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.     

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     

Tebufenozide resistance selected in Plutella xylostella and its cross-resistance and fitness cost

A susceptible strain of diamondback moth, Plutella xylostella (L.), was used to select for resistance to tebufenozide in the laboratory. After continuous selection with tebufenozide 17 times during 35 generations, a resistant strain was achieved with high resistance to tebufenozide (RR 93.8). Bioassay revealed that this strain showed high cross-resistance to abamectin (RR 35.7), methoxyfenozide (29.1) and JS118 (16.5), and a little to deltamethrin (3.9), but no obvious cross-resistance was found to cypermethrin (1.3), fipronil (1.3), trichlorfon (1.1), chlorfenapyr (1.0), phoxim (0.9) and acephate (0.8). The resistant and susceptible insects had similar development rates, but life table tests indicated that the resistant strain showed reproductive disadvantages, including decreased copulation rate, reproductivity and hatchability. When compared with the susceptible strain, the resistant insects had a relative fitness of only 0.3. This indicated that tebufenozide resistance selected under laboratory conditions had considerable fitness costs in this pest, and therefore rotational use of insecticides without cross-resistance is recommended to delay development of resistance.     

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     

Synergism and stability of acetamiprid resistance in a laboratory colony of Plutella xylostella

The involvement of metabolic enzymes in the resistance of a laboratory colony of diamondback moth, Plutella xylostella (L), to the neonicotinoid insecticide acetamiprid was determined with the synergists piperonyl butoxide (PBO), which suppresses the activity of cytochrome P-450 monooxygenases, and S,S,S-tributyl phosphorotrithioate (DEF), an inhibitor of esterases, using the leaf-dipping method. Both PBO and DEF enhanced the insecticidal activity of acetamiprid significantly in the resistant P. xylostella strain but not in a reference strain, suggesting that cytochrome P-450 monooxygenases and esterases play an important role in the resistance of P. xylostella to acetamiprid. The resistant P. xylostella strain was also reared without further exposure to acetamiprid to determine the stability of resistance. Maintaining the resistant strain for seven generations in the absence of selection pressure resulted in a drop in resistance ratio from 110 to 2.42, indicating that acetamiprid resistance in P. xylostella is not stable.     

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.     

Regional differences in pheromone responses of diamondback moth in Indonesia

Trap captures with two‐ and three‐component blends of synthetic sex pheromone for the diamondback moth, Plutella xylostella L. (Lepidoptera: Plutellidae), were assessed in Indonesia. In West Java, the two‐component blend containing 10g of (Z)‐11‐hexadecen‐1‐ol acetate and (Z)‐11‐hexadecena| in a 4:6 ratio captured the greatest number of diamondback moths. Three and five virgin females were more attractive than the two‐component lures, which were as attractive as lures that also contained (Z)‐9‐tetradecen‐1‐ol acetate. In North Sulawesi, a 100 g dose of the two‐component blend attracted more males than the 10 g dose but was not significantly more potent than five virgin females. These results suggests that pheromone production and bioactivity should be assessed in separate populations prior to attempts to develop pheromone‐based monitoring or mating disruption programmes.     

Inheritance of resistance and cross-resistance to deltamethrin in Plutella xylostella (Lepidoptera: Plutellidae) from Pakistan

A field population of Plutella xylostella (L) from Pakistan was found to be highly resistant to deltamethrin (>500-fold) but had little or no resistance to spinosad, fipronil, indoxacarb, abamectin, Bacillus thuringiensis (Bt) var kurstaki, Bt var aizawai or Cry1Ac when compared with a susceptible laboratory population, Lab-UK. A sub-population was selected for six generations (laboratory G3-G8) with deltamethrin (delta-SEL), while a second sub-population was left unselected (UNSEL). Bioassays at G9 found that selection with deltamethrin gave resistance ratios of >230 compared with UNSEL (>6730 compared with Lab-UK). The delta-selected population showed no apparent cross-resistance to spinosad, fipronil or indoxacarb. Logit regression analysis of F1 reciprocal crosses between delta-SEL and Lab-UK indicated that resistance to deltamethrin in the delta-SEL population was inherited as an autosomal, incompletely dominant (D(LC) = 0.67) trait. A direct test of monogenic inheritance based on a back-cross of F1 progeny with delta-SEL suggested that resistance to deltamethrin was controlled by more than one factor.     

