Effects of Bt-toxin Cry1Ac on Propylaea japonica Thunberg (Col., Coccinellidae) by feeding on Bt-treated Bt-resistant Helicoverpa armigera (Hübner) (Lep., Noctuidae) larvae

Abstract:  Propylaea japonica is an important predatory insect of common cotton pests. To assess the ecological effects of transgenic Bt cotton, expressing Cry1Ac toxin, on this predator, we examined the life history parameters of P. japonica for two generations by feeding them with Bt-resistant Helicoverpa armigera . After ingesting Bt-treated Bt-resistant H. armigera larvae in the third and fourth instar, the body mass and body length of adult P. japonica decreased, a combined effect of poor prey quality and Cry1Ac Bt-toxin may account for these effects. However, larval survivorship and development in these two instars, pupal mortality, fecundity and adult longevity of P. japonica were not affected in both the generations. These results suggest that ingesting Bt-toxin Cry1Ac-treated pests in advanced larval stage might have no significant effect on the fitness of predator P. japonica .     

Effects of transgenic Cry1A＋CpTI cotton and Cry1Ac toxin on the parasitoid, Campoketis chlorideae （Hymenoptera：Ichneumonidae）

Abstract The effect of transgenic double genes, Cry1A + CpTI cotton and Cry1Ac toxin on the parasitoid, Campoketis chlorideae Uchida of cotton bollworm, Helicoverpa armigera (Hübner), was investigated in the laboratory. Helicoverpa armigera larvae when in the first, second and third instar could not survive if fed on transgenic cotton leaves. Consequently, C. chlorideae larvae could not complete their development if parasitizing on such hosts. After H. armigera larvae were reared on transgenic or traditional cotton leaves for 12J48 hours, they were parasitized by C. chlorideae females. Parasitized larvae continued to feed on transgenic or traditional cotton for 12–48 h. The present results showed that the body weight of larvae of the parasitoids were significantly reduced when parasitized hosts fed on transgenic cotton leaves compared to those fed on traditional cotton. Duration of egg and larvae stage were significantly prolonged, pupal and adult weight of C. chloridae was decreased when the host larvae fed on transgenic cotton leaves longer than 48 h. The development duration of C. chlorideae pupae on the hosts fed on transgenic cotton leaves in each treatment was not significantly different from those of controls. The longevity of parasitoid females and males fed with a solution containing Cry1Ac toxin was not significantly different with that of the control.     

Survival and development of Campoletis chlorideae on various insect and crop hosts: implications for Bt-transgenic crops

Abstract:  The parasitic wasp, Campoletis chlorideae is an important larval parasitoid of Helicoverpa armigera a serious pest of cotton, grain legumes and cereals. Large-scale deployment of Bt -transgenic crops with resistance to H. armigera may have potential consequences for the development and survival of C. chlorideae . Therefore, we studied the tritrophic interactions of C. chlorideae involving eight insect host species and six host crops under laboratory conditions. The recovery of H. armigera larvae following release was greater on pigeonpea and chickpea when compared with cotton, groundnut and pearl millet. The parasitism by C. chlorideae females was least with reduction in cocoon formation and adult emergence on H. armigera larvae released on chickpea. Host insects also had significant effect on the development and survival of C. chlorideae . The larval period of C. chlorideae was prolonged by 2–3 days on Spodoptera exigua , Mythimna separata and Achaea janata when compared with H. armigera , Helicoverpa assulta and Spodoptera litura . Maximum cocoon formation and adult emergence were recorded on H. armigera (82.4% and 70.5%, respectively) than on other insect hosts. These studies have important implications on development and survival of C. chlorideae on alternate insect hosts on non-transgenic crop plants, when there is paucity of H. armigera larvae on transgenic crops expressing Bt -toxins.     

