Characteristics of parasitism of diamondback moth by Oomyzus sokolowksii (Hymenoptera: Eulophidae)

N. S. Talekar Asian Vegetable Research and Development Center, Shanhua, Tainan 741, Taiwan, ROC

Abstract Laboratory, greenhouse and field studies were conducted on Oomyzus sokolowskii Kurdjumov, a parasite of diamondback moth, Plutella xylostella (L.), to judge its suitability for introduction in the field to control the plutellid. Oomyzus sokolowskii preferred the third and fourth instar diamondback moth larvae over fresh pupae for parasitization. It is thus a larval parasite. Within the range of 10 °C to 35 °C, the higher the temperature the higher was the parasitism rate. High parasitism at temperatures of 30 °C and 35 °C indicates that this insect is suitable for introduction in the tropical lowlands. In a no-choice test where only fresh pupae of Cotesia plutellae Kurdjumov (another potentially competing larval parasite of diamondback moth) were offered, O. sokolowskii failed to parasitize the pupae. In a choice test where the fourth instar diamondback moth larvae and fresh C. plutellae pupae were offered, O. sokolowskii parasitized only diamondback moth larvae. This parasite, therefore, is not a hyperparasite of diamondback moth. When C. plutellae-oviposited diamondback moth larvae were offered at intervals for parasitism by O. sokolowskii, it parasitized only freshly oviposited host larvae. The longer the period that elapsed after C. plutellae oviposition of diamondback moth larvae, the lesser was the parasitism of these larvae by O. sokolowskii. In a field cage study, as the diamondback moth population increased, the parasitism of the pest by the eulophid increased, parasitism by C. plutellae, however, decreased. Host-plant (cabbage) age did not affect the parasitism of diamondback moth larvae by O. sokolowskii; in both seedlings and mature plants the level of parasitism of the plutellid larvae was comparable. Most organic insecticides tested were toxic to both pupae and adults of O. sokolowskii but Bacillus thuringiensis was not toxic. Introduction of O. sokolowskii in a large field cage erected over a cabbage field reduced the infestation of cabbage by diamondback moth and doubled the yield of cabbage over the control plot where no parasite was used.

Key words: Oomyzus sokolowskii, diamondback moth, parasitism, temperature effect, hyperparasitism, parasite competition

Introduction this braconid is an important mortality factor in the In tropical to subtropical Asia, major cruciferous lowlands, its effectiveness in controlling diamondback vegetables are grown in two distinct ecological zones: moth has not been consistent. Therefore, another cool highlands and hot lowlands. In both areas, parasite, Oomyzus sokolowskii Kurdjumov diamondback moth, Plutella xylostella (L.) (Hymenoptera: Eulophidae), which has given very (Lepidoptera: Plutellidae), is a serious pest. The effective control of the plutellid pest in Cape Verde climate, especially temperatures, in the highlands Island (Lima and van Harten, 1985; Carl, 1992), was resembles that of temperate areas. In the lowlands, high imported from that tropical West African country via temperatures reaching and at times exceeding 35 °C the International Institute of Biological Control for are common. In Europe, where the diamondback moth introduction in lowlands of Asia. Several laboratory, originated, the pest is kept under control by a plethora greenhouse, and field experiments have been of temperate-climate natural enemies, mainly parasites conducted to study characteristics of its parasitism to (Mustata, 1992). Introduction of some of these judge the suitability of this parasite for introduction temperate-climate parasites, especially Diadegma in tropical to subtropical areas of Asia. semiclausum Hellen, and to some extent Diadromus collaris Gravenhorst, in countries in Asia, has resulted Preference of O. sokolowskii for various immature in their establishment in highlands resulting in stages of diamondback moth considerable reduction in the severity of diamondback Several reports indicate that O. sokolowskii is a pupal moth damage (Talekar, 1996a). In lowlands, however, parasite (Bennet and Yaseen, 1972; Wakisaka et al. none of these parasites is effective due to their 1991; Chelliah and Srinivasan, 1986). In our first study sensitivity to high tempeatures. Cotesia plutellae we compared the parasitism of diamondback moth Kurdjumov, which is tolerant to the high temperatures pupae with that of third and fourth instar larvae. commonly found in the tropical lowlands (Talekar and Ten third and fourth instar larvae and freshly Yang, 1991), occurs naturally in Taiwan (Wu, 1968), formed diamondback moth pupae were placed on a Philippines (Velasco, 1983), Malaysia (Lim and Ko, cabbage leaf in a 1.5-liter plastic container. Thirty 1975) and Thailand (Keinmeesuke, 1992). Although 5-day-old O. sokolowskii adults were then introduced

