The expression of proteins involved in digestion and detoxification are regulated in Helicoverpa armigera to cope up with chlorpyrifos insecticide

Helicoverpa armigera is a key pest in many vital crops, which is mainly controlled by chemical strategies. To manage this pest is becoming challenging due to its ability and evolution of resistance against insecticides. Further, its subsequent spread on nonhost plant is remarkable in recent times. Hence, decoding resistance mechanism against phytochemicals and synthetic insecticides is a major challenge. The present work describes that the digestion, defense and immunity related enzymes are associated with chlorpyrifos resistance in H. armigera. Proteomic analysis of H. armigera gut tissue upon feeding on chlorpyrifos containing diet (CH) and artificial diet (AD) using nano‐liquid chromatography–mass spectrometry identified upregulated 23‐proteins in CH fed larvae. Database searches combined with gene ontology analysis revealed that the identified gut proteins engrossed in digestion, proteins crucial for immunity, adaptive responses to stress, and detoxification. Biochemical and quantitative real‐time polymerase chain reaction analysis of candidate proteins indicated that insects were struggling to get nutrients and energy in presence of CH, while at the same time endeavoring to metabolize chlorpyrifos. Moreover, we proposed a potential processing pathway of chlorpyrifos in H. armigera gut by examining the metabolites using gas chromatography–mass spectrometry. H. armigera exhibit a range of intriguing behavioral, morphological adaptations and resistance to insecticides by regulating expression of proteins involved in digestion and detoxification mechanisms to cope up with chlorpyrifos. In these contexts, as gut is a rich repository of biological information; profound analysis of gut tissues can give clues of detoxification and resistance mechanism in insects.     

P-glycoprotein ATPase from the resistant pest, Helicoverpa armigera: Purification, characterization and effect of various insecticides on its transport function

Helicoverpa armigera is a major pest of agricultural crops and has developed resistance to various insecticides. A P-glycoprotein (Pgp) with ATPase activity likely to be involved in insecticide resistance was purified and characterized from insecticide-resistant H. armigera. The purification was 18-fold with 3% yield. The optimum pH and temperature were found to be 7.4 and 30-40 °C, respectively. Kinetic studies indicated that this enzyme had a K_m value of 1.2 mM for ATP. Pgp from H. armigera was partially sequenced and found to be homologous to conserved sequences of mammalian Pgps. Pesticides stimulated H. armigera Pgp ATPase activity with a maximum stimulation of up to 40%. Quenching of the intrinsic tryptophan fluorescence of purified Pgp was used to quantitate insecticide binding. Using the high-affinity fluorescent substrate, tetramethylrosamine, transport was monitored in real time in proteoliposomes containing H. armigera Pgp. The presence of Pgp could be one of the reasons for insecticide resistance in this pest.     

Activity of glutathione S‐transferase and esterase enzymes in Helicoverpa armigera (Hübner) after exposure to entomopathogenic fungi

Helicoverpa armigera, a polyphagous insect of crops and vegetables, is acquiring resistance against many commercial insecticides. The present study shows variations in the activity of two detoxification enzymes, namely esterase and glutathione S‐transferase (GST), in H. armigera after exposure to different isolates of entomopathogenic fungi. After treatment of larvae with the different isolates (Day 0), samples were collected on three days (Days 3, 5 and 7) for enzyme analysis. High GST activity was found in samples of hemolymph, intestine and fat bodies of H. armigera following treatment with Beauveria bassiana (isolate Bb‐08), Metarhizium anisopliae (isolates Ma‐11.1 and Ma‐4.1), and Isaria fumosorosea (isolates If‐02 and If‐2.3). High esterase activity was recorded in samples of the intestine and fat bodies on various days after treatment, whereas increased esterase activity in hemolymph was noted only in samples from Day 5 after treatment with M. anisopliae (Ma‐4.1). The detection of high GST and esterase activity demonstrates the possibility of the development of resistance against these microbial control agents in H. armigera.     

