Effects of putrescine on diapause induction and intensity,and post‐diapause development of Helicoverpa armigera

Effects of putrescine on diapause induction and intensity, and post‐diapause development in Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) from Wuhan, Hubei, China were studied in the laboratory at different temperatures and photoperiod conditions. The results showed a generally higher incidence of diapause in putrescine‐feeding groups. Putrescine feeding distinctly restricted the development of non‐diapause‐destined and diapause‐destined larvae, except at 0.01% putrescine concentration, which accelerated the development of larvae at 21 °C. Putrescine had no significant effect on the duration of diapause, although it inhibited the post‐diapause development of pupae. Photoperiod played a different role in diapause induction and post‐diapause development between 21 and 23 °C. Putrescine played a definite role in diapause induction and intensity, and post‐diapause development in H. armigera, and a significant interaction between putrescine, photophase, and temperature is to be expected.     

Fitness costs of sublethal exposure to Bacillus thuringiensis in Helicoverpa armigera: a carryover study on offspring

Bacillus thuringiensis (Bt) is an efficient entomopathogen used for pest control. While Bt pathogenesis has been thoroughly studied, less is known about the biological effects of sublethal Bt exposure. To address this knowledge gap, we document sublethal effects of Bacillus thuringiensis var. kurstaki (Btk) on the biology and development of Helicoverpa armigera (Hübner) under laboratory conditions. The results obtained revealed that duration of the different life stages in treated neonates of H. armigera was significantly affected by sublethal treatments. Furthermore, fecundity was also negatively affected in female moths developed from Btk‐treated neonates, with the rate of egg hatchability reaching zero in the LC₂₅. We also present data supporting that the effect of sublethal Btk concentrations could carry over to the next generation. Sublethal Btk concentrations reduced the net reproduction rate (R₀), and there were also significant differences among the values of this parameter at all treatments tested when compared with controls. The intrinsic and finite rates of increase (r_m and λ, respectively) were significantly lower in insects treated with sublethal Btk concentrations compared with control insects. Consequent with the reduce rate of development observed for H. armigera treated with Btk, the mean generation time (T) and doubling time (DT) were significantly higher in insects exposed to any Btk concentration tested compared with control. Our data demonstrate significant fitness costs resulting from sublethal Btk exposure in H. armigera. These observations underline the importance of considering the role of sublethal effects when attempting to evaluate the impact of Bt treatment on an insect pest population and its progeny.     

Geographic variation in diapause induction under constant and changing conditions in Helicoverpa armigera

Variation in the incidence of diapause in local populations of Helicoverpa armigera (Hübner) and Helicoverpa assulta (Guenée) (Lepidoptera: Noctuidae) was examined in relation to changes in photoperiod and/or temperature during the larval period. Temperate zone populations of H. assulta, a native species in temperate Japan, showed a high incidence of diapause induction when only the photoperiod was decreased during the larval period, even at favorable temperatures. This photoperiod‐dependent response may allow H. assulta to foresee the beginning of autumn well in advance in the temperate zone, where temperature conditions are severe. In contrast, temperate zone populations of H. armigera, an invasive and polyphagous species mainly distributed in the subtropics, showed a high incidence of diapause only when both photoperiod and temperature decreased, whereas subtropical populations showed a very low incidence of diapause under the same conditions. Furthermore, both temperate zone and subtropical populations of H. armigera enter diapause under constant low temperatures at short‐day photoperiod. Thus, there is geographic variation in sensitivity to diapause‐inducing stimuli (changes in photoperiod and temperature) in H. armigera. This variation may be a part of the climatic adaptation achieved by H. armigera in Japan.     