Effect of Bt broccoli and resistant genotype of Plutella xylostella (Lepidoptera: Plutellidae) on life history and prey acceptance of the predator Coleomegilla maculata (Coleoptera: Coccinellidae)

The ecological implications on biological control of insecticidal transgenic plants, which produce crystal (Cry) proteins derived from the soil bacterium Bacillus thuringiensis (Bt), remains a contentious issue and affects risk assessment decisions. In this study, we used a unique system of resistant insects, Bt plants and a predator to critically evaluate this issue. The effects of broccoli type (normal or expressing Cry1Ac protein) and insect genotype (susceptible or Cry1Ac-resistant) of Plutella xylostella L. (Lepidoptera: Plutellidae) were examined for their effects on the life history of the predator, Coleomegilla maculata DeGeer (Coleoptera: Coccinellidae) over two generations. Additional behavioral studies were conducted on prey choice. C. maculata could not discriminate between Bt-resistant and susceptible genotypes of P. xylostella, nor between Bt and normal broccoli plants with resistant genotypes of P. xylostella feeding on them. The larval and pupal period, adult weight and fecundity of each female were not significantly different when C. maculata larvae fed on different genotypes (Bt-resistant or susceptible) of insect prey larvae reared on Bt or non-Bt broccoli plants. The life-history parameters of the subsequent generation of C. maculata fed on Bt broccoli-reared resistant P. xylostella were also not significantly different from those on non-Bt broccoli. These results indicated that Cry1Ac did not harm the life history or prey acceptance of an important predator after two generations of exposure. Plants expressing Cry1Ac are unlikely to affect this important predator in the field.     

Effects of Bt plants on the development and survival of the parasitoid Cotesia plutellae (Hymenoptera: Braconidae) in susceptible and Bt-resistant larvae of the diamondback moth, Plutella xylostella (Lepidoptera: Plutellidae)

A range of crops have been transformed with delta-endotoxin genes from Bacillus thuringiensis (Bt) to produce transgenic plants with high levels of resistance to lepidopteran pests. Parasitoids are important natural enemies of lepidopteran larvae and the effects of Bt plants on these non-target insects have to be investigated to avoid unnecessary disruption of biological control. This study investigated the effects of Cry1Ac-expressing transgenic oilseed rape (Brassica napus) on the solitary braconid endoparasitoid Cotesia plutellae in small-scale laboratory experiments. C. plutellae is an important natural enemy of the diamondback moth (Plutella xylostella), the most important pest of brassica crops world-wide. Bt oilseed rape caused 100% mortality of a Bt-susceptible P. xylostella strain but no mortality of the Bt-resistant P. xylostella strain NO-QA. C. plutellae eggs laid in Bt-susceptible hosts feeding on Bt leaves hatched but premature host mortality did not allow C. plutellae larvae to complete their development. In contrast, C. plutellae developed to maturity in Bt-resistant hosts fed on Bt oilseed rape leaves and there was no effect of Bt plants on percentage parasitism, time to emergence from hosts, time to adult emergence and percentage adult emergence from cocoons. Weights of female progeny after development in Bt-resistant hosts did not differ between plant types but male progeny was significantly heavier on wildtype plants in one of two experiments. The proportion of female progeny was significantly higher on Bt plants in the first experiment with Bt-resistant hosts but this effect was not observed again when the experiment was repeated.     

Effectiveness of Bacillus thuringiensis-transgenic chickpeas and the entomopathogenic fungus Metarhizium anisopliae in controlling Helicoverpa armigera (Lepidoptera: Noctuidae)