Resurgence of the cotton bollworm Helicoverpa armigera in northern Greece associated with insecticide resistance

Helicoverpa armigera has been controlled effectively with chemical insecticides in the major cotton crop production areas of northern Greece for many years. However, a resurgence of the pest was observed in 2010, which significantly affected crop production. During a 4‐year survey (2007 – 2010), we examined the insecticide resistance status of H. armigera populations from two major and representative cotton production areas in northern Greece against seven insecticides (chlorpyrifos, diazinon, methomyl, alpha‐cypermethrin, cypermethrin, gamma‐cyhalothrin and endosulfan). Full dose‐response bioassays on third instar larvae were performed by topical application. Lethal doses at 50% were estimated by probit analysis and resistance factors (RF) were calculated, compared to a susceptible laboratory reference strain. Resistance levels were relatively moderate until 2009, with resistance ratios below 10‐fold for organophosphates and carbamates and up to 16‐fold for the pyrethroid alpha‐cypermethrin. However, resistance rose to 46‐ and 81‐fold for chlorpyrifos and alpha‐cypermethrin, respectively in 2010, when the resurgence of the pest was observed. None of the known pyrethroid resistance mutations were found in the pyrethroid‐resistant insects. The possible association between resistance and H. armigera resurgence in Greece is discussed.     

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.     

Binding of Cry δ-endotoxins to brush border membrane vesicles of Helicoverpa armigera and Helicoverpa punctigera （Lepidoptera： Noctuidae）

The relatively low susceptibility ofHelicoverpa armigera to CrylAc, its history of resistance to chemical insecticides and the seasonal decline in expression of CrylAc in transgenic cotton necessitated the development of cotton expressing two insecticidal proteins to provide sustainable control of this multinational pest. To manage the resistance issue, it was essential that the second insecticidal protein have a significantly different mode of action to CrylAc. A common feature of resistance to CrylA proteins in several species as well as H. armigera has been a change in the binding site. A study of binding sites for some Cry proteins in the brush border membrane vesicles （BBMV） ofH. armigera and Helicoverpa punctigera was undertaken. The binding affinity for CrylAc was higher than for CrylAb, matching their relative toxicities, and CrylAc and CrylAb were found to share at least one binding site in both I-1. armigera and I-1. punctigera. However Cry2Aa did not compete with CrylAc for binding and so could be used in transgenic cotton in combination with CrylAc to control H. armigera and manage resistance. Variation in the susceptibilities of three different H. armigera strains to CrylAc correlated with the parameter Bmax/Kcom.     

Partial purification of Cytochrome P450 from Helicoverpa armigera (Hübner)

Abstract The cytochrome P450 (Cyt‐P450) proteins from the fat body and midgut of the cotton bollworm, Helicoverpa armigera, were respectively partially purified by a set of purification procedures including differential centrifugation, solubilization of CHAPS, protein precipitation by PEG precipitation and DE‐32 column chromatography. The Cyt‐P450 was detected by methods of CO difference spectrum and SDS‐PAGE. Fraction of detergent solubilized microsomes from the fat body of H. armigera was purified more than 17‐fold. Three protein bands were detected by SDS‐PAGE with molecular masses of 70 600, 63 300 and 571 200Da. It is possible that the proteins with molecular mass of 63 300 and 571 200Da were the isozymes of Cyt‐P450.     

Mitochondrial P-Glycoprotein ATPase Contributes to Insecticide Resistance in the Cotton Bollworm,Helicoverpa armigera (Noctuidae: Lepidoptera)

Cotton bollworm, Helicoverpa armigera, is one of the most damaging polyphagous pests worldwide, which has developed high levels of resistance to commonly applied insecticides. Mitochondrial P-glycoprotein (Pgp) was detected in the insecticide-resistant strain of H. armigera using C219 antibodies, and its possible role was demonstrated in the efflux of xenobiotic compounds using spectrofluorometer. The TMR accumulated in mitochondria in the absence of ATP, and effluxed out in presence of ATP; the process of efflux was inhibited in the presence of ortho-vandate, an inhibitor of Pgp, in insecticide-resistant larvae of H. armigera. The mitochondria isolated from insecticide-resistant larvae were resistant to insecticide-induced inhibition of oxygen consumption and cytochrome c release. Membrane potential decreased in a dose-dependent manner in the presence of higher concentration of insecticides (>50 µM) in mitochondria of insecticide-resistant larvae. In conclusion, mitochondrial Pgp ATPase detected in the insecticide-resistant larvae influenced the efflux of xenobiotic compounds. Pgp might be involved in protecting the mitochondrial DNA and the components of the electron transport chain from damage due to insecticides, and contributing to the resistance to the deleterious effects of insecticides on the growth of insecticide-resistant H. armigera larvae.     

