Effects of Nectar-Producing Plants on Diadegma Insulare (Cresson), a Biological Control Agent of Diamondback Moth, Plutella Xylostella (L.)

Effects of nectar-producing plants on Diadegma insulare (Cresson), a biological control agent of diamondback moth, Plutella xylostella (L.)

Idris, A.B.1 and Grafius, E.2 1Department of Zoology, Faculty of Life Sciences, National University of Malaysia 43600 UKM, Bangi, Selangor Darul Ehsan, Malaysia 2Department of Entomology, Natural Science Building, Michigan State University East Lansing, MI 48824-1115, USA

Abstract Effects of nectar-producing plants (NPP) on the longevity, fecundity, oviposition and nectar-collecting behaviour of Diadegma insulare were studied. Longevity and fecundity of D. insulare were varied with morphological characters of NPP’s flowers. Brassica kaber (D.C) Wheeler, Barbarea vulgaris R. Br. and Daucus carota L. supplied nectar and resulted in D. insulare longevity and fecundity equal to when honey+water used as food sources. Others were not significantly better than no food at all. Chenopodium album L. and Thlaspi arvense L. did not provide available nectar, however, adults parasitoid fed on honeydew excreted by aphids feeding on the plants. An increase in longevity and fecundity was correlated with flower corolla opening diameter but not with corolla length. The oviposition behaviour within the first minute of exposure to diamondback moth larvae was highly correlated with longevity and fecundity of D. insulare, which we considered indices of food quality. We observed five nectar-collecting behaviours of D. insulare. The most striking behaviour, on B. vulgaris and B. napus L. flowers, involved chewing at the base of the corolla and creating holes that probably released the floral nectars. D. insulare visit more frequently and spent longer time particularly at the base of flower supporting longer life and high fecundity. The charactersitics of NPP’s flower and behavioural flexibility of D. insulare should be manipulated to increase its impact in integrated diamondback moth management.

Key words: Plutella xylostella, Diadegma insulare, nectar-producing plants, food sources

Introduction were observed feeding on the flowers of weeds in the Diamondback moth (DBM), Plutella xylostella (L.), vicinity of the field (Fitton and Walker, 1992). The is the major pest of Brassica crop worldwide. It possess selective use of floral nectar resources by the the ability to develop resistance to all pesticides used parasitoids was reported by Cowgill et al. (1993) and against them (Tabashnik et al., 1991). Pesticides Jervis et al. (1993). An understanding of the relative resistance problems have forced growers to increase importance of NPP to D. insulare may be important if the frequency and rate of spray, and continue using we want to enhance its role and effectiveness in DBM whatever available pesticides to control DBM. This management. leads to excessive and indiscriminate use of pesticides The objectives of our study were to assess the that destroys the DBM natural biocontrol agents, effects of NPP on the longevity and fecundity, especially the parasitoids and predators, in Brassica oviposition and nectar-collecting behaviour of D. crops agroecosystem (Lim et al., 1986). Diadegma insulare, and to correlate flower structures with D. insulare (Cresson) is a major DBM parasitoid in insulare and fecundity. Canada (Harcourt, 1986) and United States of America (Idris and Grafius, 1993b). Judicious use of pesticides Material and Methods and good Brassica ecosystem management should be Sources of NPP. Flowers of 8 Brassicaceous weeds; adopted because pesticides is detrimental to D. insulare Barbarea vulgaris R. Br., Berteroa incana (L.) D.C., (Srinivasan and Krishna Moorthy, 1991; Idris and Brassica kaber (D.C.) Wheeler, Brassica napus L., Grafius, 1993a and b). Capsella bursa-pastoris (L.) Medic., Erysimum Earlier studies indicated that the presence of cheiranthoides L., Lepidium campestre (L.) R. Br. and nectar-producing plants (NPP) in the field provides Thlaspi arvense L.; 5 non-Brassicacaeae, an important food source for the parasitoid which Chrysanthemum leucanthemum L. and Sonchus directly increases their effectiveness (van Emden, arvensis L. (Asteraceae), Rumex crispus L. 1963; Leius, 1967; Keven, 1973; Syme, 1975). For (Polygonaceae), Chenoppodium album L. D. insulare, Zhao et al. (1992) found that parasitism (Chenopodiaceae),and Daucus carota L. of DBM by this parasitoid was higher in the broccoli (Umbelliferae), and one cultivated Brassica plant adjacent to NPP than in the broccoli that was not (canola) were used as nectar sources for the parasitoid. surrounded by NPP. In England, Diadegma species Brassica weeds were emphasized because they were