Biologically-based technologies 97 in the container for oviposition. We then removed the Table 1. Preference of O. sokolowskii for parasitism of host larvae and maintained them until pupation. The various immature stages of diamondback moth numbers of larvae pupating into diamondback moth Test Parasitism (%) or parasite pupae were recorded. We maintained the plutellid pupae that were also exposed to O. 3rd instar 4th instar Pupae larvae larvae sokolowskii for oviposition and recorded the number of pupae that produced the plutellid adults and the First 66.6±20.8 52.2±19.5 0 ± ± number that produced parasite adults. This experiment Second 68.9 20.1 67.5 27.0 0 ± ± was conducted three times, each time with three Third 75.2 4.5 81.8 5.1 0 Mean 70.2± 4.5 67.2±14.8 0 replicates. In the second experiment, 20 first, second, third, Ten larvae or fresh pupae of diamondback moth were and fourth instar larvae and 20 freshly formed pupae exposed to 30 O. sokolowskii adults for oviposition. of diamondback moth were placed on large cabbage Table 2. Preference of O. sokolowskii for parasitism of leaves inside each of four 1.5-liter round jars. Two various instars and pupae of diamondback moth hundred O. sokolowskii adults were then introduced (a) in each jar and allowed 24 hours for oviposition. The Instar Parasitism (%) number of pupae that developed into plutellid adults First 25.00 + 14.14 and the number that produced parasite adults were Second 41.25 + 17.01 recorded. Host larvae were reared until pupation and Third 73.75 + 16.01 Fourth 76.25 + 14.36 the number of those pupating into diamondback moth Pupae 0 or O. sokolowskii pupae was recorded. LSD(b) 20. 80 The rates of parasitism of immature stages from (a) the above two experiments were analyzed by ANOVA. Parasitism data are means + standard deviation of 4 replicates Mean percentage parasitism was compared by the test (b)LSD = Least significant difference of Least Significant Difference (LSD). Oomyzus sokolowskii parasitized the third and O. sokolowskii adults were then introduced in a 15- fourth instar diamondback moth larvae (average 70% cm-diameter, 30-cm-long acrylic cylinder containing and 61%, respectively) but failed to parasitize pupae 50 plutellid larvae feeding on a cabbage leaf. Both ends (Table 1). It is thus a larval parasite. Cotesia plutellae, of the cylinder were covered with a single layer of another larval parasite of diamondback moth with fine muslin cloth. Four such cylinders containing similar ecological requirements as O. sokolowskii, parasite adults and host larvae were maintained at 10, parasitizes second, third, and fourth instar plutellid 15, 20, 25, 30 or 35 °C for 24 hours. During this period, larvae with preference for the second instar (Talekar O. sokolowskii adults laid eggs in diamondback moth and Yang 1991). larvae. After 24 hours, the pest larvae were maintained In most of southeast Asia where C. plutellae is at 25 ± 2 °C and reared until pupation. At pupation established, the introduction of O. sokolowskii might the number of larvae developing into diamondback result in competition between the two parasites. This moth pupae and parasite pupae were recorded and led us to study the preference of O. sokolowskii adults percent parasitism was calculated. A simple linear to parasitize various instars of diamondback moth. regression correlation between temperature and Results (Table 2) indicate that O. sokolowskii prefers percentage parasitism was calculated (Little and Hills, third and fourth instars over first and second instars. 1975). The preference of O. sokolowskii for third and fourth As the temperature increased from 10 °C to 35 °C, instars and that of C. plutellae for second instar could parasitism of diamondback moth by O. sokolowskii reduce competition between these two larval parasites, increased significantly (r = 0.987, p = 0.01, Figure 1). assuring survival of both. This could contribute to the High parasitism at temperatures of 30 °C and 35 °C biological control of diamondback moth in lowland indicates that this parasite might be suitable for the areas of Asia where this plutellid pest is especially tropical lowlands. Parasite mortality ranged from 4.5% serious. However, the reduction of competition will to 14.6% and was not related to temperature. Oomyzus depend on the interval between parasitism of second sokolowskii is now being introduced in crucifer- instar host larvae by C. plutellae and molting into third growing lowland areas of Taiwan, Thailand, and instar when chances of its being attacked by Malaysia. O. sokolowskii increases. The longer the interval, the better are the chances of survival of C. plutellae (see Hyperparasitism study later discussion). Because environmental conditions, especially temperature, for survival and multiplication of C. Effect of temperature on parasitism plutellae and O. sokolowskii are similar, and because Three-to five-day-old O. sokolowskii adults and third O. sokolowskii is a minute insect, it has often been and fourth instar diamondback moth larvae were postulated Ð but never documented Ð that O. sokolowskii separately maintained at various temperatures: 10, 15, could be a hyperparasite of diamondback moth. 20, 25, 30, and 35 °C for 6 hours to condition both Both no-choice and choice tests were used to study host and parasite to these temperatures. Fifty the preference of O. sokolowskii for oviposition in