The use of genetically modified (Bt) crops expressing lepidopteran-specific Cry proteins derived from the soil bacterium Bacillus thuringiensis is an effective method to control the polyphagous pest Helicoverpa armigera. As H. armigera potentially develops resistance to Cry proteins, Bt crops should be regarded as one tool in integrated pest management. Therefore, they should be compatible with biological control. Bioassays were conducted to understand the interactions between a Cry2Aa-expressing chickpea line, either a susceptible or a Cry2A-resistant H. armigera strain, and the entomopathogenic fungus Metarhizium anisopliae. In a first concentration-response assay, Cry2A-resistant larvae were more tolerant of M. anisopliae than susceptible larvae, while in a second bioassay, the fungus caused similar mortalities in the two strains fed control chickpea leaves. Thus, resistance to Cry2A did not cause any fitness costs that became visible as increased susceptibility to the fungus. On Bt chickpea leaves, susceptible H. armigera larvae were more sensitive to M. anisopliae than on control leaves. It appeared that sublethal damage induced by the B. thuringiensis toxin enhanced the effectiveness of M. anisopliae. For Cry2A-resistant larvae, the mortalities caused by the fungus were similar when they were fed either food source. To examine which strain would be more likely to be exposed to the fungus, their movements on control and Bt chickpea plants were compared. Movement did not appear to differ among larvae on Bt or conventional chickpeas, as indicated by the number of leaflets damaged per leaf. The findings suggest that Bt chickpeas and M. anisopliae are compatible to control H. armigera.     

转Bt棉花对蜘蛛生长发育及捕食行为的影响

室内评价了取食转Bt棉叶的棉铃虫幼虫对草间钻头蛛和八斑鞘腹蛛生长发育的影响.并通过捕食功能反应评价了取食了Bt棉叶的棉铃虫幼虫对成熟草间钻头蛛捕食行为的影响.室内饲养实验结果表明草间钻头蛛、八斑鞘腹蛛取食用转Bt棉叶处理的棉铃虫幼虫与取食普通棉叶处理的棉铃虫幼虫的发育历期、成蛛体重都没有显著差异.捕食功能反应实验结果表明草间钻头蛛对棉铃虫幼虫的捕食功能反应符合HollingⅡ型圆盘方程,两组不同猎物饲养成熟的草间钻头蛛对同种处理的棉铃虫幼虫的捕食行为没有显著差异.综合考虑：转Bt棉对蜘蛛生长发育、捕食能力没有显著的负作用.     

Impact of single-gene and dual-gene Bt broccoli on the herbivore <Emphasis Type="Italic">Pieris rapae</Emphasis> (Lepidoptera: Pieridae) and its pupal endoparasitoid <Emphasis Type="Italic">Pteromalus puparum</Emphasis> (Hymenoptera: Pteromalidae)

Transgenic brassica crops producing insecticidal proteins from Bacillus thuringiensis (Bt) are being investigated as candidates for field release to control lepidopteran pests. Information on the potential impact of Bt brassica crops on pests and non-target natural enemies is needed as part of an environmental risk assessment prior to the commercial release. This first tier study provides insight into the tritrophic interactions among Bt broccoli plants, the herbivore Pieris rapae and its parasitoid Pteromalus puparum. We first evaluated the efficacy of three types of Bt broccoli plants, cry1Ac, cry1C and cry1Ac + cry1C, on different instars of P. rapae. Bt broccoli effectively controlled P. rapae larvae, although later instars were more tolerant. The efficacy of different Bt broccoli plants on P. rapae larvae was consistently cry1Ac > cry1Ac + cry1C > cry1C. When the parasitoid P. puparum developed in a P. rapae pupa (host) that had developed from Bt plant-fed older larvae, developmental time, total number and longevity of the P. puparum generated from the Bt plant-fed host were significantly affected compared with those generated from the non-Bt control plant-fed host. Simultaneously, negative effects on P. rapae pupae were found, i.e. pupal length, width and weight were significantly reduced after older P. rapae larvae fed on different Bt plants for 1 or 2 days. Cry1C toxin was detected using ELISA in P. rapae pupae after older larvae fed on cry1C broccoli. However, no Cry1C toxin was detected in newly emerged P. puparum adults developing in Bt-fed hosts. Only a trace amount of toxin was detected from entire P. puparum pupae dissected from the Bt plant-fed host. Moreover, no negative effect was found on the progeny of P. puparum developing from the Bt plant-fed host when subsequently supplied with a healthy host, P. rapae pupae. The reduced quality of the host appears to be the only reason for the observed deleterious effects on P. puparum. Our data suggest that the effects on P. puparum developing in Bt plant-fed P. rapae are mediated by host quality rather than by direct toxicity.     