90 Proceedings: The Management of Diamondback Moth and Other Crucifer Pests common in and near cabbage fields. They are also Relationship between flower structure with D. potential hosts for DBM larvae and are tolerant to insulare longevity and fecundity. The corolla length many herbicides used in cole crops. and diameter of the opening for a sample of 10 flowers (selected randomly) for each species per replicate were Sources of insects and site of study. We used measured and used to relate it with the longevity and F 18Ð20 DBM (Geneva strain) reared in the laboratory fecundity and opening of D. insulare (from the above on broccoli leaves grown in the greenhouse, and F2Ð3 study). field collected D. insulare reared on DBM. Study was conducted at the Michigan State University Nectar-collecting behaviour of D. insulare. Choice Entomology Research Farm in May through tests. Stalks of three flowers of each species were September, 1993 using NPP species available during inserted through holes in the lid of a 300 ml plastic each month. container filled with sucrose solution (0.5 g/ml). The flower species were randomly arranged in a circle Longevity and Fecundity. The flowers of NPP and about 4.0 cm from the center of the cover. A second D. insulare were enclosed in a cylindrical screen cage 300 ml container, with 1.5 cm diameter screened holes (20 cm high and 10 cm diameter) with sponge covering in the side, was put upside down on the first container the top and bottom of the cage and small slit at the and fastened with tape, creating a testing arena. We side of the screen for introducing insects. We cut a 5 randomly arranged the arenas parallel to the white cm slit from the edge to the center of the bottom for inflorescence light, 30 cm from the bulb. An unfed the flower stem(s). Each cage was tied to a wooden female D. insulare (1-d old) was released in the center stake erected close to individual flowering weeds. The of the testing arena through a hole in the upper cage was moved to a new flower when the earlier container. Females were allowed to acclimatise for 2 flower began to wilt. For honey+water (10% honey) h in the arena before observation. The nectar-collecting treatment and water alone treatments, filled in the glass behaviour of D. insulare included the following; tried vials (21 by 70 mm) the change were made every every to get in or entered corolla tube, kicked sepal or petal, 4-d. A piece of tissue paper was dipped into the vial sucked or chewed at corolla base were observed. We to avoid excessive evaporation. We inserted the vial also quantified the number of visits per flower species through a hole in the bottom foam. In September, two and the numbers of visits and time spent at the corollas. branches of the C. album and S. arvensis (naturally Behaviour were recorded using audio tape recorder infested by bean aphids, Aphis fabae Scopli) with for 30 min per observation session. These observation aphids and without aphids were inserted into the cage were repeated five times with new flowers and insects in place of the flowers. One male-female pair of D. each time. insulare (1-d old and not yet fed) was released into the cage through a slit on the side of the screen. The No-choice tests. Freshly emerged unfed adult D. treatments, including the no food, were replicated 8 insulare females were released into screen cages (30 times. Survival of the D. insulare females was recorded x 30 x 20 cm, 30 D. insulare per cage) 1-d before the daily to measure the longevity. To measure fecundity, experiment to acclimatise them to the cage the adult female parasitoid were removed out from the environment. We inserted stalks of flowers of each cage (1100 to 1450 h, during which females are most species into glass vials (3 flowers per vial) filled with active) (Idris,1995) every 3-d (started on the 3rd day sucrose solution. Six vials with flowers of a single after it was released into the cage) and released it into species were put in the middle of each cage. Fifteen a 400-ml transparent plastic container with a screen min after introduction of the flowers we recorded the lid with 30 3rd-instar DBM larvae for 3 h before numbers of individual D. insulare visiting the flowers putting it back into the cage. The presumably using audio tape recorder in 30 sec. We then took out parasitized DBM larvae reared in the laboratory on the flowers with vials. We introduced new flower broccoli foliage until pupation, when the number of species with vials in the another cage for the next D. insulare and DBM pupae were recorded. Fecundity observation. After the sixth cage we returned to the was calculated as the sum of all D. insulare pupae first cage and repeated this process five times (= five produced by a female D. insulare during her life (30 replicates per species). host larvae offered every 3-d). Data analysis. Longevity and fecundity of D. Ovipositional behaviour. On day 9, 4 of the 8 insulare, ovipositional behaviour of D. insulare fed replicates for D. carota, B. kaber , B. incana, C. bursa- on different food sources, the number of visits and time pastoris, B. napus and T. arvense, and honey+water spent per visit on flower, and comparisons of total treatments were observed in the above study and visitors per 30 sec for each flower species were recorded oviposition behaviour (any attack on host analyzed using 1-way ANOVA, and means were made by the parasitoid that ended with inserting its separated using the Fisher Protected Least Significant ovipositor into host body) of D. insulare, within 1, 5, Difference (LSD) test. Relationships between 20 min of exposure to DBM larvae. longevity and fecundity and length and opening

Biologically-based technologies 91 D.