98 Proceedings: The Management of Diamondback Moth and Other Crucifer Pests diamondback moth larvae or C. plutellae pupae. In Competition for parasitism between C. plutellae and the no-choice test, 50 fresh C. plutellae pupae were O. sokolowskii placed on a cabbage leaf in each of eight acrylic Since C. plutellae and O. sokolowskii share similar containers. Twenty two-day-old O. sokolowskii adults ecological niches, and they both attack diamondback were then introduced for oviposition in each of four moth larvae, it is possible that these insects would containers. The remaining four containers were compete for host larvae and that the less competitive maintained as control. The host and parasite insects of the two species might not survive. Therefore, we were maintained together at 26 ± 2 °C for 48 hours. performed an experiment to determine competition Oomyzus sokolowskii adults were then removed and between the two parasites. Because C. plutellae can C. plutellae pupae transferred individually into glass infest all four instars of diamondback moth (Velasco, vials to observe pupation and emergence of C. plutellae 1983; Talekar and Yang, 1991) and because it is already or O. sokolowskii adults. established in most countries of Asia, we exposed the In the choice test, 50 fourth instar diamondback host larvae first to C. plutellae and then to O. moth larvae and 50 fresh C. plutellae pupae maintained sokolowskii. on a cabbage leaf were placed in each of four acrylic Twenty fourth instar diamondback moth larvae containers. Twenty two-day-old O. sokolowskii adults were individually confined with a gravid C. plutellae were then introduced inside each of these containers female in a test tube. After oviposition, each plutellid and allowed to lay eggs for 48 hours. The plutellid larva was observed under the microscope to make sure larvae and C. plutellae pupae were then maintained that C. plutellae had indeed laid eggs in each of them. separately at 25 ± 2 °C. The number of diamondback The parasite eggs could be seen through larval cuticle. moth larvae producing parasite pupae and the number At 0, 24, 48, 72, ans 96 hours after oviposition, the C. developing into diamondback moth pupae were plutellae-oviposited larvae were individually exposed recorded. Cotesia plutellae pupae were observed and to oviposition by O. sokolowskii. We recorded the the number of those that showed parasitism by O. number of diamondback moth larvae pupating into C. sokolowskii was recorded. plutellae or O. sokolowskii pupae. We also recorded In both choice and no-choice tests, O. sokolowskii the mortality of diamondback moth larvae and parasite failed to parasitize C. plutellae pupae (Table 3). In the pupae. choice test O. sokolowskii parasitized the fourth instar When C. plutellae-oviposited diamondback moth diamondback moth larvae but not C. plutellae pupae. larvae were immediately exposed to parasitization by It was not possible to expose larvae of C. plutellae O. sokolowskii, most of the diamondback moth larvae and diamondback moth for O. sokolowskii oviposition were oviposited by the latter parasite and yielded O. simultaneously for fair comparison because C. sokolowskii pupae (Figure 2). Even 24 hours after plutellae larvae develop inside diamondback moth oviposition by C. plutellae, practically 50% of the larvae. Instead we used freshly formed C. plutellae plutellid larvae were successfully parasitized by O. pupae. The fact that in the no-choice test O. sokolowskii. However, after 48 hours, practically all sokolowskii did not parasitize C. plutellae shows that C. plutellae-oviposited diamondback moth became C. O. sokolowskii is not a parasite of C. plutellae and thus plutellae adults. It is possible that at 48 hours and later, is not a hyperparasite of diamondback moth. C. plutellae embryos, which are in an advanced stage It is possible that O. sokolowskii parasitizes other of development, kill O. sokolowskii eggs as they do diamondback moth parasites such as D. semiclausum D. semiclausum eggs (Yang et al., 1994). This implies or D. collaris. However, D. semiclausum is a cool that O. sokolowskii could become the dominant climate parasite (Talekar and Yang, 1991) and D. parasite when introduced in an area where C. plutellae collaris, which also prefers cool climate, is a pupal is already established. The latest information from parasite. These factors rule out O. sokolowskii being a Cape Verde Island indicates this to be the case (Carl, hyperparasite of diamondback moth. This finding 1992). However, the fact that C. plutellae can parasitize allows the introduction of this parasite in all lowland earlier instars of diamondback moth larvae should areas of southeast Asia where C. plutellae also enable the parasites to co-exist, as has been shown in parasitizes diamondback moth.

