Mode of inheritance and stability of resistance to Bacillus thuringiensis var kurstaki in a diamondback moth (Plutella xylostella) population from Malaysia

Genetic inheritance of resistance to Bacillus thuringiensis var kurstaki (BTK) was examined in a diamondback moth (Plutella xylostella) population collected from the Melaka region of Malaysia. A BTK‐selected sub‐population (BTK‐SEL) which was more than 100‐fold resistant to BTK compared with a susceptible (ROTH) population of P xylostella was used with standard reciprocal crosses and back‐crosses between ROTH and BTK‐SEL. Logit regression analysis of F ₁ reciprocal crosses indicated that BTK resistance was inherited as an incompletely recessive autosomal trait and controlled by a single locus. In contrast, other studies have shown that resistance to Cry1Ac is inherited as an incompletely dominant autosomal trait in a Cry1Ac‐selected sub‐population of the same Melaka population. The frequency of the allele responsible for resistance decreased without exposure to insecticide in the laboratory. © 2000 Society of Chemical Industry     

Cross-resistance and inheritance of resistance to Bacillus thuringiensis toxin Cry1Ac in diamondback moth (Plutella xylostella L) from lowland Malaysia

A field population of Plutella xylostella from Malaysia (SERD4) was divided into five sub-populations and four were selected (G2-G5) with the Bacillus thuringiensis insecticidal crystal (Cry) toxins Cry1Ac, Cry1Ab, Cry1Ca and Cry1Da. Bioassay at G6 gave resistance ratios of 88, 5, 2 and 3 for Cry1Ac, Cry1Ab, Cry1Ca and Cry1Da respectively compared with the unselected sub-population (UNSEL-SERD4). The Cry1Ac-selected population showed little cross-resistance to Cry1Ab, Cry1Ca and Cry1Da, (3-, 2- and 3-fold compared with UNSEL-SERD4), whereas the Cry1Ab-SEL sub-population showed marked cross-resistance to Cry1Ac (40-fold), much greater than Cry1Ab itself. In contrast, the Cry1Ca- and Cry1Da-SEL sub-population showed little if any cross-resistance to Cry1Ac and Cry1Ab. The mode of inheritance of resistance to Cry1Ac was examined in Cry1Ac-selected SERD4 by standard reciprocal crosses and back-crosses using a laboratory insecticide-susceptible population (ROTH). Logit regression analysis of F1 reciprocal crosses indicated that resistance to Cry1Ac was inherited as an incompletely dominant trait. At the highest dose of Cry1Ac tested, resistance was recessive, while at the lowest dose it was almost completely dominant. The F2 progeny from a back-cross of F1 progeny with ROTH were tested with a concentration of Cry1Ac that would kill 100% of ROTH. The mortality ranged between 50 and 95% in seven families of back-cross progeny, which indicated that more than one allele on separate loci were responsible for resistance to Cry1Ac.     

Susceptibility pattern and development of resistance in the diamondback moth,Plutella xylostella L,to Bacillus thuringiensis Berl var kurstaki in India

Base‐line susceptibility for six‐day‐old larvae of the diamondback moth, Plutella xylostella, against Bacillus thuringiensis var kurstaki (Biobit^®) was studied by a cabbage leaf disc dip bioassay technique. Diamondback moth from 13 locations in seven different states spread over a distance of about 3000 km longitudinally was used for these studies. Forty‐eight‐hour LC₅₀ values varied from 1.0 to 10.97 mg AI litre⁻¹. Further investigations on the development of resistance under laboratory conditions showed an increase in LC₅₀ from 2.76 (for unselected F₁ generation) to 5.28 mg AI litre⁻¹ (for selected F₉ generation), using a selection concentration of 6.4 mg AI litre⁻¹. This suggested a possibility of the development of resistance under field conditions if there were to be extensive and indiscriminate use of B thuringiensis. These findings are discussed in relation to integrated pest management and the mechanisms of resistance in resistance management tactics. © 2000 Society of Chemical Industry     