8.5b

12.2b

20.2a

0.5c

5.3b 74.3

1.3d 6.7

4.7c 65.4 0.3e 0c

5.4a 135.4

1.6e 0c

± ±

< 0.05)

; F = fecundity (total number of

23.2a * *

7.8bc * *

8.9b 22.2

5.6e * *

2.1b 132.1

2.3b 140.4

3.1a 160.3

0.8e 0f 2.2

2.6d 75.8

ferent (Fisher Protected LSD,

7.2d 11.5

16.5a 23.2

14.2b 19.5

7.4ab 19.3

1.2e * * 4.3

ferent letters are significantly dif

1.6c 68.5

4.6a 130.5

3.2a 120.7

0.4d 0e * * 2.5

2.5ab 127.5

1.3d 5.4

0.2d 0e 2.4

females fed on various wildflowers as nectar sources during summer 1993

12.6b * * * * * *

0.7f * * * * * *

5.3d * * * * * *

2.3e * * * * * *

0.8f * * * * * *

1.4f * * * * * *

0.5c * * * * * *

5.3a 18.2

Diadegma insular

June July August September

S.E.) of

4.3b 104.3

0.5ef 5.2

2.1c 33.5

1.8d 8.5

2.2de 3.8

0.5f 7.3

2.1d 6.3

3.2a 128.2

0.4f 0g 2.0

LFLFLFLF ±

* * 10.2

* * 19.2

* * 19.1

2.5

8.5

4.2

3.2

2.2

8.0

14.5

- aphids * * 2.2

+ aphids * * * * * * 12.1

- aphids * * 1.4 + aphids * * * * * * 13.6

pupae formed of parasitized DBM larvae); Columns with dif

water 19.4

Result in May was somewhat similar to the result of June, 1993; *, not tested or was not found in the field; L, longevity (day)

