4" O

.

-~ 0.3-

"~ 0.2"

~. . , . 0.1' 0

0 z 0.0

. c~tatrol , . 20 , C //peak of la~ stage g

~ 8'

peak of early stage ~ 4

m 0 Y - J - T - T - i - i

Nov. Dec. Jan. Feb. Mar. Apr.

Post-treatment counts

d

peak of late stage

~ . a . . . . . ~ peak of early stage

Nov. Dee. Jan. Feb. Mar. Apr.

Post-treatment counts

Fig. 1. Effect of mevinphos stem spray at peaks of early (lst and 2nd) and late (3-5th) stage nymphs on C. thysanura eggs (a), nymphs (b), parasitoids (c), and the production of new nodes (d) on boronia plants at Copping, 1988-89. Spray treatments were applied initially in November 23, 1987 (for early stage nymphs) and December 20, 1987 (for late stage nymphs) followed by a second application on February 16, 1988 and March, 1988 respectively.

caused higher kill and lower survival of C. thys- anura nymphs (P<0.01) than stem sprays (SS) except for mevinphos SS (Table 1).

Predators identified from the plots were coc- cinellids (mostly Cleobora mellyi Mulsant, Har- monia conformis Boisduval, Coccinella repanda Thunberg and Coccinella undecimpunctata Linnae- us), syrphid larvae Syrphus sp. and spiders (most- ly Xysticus cristatus Clerck (Thomisidae), Evarcha sp. (Salticidae), Linyphia triangularis Clerck and Theridion ovatum Clerck). Significantly higher numbers of predators (P < 0.001) were recorded on the SS plots compared with the FS plots. The former did not differ significantly (P > 0.05) from the control plots (Table 2).

Parasitoids that emerged from mummified nymphs included Psyllaephagus sp. (Encyrtidae),

65

Moranilla sp. (Pteromalidae) and Cocophagus sp. (Aphelinidae). There was a higher percentage of parasitoid emergence and survival from SS plots compared with FS plots. The survival of the par- asitoids on the SS plots did not differ significantly (P>0.05) from that recorded in the unsprayed plots (Table 3). No parasitoids emerged from the mummified nymphs collected from FS plots with the exception of demeton-S-methyl FS plots which had 16.4~o parasitoid emergence.

Boronia plants receiving foliage sprays with each of the insecticides tested produced greater numbers of new nodes per shoot (P <0.01) than did plants which received stem sprays, with the exception of mevinphos SS plants. Monocroto- phos FS and dimethoate FS plants showed most growth (7.30 + 0.21 SD new nodes per shoot) al-

10.

~ 6 ~ua

,- 4 0

z 2

c o n t r o l 20"

a / ' ~ ' " ~ - - ' ~ ' ~ peak ~ earlY stage ~ 16'

. ~ 1 2 .

~ ~ ,,~ peak of~e rose ~' 4

0 , . , . , . , - , . , Z 0

Nov. Dec. Jan. Feb. Mar. Apr.

Post- treatment counts

/ / ~ peak of e a r l y s l a g e

peak of l a t e stage

. , ~ . .

Nov. Dec. Jan. Feb. Mar. Apr.

Post- treatment counts

0.4 0

20.3 ~

~ '

z 0.0

"~ 20"

8 gl

peak of early stage '~ 4

. ! . 0 Nov. Dec. Jan. Feb. Ma" Apr.

Post-treatment counts

d peak of late =age

~ peak of e a r l y s t a g e

O01111"01

..... . ~ . , . , . , _ , _ , Nov. Dec. Jan. Feb. Mar Apr.

Post- t reatment counts

Fig. 2. Effect of monocrotophos foliage spray at peaks of early (lst and 2nd) and late (3-5th) stage nymphs on C. thysanura egg (a), nymphs (b), parasitoids (c), and the production of new nodes (d) on boronia plants at Copping, 1988-89. Spray treatments were applied initially in November 23, 1987 (for early stage nymphs) and December 20, 1987 (for late stage nymphs) followed by a second application on February 16, 1988 and March, 1988 respectively.