Inheritance of resistance to Bt canola in a field-derived population of Plutella xylostella

Crops expressing Bacillus thuringiensis (Bt) insecticidal Cry proteins are grown on millions of hectares. Recommendations to delay resistance are based on a high expression/refugia strategy that aims to kill resistant heterozygotes and enable some susceptible insects to survive. Leaf-dip bioassays on F1 crosses of Malaysian populations of diamondback moth (Plutella xylostella (L)) showed that CrylAc resistance was not fully recessive. The survival of ca 50% of heterozygotes on Bt canola (Brassica napus L) leaves expressing low concentrations of CrylAc agreed with a non-fully-recessive model for resistance. Extrapolations based on log dose-logit mortality regressions for heterozygotes using leaf-dip bioassays showed that a relatively high level of expression, of ca 2000 ng CrylAc mg(-1) total leaf protein, would be required to give 90% mortality to heterozygotes. If high enough levels of expression of Bt toxin to kill heterozygotes cannot be achieved and maintained under field conditions, the effectiveness of the high-dose/refugia strategy would be reduced.     

Differential toxicity of Bacillus thuringiensis strains and their crystal toxins against high-altitude Himalayan populations of diamondback moth, Plutella xylostella L

BACKGROUND: Diamondback moth, Plutella xylostella (L.), is a major insect pest of crucifers in the biodiversity‐rich north‐western Indian Himalayan hills. The present investigation was aimed at determining the susceptibility pattern of P. xylostella populations collected from different locations of this region to autochthonous and standard Bacillus thuringiensis strains. RESULTS: Among the reference as well as indigenous B. thuringiensis strains tested, sub spp. kurstaki HD‐1, kurstaki HD‐73, galleriae HD‐8, local galleriae/colmeri strain BtOa1 and some of their Cry1 class toxins were found to be highly toxic. Surprisingly, the sub sp. tolworthi HD‐125, local tolworthi strain BtHa1 and Cry9 class toxins were found to be non‐toxic. Midgut homogenate from fourth‐instar larvae was found to activate 130 kDa protoxin from the local tolworthi strain BtHa1 into 68 kDa toxin, but failed to exert any larval mortality, probably owing to lack of receptor binding. CONCLUSION: The present study provides valuable baseline susceptibility data for the deployment of B. thuringiensis‐based control methods, as well as for future monitoring of development of resistance in P. xylostella to B. thuringiensis in this ecologically sensitive region. Copyright © 2008 Society of Chemical Industry     

Genetic basis of resistance and studies on cross-resistance in a population of diamondback moth, Plutella xylostella (Lepidoptera: Plutellidae)

The genetic basis of abamectin resistance was studied in a strain of the diamondback moth, Plutella xylostella (L), following laboratory selection of a field population collected at Xuanhua, Hebei Province, China. Data from the testing of F1 progeny from reciprocal crosses between abamectin-resistant and abamectin-susceptible strains indicated that resistance might be autosomal and incompletely recessive with a degree of dominance of -0.13. Chi-squared analyses from the response of a backcross of crossed F1 progeny and the resistant strain and F2 progeny were highly significant, suggesting that the resistance was probably controlled by more than one gene. The results of cross-resistance studies showed that there was little cross-resistance between abamectin and four pyrethroid insecticides (deltamethrin, beta-cypermethrin, fenvalerate and bifenthrin) and no cross-resistance between abamectin and the acylureas chlorfluazuron or flufenoxuron.     