Characterization of glutathione S‐transferase in the saturniid moth,Samia Cynthia pryeri (Lep.: Saturniidae)

An enzyme, which possesses glutathione S‐transferase (GST) activity, has been found in the midgut of the saturniid moth, Samia cynthia pryeri. The enzyme was initially purified into homogeneity by ammonium sulphate fractionation, affinity chromatography, and ion‐exchange chromatography. The resulting enzyme revealed a single band with a molecular mass of 23 kDa by sodium dodecyl sulfate polyacrylamide electrophoresis under reduced conditions. When tested with 1‐chloro‐2,4‐dinitrobenzene, a universal substrate of GST, the purified remnants had an optimum pH of 8.0 for enzymatic activity, and was fairly stable at pH 5–9 and at temperatures below 40°C. The enzyme was also responsive to 4‐hydroxynonenal, a cytotoxic lipid‐peroxidation product. The present GST was inhibited by organophosphorus and pyrethroid insecticides including fenitrothion, permethrin and deltamethrin.     

棉铃虫核型多角体病毒与化学杀虫剂和卵磷脂混用的增效作用

棉铃虫核型多角体病毒(HaNPV)分别与三氟氯氰菊酯、溴氰菊酯、氰戊菊酯、灭净菊酯、灭多威、辛硫磷、甲基对硫磷和乙酰甲胺磷等化学杀虫剂混合饲喂棉铃虫幼虫,统计致死中浓度LC₅₀,计算增效比,测定虫体内与抗性有关的三种重要酶：多功能氧化酶(MFO)、羧酸酯酶(CarE)、乙酰胆碱酯酶(AChE)的活性。研究大豆卵磷脂对HaNPV致病性的影响。结果表明：HaNPV与化学杀虫剂混合饲喂抗性棉铃虫,生测统计增效比均大于1.0,特别是病毒与甲基对硫磷混用,增效比更是达到3.53,表现出良好的增效作用。混剂感染抗性棉铃虫,虫体内MFO的活性比化学杀虫剂单用时降低3～12倍,CarE和AChE的活性也比化学杀虫剂单用时低,HaNPV明显抑制了化学杀虫剂对MFO和CarE的诱导作用。HaNPV与大豆卵磷脂混用,提高了HaNPV对棉铃虫的感染致死率,缩短了致死中时间(LT₅₀)。     

Oviposition and feeding avoidance in Helicoverpa armigera (Hübner) against transgenic Bt cotton

Helicoverpa armigera (Hübner), the major target pest of transgenic Bacillus thuringiensis (Bt) cotton, remains susceptible to Bt cotton in China at present. Behavioural avoidance by ovipositing females might lead to reduced exposure to Bt cotton and minimize selection for physiological resistance. We examined the behavioural responses of H. armigera to Bt and non‐Bt cottons to determine whether behavioural avoidance to Bt cotton may be present. In oviposition choice tests, the number of eggs on non‐Bt cotton plants was significantly higher than on Bt cotton plants. Similarly, in no‐choice tests, Bt cotton plants attracted significantly fewer eggs compared with non‐Bt cotton plants. H. armigera neonates showed higher dispersal and lower establishment on Bt cotton than on non‐Bt cotton. First instars were found to feed consistently on non‐Bt cotton leaves, creating large feeding holes, but only produced tiny feeding holes on Bt cotton leaves. The H. armigera population used in this study showed avoidance of oviposition and feeding on Bt cotton. Our results provide important insights into one possible mechanism underlying the durability of Bt cotton resistance and may be useful for improving strategies to sustain the effectiveness of Bt crops.     