核型多角体病毒感染对棉铃虫幼虫同类相残行为的影响

在室内研究核型多角体病毒（HaSNPV）感染对棉铃虫Helicoverpa armigera（Htibner）幼虫同类相残行为的影响。结果显示：感病棉铃虫随感病程度的加重,越容易被健康棉铃虫残食,而自然死亡的感病棉铃虫、冻死的感病棉铃虫和冻死的健康棉铃虫三者被健康棉铃虫残食的百分率无显著差异。表明感病棉铃虫和病虫尸体更易于被健康棉铃虫残食,是由于棉铃虫体力减弱而失去反击能力,不是由于病毒本身的影响。以健康棉铃虫、感病棉铃虫为残食者,冻死的病虫为被残食者,相残率无显著差异,表明病毒并未改变棉铃虫残食同类的天性。残食病虫的健康棉铃虫的化蛹率和羽化率均低于正常的健康棉铃虫,残食者为相残行为付出了很高的代价。     

Inhibition of Helicoverpa armigera gut pro‐proteinase activation in response to synthetic protease inhibitors

Protease inhibitors play an important role in host plant defence against herbivores. However, insects have the ability to elevate the production of proteinases or resort to production of a diverse array of proteinases to offset the effect of proteinase inhibitors. Therefore, we studied the inhibition of pro‐proteinase(s) activation in the midgut of the polyphagous pest Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) in response to protease inhibitors to develop appropriate strategies for the control of this pest. Gelatin coating present on X‐ray film was used as a substrate to detect electrophoretically separated pro‐proteinases and proteinases of H. armigera gut extract on native‐ and sodium dodecyl sulphate‐polyacrylamide gel electrophoresis. Six activated pro‐proteinase bands were detected in H. armigera gut lumen, which were partially purified and characterized using substrate assays. Activated H. armigera midgut pro‐proteinase(s) showed activity maxima at pH 8 and 10, and exhibited optimal activity at 40 °C. The activation of H. armigera gut pro‐proteinase isoforms was observed in the fraction eluted on benzamidine‐sepharose 4B column. Purification and substrate assay studies revealed that 23–70 kDa polypeptides were likely the trypsin/chymotrypsin‐like pro‐proteinases. Larvae of H. armigera fed on a cocktail of synthetic inhibitors (antipain, aprotinin, leupeptin, and pefabloc) showed maximum activation of pro‐proteinases compared with the larvae fed on individual inhibitors. The implications of these results for developing plants expressing proteinase inhibitors for conferring resistance to H. armigera are discussed.     

Bt棉花对棉铃虫幼虫选择性行为的影响

利用“H”型嗅觉仪测定结果表明 :在棉花蕾期、花铃期 ,棉铃虫 2龄幼虫对常规棉的棉叶、嫩头的选择性明显高于转基因棉花品种 ,差异达显著或极显著水平。但 3龄幼虫对两者的选择性差异并不显著 ;而在棉花蕾期 ,果枝对棉铃虫 2龄幼虫选择性行为有一定的影响。试验初步说明Bt棉对棉铃虫低龄幼虫有一定的忌避作用 ,而对高龄幼虫忌避效应不显著。     

Influence of tannic acid and Cry1Ac toxin of Bacillus thuringiensis on larval survival, growth, and development of Helicoverpa armigera

Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) causes huge economic losses in cotton production around the world. Tannin, one of the important secondary substances in cotton plants, can increase the δ‐endotoxin activity of Bacillus thuringiensis ssp. kurstaki. The mechanism of interaction between tannin and Bt toxin on H. armigera is unclear. We investigated the interaction between tannic acid and Cry1Ac toxin in H. armigera, and monitored survival, growth, and development during the larval period after treating the larvae with four concentrations of Cry1Ac toxin (0, 2, 8, and 14 μg^?1) alone or in combination with four concentrations of tannic acid (0, 0.5, 1, and 2 mg g^?1). Mortality of larvae treated with both tannic acid and Cry1Ac was higher than the mortality of larvae treated with tannic acid or Cry1Ac alone. Mortality was 47.5 and 51.5% in larvae treated with 14 μg g^?1 Cry1Ac alone or 2 mg g^?1 tannic acid alone, respectively. In contrast, larval mortality was 75% when treated with the mixture of 14 μg g^?1 Cry1Ac and 2 mg g^?1 tannic acid, suggesting that a mixture of the two enhanced the effectiveness of each one alone. The developmental time of larvae treated with the combination of tannic acid and Cry1Ac was significantly longer than when they were treated with Cry1Ac or tannic acid alone. Larval weight, pupal weight, and pupation rate were also significantly reduced in larvae treated with both toxins, compared with the larvae treated with either toxin alone. These results showed that the interactive effect of tannic acid and Cry1Ac on larval growth inhibition is additive, and that tannic acid improves Cry1Ac toxicity to insects. Tannic acid used in combination with B. thuringiensis might potentially reduce overall insecticide use, thus delaying development of insecticide resistance.     