Table 1. Longevity and fecundity ( Table

Food Sources

B. vulgaris

E. cheiranthoides

C. bursa - pastoris

T. arvense T. insulare

L. campestre

C. leucanthemum

R. crispus

B. incana

B. kaber

D. carota

Honey

S. arvensis

C. album C. album

No food 2.1

S. arvensi

92 Proceedings: The Management of Diamondback Moth and Other Crucifer Pests diameter of flower corolla, ovipositional behaviour of Oviposition behaviour. The frequency of D. insulare within 1 min of exposure to DBM larvae ovipositional behaviour made by D. insulare, within were analyzed using regresssion analysis. 1 min of exposure to the larvae, was signifcantly higher when they were fed on D. carota, B. kaber, or Result and discussion honey+water than when fed on B. napus, B. incana, Longevity. Result in May which was somewhat C. bursa-pastors or T. arvense. However, result similar to June is not presented here. In June, parasitoid showed otherwise for the other two time intervals (1Ð longevity was significantly longer when fed on B. 5 or 6Ð20 min). Longevity and fecundity of D. insulare, vulgaris than with other flowers, including R. crispus which we consider as indices of food quality, strongly L. and C. leucanthemum L. (Table 1). In July, D. carota correlated with the frequency of individual parasitoids and B. kaber had similar effects on the longevity of initiating oviposition behaviour within 1 min of D. insulare, comparable to honey+water. Although D. exposure to the host [r = 0.91, F = 255.7, P < 0.05 insulare longevity on B. incana was shorter than on (longevity); r = 0.87, F = 14.8, P < 0.05 (fecundity)]. B. kaber it supported D. insulare better than C. album and S. arvensis. In August, longevity of D. insulare Relationship of flower characters to D. insulare was higher when fed on B. kaber than on other food longevity and fecundity. Regression analysis sources. In September, C. album and S. arvensis indicated that 14.4% and 59.9% of variation in the offered aditional food for D. insulare. These weeds longevity of D. insulare could be explained by the haboured bean aphids, Aphis fabae (Scopli), which corolla length and opening diameter, respectively. apparently provided honeydew for D. insulare to live There was a significant positive correlation between longer on weed+aphids than on weeds-aphids. D. insulare longevity and corolla openinga and length However, longevity of D. insulare fed on these weeds even though a negative correlation was expected with with aphids was significantly less than on honey+water corolla length, if a narrow corolla limited access to indicating honeydew may not have certain sugars or nectar by D. insulare (Fig. 1a and b). For D. carota essential amino acids or they may be present in its extremely short corolla length plus widely open insufficient quantity compared to floral nectar (Baker corolla opening did not influence longevity. B. kaber and Baker, 1983). petals are separated down to the base of the corolla providing easy access of the parasitoid to the nectaries, Fecundity. Fecundity of D. insulare in June was in spite of its length. There was no significant significantly higher when B. vulgaris flowers or relationship between the corolla length and the honey+water was used as food, compared with other fecundity of D. insulare (Fig. 2a). However, corolla foods offered (Table 1). In July, parasitoid feeding on opening explained 75% of the variation in D. insulare B. kaber, D. carota or honey+water resulted in higher fecundity (Fig. 2b). There are also other factors fecundity than on other food sources. Although B. affecting access to nectar besides corolla length and incana was not as beneficial for D. insulare fecundity opening. For example, thickness of the petals and as B. kaber, it still offered better food than the non- sepals at the base of the corolla and sepals attached at brassicas wildflowers, S. arvensis and C. album. In the base, covering the bottom half of the corolla may August, fecundity of of D. insulare was significantly also be important. higher when fed on B. kaber than on other food sources. Longevity and fecundity of D. insulare fed Nectar collecting behaviour of D. insulare.In on B. kaber were significantly higer than when fed choice tests, we observed five distinct nectar-collecting with honey+water in August, suggesting that B. kaber behaviours of D. insulare (Table 2). D. insulare tried is an excellent food for D. insulare. Fecundity of D. to get in the corolla through the corolla opening of all insulare fed on C. album or S. arvensis with aphids flowers species. However, they only successful in was significantly higher than these weeds-aphids entering the corolla of B. incana, T. arvense, C. bursa- pastoris and D. carota. Kicking the soft, separated sepal or petal, was observed on B. incana, E.

Table 2. Nectar-collecting behaviour of Diadegma insulare females observed in choice test with various flowers

Behaviour Flowers B. vulgaris B. napus B. kaber E. cheiranthoides T. arvense C. bursa-pastoris D. carota B. incana Tried to get in corolla + + + + + + + + tube Entered corolla tube Ð Ð Ð Ð + + + + Kicked sepal or petal Ð Ð Ð + + + Ð + Sucked or chewed at + + + Ð Ð Ð Ð Ð corolla base Circled at the corolla + + + + + + Ð + base +, yes; Ð, no

Biologically-based technologies 93 30 200 Y = 5.67 + 1.48X, r = 0.38 (a) Y = 26.08 = 14.13X, r = 0.37 (a) F = 11.75, n = 72, P = 0.001) F = 1.13, n = 72, P = 0.33 B. kaber B. kaber 150 20 D. carota D. carota B. vulgaris 100 B. vulgaris

B. incana 30 B. incana

S. E.

± B. napus 50 B. napus

T. arvense S.E. ± T. arvense C. bursa-pastoris E. cheiranthoides (days) L. campestre L. campestre E. cheiranthoides 0 0

female 01 23 4 5 012345 Corolla length (mm) Corolla length (mm)

D. insulare D. insulare male D. insulare 30 200 Y = 4.05 + 2.17X, r = 0.77 (b) Y = 24.76X - 3.01, r = 0.87 (b) F = 102.82, n = 72, P = 0.001 F = 21.01, n = 72, p = 0.003 B. kaber B. vulgaris B. kaber 150