66

Table 4. Average numbers of C. thysanura predators per terminal shoot on boronia plants stem sprayed with mevinphos at peak of early, late stage nymphs and untreated

Dates of assessment Time of spray treatment application Control (untreated)

At peak of early nymphal stage population

At peak of late nymphal stage population

November 22, 1987 0.019a (24h pretreatment counts)

November 23, 1987 0.016a (lst spray at peak of early stage)

December 20, 1987 0.028a (lst spray at peak of late stage)

January 17, 1988 0.031a February 16, 1988 0.028a

(2nd spray peak of early stage) March 16, 1988 0.036a

(2nd spray at peak of late stage) April 0.050a

0.016a 0.021a

0.020a 0.020a

0.032a 0.030a

0.029a 0.031a 0.030a 0.032a

0.037a 0.035a

0.052a 0.055a

Means between treatments within rows followed by the same letters are not significantly different (P > 0.05) Duncan's multiple range test.

Table 5. Average numbers of C. thysanura predators per terminal shoot on boronia plants stem sprayed with monocrotophos at peak of early, late stage nymphs and untreated

Dates of assessment Time of spray treatment application Control (untreated)

At peak of early nymphal stage population

At peak of late nymphal stage population

November 22, 1987 0.029a (24h pretreatment counts)

November 23, 1987 0.000a (lst spray at peak of early stage)

December 20, 1987 0.008a (lst spray at peak of late stage)

January 17, 1988 0.010a February 16, 1988 0.000a

(2nd spray peak of early stage) March 16, 1988 0.001a

(2nd spray at peak of late stage) April 0.002a

0.024a 0.021a

0.026b 0.028b

0.000a 0.033b

0.001a 0.030b 0.005a 0.036b

0.000a 0.032b

0.000a 0.045b

Means between treatments within rows followed by the same letters are not significantly different (P > 0.05) Duncan's multiple range test.

though this was not significantly different ( P > 0.05) from plants on the mevinphos SS plot (7.10 + 0.86 SD new nodes/shoot) or the other FS plants. Plants in the unsprayed plots had sig- nificantly less growth (2.64 + 0.52 SD new nodes/ shoot) (P < 0.01).

Optimum timing of insecticide application

Mevinphos SS was found to have the least effect on the natural enemy population and monocro- tophos FS the highest toxicity to C. thysanura and natural enemies. Applications of these materials

at peak densities of (i)early (lst and 2nd) and (ii) late (3rd-5th) stage nymphs on C. thysanura eggs, nymphs, parasitoids, predator populations and host plant growth coincided with the time when (i) parasitoids and predators were attacking nymphal stages 1 and 2 and (ii)parasitoids had killed host nymphs in the 3-5 stage and were pupating within the mummified hosts re- spectively.

The effects of mevinphos stem and monocro- tophos foliage sprays on all C. thysanura stages, parasitoids and the growth ofboronia plants (new nodes per shoot) are shown in Figs. 1 and 2. Significantly lower numbers of eggs and nymphs (P<0.01) were recorded on plots sprayed with both chemicals at peak numbers of late (3rd-5th) stage nymphs compared with plots sprayed at peak numbers of early (1 st and 2nd) stage nymphs (Figs. 1 and 2a,b). Poor control of C. thysanura eggs and nymphs was obtained when either in-

67

secticide was applied to the early stage nymphs, but it was significantly better (P <0.01) than in the unsprayed control plots (Figs. 1 and 2a,b). The second spray on February 16, 1988 applied at peak numbers of early stage nymphs (Figs. 1 and 2) appeared to have had little effect because ovipositing psyllid females could have laid on the plants after spraying resulting in an increase in psyllid numbers.

In insecticide treated plots, significantly higher numbers of parasitoids (P< 0.01) were recorded on mevinphos SS plots when sprays were applied at peak numbers of late stages and parasitoid numbers were not significantly different (P > 0.05) from numbers in the unsprayed plots (Fig. lc). But when sprays were applied at peak numbers of early stage nymphs no parasitoids survived (Fig. lc). This indicated that early applications of mevinphos SS killed the parasitoids. In contrast, parasitoid numbers in the monocrotophos FS

A

30 t20 ] mevinphos - stem/ / / / No2 spraySsprays ~'~] 30"20"

10 3 sprays "~

Z 0 . . . . . . . . . . . . . . . . . . . . . . . . . .