Effect of Bt broccoli and resistant genotype of <Emphasis Type="Italic">Plutella xylostella</Emphasis> (Lepidoptera: Plutellidae) on development and host acceptance of the parasitoid <Emphasis Type="Italic">Diadegma insulare</Emphasis> (Hymenoptera: Ichneumonidae)

The ecological implications on biological control of insecticidal transgenic plants, which produce crystal (Cry) proteins from the soil bacterium Bacillus thuringiensis (Bt), remain a contentious issue and affect risk assessment decisions. In this study, we used a unique system of resistant insects, Bt plants and a parasitoid to critically evaluate this issue. The effects of broccoli type (normal or expressing Cry1Ac protein) and insect genotype (susceptible or Cry1Ac-resistant) of Plutella xylostella L. (Lepidoptera: Plutellidae) were examined for their effects on the development and host foraging behavior of the parasitoid, Diadegma insulare (Cresson) (Hymenoptera: Ichneumonidae) over two generations. Parasitism rate and development of D. insulare were not significantly different when different genotypes (Bt-resistant or susceptible) of insect host larvae fed on non-Bt broccoli plants. D. insulare could not discriminate between resistant and susceptible genotypes of P. xylostella, nor between Bt and normal broccoli plants with different genotypes of P. xylostella feeding on them. No D. insulare could emerge from Bt broccoli-fed susceptible and heterozygous P. xylostella larvae because these larvae were unable to survive on Bt broccoli. The parasitism rate, developmental period, pupal and adult weights of D. insulare that had developed on Bt broccoli-fed Cry1Ac-resistant P. xylostella larvae were not significantly different from those that developed on non-Bt broccoli-fed larvae. Female D. insulare emerged from Cry1Ac-resistant P. xylostella that fed on Bt plants could successfully parasitize P. xylostella larvae. The life parameters of the subsequent generation of D. insulare from P. xylostella reared on Bt broccoli were not significantly different from those from non-Bt broccoli. The Cry1Ac protein was detected in P. xylostella and in D. insulare when hosts fed on Bt broccoli. These results are the first to indicate that Cry1Ac did not harm the development or host acceptance of an important endoparasitoid after two generations of exposure. We suggest that using other Bt crops and resistant insect species would likely lead to similar conclusions about the safety of the presently used Bt proteins on parasitoids.     

Tritrophic Choice Experiments with Bt Plants,the Diamondback Moth (Plutella xylostella) and the parasitoid Cotesia plutellae

Parasitoids are important natural enemies of many pest species and are used extensively in biological and integrated control programmes. Crop plants transformed to express toxin genes derived from Bacillus thuringiensis (Bt) provide high levels of resistance to certain pest species, which is likely to have consequent effects on parasitoids specialising on such pests. A better understanding of the interaction between transgenic plants, pests and parasitoids is important to limit disruption of biological control and to provide background knowledge essential for implementing measures for the conservation of parasitoid populations. It is also essential for investigations into the potential role of parasitoids in delaying the build-up of Bt-resistant pest populations. The diamondback moth (Plutella xylostella), a major pest of brassica crops, is normally highly susceptible to a range of Bt toxins. However, extensive use of microbial Bt sprays has led to the selection of resistance to Bt toxins in P. xylostella. Cotesia plutellae is an important endoparasitoid of P. xylostella larvae. Although unable to survive in Bt-susceptible P. xylostella larvae on highly resistant Bt oilseed rape plants due to premature host mortality, C. plutellae is able to complete its larval development in Bt-resistant P. xylostella larvae. Experiments of parasitoid flight and foraging behaviour presented in this paper showed that adult C. plutellae females do not distinguish between Bt and wildtype oilseed rape plants, and are more attracted to Bt plants damaged by Bt-resistant hosts than by susceptible hosts. This stronger attraction to Bt plants damaged by resistant hosts was due to more extensive feeding damage. Population scale experiments with mixtures of Bt and wildtype plants demonstrated that the parasitoid is as effective in controlling Bt-resistant P. xylostella larvae on Bt plants as on wildtype plants. In these experiments equal or higher numbers of parasitoid adults emerged per transgenic as per wildtype plant. The implications for integrated pest management and the evolution of resistance to Bt in P. xylostella are discussed.     