Fecundity of Longevity of 20 B. vulgaris 100 D. carota B. incana D. carota 30 B. incana C. bursa- B. napus 50 B. napus pastoris C. bursa- T. arvense L. campestre E. cheiranthoides pastoris L. campestre T. arvense E. cheiranthoides 0 0 01234567 0123456 7 Corolla opening (mm) Corolla opening (mm) Figure 1. Longevity of D. insulare females in relation to Figure 2. The relationship of the fecundity of D. insulare corolla length (a) and opening (b) of wildflowers females to the corolla length (a) and opening (b) of wildflowers cheiranthoides, T. arvense or C. bursa-pastoris. D. visit on B. napus, B. vulgaris, B. kaber and D. carota insulare did not try to entered the corolla tubes of B. than on other flower species (Fig. 3b). This suggest kaber flowers because the corolla base has a wide that visiting these flowers is more rewarding. The separation between the sepals or petals, and between numbers of visit and times spent at the corolla bases the sepals and petals; to reach the nectar at the base of were significantly higher on B. vulgaris, B. napus and the corolla, D. insulare could easily entered from the B. kaber than on the other flower species (Fig. 3a and side. In contrast, sepals and petals of E. cheiranthoides b). D. insulare did not visit the base of D. carota corolla are attached to form a corolla tube, and given the because its corolla tube is extremely short and widely narrow corolla opening D. insulare could not entered open. the tube or reach the nectar. In contrast, D. insulare In no-choice tests, there were significantly more easily entered the wide, shallow corolla of D. carota. visitors to B. kaber, B. vulgaris and D. carota than to D. insulare circled the corolla bases of all flower other flowers (Fig. 4). There were fewer visitors to E. species offered, indicating a high affinity to get close cheiranthoides flowers than to any other flower to the actual food source. D. insulare appeared to suck species, reflecting the poor quality or quantity of its or chew at the corolla base of B. vulgaris and B. napus nectar. Results may be different in nature as the flowers and these were subsequently found to have diversity and abundance of wildflowers vary with holes that probably released the floral nectar. habitat or landscape. In the field, like our no-choice Apparently, D. insulare used its mandibles to make tests, some flower types are visited more frequently the holes to reach the nectar. Theses results indicate or have more visitors than would be expected, based that there is behavioural flexibility of D. insulare in on their respective abundance. collecting floral nectar. Most of these behaviours ware In choice tests, there was no significant difference reported for bumble bees (Guiterman, 1959) and not in the number of visits to E. cheiranthoides, B napus for parasitoids, especially the ichneumonids (Jervis et (yellow) or D. carota (white) flowers made by D. al., 1993). Therefore, this is the first report that an insulare (Fig. 3a). Whilst in no-choice tests the ichneumonid can behave like bumblebee in trying to numbers of visitors on D. carota were as high as on B. reach the floral nectar sources. D. insulare made vulgaris (yellow) but signifiantly higher than on B. significantly more visits to B. vulgaris than to other incana (white) (Fig. 4). Therefore, colour appeared flower species (Fig. 3a). They spent longer times per

94 Proceedings: The Management of Diamondback Moth and Other Crucifer Pests S.E.

± 400 8 (a) (b)

S.E. 6 ± 300 Visit on flower Time spent on flower

in 30 min Visit at corolla base Time spent at corolla base 4 200

100

D. insulare 2

Time (sec.) per visit Time 8 0

Visit per Visit

B. kaber

B. napus

B. incana

D. carota

B. incana

D. carota

T. arvense T.

B. vulgaris

E. cheranthoides

C. bursa-pastoris

E. cheranthoides

C. bursa-pastoris Figure 3. Number of visit (a) and time spent per visit (b) on flower or at the corolla base made by D. insulare females in 30 minutes of choice experiments

D. carota, which are abundant in weedy areas and idle 12 fields in Michigan during early and middle-to-late season, respectively, could influence effectiveness of

S.E. D. insulare as a biocontrol agent of DBM. The

± 6 distribution of these weeds which flower has accessible nectar should be manipulated in cabbage cropping systems to favour D. insulare. Design of crop 4 management systems including management of natural enemy food sources (for example, planting B. kaber, Visitors per 30 sec. Visitors B. vulgaris or D. carota in the cabbage field 0 ecosystem) will become more important as we try to integrate biological control with production of high value vegetable crops.