云南小菜蛾对Bt的抗药性及盆栽药效评价

2008-2012年, 采用浸叶法连续5年测定了云南省2个主要蔬菜种植区通海县和弥渡县的小菜蛾田间种群对Bt制剂的抗药性,并进行了盆栽药效评价。结果表明,两地区小菜蛾对Bt制剂均表现为低抗或无抗性,抗药性无明显上升趋势。比较了在光照培养箱和自然条件下3种不同Bt制剂对通海和弥渡县小菜蛾盆栽药效,药后第5天通海和弥渡小菜蛾种群在恒温（25±1 ℃,RH65%~70%）和自然条件下(12~28 ℃,RH50%~75%)的校正死亡率分别为88.3%~95.5%和80.2%~90.6%、78.8%~89.1%和73.4%~85.7%,两者差异不显著。云南小菜蛾种群对Bt制剂均有较高的敏感性,可在十字花科蔬菜生产中有选择地使用。     

Cross-resistance between a Bacillus thuringiensis Cry toxin and non-Bt insecticides in the diamondback moth

BACKGROUND: Bacillus thuringiensis Berliner (Bt) crystal (Cry) toxins are expressed in various transgenic crops and are also used as sprays in integrated pest management and organic agricultural systems. The diamondback moth (Plutella xylostella L.) is a major worldwide pest of crucifer crops and one that has readily acquired field resistance to a broad range of insecticides.RESULTS: Selection of a subpopulation of the P. xylostella SERD4 population with the pyrethroid deltamethrin increased resistance to both deltamethrin and Cry1Ac relative to an unselected subpopulation. Selection of a second subpopulation with the Bt toxin Cry1Ac also increased resistance to both Cry1Ac and deltamethrin. A complementation test between the Cry1Ac-selected and deltamethrin-selected subpopulations suggested the presence of a common genetic locus or loci that control resistance to both insecticides. A piperonyl butoxide analogue with potent inhibitory activity against insect esterases significantly increased the toxicity of Cry1Ac and deltamethrin against the respective resistant subpopulations, but showed no such synergism with the unselected subpopulation of SERD4.CONCLUSION: Selection of one resistance phenotype resulted in the simultaneous selection of the other. This phenomenon could be due to a single mechanism acting against both classes of insecticide or to genetically linked, but separate, mechanisms.     

Genetics and evidence for an esterase-associated mechanism of resistance to indoxacarb in a field population of diamondback moth (Lepidoptera: Plutellidae)

Bioassays (at generation G2) with a newly collected field population (designated CH3) of Plutella xylostella L. from farmers' fields in the Cameron Highlands, Malaysia, indicated resistance ratios of 813-, 79-, 171-, 498- and 1285-fold for indoxacarb, fipronil, spinosad, deltamethrin and Bacillus thuringiensis toxin Cry1Ac respectively compared with a laboratory susceptible population (Lab-UK). At G2 the field-derived population was divided into two subpopulations: one was selected (G2 to G7) with indoxacarb (indoxa-SEL), while the second was left unselected (UNSEL). A significant reduction in the resistance ratio for each compound was observed in UNSEL at G8. For indoxa-SEL, bioassays at G8 found that selection with indoxacarb gave a resistance ratio of 2594 compared with Lab-UK and of 90 compared with UNSEL. The toxicity of fipronil, spinosad and deltamethrin was not significantly different in indoxa-SEL at G8 compared with G2 but was significantly greater than UNSEL at G8. The toxicity of Cry1Ac was significantly reduced in indoxa-SEL at G8 compared with G2 but was also significantly greater than UNSEL at G8. This suggests that indoxacarb selection maintained resistance to these compounds in the indoxa-SEL population. Synergist studies indicated that resistance to indoxacarb in indoxa-SEL was esterase associated. Logit regression analysis of F1 reciprocal crosses between indoxa-SEL and Lab-UK indicated that resistance to indoxacarb was inherited as an autosomal, incompletely recessive (D(LC) = 0.35) trait. Tests of monogenic inheritance suggested that resistance to indoxacarb was controlled by a single locus.     