Depressed performance and detoxification enzyme activities of Helicoverpa armigera fed with conventional cotton foliage subjected to methyl jasmonate exposure

Methyl jasmonate (MeJA)‐mediated defense in conventional cotton, Gossypium hirsutum L. (Malvaceae), against cotton bollworm, Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae), was investigated with respect to the activities of the detoxification enzymes acetylcholinesterase (AChE), carboxylesterase (CarE), and glutathione S‐transferases (GST) in pupae as well as the performance of larvae. The results suggested that exogenous application of MeJA to cotton leaves depressed the activities of AChE, CarE, and GST of cotton bollworm pupae. Both the absolute and protein‐specific AChE activities of pupae were depressed at all three MeJA concentrations applied as compared with a control, and the effects of 0.4 mM MeJA were significantly higher than those of 0.1 and 0.2 mM. A marked reduction in absolute CarE activity was observed at the 0.4 mM MeJA treatment, whereas the protein‐specific activity was increased by 0.2 and 0.4 mM. Absolute GST activity was significantly depressed only by the 0.4 mM MeJA treatment, whereas protein‐specific GST activity was not markedly affected by MeJA. Protein content of pupae was reduced by 0.4 mM MeJA‐induced defense in cotton leaves. The development time of larvae was protracted and pupal weight was reduced by 0.1 and 0.4 mM MeJA‐treated cotton leaves. Larval weight gain was inhibited significantly on 0.2 and 0.4 mM MeJA‐treated cotton leaves. The results suggested that MeJA‐induced plant defense may have adverse effects on H. armigera. In addition to the inhibition of growth and development, induced defense may also impair the insect's ability to detoxify toxic plant secondary metabolites.     

棉铃虫温度依赖的生长发育及雌性先熟现象

在昆虫中,雄虫先于雌虫羽化,称为雄虫先熟现象,而雌虫先于雄虫羽化,称为雌虫先熟现象。前者最为普遍,后者报道较少。本试验在20、22和25℃下对棉铃虫Helicoverpa armigera（Hilbner）的生长发育进行了详细的研究。结果显示发育历期随温度的升高而缩短,雌雄间发育历期有着显著的差异,各个温度下雌虫均比雄虫先羽化,表明棉铃虫属于雌性先熟种类,而这种差异主要是由于雌虫的蛹期较短所致。幼虫发育历期与蛹重呈显著的正相关性。     

Host crop influence on the susceptibility of the American bollworm, Helicoverpa armigera, to Bacillus thuringiensis ssp. kurstaki HD-73