Field evaluation of eco-friendly biocontrol package for the management of pod borer,Helicoverpa armigera Hubner,and fusarium wilt in chickpea,Cicer arietinum

Helicoverpa armigera is a serious pest of chickpea and causes great damage to crop. Extensive and indiscriminate use of insecticides has led to the development of resistance in H. armigera. Among the several alternative methods for management of H. armigera, the nuclear polyhedrosis virus (NPV) is promising, whereas Trichoderma sp. have shown promising results against chickpea wilt. The experiments to evaluate biocontrol package against H. armigera and wilt disease under field conditions were conducted. Lowest H. armigera larval population (0.71 larvae/plant) was recorded in chemical control, which was at a par with biocontrol package (0.91 larvae/plant), and both the treatments were significantly better than control. Lowest per cent pod damage (3.85%) was recorded in chemical control followed by biocontrol treatment (5.08%) and unsprayed control (8.61%). The yields from biocontrol package (13.45 q/ha) and chemical control (15.37 q/ha) were significantly higher than unsprayed control (10.7 q/ha). There was no disease incidence in all treatments in both 2008 and 2009.     

A single linkage group confers dominant resistance to Bacillus thuringiensis δ‐endotoxin Cry1Ac in Helicoverpa armigera

The BKBT strain of Helicoverpa armigera was derived from a susceptible BK77 strain (collected from Bouake, Cote D’Ivoire in 1977) through 30 generations of selection with activated Bacillus thuringiensis δ‐endotoxin Cry1Ac. Unlike recessive inheritance of Cry1Ac resistance in H. armigera from previous reports, resistance to activated Cry1Ac in the BKBT strain is dominant. A backcross approach was used to map dominant resistance to Cry1Ac in the BKBT strain. One hundred and forty‐seven informative amplified fragment length polymorphism (AFLP) DNA markers covered all 31 linkage groups of H. armigera. Five AFLP markers linked to Cry1Ac resistance in the BKBT strain were on the same autosomal linkage group, which is the only linkage group contributing dominant Cry1Ac resistance in the BKBT strain of H. armigera.     

Effect of jasmonic acid and salicylic acid induced resistance in groundnut on Helicoverpa armigera

Induced resistance in plants affects insect growth and development as a result of the up‐regulation of defence‐related secondary metabolites or enzyme‐binding proteins. In the present study, the effects of jasmonic acid (JA) and salicylic acid (SA) induced resistance in groundnut on Helicoverpa armigera (Hübner) are examined. Larval survival, larval weights and the activities of digestive enzymes (total serine protease and trypsin) and of detoxifying enzymes [glutathione S‐transferase (GST) and esterase (EST)] are studied in insects fed on four groundnut genotypes with moderate levels of resistance to H. armigera (ICGV 86699, ICGV 86031, ICG 2271 and ICG 1697) and a susceptible genotype (JL 24). The plants are pre‐ and/or simultaneously treated with JA and SA, and then infested with H. armigera, which are allowed to feed for 6 days. Significantly lower serine protease and trypsin activities are observed in H. armigera fed on plants treated with JA. Greater GST activity is recorded in insects fed on JA and SA treated plants, whereas EST activity is low in H. armigera larvae fed on plants treated with JA and SA. Serine proteases, trypsin and GST activities and larval weights (r = 0.74–0.95) and larval survival (r = 0.77–0.93) are positively correlated, whereas EST activity and larval weight (r = ?0.55) and larval survival (r = ?0.65) are negatively correlated. The results suggest that midgut digestive and detoxifying enzymes can be used as indicators of the adverse effects of constitutive and/or induced resistance in crop plants on the insect pests and the role of JA and SA in insect pest management.     

Effects of three insecticides on the expression of cytochrome P450 CYP6B7 in Helicoverpa armigera

Cytochrome P450 genes can be induced by xenobiotics, which may contribute to insect's adaptability to the environments and resistance to insecticides. Previous studies indicated that cytochrome P450 CYP6B7 played a vital role in the resistance of Helicoverpa armigera to fenvalerate. However, effects of different insecticides on the expression of CYP6B7 in H. armigera are still unclear. In this study, resistance level of H. armigera to six insecticides was determined by topical application method, and effects of fenvalerate, phoxim and indoxacarb on the expression of CYP6B7 in susceptible (HDS) and fenvalerate-resistant (BJR) strains of H. armigera were evaluated by RT-qPCR. The results showed that BJR strain had an extremely high level of resistance to fenvalerate (1990.57-fold), and the induction of CYP6B7 in different tissues of BJR strain was significantly higher than that of HDS strain after exposure to fenvalerate for 24 and 48 hr. The highest induction level by fenvalerate was observed in the midgut, which were 13.7-fold in HDS strain and 127.9-fold in BJR strain at 24 and 48 hr, respectively. After exposure to phoxim, the expression level of CYP6B7 in HDS and BJR strains was induced by 2.3- and 316.8-fold at 24 hr, respectively. It is worth to note that CYP6B7 could be induced by phoxim at different time points in BJR strain, but only induced at 24 and 72 hr in HDS strain. After indoxacarb exposure, the expression of CYP6B7 was induced by 1.6-fold at 72 hr in BJR strain, whereas it was induced at 24 and 48 hr in HDS strain. These results demonstrated that the expression level of CYP6B7 could be induced by fenvalerate, phoxim and indoxacarb, but the induction time and levels varied; moreover, the induction in BJR strain was markedly higher than that in HDS strain after exposure to fenvalerate and phoxim.     