Post - t r e a t m e n t c o u n t s

monocrotophos - foliage / 2 sprays

. i ] ,L ~ / / F No sprays

10 3 sprays

O - - i - - i - - i - - i - - i - , i - - i - - i - - i

Dec Jan Feb Mar Apr May Jun Jul Aug

P o s t - t r e a t m e n t c o u n t s

3o r

20' Q.

>-, m 10 �84 d Z

0

mevinphos - stem

I ~ NO spray 2 sprays

3 sprays

"~" J~" ~b I ~ ~,i~i ~ ' J ~ "J~f ;,~g

Post - t r e a t m e n t c o u n t s

B 301 monocrotophos - foliage

2 0 No sprays 2 sprays

m l 0

3 sprays

o . . ~ .~. ~6 bt~ Ai,i ~ , J~ ~ ~.~xg

P o s t - t r e a t m e n t c o u n t s

Fig. 3. Effect of different applications of mevinphos as a stem spray and monocrotophos as a foliage spray on C. thysanura eggs (A) and nymphs (B) on boronia plants at Copping, 1987-88. (Arrows indicate spray times).

68

~ 0 .4 ==

~* 0.2 t _

d z

0.0

/ m e v i n p h o s - s t e m

3 sways

2 sprays No sprays

" b~c Jdn" #~b" i~ar ~ r i~;~ J,~ri "jb," A~g P o s t - t r e a t m e n t c o u n t s

• L m o n o c r o t o p h o s - fol iage 0.3

,.1=

0.2 No sprays

t _

~. 0.1 2 sprays

O 3 sprays O

Z 0 . C - . , . - , . . T . . ~ - . T . . T . ' - D " " ' " " ' g

P o s t - t r e a t m e n t c o u n t s

Fig. 4. Effect of different numbers of applications of mevinphos stem spray and monocrotophos foliage spray on C. thysanura parasitoid population on boronia plants. (Arrows indicate spray times).

plots were significantly lower (P < 0.01) irrespec- tive of the time of application compared with the unsprayed plots (Fig. 2c). Predator numbers were not significantly affected (Table 4) (P> 0.05) ir- respective of time of application of mevinphos S S, but monocrotophos FS spray killed the pred- ators on all the treated plots (Table 5). Plants sprayed with either insecticide at peak numbers of late nymphal stages had significantly higher growth (new nodes/shoot) (P < 0.05) than those sprayed at the peak numbers of early stage nymphs. However, the growth of the latter was significantly higher (P < 0.05) than plants left un- sprayed (Figs. ld and 2d).

Number of applications for effective control

The objectives of this experiment were to com- pare the consequences of spraying (a) mevinphos

SS and (b) monocrotophos FS on all or two of the three generations of C. thysanura (i.e. twice or three times) per annum. The numbers of C. thys- anura eggs and nymphs per terminal shoot on plots that received three sprays in a season of either mevinphos S S or monocrotophos FS were significantly lower (P < 0.01) than those plots that received two chemical sprays or no spray at all (Fig. 3).

Numbers of parasitoids per terminal shoot are shown in Fig. 4. There was no significant differ- ence (P>0.05) in the number of parasitoids per shoot in mevinphos SS plots which received ei- ther two or three spray applications and the un- sprayed plots. In the monocrotophos FS plots, the number of parasitoids per shoot was signifi- cantly lower (P<0.01) than in the unsprayed plot, irrespective of the number of spray applica- tions.

Plots which received three spray applications of either chemical produced significantly more growth (P < 0.01) than plots which received either two or no spray applications, respectively. At the end of the study, monocrotophos FS sprayed plots, which received three applications, produced 20.5 new nodes per terminal shoot, which was significantly higher (P < 0.01) than plants which received two spray applications of the same chemical (11.0 new nodes per shoot) or unsprayed plants (10.0 new nodes per shoot). The mevinphos SS plots which received three sprays produced 19.2 new nodes per shoot, which was significantly higher (P < 0.01) than those which received two sprays (11.2 new nodes per shoot) and the un- sprayed plants (9.3 new nodes per shoot).