Inheritance of resistance to a new non‐steroidal ecdysone agonist,fufenozide, in the diamondback moth,Plutella xylostella (Lepidoptera: Plutellidae)

BACKGROUND: The diamondback moth (DBM), Plutella xylostella (L.), is a cosmopolitan pest of cruciferous crops. Fufenozide, a novel non‐steroidal ecdysone agonist, exhibits good efficacy and plays an increasingly important role in the control of Lepidopterous pests in China. A laboratory strain of DBM was selected for resistance to fufenozide, and the genetic basis of resistance was studied. RESULTS: The resistant strain, selected under laboratory conditions, exhibited a higher level of resistance to fufenozide (302.8‐fold based on LC₅₀s) than the laboratory susceptible strain. Mortality data from the testing of F₁ progeny of reciprocal crosses of resistant and susceptible DBM indicated that resistance was autosomal and incompletely recessive with a degree of dominance of ?0.664. Chi‐square analysis from responses of a backcross of crossed F₁ progeny and the resistant strain and F₂ progeny were highly significant, suggesting that the resistance was probably controlled by more than one gene. The estimated realised heritability (h²) of fufenozide resistance was 0.08, indicating that diamondback moth may have a lower chance of developing resistance to fufenozide than other kinds of insecticide. CONCLUSION: The resistance of DBM to fufenozide might be autosomal and incompletely recessive, and the resistance is probably controlled by more than one gene. These results provide the basic information for pest management programmes. Copyright © 2009 Society of Chemical Industry     

Rapid report acetamiprid resistance and cross-resistance in the diamondback moth, Plutella xylostella

A 110-fold acetamiprid-resistant Plutella xylostella (L) strain was established after four selection experiments (in five generations) on a 9.5-fold resistant colony in the laboratory. The resistant strain did not show cross-resistance to chlorfluazuron or Bacillus thuringiensis subsp kurstaki Berliner, but displayed low resistance to cartap and phenthoate.     

Cross-resistance patterns and fitness in fufenozide-resistant diamondback moth, Plutella xylostella (Lepidoptera: Plutellidae)

BACKGROUND: Fufenozide is a novel non‐steroidal ecdysone agonist with good efficacy against diamondback moth (DBM), Plutella xylostella (Lepidoptera: Plutellidae). At present, it is widely applied for the control of a range of lepidopterous pests in China. This study compared the activities of fufenozide and 12 other insecticides against unselected and fufenozide‐selected strains of DBM to examine potential patterns of cross‐resistance. The relative fitness of the fufenozide‐selected strain was assessed to provide information pertinent to insecticide resistance management. RESULTS: Compared with the susceptible strain (JSS), the fufenozide‐resistant strain (JSR) showed high cross‐resistance to dibenzoylhydrazines and benzoylphenylureas, low cross‐resistance to abamectin and no cross‐resistance to organophosphates, carbamates and pyrethroids. JSR had a lower reproductive ability and a relative fitness of 0.5 compared with JSS. CONCLUSION: P. xylostella has the potential to develop resistance to fufenozide, albeit at the expense of fitness. Cross‐resistance between the same and other classes of insecticides is of concern, and should be a key consideration when implementing fufenozide‐based control strategies for this species. Copyright © 2011 Society of Chemical Industry     

氯虫苯甲酰胺对小菜蛾亚致死效应的研究

探讨亚致死剂量氯虫苯甲酰胺对小菜蛾2、3龄幼虫的亚致死效应,为氯虫苯甲酰胺的合理使用提供依据。采用药膜法确定氯虫苯甲酰胺对小菜蛾2龄和3龄幼虫的亚致死剂量(LC25、LC40),以试虫死亡率、取食量、化蛹时间、蛹重、羽化率为指标研究其对小菜蛾的亚致死效应。与对照相比,亚致死剂量氯虫苯甲酰胺处理的小菜蛾除死亡率显著增高外,幼虫生长明显受到抑制,幼虫至化蛹平均历期显著延长,取食量、蛹重和化蛹率明显降低。结果表明亚致死剂量氯虫苯甲酰胺对小菜蛾种群增长有一定抑制作用,对小菜蛾综合防治策略的制定有积极意义。     

Genetics of spinosad resistance in a multi-resistant field-selected population of Plutella xylostella