Table 3. Parasitism of P. xylostella or C. plutellae by O. sokolowskii in choice and no-choice test

Test condition Parasitism (%) Adults emerged (%) Mortality (%) P. xylostella C. plutellae P. xylostella C. plutellae P. xylostella C. plutellae No choice(a) Ð 0 Ð 98.50 ± 1.91 Ð 1.50 ± 1.91

Choice(b) 30.90 ± 1.39 0 58.31 ± 8.08 97.50 ± 1.00 10.79 ± 7.04 2.50 ± 1.00 Data are means ± standard deviation of 4 replicates. (a)Only C. plutellae pupae were offered for parasitism by O. sokolowskii (b)Both 4th instar P. xylostella larvae and C. plutellae pupae were offered for parasitism by O. sokolowskii.

Biologically-based technologies 99 Parasitism (%) Paratisim (%) by 100 30 y = Ð19.173+4.6168x r2 = 0.713 80 20 60

40 10 20

0 0 10 15 20 25 30 35 345678 Temperature (°C) No. larvae/plant Figure 1. Parasitism of diamondback moth larvae by O. sokolowskii at various temperatures Figure 3. Relationship of population of diamondback moth larvae per plant and parasitism by O. sokolowskii

Paratisim (%) by 100 Survival rate (%)( ) No. adults emerged/pupa ( ) 100 40

80 ▼ 80 C. plutellae 30 60 60 20 40 40 O. sokolowskii 20 10 ▼ 20

0 0 0 0 24 48 72 96

Bt Hours after oviposition by C. plutellae

Cartap

Sticker

Bifenthrin

Abamectin

Profenofos Figure 2. Effect of time elapsed after C. plutellae Mevinphos

Cyromaszine oviposition in diamondback moth larvae on the success of Figure 4. Effect of various insecticides on the survival of parasitism of the same larvae by O. sokolowskii. (Each pupae and emergence of O. sokolowskii adults point is the average of 20 larvae exposed to parasitism).