Large scale evaluation of stem and foliage sprays

The objective of the study was to determine whether mevinphos SS and monocrotophos FS could perform equally well in different areas in Tasmania. The performance of mevinphos SS and monocrotophos FS in controlling C. thysa- nura eggs and nymphs at Copping, Huonville and Bakers Beach are shown in Fig. 5. The numbers of C. thysanura eggs and nymphs per terminal

69

Copping (E. Tasmania) B 40 A 20

1

l o

o/ o �9 Dec Jan Feb Mar Apt May Jtm Jun Jul Aug

80"

"~ 60

== 40' U

'~ 20' Z

Huonville (S.

4oi ~30" ~20'

O

- , - - , - - , - - , - - , - - J - - T . . Z

0

Tasmania)

�9 - �9 - | �9 i

Dee Jan Feb M z Apr May Jun Jul

r .m

U IN I 0

r

Z

30-

20

10 �84

Bakers Beach (N. Tasmania)

J t ~ 80' E -- 60

40 �84

'3 20' O ~= J~ Fib Zdar Z 0

P o s t - t r e a t m e n t c o u n t s

,t

P o s t - t r e a t m e n t c o u n t s

Fig. 5. Effect of mevinphos applied as a stem spray- - i - - , and monocrotophos as a foliage spray [] and no spray (control) on C. thysanura eggs (A) and nymphs (B) on boronia plants at Copping (1987-88), HuonviUe (1988-89) and Bakers Beach

1988-89. (Arrows indicate spray times).

shoot in mevinphos SS and monocrotophos FS plots were significantly lower (P< 0.01) than in the control plots at all study areas.

The number of parasitoids per terminal shoot recorded in the monocrotophos FS plots was sig- nificantly lower (P < 0.01) than in mevinphos SS plots at all study areas and numbers in the latter

did not differ significantly (P > 0.05) from those in the control plots (Fig. 6A). The mummified psyl- lid nymphs collected from mevinphos SS plots had a significantly higher (P < 0.01) parasitoid emergence than those from monocrotophos FS plots, but did not differ significantly (P> 0.05) from those collected from unsprayed plots, indi-

70

Copping (E. Tasmania

A ,-, 0.3" _ r O

~, 0.2 ~ .

0.1'

�9 . f o l ~ O

z 0.0 Dec Jan r-,eb Mat- At:It May Jtllll Jgn Ju] Aug

A 100'.

80"

g 6 0 2

4 0

~' 20:

~. 0

~ foliage

Dec Jan Feb Mar Apt- May Jun Jun Jul Aug

,~ 0.8" O

. l =

r o.6, = "~ 0.4' e l

t _

e l

,.~ 0.2

0

z 0.0

1

De: J,,- Feb 1 ~ AlX May Jun Jul

Huonville (S. Tasmania)

~ '100

80. m

6 0 E

i 40 m

20"

0' - - J - - ~ - -T . . . . i - - T - - T - - |

Dec Jan Feb Mar Apt May Jun Jul

"~ 1.0 O

, t g

0.8

0.6 == == 0.4

"~ 0.2, O

z 0.0

Bakers Beach (N. Tasmania)

.:,ooj I i j. oo]

P o s t - t r e a t m e n t c o u n t s P o s t - t r e a t m e n t c o u n t s

Fig. 6. Effect of mevinphos stem spray -!1-, monocrotophos foliage spray [] and no spray (control) ---0- on C. thysanura parasitoid populations (A) and percentage of parasitoid emergence (B) from mummified psyllid nymphs on boronia plants at Copping 1987-88, Huonville 1988-89, and Bakers Beach 1988-89. (Arrows indicate spray times).

cating that mevinphos S S conserved the parasi- toids (Fig. 6B).

The effects of mevinphos S S and monocroto-

phos FS on the growth of boronia plants at the three study areas are shown in Fig. 7. Plants which received either mevinphos S S or monocro-

20. Copping (E. Tasmania) f(

1 0

~ - - ~ - . i - - | - - | . . . . . . | . . . . a , -

Dec dan Feb Mar Apr May Jun Jun dul Aug

*~ 20" O O

, , r

~ 15" O

10

, . 5 o O

0

Huonville (S. Tasmania) foliage

conU'ol

Dec Jan Feb Mar Apr May Jun Jul

foliage

control

20-

lsl O

= 1 0

= 5

? O

z 0

Bakers beach (N. Tasmania)

i i i i

D c Jan Feb Mar Apr

P o s t - t r e a t m e n t c o u n t s

Fig. 7. Effect ofmevinphos stem spray--I-- , monocrotophos foliage spray [] and no spray ( c o n t r o l ) ~ of C. thysanura nymphs on the growth (new nodes per terminal shoot) of boronia plants at Copping, Huonville and Bakers Beach. (Ar- rows indicate spray times).