Resistance to the bacteria-derived insecticides spinosad (Conserve), abamectin (Vertimec), Bacillus thuringiensis var kurstaki (Btk) (Dipel), B thuringiensis var aizawai (Bta) (Xentari), B thuringiensis crystal endotoxins Cry1Ac and Cry1Ca, and to the synthetic insecticide fipronil was estimated in a freshly-collected field population (CH1 strain) of Plutella xylostella (L) from the Cameron Highlands, Malaysia. Laboratory bioassays at G1 indicated significant levels of resistance to spinosad, abamectin, Cry1Ac, Btk, Cry1Ca, fipronil and Bta when compared with a laboratory insecticide-susceptible population. Logit regression analysis of F1 reciprocal crosses indicated that resistance to spinosad in the CH1 population was inherited as a co-dominant trait. At the highest dose of spinosad tested, resistance was close to completely recessive, while at the lowest dose it was incompletely dominant. A direct test of monogenic inheritance based on a back-cross of F1 progeny with CH1 suggested that resistance to spinosad was controlled by a single locus.     

Insecticidal action of mammalian galectin‐1 against diamondback moth (Plutella xylostella)

BACKGROUND: Previous studies showed that mammalian galectin‐1 (GAL1) could interact with chitosan or chitin, one component of the peritrophic membrane (PM). This finding suggests that the PM could be a target of GAL1, which prompted the authors to explore the effect of GAL1 on larval growth and its potential mechanism. RESULTS: The development of Plutella xylostella (L.) larvae was significantly disturbed after they were fed recombinant GAL1. The histochemical structure and immunostaining pattern suggested that GAL1 treatment resulted in dose‐ and time‐dependent disruption of the microvilli and abnormalities in these epithelial cells. Ultrastructural studies showed that the PM was not present in the midgut of GAL1‐treated insects; instead, numerous bacteria were found in the lumen area. These results indicate that the protective function of the PM was disrupted by GAL1 treatment. Moreover, in vitro data showed that GAL1 interacts with chitosan/chitin in a dose‐dependent manner, and also specifically binds to the PM in vitro. CONCLUSION: In view of the fact that the carbohydrate recognition domain of GAL1 recognises the structural motif N‐acetyl lactosamine (Gal β 1–4 GlcNAc), which is similar to that of chitin (β‐1,4 N‐acetyl‐D ‐glucosamine), it is proposed that the insecticidal mechanism of GAL1 involves direct binding with chitin to interfere with the structure of the PM. Copyright © 2009 Society of Chemical Industry     

高效氯氰菊酯对小菜蛾阿维菌素抗性、敏感种群的亚致死效应

在实验室条件下研究了高效氯氰菊酯亚致死剂量LC10(43.44mg/L)(小菜蛾阿维菌素抗性种群)和LC10(12.61mg/L)(敏感种群)对小菜蛾阿维菌素抗性(AV-R)、敏感(AV-S)种群的亚致死效应。结果表明:高效氯氰菊酯亚致死剂量12.61mg/L处理小菜蛾阿维菌素敏感、抗性种群3龄幼虫后,处理组AV-S(SLC10)和AV-R(SLC10)的化蛹率、羽化率显著低于AV-S(ck)对照组,与AV-R(ck)对照组无显著性差异;用高效氯氰菊酯亚致死剂量43.44mg/L处理抗性种群3龄幼虫后,其处理组AV-R(RLC10)的化蛹率、蛹重、羽化率都显著低于对照组。AV-S(SLC10)组的单雌产卵量为176.45±36.11粒,显著高于对照组和处理的抗性种群,AV-R(SLC10)和AV-R(RLC10)组的单雌产卵量与对照组间无显著性差异,AV-S(SLC10)和AV-R(RLC10)组的产卵期明显缩短。AV-S(SLC10)组的内禀增长率(rm)、周限增长率(λ)和净增殖率(R0),显著高于对照和处理的抗性种群。结果表明高效氯氰菊酯亚致死剂量对小菜蛾阿维菌素敏感种群具有一定的刺激增殖作用。