Survival rate (%) 100

Sticker Bt 80 Abamectin Cyromazine 60

40 Bifenthrin

20 Profenofos 0 Mevinphos Cartap

012 3 Days after treatment Figure 5. Effect of various insecticides on the survival of adults of O. sokolowskii

100 Proceedings: The Management of Diamondback Moth and Other Crucifer Pests southern Japan, India, and the West Indies (Hirashima second observation (five days). There was no et al., 1989, Chelliah and Srinivasan, 1986, Yaseen, statistically significant relationship between plant age 1978). and parasitism. Oomyzus sokolowskii parasitism of diamondback moth is thus not affected by host-plant Relationship between diamondback moth larval age. This parasite, therefore, can be introduced in the population density and parasitism by O. sokolowskii field for the biological control of the plutellid at any In this field experiment we studied the dependence of stage of plant growth. rate of O. sokolowskii parasitism on the density of diamondback moth larval population. In a 0.1-ha parcel Effect of various insecticides on the survival of O. of land planted to common cabbage we introduced 500 sokolowskii diamondback moth adults to initiate pest infestation. Our experience indicates that despite best efforts by Two days later we introduced 1 000 O. sokolowskii researchers and extension authorities, some farmers adults in the same area. In addition, 500 parasite adults continue to use insecticides in crucifer growing areas each were also introduced two, three, and four weeks where parasites are newly established and later. Once a week we monitored the larval population diamondback moth is no longer a serious pest. Some of diamondback moth on cabbage plants and of the insecticide use is for controlling insect pests parasitism of the pest larvae by O. sokolowskii or C. other than diamondback moth. It is possible that some plutellae which is already established in lowland areas of the insecticides used could adversely affect of Taiwan. Diamondback moth population increased diamondback moth parasites and thereby exacerbate steadily from 10 days after the plutellid adult release diamondback moth problem. We conducted, therefore, up to harvest, from 2 to 22 per 10 plants. Parasitism a laboratory experiment to study toxicity of some of larvae by O. sokolowskii increased steadily from commonly used insecticides to O. sokolowskii. 1.3% to 21.9%. There was significant correlation (r = Commercial formulations of each of seven 0.844) between larval population density and the rate insecticides and one commonly used sticker were of parasitism (Figure 3). Parasitism by C. plutellae diluted as directed on the insecticide container for use decreased from 48% to 3.1% during this period. In in the field. Freshly formed pupae of O. sokolowskii our earlier study we found similar decrease in were then dipped in insecticide solution for five parasitism of C. plutellae from the beginning towards seconds. Treated pupae were air-dried under a gentle the end of the season (AVRDC, 1992). Based on our flow of air. The dry pupae were placed at 28 ± 2 °C present findings, it appears that introduction of O. and emergence into O. sokolowskii adults was sokolowskii will not compete but supplement the monitored. The number of pupae that failed to emerge control of diamondback moth achieved by C. plutellae. were considered as dead. The total number of adults that emerged from surviving pupae were recorded. Effect of host-plant age on the parasitism of In a simultaneous test with adults, the insecticide diamondback moth by O. sokolowskii solutions were sprayed on fresh cabbage leaves. The A field experiment was conducted to study the treated leaves were placed in a 15-cm diameter acrylic influence of host-plant (cabbage) age on the parasitism cylinder. Twenty O. sokolowskii adults were released of diamondback moth larvae by O. sokolowskii. A inside each cylinder and insect mortality was recorded parcel of land was rototilled and worked into 24, 1.5- at 72 hours after treatment. m wide and 5.0-m long single bed plots. The whole The survival rate and the number of O. area on four sides was confined by 2-m high fine-mesh sokolowskii adults which emerged from the surviving net. The same mesh net was used to cover the top. pupae are shown in Figure 4. Bifenthrin was the most Once every week for eight consecutive weeks we toxic and Bacillus thuringiensis were the least toxic transplanted four-week-old cabbage seedlings in three insecticides. The order of toxicity was bifenthrin > randomly selected plots; one plot per replicate. Plants mevinphos > cyromazine > cartap > abamectin > were maintained free of plutellid infestation. When the profenofos > B. thuringiensis. For adults, mevinphos cabbage plants in the last transplanted plot were in and cartap were equally toxic and B. thuringiensis was the field for one week, we introduced 10 third-instar the least toxic (Figure 5). The order of toxicity was diamondback moth larvae per plant on each of 10 mevinphos = cartap > profenofos > bifenthrin > plants selected at random in each plot. The plants that abamectin = cyromazine > B. thuringiensis. The sticker received the pest larvae were marked. was nontoxic to adults and its toxicity to pupae was Immediately after the introduction of lower than any products included in the test. Bacillus diamondback moth we released 5 000 O. sokolowskii thuringiensis was the least toxic to both adults and adults inside the cage for parasitism. At three and five pupae. This biological insecticide is frequently used days after parasite introduction, we collected 30 larvae to control diamondback moth. Abamectin, at present from each plot and reared them in the laboratory until the most popular chemical for the control of pupation. We recorded the number of O. sokolowskii diamondback moth, was relatively less toxic to both and diamondback moth pupae that developed and stages of O. sokolowskii. Cyromazine is frequently computed the percent parasitism. used for the control of leaf miner. This chemical is Parasitism varied between 18% and 54% in the relatively safer to O. sokolowskii adults but not to first observation (three days) and 30 and 50% in the