tophos FS produced more new nodes per termi- nal shoot (P<0.01) than plants which were left unsprayed. The difference in the growth of plants which received either mevinphos SS or monocro- tophos FS was not significant (P> 0.05). Plants sprayed with either mevinphos S S or monocro- tophos FS produced 1.7 times more new nodes at Copping and 2.8 times more at Huonville and

71

Bakers Beach than the unsprayed control plants, respectively.

The number of flowers formed per terminal shoot in mevinphos SS and monocrotophos FS plots at both Copping and Huonville indicate that significantly more flowers per shoot (P < 0.01) oc- curred on sprayed than on unsprayed plants (Ta- ble 6). The mean flower yields were equal in the monocrotophos FS and mevinphos S S plots (9.5 and 9.1 kgs respectively at Copping and 5.4 and 5.0kgs at Huonville). This was significantly greater (P < 0.01) than the weight of flowers from the unsprayed plots (5.5 and 2.8 kgs) at both Copping and Huonville respectively.

The oil yields of flowers harvested from sprayed and unsprayed plants at Copping were 71 ~o and 62~o on a fresh weight basis for the monocroto- phos FS and mevinphos SS plots respectively. This difference represents a gain of $1.81 per kg of flowers for FS over SS plots. The unsprayed plot had the lowest oil yield (48 ~o). The difference between oil yields were significant (P < 0.05) be- tween treatments and the control plots.

Economics of control programmes

This study compared the economics of psyllid control for the insecticide schedule used by grow- ers (i.e. 10 applications of demeton-S-methyl at 0.04~o a.i.) prior to 1988 and that developed in this study (i.e. 3 applications ofmevinphos SS at

Table 6. Effect of mevinphos stem and monocrotophos foli- age sprays on the production of flowers on boronia plants at Copping (E. Tasmania) and Huonville (S. Tasmania)

Treatment No. of flowers per terminal shoot

Copping Huonville X + S D X + S D

Mevinphos stem spray Monocrotophos foliage spray Control (No spray)

32.00+1.90a 38.20+2.15a 33.80+_ 1.57a 39.60 + 1.91a 19.40 + 2.80b 14.00 + 2.05b

Means within columns followed by the same letters are not significantly different (P > 0.05) Duncan's multiple range test.

72

Table 7. Comparison of the cost of application of dementon-S-methyl (conventional chemical spray programme) and mevinphos stem spray (IPM programme) on commercial boronia farm at Copping, 1986-87

a. Demeton-S-methyl foliage spray HO sprays per annum) Cost of insecticide alone @ $16.86 per spray for 10 sprays Cost of labour required to spray the crops per annum @ $140.00 per spray for 10 sprays Cost allowance for wear and tear of spraying equipments @ $112.00 per spray for 10 spray applications Total cost of insecticide application per annum Gross profit Net profit (less total cost of insecticide application) Growers profit with respect to control (unsprayed) plots

b. Mevinphos stem spray (3 sprays per annum) Cost of insecticides alone @ $24.12 per spray for 3 sprays Cost of labour required to spray crops per annum @ $140.00 per spray for 3 spray applications Cost allowance for wear and tear of spraying equipment @ $112.00 per spray for 3 spray applications Total cost of insecticide application per annum Gross profit Nett profit (less total cost of insecticide application) Growers profit with respect to control (unsprayed) plots

= $168.60 = $1,400.00 = $1,120.00 = $2.688.00 = $6,693.88 = $4,005.88 = $1,515.06

= $72.37 = $420.00 = $336.00 = $828.37 = $21.885.00 = $21,056.63 = $18,538.63

0.02~o a.i.). The total cost in applying each in- secticide for each season was calculated using 1986/87 values for materials, labour, depreciation (wear and tear of spraying equipment), flowers and oil.