Potentialities of methoxyfenozide for the integrated management of Helicoverpa armigera (Lepidoptera: Noctuidae) on cotton in Benin,West Africa

Intensive use of chemical insecticides against Helicoverpa armigera has led to the development of resistance to the major chemical families of insecticides. Consequently, management of H. armigera using conventional chemical insecticides is increasingly difficult. Methoxyfenozide is an agonist of the insect moulting hormone 20-hydroxyecdysone that acts faster than chitin synthesis inhibitors. The present work is aimed to assess the effectiveness of methoxyfenozide for use against H. armigera on cotton in Benin, West Africa. Laboratory tests and field experiments have been carried out. For laboratory studies, topical application of methoxyfenozide was done using L2 and L5 instar larva of H. armigera. Tested methoxyfenozide concentrations varied from 24 μl/ml to 144 μl/ml and the control is water only. For field experiments, a complete randomised block design was used with methoxyfenozide (72 μl/ml) and a control (no spraying). Berthoud Ultra Low Volume sprayer was used to spray methoxyfenozide suspension at 60-l per hectare. Two sprays were applied, 7 days apart. Laboratory tests indicated that 24 h after application of methoxyfenozide, about 100% of treated L2 and L5 larva were morbid or dead compared with 0% for the control larva. There are no significant differences between tested concentrations. Morbid larvae died within 2 days. In field experiments, cotton yield harvested on methoxyfenozide treated plants was double of that obtained on untreated plants (9375 kg and 4875 kg per hectare respectively). Thus methoxyfenozide may be used as component of Integrated Pest Control Programme on cotton in Benin, West Africa.     

Are Helicoverpa armigera and Tetranychus spp. populations still susceptible to pesticides? A Zimbabwean study

The African bollworm, Helicoverpa armigera (Hübner), and the cotton red spider mite, Tetranychus spp., are important pests of cotton in Zimbabwe. A study to assess H. armigera resistance to fenvalerate 20 EC (Cyano (3-phenoxyphenyl) methyl 4-chloro-α-(1-methylethyl)benzene acetate) and Tetranychus spp. resistance to amitraz 20 EC (n’-(2,4-dimethylphenyl)-n-[[(2,4-dimethylphenyl)imino]methyl]-n-) was conducted at the Cotton Research Institute (CRI) during the 2005/06 cotton-growing season. Field populations of H. armigera and Tetranychus spp. were collected from some of Zimbabwe’s major cotton-growing areas of Sanyati, Umguza, Chisumbanje, Chinhoyi and the CRI in Kadoma and exposed to bioassays. The African bollworm leaf disc technique and the red spider mite attached leaf-dipping technique were used to assess responses of the African bollworm and red spider mite to the pesticides. Susceptible laboratory populations served as the standard populations and their responses were compared with those of the field populations. The graphical method and MSTAT-C probit analysis computer program were used to calculate LC₅₀ values. Although the CRI field population, used as a reference population for the registration of H. armigera insecticides, had the highest LC₅₀ value (graphical?=?0.000100000; MSTAT-C?=?0.000088195) compared with all the other field populations, overall log-dose probit bioassays on all field-collected strains of the bollworm showed no resistance to the pyrethroid (RFs?=?0.04–0.54-fold). Tetranychus spp. showed very low levels of resistance (RFs?=?1.26–2.00-fold). Continuous monitoring of major cotton pests, especially H. armigera and Tetranychus spp., from all cotton districts of Zimbabwe is vital for early detection of resistance development.     