Studies on the susceptibility of F₁ neonates of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) collected from chickpea in Delhi and cotton in Punjab, Haryana and Rajasthan in northern India, to Bacillus thuringiensis ssp. kurstaki HD‐73, and the impact of host crop diets on insect susceptibility, were carried out by diet incorporation bioassays. The susceptibility of F₁ neonates of H. armigera to Bacillus thuringiensis ssp. kurstaki HD‐73 ranged from twofold (LC₅₀ 96 h, 84.5–164.2 µg (ai) l^?1) for chickpea to about fivefold (LC₅₀ 96 h, 51.1–247.7 µg (ai) l^?1) for cotton. The F₁ neonates of insects collected from pearl millet were twice as tolerant as those collected from cotton and sunflower at Sirsa to B. thuringiensis ssp. kurstaki HD‐73, suggesting that there was an influence of host crops on insect susceptibility. Insects originally collected from cotton fields at Bhatinda and reared for four generations on a chickpea‐based meridic diet were used to initiate host‐specific colonies of H. armigera. These host‐specific colonies were allowed to complete one generation on meridic diets prepared with different hosts, viz., cabbage, cauliflower, chickpea, green pea, pearl millet, and pigeon pea. Larvae of H. armigera were heaviest on the 15th day, and had a higher growth rate on a pigeon pea‐based diet than all other host diets. The larval period was shorter on chickpea and pigeon pea, with higher percentage pupation than all other host‐diets. The pupal weight of H. armigera was greater on chickpea and pigeon pea diets than on other host diets. The growth and development of larvae was significantly poorer on pearl millet diet than on other host diets. The F₁ neonates of H. armigera belonging to cabbage, cauliflower, and pearl millet host‐specific colonies were more susceptible than those belonging to chickpea, green pea, and pigeon pea host‐specific colonies to B. thuringiensis ssp. kurstaki HD‐73, suggesting the importance of proteinaceous nutrients in tolerance. The F₁ neonates of the pearl millet colony of H. armigera grown on a chickpea‐diet for 4 days were significantly more tolerant to B. thuringiensis ssp. kurstaki HD‐73 than those reared on the pearl millet‐based diet. These studies show the impact of the host diet of H. armigera on tolerance to B. thuringiensis.     

Survival of Helicoverpa armigera larvae on and Bt toxin expression in various parts of transgenic Bt cotton (Bollgard II) plants

There is no conclusive evidence that Helicoverpa spp. (Lepidoptera: Noctuidae) in Australia have evolved significant levels of resistance to Bollgard II^® cotton (which expresses two Bt toxin genes, cry1Ac and cry2Ab). However, there is evidence of surviving larvae on Bollgard II cotton in the field. The distribution and survival of early‐instar Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) larvae were examined on whole Bollgard II and non‐Bt cotton plants in greenhouse bioassays. The expression of Cry toxins in various parts of Bollgard II plants was compared to the survival of larvae in those locations. Only 1% of larvae survived after 6 days on greenhouse‐grown Bollgard II plants compared to 31% on non‐Bt cotton plants. Overall, and across all time intervals, more larvae survived on reproductive parts (squares, flowers, and bolls) than on vegetative parts (leaves, stems, and petioles) on Bollgard II plants. The concentration of Cry1Ac toxin did not differ between plant structures, whereas Cry2Ab toxin differed significantly, but there was no relationship between the level of expression and the location of larvae. This study provides no evidence that lower expression of Cry toxins in the reproductive parts of plants explains the survival of H. armigera larvae on Bollgard II cotton.     

棉铃虫成虫种群空间结构的研究

利用性诱捕器调查了棉铃虫越冬代至 3代棉铃虫成虫种群的种群密度 ,而后用 4种地统计模型拟合其种群的空间结构 ,并分析它们的空间关系 ,其结果如下 :( 1 )越冬代种群在全方位、90°及 1 3 5°方向上空间模型均为线型 ;在 0°及 4 5°方向上分别为球型和指数型 ,模型的参数表明越冬代成虫的空间相关距离为 6.0 1～ 8.0 1空间单位 (单位为 1 0 0 m,下同 ) ,异质系数为 54.60～ 83 .50 ,空间依赖度为 1 50 .0 0～ 1 80 .60。 ( 2 )一代种群在全方位、0°、4 5°、90°及 1 3 5°方向上的空间模型分别为线型、球型、线型、球型和球型 ;模型的种群参数表明一代成虫的空间异质系数是 53 6.0 0～ 588.1 0 ,相关距离为1 6.0 2～ 1 9.0 7空间单位 ,空间取样方差约是 2 60 0。 ( 3 )二代成虫在全方位、0°和 4 5°方向的空间模型均为指数型 ,在 90°及1 3 5°方向的模型均为球型 ;模型的参数表明二代成虫的空间异质系数为 5.56～ 2 5.93 ,空间取样方差是 53 .4 9～ 64 .96,相关距离为 4 .54～ 5.3 3空间单位。 ( 4)三代种群在全方位、0°、4 5°、90°及 1 3 5°方向的模型分别为指数型、球型、指数型、线型和指数型 ,模型的参数表明三代成虫的空间异质系数为 2 91 .93～ 4 93 .67,空间取样方差为 1 1 99.53～ 2     