For crops sprayed with mevinphos SS, flower and oil yields were 1500 kg/ha and 58~o respec- tively. The yields for the control plots were 200 kg/ha for flowers and 48 % of oil. The total costs, growers gross and nett profits per annum and the gain for the grower with respect to con- trol (unsprayed plots) in using the two materials are given in Table 7. The benefit to cost ratio for 10 applications of demeton-S-methyl was 0.56 to 1.00 but measured 22.40 to 1.00 when mevinphos S S was used. Thus the IPM strategy developed in this study was 40 times more profitable than the conventional chemical control programme.

Discussion

The results of this study indicate that a reduction of insecticide applications for control of C. thys- anura on boronia crops from 10 sprays per annum to 3 in the initial stages of the IPM programme 1987/88 significantly increased crop yield and profitability by conserving the natural enemies.

This was achieved by using a lower dosage of mevinphos as a stem spray and applications timed to coincide with the peak densities of late (3rd- 5th) stage C. thysanura nymphs. Mensah (1990) reported that the effectiveness of predators viz. coccineUids, spiders, syrphid larvae and parasi- toids, Psyllaephagus sp. (Encyrtidae) was nega- tively correlated with C. thysanura density so re- ducing C. thysanura numbers without affecting the natural enemy population would ensure effective control. Therefore properly timed applications of mevinphos as a stem spray provided a degree of ecological selectivity and made the environment more favourable to the natural enemies.

Insecticide selectivity was not achieved when mevinphos was used as a foliage spray (Tables 2 and 3) or when it was applied as a stem spray at the peak numbers of early (1st and 2nd) stage nymphs (Table 4). This was because insecticides applied to the foliage had a general contact effect which resulted in the death of parasitoids and predators on the host plant including those par- asitoids pupating in the mummies (Tables 2, 3 and 5). No parasitoids survived when mevinphos was applied at the peak of early stage nymphal densities (Fig. 1) because during early nymphal development, both parasitized and unparasitized psyllid nymphs were active and feeding and were

killed although no direct contact between spray and parasitoid had occurred as with foliage sprays. However, when stem applications of mevinphos were delayed until the peak of the late stage nymphs, parasitoids which had attacked the psyllids had pupated within mummified psyllids. This inactive stage was protected from the effects of the systemic spray and parasitoids survived. Furthermore coccinellid, spider and syrphid predators occurred only on the foliage of the host plant and were not significantly affected (Table 4) since stem sprays minimized any possible contact effect.

The use of systemic insecticides to enhance selectivity, especially against sap-sucking insects such as aphids, mites, thrips, psyllids etc. has been reported before (Metcalf, 1974). Van den Bosch & Stern (1962) also reported that ecolog- ical selectivity of chemicals occurred when spe- cific placement of a toxic material on the host plant resulted in less disruption of the agro- ecosystem. The view was shared by Wood (1972) who reported that applying the chemical to a re- stricted part of the environment could help to achieve selectivity.

Apart from mevinphos SS, the other chemicals tested did not combine high C. thysanura kills with high parasitoid survival and therefore, proved to be unsuitable for incorporation into any integrated control programme for C. thysanura. The stem treatment method of applying systemic insecti- cides to plants was previously limited almost en- tirely to trees. Some work on stem treatment of systemic insecticides on cotton was summarized by Mitchell etal. (1960) and Lindquist etaL (1965), but no major studies of the economic use of the stem treatment method on crop plants has been reported. Results of these tests indicate that stem treatment of crop plants is possible with less effect to the agro-ecosystem than foliage sprays, if applications are properly timed. A degree of ecological selectivity has also been achieved in chemical sprays through proper timing of treat- ments (Ripper, 1956; Franz, 1961; Wilson & Armbrust, 1970; Walker et al.,, 1979).

The most critical factors in the success of this programme were (a)the use of the systemic ma-

73

terial mevinphos at an effective dosage that killed 90~o of the nymphs, (b)the application of mevinphos to stems rather than foliage to mini- mize its contact effect and (c) applying mevinphos precisely when the majority of nymphs (i.e. over 7 0 ~ ) were in the third to fifth stages. Failure to address (b) and (c) resulted in destruction ofpar- asitoids and predators.