Field Evolved Resistance in Helicoverpa armigera (Lepidoptera: Noctuidae) to Bacillus thuringiensis Toxin Cry1Ac in Pakistan

Helicoverpa armigera (Hübner) is one of the most destructive pests of several field and vegetable crops, with indiscriminate use of insecticides contributing to multiple instances of resistance. In the present study we assessed whether H. armigera had developed resistance to Bt cotton and compared the results with several conventional insecticides. Furthermore, the genetics of resistance was also investigated to determine the inheritance to Cry1Ac resistance. To investigate the development of resistance to Bt cotton, and selected foliar insecticides, H. armigera populations were sampled in 2010 and 2011 in several cotton production regions in Pakistan. The resistance ratios (RR) for Cry1Ac, chlorpyrifos, profenofos, cypermethrin, spinosad, indoxacarb, abamectin and deltamethrin were 580-fold, 320-, 1110-, 1950-, 200-, 380, 690, and 40-fold, respectively, compared with the laboratory susceptible (Lab-PK) population. Selection of the field collected population with Cry1Ac in 2010 for five generations increased RR to 5440-fold. The selection also increased RR for deltamethrin, chlorpyrifos, profenofos, cypermethrin, spinosad, indoxacarb, abamectin to 125-folds, 650-, 2840-, 9830-, 370-, 3090-, 1330-fold. The estimated LC_50s for reciprocal crosses were 105 µg/ml (Cry1Ac-SEL female × Lab-PK male) and 81 g µg/ml (Lab-PK female × Cry1Ac-SEL male) suggesting that the resistance to Cry1Ac was autosomal; the degree of dominance (D_LC) was 0.60 and 0.57 respectively. Mixing of enzyme inhibitors significantly decreased resistance to Cry1Ac suggesting that the resistance to Cry1Ac and other insecticides tested in the present study was primarily metabolic. Resistance to Cry1Ac was probably due to a single but unstable factor suggesting that crop rotation with non-Bt cotton or other crops could reduce the selection pressure for H. armigera and improve the sustainability of Bt cotton.     

Cotton bollworm resistance to Bt transgenic cotton: A case analysis

Cotton bollworm (Helicoverpa armigera) is one of the most serious insect pests of cotton. Transgenic cotton expressing Cry toxins derived from a soil bacterium, Bacillus thuringiensis (Bt), has been produced to target this pest. Bt cotton has been widely planted around the world, and this has resulted in efficient control of bollworm populations with reduced use of synthetic insecticides. However, evolution of resistance by this pest threatens the continued success of Bt cotton. To date, no field populations of bollworm have evolved significant levels of resistance; however, several laboratory-selected Cry-resistant strains of H. armigera have been obtained, which suggests that bollworm has the capacity to evolve resistance to Bt. The development of resistance to Bt is of great concern, and there is a vast body of research in this area aimed at ensuring the continued success of Bt cotton. Here, we review studies on the evolution of Bt resistance in H. armigera, focusing on the biochemical and molecular basis of Bt resistance. We also discuss resistance management strategies, and monitoring programs implemented in China, Australia, and India.     

Chemical composition,insecticidal and biochemical effects of Melaleuca alternifolia essential oil on the Helicoverpa armigera

Pesticide resistance has developed as a result of long‐term and extensive use of chemical pesticides. Essential oils from aromatic plants may provide a new and safe alternative to conventional insecticides. In this study, the insecticidal activities of the essential oil of Melaleuca alternifolia and their chemical constituents against Helicoverpa armigera Hubner were investigated, and the underlying mechanisms were studied. The essential oil showed distinct antifeedant (AFC₅₀ = 8.93 mg/ml) and good contact (LD₅₀ = 50.28 μg/larva) activities against H. armigera at 24 hr. Ten chemical components were identified using a gas chromatograph/mass spectrometer, and mainly included terpinen‐4‐ol (40.09%), γ‐terpinene (21.85%), α‐terpinene (11.34%), α‐terpineol (6.91%), α‐pinene (5.86%), terpinolene (3.24%) and 1,8‐cineole (1.83%). Among them, five components were determined and results showed that these constituents possessed obvious antifeedant activities. The activities of acetylcholinesterase and glutathione S‐transferase were notably inhibited by the essential oil, as compared with the control, with strong dose‐ and time‐dependent effects. The results provide a basis for their development and utilization in the control of insects in the future.