Effects of single and mixed infections with wild type and genetically modified Helicoverpa armigera nucleopolyhedrovirus on movement behaviour of cotton bollworm larvae

Naturally occurring insect viruses can modify the behaviour of infected insects and thereby modulate virus transmission. Modifications of the virus genome could alter these behavioural effects. We studied the distance moved and the position of virus‐killed cadavers of fourth instars of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) infected with a wild‐type genotype of H. armigera nucleopolyhedrovirus (HaSNPV) or with one of two recombinant genotypes of this virus on cotton plants. The behavioural effects of virus infection were examined both in larvae infected with a single virus genotype, and in larvae challenged with mixtures of the wild‐type and one of the recombinant viruses. An egt‐negative virus variant caused more rapid death and lower virus yield in fourth instars, but egt‐deletion did not produce consistent behavioural effects over three experiments, two under controlled glasshouse conditions and one in field cages. A recombinant virus containing the AaIT‐(Androctonus australis Hector) insect‐selective toxin gene, which expresses a neurotoxin derived from a scorpion, caused faster death and cadavers were found lower down the plant than insects infected with unmodified virus. Larvae that died from mixed infections of the AaIT‐expressing recombinant and the wild‐type virus died at positions significantly lower, compared to infection with the pure wild‐type viral strain. The results indicate that transmission of egt‐negative variants of HaSNPV are likely to be affected by lower virus yield, but not by behavioural effects of egt gene deletion. By contrast, the AaIT recombinant will produce lower virus yields as well as modified behaviour, which together can contribute to reduced virus transmission under field conditions. In addition, larvae infected with both the wild‐type virus and the toxin recombinant behaved as larvae infected with the toxin recombinant only, which might be a positive factor for the risk assessment of such toxin recombinants in the environment.     

Comparisons of calling behaviour of different geographical populations of Helicoverpa armigera

Abstract:  The cotton bollworm, Helicoverpa armigera, with worldwide distribution, evolves into different geotypes for adapting to the changes of geographical climates. Comparisons of calling behaviour of the insect collected from the temperate region in northern China (Beijing), the temperate region in north-western China (Kashi) and the tropical region in southern China (Haikou) were investigated in the laboratory as a first step to understanding the influence of reproductive behaviour on its population differentiation. There were more than 80% of virgin females of each population that showed calling behaviour. The age at which the moths of all three populations initiated calling varied significantly. The durations of calling in scotophase and the percentages of females calling also differed between populations. Only a few females of the Beijing and Haikou populations called in the first 2 h after the onset of scotophase, whereas many Kashi females called at this time. However, the main calling peak occurred during the second half of scotophase for all three populations. Females of the Beijing and Haikou populations exhibited similar calling onset times at the same age, whereas the Kashi females initiated calling significantly earlier than those of Beijing and Haikou from nights 3 to 7. The durations of each calling bout and the time spent by both Beijing and Haikou populations were similar to each other at the same age, but were significantly shorter than that of the Kashi population from nights 3 to 7. These results suggest that there are genetic variations not only in pre-period calling but also in the calling behaviour of H. armigera .     