B. kaber

B. incana

D. carota

B. vulgaris Acknowledgement

E. cheranthoides C. bursa-pastoris Special thanks to James Miller, James Kells, Walter Figure 4. Numbers of D. insulare females (visitors) per Pett and Beth Bishop (Michigan State University) for flower species per 30 sec. in no-choice test experiments their valuable assistance and critical comments. We are also indepted to S. Stephenson (Michigan State not to be a factor determining a nectar-collecting University) for weed identification. Research was behaviour of D. insulare. supported by the Michigan Agriculture Experiment Although most Ichneumonids lacking elongated Station and the Michigan Vegetable Council. mouth part that excluded them from using the nectar of many plants especially of Asteraceae, Leguminosae References and Convulaceae (Jervis et al., 1993), results of our Baker, H. G., and Baker, I. 1983. A brief historical review study indicated that there was a behavioural flexibility of the chemistry of the floral nectar. In Bentley, B. and of D. insulare in collecting nectar of flowers with Elias, T. [eds.], The biology of nectar. Columbia different morphological characters. It is possible that University Press, New York, pp. 126Ð152. D. insulare longevity and fecundity are determined by Cowgill, S.E., Wratten, S.D,, and Scotherton, N.W. 1993. The selective use of floral resources by the hoverfly its behavioural flexibility in collecting nectar, and the Episyrphus balteatus (Diptera: Syrphidae) on farmland. availability and acessibility of nectar sources in and Annual Applied Bioliology. 122: 223Ð231. around the field. The width of the corolla has a strong Fitton, M., and Walker, A. 1992. Hymenopterous parasitoids effect on both longevity and fecundity, but it did not associated with diamondback moth: the taxonomic explain all the observed variation between wildflower dilemma, . In Talekar, N.S. [ed.], Diamondback moth species as food sources. Nectar quality and extrafloral and other crucifer pests: Proceedings, 2nd nectar are probably other important factors International Workshop, 10Ð14 December 1990, determining the longevity and fecundity of D. insulare Tainan, Taiwan. Asian Vegetable Research and (Baker and Baker, 1983) but we did not measure them. Development Center, Shanhua, Taiwan, pp. 225Ð237. Guiterman,A. 1959. Bumble bees and flowers. pp, 100Ð122. C. album and S. arvensis that did not have accessible In. Free, J. B, Butler, C.G., and Yarrow, I.H.H. (eds.), nectar could indirectly provide food sources by Bumblebees. The MacMillan Company, New York. harboring aphids that produce honeydew for the Harcourt, D.G. 1986. Population dynamic of the parasitoid. Flowers with accessible nectar might help diamondback moth in southern Ontario, pp. In Talekar, increase parasitism of DBM. B. vulgaris, B. kaber, and N.S. and Griggs, T.D. [eds.], Diamondback moth moth

Biologically-based technologies 95 management. Proceedings, 1st. International Leius, K. 1967. Food sources and preferences of adults of a Workshop, 11Ð15 March 1985, Tainan, Taiwan. Asian parasites, Scambus buolianae (Hymenoptera: Vegetable Research and Development Center, Shanhua, Ichneumonidae), and their consequences. Canadian Taiwan, pp. 1Ð15. Entomologist. 99: 865Ð871. Idris, A.B. 1995. Ecology and behaviour of Diadegma Lim, G.S., Sivapragasam, A. and Ruwaida, M. 1986. Impact insulare (Cresson), a biological control agent of assessment of Apantales plutellae on diamondback diamondback moth, Plutella xylostella (L.). Ph.D. moth using insecticide-check method.. In Talekar, N. dissertation, Michigan State University, East Lansing. S. and Griggs T. D. [eds.], Diamondback moth moth Idris, A.B. and Grafius, E. 1993a. Field studies on the effect management. Proceedings, 1st International Workshop, of pesticides on the diamondback moth (Lepidoptera: 11Ð15 March 1985, Tainan, Taiwan. Asian Vegetable Plutellidae) and parasitism by Diadegma insulare Research and Development Center, Shanhua, Taiwan, (Hymenoptera: Ichneumonidae). Journal of Economic pp. 195Ð204. Entomology. 86: 1 196Ð1 202. Syme, P.D. 1975. The effects of flowers on the lonngevity Idris, A.B. and Grafius, E. 1993b. Pesticides affect immature and fecundity of two native parasites of the European stages of Diadegma insulare (Hymenoptera: pine shoot moth in Ontario. Environmental Entomology. Ichneumonidae) and its host, the diamondback moth 4: 337Ð346. (Lepidoptera: Plutellidae). Journal of Economic Van Emden, H.F. 1963. An observation on the effect of Entomology. 86: 1 203Ð1 212. flowers on the activity of parasitic Hymenoptera. Jervis, M.A., Kidd, N.A.C., and Fitton, M.G. 1993. Flower- Entomol. Mon. Mag. 98: 265Ð270. visiting by hymenopteran parasitoids. Journal of Zhao, J.Z., Ayers, G.S., Grafius, E.J., and Stehr, F.W. 1992. Natural History. 27: 67Ð105. Effects of neighboring nectar-producing plants on Keven, P.G., Baker, H.G. 1984. Insects and flowers. pp. 607Ð populations of pest Lepidoptera and their parasitoids 631. In Huffaker, C. B. Rabb, R.L. 9eds.), Ecological in broccoli plantings. Great Lakes Entomologist. 25: Entomology. John Wiley and Son, New York. 253Ð258.

96 Proceedings: The Management of Diamondback Moth and Other Crucifer Pests