Biologically-based technologies 101 pupae. Mevinphos, an old broadspectum References organophosphorus insecticide, is at times still used for AVRDC. (1992). 1991 Progress Report. Asian Vegetable controlling diamondback moth. This chemical is highly Research and Development Center, Shanhua, Taiwan, toxic to the parasite, as is bifenthrin, a synthetic 410 pp. pyrethroid. Bennet, F. D. and Yaseen, M. (1972). Parasite introductions for the biological control of three insect pests in the Lesser Antilles and British Honduras. PANS. 18: 468Ð Control of diamondback moth by O. sokolowskii 474. Prior to the introduction of O. sokolowskii for the Carl, D. (1992). DBM control project in Togo, Benin and control of diamondback moth in farmers fields, we Cape Verde. IOBC global working group on biological conducted a study at AVRDC to investigate the control of Plutella, Newsletter 1991, 24 pp. potential of this parasite under field conditions. A Chelliah, S. and Srinivisan, K. (1986) Bio-ecology and parcel of land planted to common cabbage was divided management of diamondback moth in India, In into three 27 m by 13.5 m plots. Each area was Diamondback moth management: Proceedings of the subsequently confined on all four sides and the top by first international workshop (ed Talekar N. S. and Griggs, T. D.) pp. 63Ð76. Shanhua, Taiwan: Asian fine mesh nylon net to prevent movement of insects Vegetable Research and Development Center. between the plots. In two plots we introduced 1 000 Hirashima, Y., Abe, M., Tadauchi, O., Konishi, K., and diamondback moth adults each. The third plot was Maeto, K. (1989). The hymenopterous parasitoids of maintained insect free. One week later, in one of the the diamondback moth, Plutella xylostella two plots where the pest was introduced, we released (Lepidoptera, Yponomeutidae) in Japan. Esakia 28: 63Ð all O. sokolowskii adults emerging from 1 000 73. parasitized diamondback moth cocoons. Additional Keinmeesuke, P. (1992). Integrated pest management of 500 parasite cocoons were each released at two, three, diamondback moth on crucifers in Thailand. In and four weeks later. We monitored the extent of Collaborative Vegetable Research in Southeast Asia: Proceedings of the AVNET-I Final Workshop and diamondback moth parasitism throughout the season AVNET-II Joint Planning Meeting, pp 335Ð343. and determined yield and marketable cabbage heads Shanhua, Taiwan: Asian Vegetable Research and at harvest. Development Center. In the parasite-released cage, parasitism of the Lim, G. S. and Ko, W. W. (1975). Apanteles plutellae Kurdj., plutellid larvae by O. sokolowskii ranged from 1.28% a newly recorded parasite of Plutella xylostella (L.) in to 21.74%. Parasitism, which was very low, hovering Malaysia. MARDI Research Bulletin 3: 94Ð95. around 2% early in the season, increased to 21.74% Lima, M. L. L. and Van Harten, A. (1985). Biological control two weeks before harvest. Diamondback moth larval of crop pests in Cape Verde. Current situation and future population, which remained low (around 5 larvae/ programme. Rev. Invest. Agraria, Centro de Estudos Agrarios, A, No. 1: 3Ð12. (in French). plant) through most of the season increased to 22.4 Little, T. M. and Hills, F. J. (1975). Statistical methods in larvae per plant a week before harvest. We are unable