Interspecific competition between the ichneumonid Campoletis chlorideae and the braconid Microplitis mediator in their host Helicoverpa armigera

We investigated interspecific competition between Campoletis chlorideae Uchida (Hymenoptera: Ichneumonidae) and Microplitis mediator (Haliday) (Hymenoptera: Braconidae) in their host, the cotton bollworm, Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) under laboratory conditions. Cotton bollworm larvae were allowed to be parasitized by both wasp species simultaneously or sequentially at different time intervals. When host larvae were parasitized simultaneously by both parasitoids, the majority of the cocoons produced were of M. mediator. When host larvae were parasitized initially by M. mediator followed by C. chlorideae at 12 or 24 h, parasitoids emerging from the multiparasitized hosts were mainly M. mediator. In contrast, when host larvae were parasitized initially by C. chlorideae, followed by M. mediator 12 or 24 h later, parasitoids emerging from the multiparasitized hosts were mainly C. chlorideae. Dissections of host larvae at various time intervals after parasitization by the two parasitoids showed that first instars of M. mediator could physically attack the larvae of C. chlorideae, but not the eggs of C. chlorideae. When a host was parasitized by both wasp species sequentially, more host larvae died and the number of wasp offspring was significantly reduced compared to a host parasitized by only one wasp. Conversely, in simultaneous multiparasitism, the host mortality and wasp offspring production were not significantly different from those parasitized by single wasp species.     

转双价基因抗虫棉及其杂交F1代对棉铃虫幼虫的抗性研究

利用室内生物测定法和田间调查法研究双价抗虫棉及其杂交F1代不同生育期主茎功能叶和花铃期不同组织器官的抗虫性。结果表明:双价抗虫棉及其杂交F1代的抗虫性变化规律与B t基因棉的抗虫性变化规律相近,为生育前期(苗期、蕾期)抗性强,生育后期(花铃期、吐絮期)抗性弱,在花铃期为:棉铃>棉蕾>花>棉叶,且差异极显著。与B t基因棉相比,生育前期双价抗虫棉及其杂交F1代的抗虫性略弱,但差异不显著;生育后期双价抗虫棉及其杂交F1代的抗虫性显著强于B t基因棉。     

Is there genetic structure in populations of Helicoverpa armigera from Australia?

Recent studies suggest that populations of the pest moth Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) may be genetically differentiated over short distances and time periods within Queensland, Australia. To test for genetic structure in another region of Australia, we characterized population differentiation in Victorian samples of H. armigera using eight microsatellite loci. We found no evidence of genetic structure among samples from different locations or among samples collected at different times. Moreover, Victorian samples were not differentiated from other samples of H. armigera from Queensland and New Zealand. All samples showed substantial deviations from Hardy–Weinberg equilibrium, suggesting a high frequency of null alleles typically found in microsatellites of Lepidoptera. These results indicate that populations of H. armigera are not strongly structured among regions in south‐eastern Australia.     

Field inactivation of wild-type and genetically modified Helicoverpa armigera single nucleocapsid nucleopolyhedrovirus in cotton

Cotton bollworm (Helicoverpa armigera) is a serious pest on cotton in China. A specific baculovirus, H. armigera nucleopolyhedroviruses (HaSNPV) is used as a commercial biopesticide to control this pest. To improve the pesticidal properties, HaSNPV has been genetically engineered by both deleting the ecdysteroid UDP-glucosyltransferase (egt) gene from its genome (recombinant HaSNPV-EGTD) and incorporating an insect-selective toxin gene from the scorpion Androctonus australis (AaIT) (recombinant HaSNPV-AaIT). In the field, there was no significant difference among the inactivation rates of the two recombinant HaSNPVs and their parent wild-type, HaSNPV-WT. The inactivation rate of these viruses was significantly different in different years. The average half-life of HaSNPV was 0.57, 0.90 and 0.39 days in 2000, 2001 and 2002, respectively. Inactivation rates correlated well with solar radiation over these years.