Tri-trophic interactions between Bt cotton, the herbivore Aphis gossypii Glover (Homoptera: Aphididae), and the predator Chrysopa pallens (Rambur) (Neuroptera: Chrysopidae)

Tri-trophic impacts of transgenic Bacillus thuringiensis (Bt) cotton GK12 and NuCOTN 99B were studied using a predator, the great lacewing Chrysopa pallens (Rambur), and its prey, the cotton aphid Aphis gossypii Glover, in laboratory feeding experiments. The parental nontransgenic cotton cultivar of GK12 was used as control. The predator was fed with uniform (aphids from a single cultivar) or mixed prey (aphids from the three cotton cultivars provided on alternate days). Mortality and development of the immature stages, pupal body mass, adult sex ratio, fecundity, and egg viability of C. pallens were measured. When fed GK12-originated aphid prey, pupal body mass of C. pallens was significantly higher than that of the control, more females emerged, and these females laid significantly more eggs. Other parameters were not impacted. Females emerging from larvae maintained on NuCOTN 99B-originated prey laid fewer eggs than those maintained on GK12. Other measurements did not differ significantly between the two Bt cotton cultivars. Compared with the control, mixed feeding significantly prolonged pupal development time and increased pupal body mass and percentage of females but did not affect other parameters. These results indicate that C. pallens is sensitive to aphid prey from different cotton cultivars. Transgenic Bt cotton GK12-originated aphid prey has no adverse impact on survival, development, and fecundity of C. pallens. Between the two Bt cotton cultivars, NuCOTN 99B-originated aphid prey provided to C. pallens in the larval stage may lower female fecundity. Mixed feeding of C. pallens with the two Bt cotton-originated prey and non-Bt prey may have some adverse impacts on pupal development.     

棉酚对棉铃虫生长及其寄生物齿唇姬蜂发育的影响(英文)

以中国北方棉区的主要害虫棉铃虫Helicoverpaarmigera（Hbner）及其内寄生蜂棉铃虫齿唇姬蜂Campoletischlorideae（Uchida）为试虫,研究了棉花重要抗虫次生性物质棉酚对棉铃虫生长和齿唇姬蜂发育的影响。0．1％的棉酚对棉铃虫幼虫有生长刺激作用,0．5％的棉酚则对棉铃虫幼虫生长有抑制作用。齿唇姬蜂成虫在寄生时对寄主大小有较严格的选择性,92％的被寄生幼虫体重小于18mg。0．1％的棉酚使寄主适合寄生期缩短10．75％;0．5％棉酚使寄主适合寄生期延长28．15％。棉酚对齿唇姬蜂发育有负效应。0．1％棉酚对寄主的生长刺激作用,不能使蜂成虫体重显著增加,但可显著延长蜂卵和幼虫期,缩短蛹期;高浓度的生长抑制作用,导致蜂成虫体重显著减轻,蛹期缩短,蜂卵和幼虫期亦显著延长。据此,对棉花抗虫性与生物防治在害虫综合防治实践中应用的协调性进行了讨论。     