小菜蛾对阿维菌素的抗性选育及交互抗性研究

用阿维菌素对小菜蛾进行室内抗性汰选,选择压为约杀死种群70％的剂量。连续施药7～8次即表现抗性趋势,汰选至11代,获得抗性指数为80.71的抗性种群(ABM-R)。ABM-R种群对所测试的有机磷杀虫剂乙酰甲胺磷、有机氯类的硫丹、沙蚕毒素类的杀螟丹、氨基甲酸酯类的灭多威、微生物杀虫剂Bt、磺胺脲类衍生物丁醚脲、芳基取代的吡咯杂环化合物虫螨腈和昆虫生长调节剂定虫隆、虫酰肼无交互抗性(R/S为0.73～1.19),而对苯基吡唑类氟虫腈的敏感性却有所上升(R/S为0.22)。增效剂试验显示,PB和唧对ABM-S种群无增效作用,而对ABM-R种群增效作用显著,增效比分别为24.57和13.61,表明多功能氧化酶和羧酸酯酶在抗性机制中可能起重要作用。     

The effects of kaolin particle film on Plutella xylostella behaviour and development

Studies were conducted to evaluate the effect of a kaolin-based particle film against the diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae). The effect of the particle film on development, survival and host plant selection was tested on calabrese seedlings, Brassica oleracea italica Plenck cv. Fiesta F(1), under controlled environmental conditions in the laboratory. Survival to adulthood was significantly reduced and development time increased on kaolin-treated compared with water-treated host plants. The hatch rate of neonate P. xylostella larvae from eggs laid on an artificial substrate was unaffected by the particle film applied after oviposition. Experiments showed that, when given the choice, significantly fewer larvae first made contact with the kaolin-treated compared with the water-treated plant material and that after 24 h there were still significantly fewer larvae present on kaolin-treated leaves. Adult females, however, deposited more eggs on host plants coated with the kaolin particle film. As part of this series of experiments the water control treatment was compared with plant material which had been sprayed with kaolin on the upper surface only and on both leaf surfaces. In general, any observed treatment effect was enhanced with an increase in the particle film coverage. The results warrant the extension of investigations of kaolin-based particle films to field-based P. xylostella management strategies.     

Inheritance of resistance to a Bacillus thuringiensis toxin in a field population of diamondback moth (Plutella xylostella)

Inheritance of resistance to the Bacillus thuringiensis Berl. CryIA(b) crystal protein was studied in Plutella xylostella L. (diamondback moth). A field population 50-fold more resistant to CryIA(b) than a control susceptible strain was used. Dose-mortality curves of the resistant population, the susceptible strain and the F₁ from the two reciprocal crosses were compared. Resistance transmission to the F₁ was dependent on the sex of the resistant progenitor. Sex ratio of the survivors to high doses of CryIA(b) in the F₁ of the two reciprocal crosses did not corroborate the preliminary hypothesis of resistance being due to a recessive sex-linked allele. Since, in a previous work, the loss of CryIA(b) binding capacity of resistant insects had been demonstrated, binding to midgut tissue sections from F₁ individuals was also analysed. The presence of binding in all of the F₁ preparations showed that, at least, a recessive autosomal allele was responsible for the loss of binding capacity in the resistant population.     