Considering the control economics of mono- crotophos FS and mevinphos SS plots, it can be seen that monocrotophos FS gained an extra $1.81 per kg of flowers over the IPM plots. This difference was offset by the environmental advan- tage achieved on the IPM plots which combined C. thysanura control with the conservation of nat- ural enemies and no danger of residue. The bo- ronia grower at Copping achieved a higher nett gain and a high benefit to cost ratio of $22.4:$1.0 (40 times over the conventional 10 demeton-S- methyl) when the IPM programme was adopted. The benefits achieved in IPM continued to in- crease as the mevinphos stem sprays were re- duced from three to one in 1989, and in 1990, the population of natural enemies in growers' farms, though not reported in this paper, had increased to a level at which low psyllid numbers caused no significant damage and therefore no spray has been required.

This study has shown that to grow boronia economically as a plantation crop, pest manage- ment must ensure protection of parasitoids and predators to stabilize psyllid numbers and to avoid anything that could affect stability. The study also points out clearly the important role pesticides can play in pest management systems and that they remain the most powerful agents in pest control. However, to utilize them in IPM programmes, caution should be taken in the choice of chemical, when and how to apply it to suit a particular situation so as to avoid disrup- tion of the whole agro-ecosystem. The desirabil- ity of developing pest control programmes in which chemical and biological control are fully integrated is now indisputable. This does not mean, however, that mevinphos applied as a stem spray would be the most desirable insecticide for use in other situations. Each pest problem and

74

each crop has its own unique biological and eco- logical characteristics, and these must be ana- lyzed and understood before any integrated con- trol programme can be developed. Through such ecological investigations we can expect integra- tion of chemical and biological controls to be uti- lized in a correct and practical manner.

Acknowledgements

We thank the Boronia Growers Association es- pecially Messrs. Bruce Downie, Greg Pullen and Scott Innes for cooperating in this study. We also thank Mrs Anna MCEldowney for helping in the extraction and residue analysis of the boronia oil. This work was supported by a University of Tas- mania Postgraduate Research Award and an Australian Rural Research Special Scheme grant.

References

Abbott, W. S., 1925. A method of computing the effectiveness of an insecticide. J. Econ. Ent. 18: 265-267.

Franz, J. M., 1961. Biological control of insect pests in Eu- rope. Ann. Rev. Ent. 6: 183-200.

Lindquist, D. A., D. L. Bull & R. L. Ridgway, 1965. Systemic insecticides tests in cotton plants. J. Econ. Ent. 58: 200.

Mensah, R. K., 1990. Biology, Ecology and Integrated Pest Management of Ctenarytaina thysanura Ferris & Klyver on Boronia megastigma Nees in Tasmania. Ph. D thesis, Uni- versity of Tasmania, Hobart, Tasmania, Australia.

Mensah, R. K. & J. L. Madden, 1992. Feeding behaviour and pest status of Ctenarytaina thysanura (Ferris & Klyver) (Hemiptera: Psyllidae) on Boronia megastigma (Nees.) in Tasmania. J. Aust. ent. Soc. 31: 71-78.

Metcalf, R.L., 1974. Insecticides in pest management. In: Introduction to Insect Pest Management (ed. W. H. Luck- mann) pp 235-273, John Wiley and Sons Press, New York.

Mitchell, J. W., B. C. Smale & R. L. Metcalf, 1960. Absorp- tion and translocation of regulators and compounds used to control plant diseases and insects. In: Advances in pest control Research, (ed. R. L. Metcalf) Vol. 3, 448 pp, Inter- science Publishers, Inc. New York.

Ripper, W. E., 1956. Effect of pesticides on balance of arthro- pod populations. Ann. Rev. Ent. 1: 403-438.

Van den Bosch, R. & V. M. Stern, 1962. The integration of chemical and biological control of anthropod pests. Ann. Rev. Ent. 7: 367-386.

Walker, J. T. S., E. Ashley, C. H. Wearing, W. P. Thomas & G. F. McLaren, 1979. Timing sprays for different European red mite control. The Orchardist of N.Z., 289-290.

Wilson, M.C. & E.J . Armbrust, 1970. Approach to inte- grated control of the alfalfa weevil. J. Econ. Ent. 63: 554- 557.

Wood, A., 1972. Integrated control, pest management and the future of pest control. In: Pest control, a survey, (eds. A. Wood and D.L. Lee) pp 333-359, McGraw-Hill Book Company, New York.

Zar, J. H., 1984. Biostatistical analysis. Prentice-Hall, Engle- wood, Cliffs, N.J. 718 pp.