Processing of the maize Bt toxin in the gut of Mythimna unipuncta caterpillars

Mythimna unipuncta Haworth (Lepidoptera: Noctuidae) is a well‐known moth species whose larvae can cause devastating damage to some Poaceae crops, including maize (Zea mays L.). The low susceptibility to the Bacillus thuringiensis Berliner (Bt) toxin observed in L6 larvae of this species has been the object of several studies. This study aimed to clarify whether the toxin eliminated from the content of the peritrophic membrane is degraded or excreted and whether the effects of the Bt toxin depend on the doses ingested. To this end, L6 larvae were fed on diets with different amounts of lyophilized Bt or non‐Bt maize leaves. The effect of the Bt concentrations on larval development was measured and the fate of the toxin in the larval tissues was tracked. Results indicated that the larvae of M. unipuncta fed on the various diets showed few differences in weight gain, duration of development, or pupal weight between sublethal Bt concentrations. The larvae rapidly excreted a large part of the toxin ingested, whereas inside the peritrophic membrane the toxin was eliminated, degraded, or sequestered at a rate that increased with the dose and the duration of feeding. As a consequence, little toxin reached the midgut epithelium and therefore the binding sites of the toxin. Moreover, larvae fed on the Bt toxin recovered quickly when they were transferred to a non‐Bt diet.     

Effect of pyramiding Bt and CpTI genes on resistance of cotton to Helicoverpa armigera (Lepidoptera: Noctuidae) under laboratory and field conditions

Transgenic cotton (Cossypium hirsutum L.) varieties, adapted to China, have been bred that express two genes for resistance to insects, the CrylAc gene from Bacillus thuringiensis (Berliner) (Bt), and a trypsin inhibitor gene from cowpea (CpTI). Effectiveness of the double gene modification in conferring resistance to cotton bollworm, Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae), was studied in laboratory and field experiments. In each experiment, performance of Bt+CpTI cotton was compared with Bt cotton and to a conventional nontransgenic variety. Larval survival was lower on both types of transgenic variety, compared with the conventional cotton. Survival of first-, second-, and third-stage larvae was lower on Bt+CpTI cotton than on Bt cotton. Plant structures differed in level of resistance, and these differences were similar on Bt and Bt + CpTI cotton. Likewise, seasonal trends in level of resistance in different plant structures were similar in Bt and Bt+CpTI cotton. Both types of transgenic cotton interfered with development of sixth-stage larvae to adults, and no offspring was produced by H. armigera that fed on Bt or Bt+CpTI cotton from the sixth stage onward. First-, second-, and third-stage larvae spent significantly less time feeding on transgenic cotton than on conventional cotton, and the reduction in feeding time was significantly greater on Bt+CpTI cotton than on Bt cotton. Food conversion efficiency was lower on transgenic varieties than on conventional cotton, but there was no significant difference between Bt and Bt+CpTI cotton. In 3-yr field experimentation, bollworm densities were greatly suppressed on transgenic as compared with conventional cotton, but no significant differences between Bt and Bt+CpTI cotton were found. Overall, the results from laboratory work indicate that introduction of the CpTI gene in Bt cotton raises some components of resistance in cotton against H. armigera, but enhanced control of H. armigera under field conditions, due to expression of the CpTI gene, was not demonstrated.     

寄生取食Cry1Ab杀虫蛋白的粘虫幼虫对伞裙追寄蝇寄生率及生长发育的影响

【Aim】 To demonstrate the effect of transgenic Bt-crop on the bionomics of the tachinid fly Exorista civilis Rondani, the parasitism rate and life history parameters of E. civilis developed from larvae of the oriental armyworm, Mythimna separata (Walker), fed on artificial diets with Cry1Ab toxin were investigated in laboratory. 【Methods】 M. separata larvae were fed on diets containing 0, 3.125, 6.25, 12.5 and 25 μg/g of Cry1Ab toxin, respectively, and used as the host for E. civilis. The parameters related to the parasitism and the growth and development of E. civilis on the host were observed and recorded. 【Results】 The results showed that the parasitism rate and fecundity of the fly on M. separata larvae feeding on diets containing various doses of Cry1Ab protein were insignificantly different (P≥0.05), suggesting that host selective behavior of the E. civilis is not affected by the dose of Bt-toxin in the caterpillar. The developmental period (egg-larva, pupa, adult oviposition and generation), emergence rate, sex ratio, and fecundity of E. civilis developed from M. separata larvae treated by various concentrations of Cry1Ab toxin were insignificantly different (P≥0.05). However, the survival rate of the maggots in the host feeding on diet containing 3.125 μg/g of Cry1Ab toxin was significantly greater than that of the control and the rest treatments (P<0.05), while insignificantly different among the remained 4 treatments (P≥0.05). The pupal weight significantly declined as the concentration of Cry1Ab toxin fed by their hosts increased (P<0.05). The pupal weight in the control group was 49.8 mg, while that in treatment groups of 6.25 and 25 μg/g Cry1Ab toxin was only 41.0 and 36.7 mg, respectively. 【Conclusion】 These results indicate that parasitizing host M. separata larvae fed with Cry1Ab toxin has no dramatically negative effect on parasitoid E. civilis. This study provides a basis for the evaluation of the risk of transgenic Bt-crops on the tachinid parasitoids in fields.     