agricultural research. DAVIS, University of California. to determine the reason for this sudden increase in Mustata, G. (1992). Role of parasitoid complex in limiting population. The rate of parasitism was obviously not the population of diamondback moth in Moldavia, adequate to prevent pest population build up. In the Romania. In Diamondback moth and other crucifer diamondback moth-only plot, the larval population pests: Proceedings of the second international workshop was high and reached 36.9 larvae/plant a week before (ed. Talekar, N. S. and Griggs, T. D.) pp. 203Ð211. harvest. In this plot, cabbage heads, on an average, Shanhua, Taiwan: Asian Vegetable Research and weighed 1.43 kg per head. The head weight increased Development Center. Talekar, N. S. and Yang, J. C. (1991). Characteristic of to 1.53 kg in the plot where both diamondback moth parasitism of diamondback moth by two larval and O. sokolowskii were released. In the control plot, parasites. Entomophaga. 36: 95Ð104. where no diamondback moth nor parasite was released, Talekar, N. S. (1996a). Role of biological control in IPM of each cabbage head weighed 1.62 kg. Only 26.1% of diamondback moth in Southeast Asia. Paper presented the heads were marketable in the diamondback moth- at the Workshop on Biological Control as a Cornerstone only plot; marketability increased to 44% in the of IPM for Sustainable Agriculture in Southeast Asia, parasite-released plot but it was below 76.1% Serdang, Malaysia (in Press). marketability of the control plot where no insects were Talekar, N. S. (1996b). Biological control of diamondback released. Cabbage yield was 6.84 t/ha in the only moth in Taiwan Ð a review. Plant Protection Bulletin (Taiwan), (in press) diamondback moth-plot; it increased to 12.81 t/ha due Velasco, L. R. I. (1983). Field parasitism of Apanteles to parasite introduction but it was still below the 21.44 plutellae Kurdj (Braconidae: Hymenoptera) on the t/ha obtained in the control plot. Marketable heads, diamondback moth on cabbage. Philippine rather than head weight, contributed to increased yield. Entomologist 6: 539Ð553. Introduction of O. sokolowskii to control diamondback Wakisaka, S., Tsukuda, R. and Nakasuji, F. (1991). Life moth increased head weight, marketable heads, and tables of diamondback moth, Plutella xylostella (L.) practically doubled the yield of cabbage. These data (Lepidoptera: Yponomeutidae) and effects of rainfall indicate the merits of introduction of O. sokolowskii temperature and host plants on survival and to control diamondback moth to increase cabbage reproduction. Japanese Journal of Applied Entomology and Zoology 35: 115Ð122. yield.

102 Proceedings: The Management of Diamondback Moth and Other Crucifer Pests Wu, K. C. (1968). Bionomic study of Plutella maculipennis Curtis. Journal of Taiwan Agricultural Research 17: 51Ð63. Yang, J. C., Chu, Y. I. and Talekar, N. S. (1994) . Studies on the characteristics of parasitism of Plutella xylostella (Lep.: Plutellidae) by a larval parasite Diadegma semiclausum (Hym.: Ichneumonidae). Entomophaga 39: 397Ð406. Yaseen, M. (1978). The establishment of two parasites of the diamondback moth, Plutella xylostella (Lepidoptera, Plutellidae) in Trinidad, W. I. Entomophaga 23: 111Ð114.

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