转基因棉花对棉铃虫天敌寄生率的影响

采用分期接虫、分期回收法研究常规棉与转基因棉花品种 (系 )上棉铃虫寄生性天敌在不同棉花品种上的寄生作用。结果表明 ,无论是第 2代棉铃虫发生期间还是第 3 ,4代棉铃虫发生期间 ,无论是棉铃虫卵期还是幼虫期 ,转基因棉花品种 (系 )的棉铃虫卵、幼虫寄生率均显著低于常规棉花品种上的寄生率。棉铃虫卵期寄生蜂主要是拟澳洲赤眼蜂 ,幼虫寄生蜂为棉铃虫齿唇姬蜂等。由此看出转基因棉对棉铃虫寄生性天敌存在非亲和性。     

Effect of mating and parasitism regimes on progeny production and sex-ratio of Campoletis chlorideae Uchida

The ichneumonid parasitoid, C. chlorideae is an important natural enemy of pod borer/bollworm, Helicoverpa armigera (Hubner) in different agro-ecosystems. The sex-ratio of parasitoids has an important bearing on the population build up of the natural enemies for biological control of insect pests. Therefore, the present studies were conducted to gain an understanding of the influence of mating behaviour and abundance of the insect host on fecundity and sex-ratio of the parasitoid, C. chlorideae. There was no significant influence of number of matings and abundance of the insect host on cocoon formation, adult emergence, and larval and pupal periods of C. chlorideae. However, fecundity and female longevity were significantly influenced by mating and abundance of the insect host. There was a significant and positive correlation (r = 0.84**) between longevity and fecundity of C. chlorideae females. The unmated C. chlorideae females produced only males. Nearly 20% of the females that had mated twice were able to parasitize the H. armigera larvae successfully. The sex-ratio of the progeny from females that had mated twice was male biased. Females mated with males from the unmated females produced significantly less numbers of females than those mated with males from the fertilized females, indicating genetic regulation of sex-ratio in C. chlorideae.     

Effect of corn hybrids expressing the coleopteran-specific cry3Bb1 protein for corn rootworm control on aboveground insect predators

Field and laboratory studies were conducted to determine the effect of transgenic Bacillus thuringiensis (Bt) corn, Zea mays L. (YieldGard Rootworm), expressing the Cry3Bb1 protein on aboveground nontarget insect predators (minute pirate bug, ladybird beetles, and carabids). Visual counts of adult and immature Orius insidiosus (Say), Coleomegilla maculata (DeGeer), Hippodamia convergens Gurin-Meneville, and Scymnus spp. occurring in Bt corn and its non-Bt isoline were made at Manhattan, KS, in 2002 and at Manhattan and Scandia, KS, in 2003. No significant differences were found between the Bt corn and non-Bt isoline plots in the abundance (number per plant) of O. insidiosus, C. maculata, H. convergens, and Scymnus spp. Field predation on Ostrinia nubilalis (Hübner) (Lepidoptera: Crambidae) egg masses was also observed during the silking stage of corn at Manhattan and Scandia in 2003. No significant differences were observed among treatments in predation rate for predators with chewing versus sucking mouthparts. Two laboratory studies determined the effect of Cry3Bb1 protein expressed in Bt corn pollen on C. maculata and carabids. The larvae of C. maculata were reared on Bt pollen, non-Bt pollen, or greenbugs, Schizaphis graminum (Rondani). The duration of larval and pupal stages, developmental time from egg hatch to adult emergence, percentage of survival, and elytra length were compared among treatments. There were no significant differences in developmental time of larvae fed pollen or greenbugs during their first two instars. However, significantly prolonged development of the third (1 d) and fourth instars (2 d) was observed for larvae fed greenbugs only. Total time for larval development was significantly longer for larvae that fed on greenbugs versus larvae fed on pollen. No significant differences were observed among treatments in the percentage of larvae that pupated or pupal stage duration. Larvae that fed on greenbugs had higher pupal and adult weights compared with pollen-fed larvae. However, pupal and adult weights did not vary between the Bt and non-Bt pollen treatments. No significant differences occurred in longevity and elytra length of beetles among all treatments. Two carabid species, Harpalus caliginosus F. and Harpalus pensylvanicus DeGeer, were reared on moistened dog food sprinkled with Bt or non-Bt corn pollen. No significant differences in mortality of H. caliginosus and H. pensylvanicus were detected among any of the treatments. There was no significant effect of Bt pollen on fecundity and egg viability of H. caliginosus. Our studies showed that YieldGard Rootworm had no effect on the selected coleopteran predators; therefore, this Bt corn hybrid could be used in an integrated pest management system.     

Fitness costs of resistance to Bacillus thuringiensis in the Indianmeal moth, Plodia interpunctella

Genetic changes in insects that result in insecticide resistance can also affect their fitness. Here, we report measurements of development time and survival of the Indianmeal moth, Plodia interpunctella (Hübner), to compare the relative fitness of Bacillus thuringiensis (Bt)-susceptible and -resistant colonies. Measurements of larval development time and survival indicated that a fitness cost was associated with resistance to Bt in some Bt-resistant colonies but not others. Comparisons of geographically different populations revealed inherent differences in development time and survival. In most cases, Bt-resistant moths suffered no disadvantage when feeding on a Bt-treated diet. In many cases, the development of Bt-resistant moths on Bt-treated diet was slower than the unselected moths on untreated diet, but it is unclear whether these differences would affect the successful mating of susceptible and resistant moths.     

The interactions between soybean trypsin inhibitor and delta-endotoxin of Bacillus thuringiensis in Helicoverpa armigera larva

No significant difference in larval mortality was observed when a sublethal dose of Bacillus thuringiensis (Bt) var. kurstaki HD-1 crystal was supplemented with soybean trypsin inhibitor (STI) in the artificial diet fed to Helicoverpa armigera in the laboratory, but supplementing a nonlethal dose of crystal with STI in the diet led to a pronounced reduction of larval growth. This concentration of crystal and two lower concentrations of STI alone had no significant effects on larval growth. The results of substrate-gel electrophoresis demonstrated that the proteases in the H. armigera midgut fluid responsible for the degradation of protoxin consisted of at least four proteases with molecular weights of 71, 49, 36, and 30 kDa. All four proteases could utilize casein also as the substrate. When larvae were fed with STI or Bt + STI, the proteolytic activities of the 49-kDa enzyme disappeared, and the activities of the other three enzymes were reduced. Enzyme assays also indicated that feeding larvae with diets containing Bt, STI, or Bt + STI significantly decreased the specific activities of larval general proteases and the trypsin-like enzyme. The protein concentration of midgut fluid was elevated, especially in the larvae fed on the diets containing STI and Bt + STI. Both in vitro and in vivo studies showed that the degradation of protoxin and toxin could be inhibited by soybean trypsin inhibitors, but when the incubation time was prolonged, the protoxin could be degraded completely, while the degradation of toxin was inhibited further. This suggested that the retention time of toxins in the larval midgut was extended and synergism between insecticidal crystal protein and soybean trypsin inhibitor occurred, which showed as the inhibition of H. armigera larval growth.