小菜蛾越冬生物学特性研究

研究了小菜蛾不同虫态的过冷却点,蛹的低温生存能力和越冬能力。小菜蛾的过冷却现象比较明显,蛹期过冷却点最低(-20.12℃),成虫次之(-16.56℃),幼虫期高(平均为-13.72℃),其中4龄幼虫过冷却点最高(-8.5℃)。表明在不同虫态中,蛹的抗低温能力最强。在-10、-5、0℃和5℃条件下,小菜蛾蛹的LT50、LT90、LT99.9随着温度的降低而缩短;蛹死亡99.9%需要的时间分别为10.29、21.68、27.77、41.39d,表明在冬季温度连续低于0℃时间超过28d的地区,小菜蛾不能越冬。连续两年冬天的埋蛹试验结果,蛹在北京4个地点的越冬死亡率均为100%。结合我国的气候区划分析,初步确定小菜蛾在北京地区野外不能越冬。     

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。     

Molecular analysis of pyrethroid resistance conferred by target insensitivity and increased metabolic detoxification in Plutella xylostella

BACKGROUND: The pyrethroid resistance of the diamondback moth Plutella xylostella (L.) is conferred by increased gene expression of cytochrome P450 to detoxify the insecticide and/or through gene mutation of the sodium channel, which makes the individual insensitive to pyrethroids. However, no information is available about the correlation between the increased metabolic detoxification and the target insensitivity in pyrethroid resistance. RESULTS: Frequencies of pyrethroid‐resistant alleles (L1014F, T929I and M918I) and two resistance‐related mutations (A1101T and P1879S) at the sodium channel and expression levels of the cytochrome P450 gene CYP6BG1 were examined individually using laboratory and field strains of P. xylostella. Real‐time quantitative PCR analysis using the laboratory strains revealed that levels of larval expression of the resistant strain, homozygous for the pyrethroid‐resistant alleles other than the M918I, are significantly higher than those of the susceptible strain. In the field strains, the expression levels in insects having the same resistant alleles as those of the resistant strains varied greatly among individuals. The expression levels were not significantly higher than those in the heterozygotes. CONCLUSION: Significant correlation between the target insensitivity and the increased metabolic detoxification in pyrethroid resistance of P. xylostella was observed in the laboratory but not in the field. Copyright © 2010 Society of Chemical Industry     

Lack of cross-resistance to indoxacarb in insecticide-resistant Spodoptera frugiperda (Lepidoptera: Noctuidae) and Plutella xylostella (Lepidoptera: Yponomeutidae)

Two field strains of the fall armyworm, Spodoptera frugiperda (JE Smith), collected from corn in north Florida showed high resistance to carbaryl (626- and 1159-fold) and moderate resistance to parathion-methyl (30- and 39-fold) as compared with a laboratory susceptible strain. A field strain of the diamondback moth, Plutella xylostella (L.) collected from cabbage in north Florida and selected for 20 generations with permethrin showed high resistance to permethrin (987-fold) as compared with a susceptible strain. However, in all instances, no cross-resistance to indoxacarb, a novel oxidiazine insecticide, was observed in these two species. Biochemical studies revealed that, in S. frugiperda, activities of detoxification enzymes (microsomal oxidase, glutathione S-transferase and general esterase) were significantly higher in the field strains than in the susceptible strain, indicating that these detoxification enzymes were not actively involved in the resistance to indoxacarb. The lack of cross-resistance between indoxacarb and permethrin in P. xylostella further supports the notion that the mode of action of these insecticides on the insect sodium channel is different.     

南京小菜蛾对拟除虫菊酯的抗性机制

通过解毒酶活性测定与钠离子通道基因片段的克隆、测序,研究了南京小菜蛾对拟除虫菊酯产生高水平抗性的生化和分子机制。结果表明,南京抗性种群的酯酶和多功能氧化酶O-脱甲基活性分别是敏感种群的1.06和1.16倍,无显著差异;以2,4二硝基氯苯(CDNB)和1,2-二氯-4-硝基苯(DCNB)为底物,南京抗性种群的谷胱甘肽S-转移酶活性分别是敏感种群的0.68倍和1.03倍;进一步利用聚合酶链式反应(PCR)分别从敏感和抗性小菜蛾基因组DNA中扩增出了位于钠离子通道结构域IIS6的232bp和248bp的DNA片段;与敏感种群相比,南京抗性种群钠离子通道基因存在一个保守性点突变,即C突变为T,并导致亮氨酸突变为苯丙氨酸,表明神经不敏感性是南京小菜蛾对拟除虫菊酯产生高水平抗性的主要机制。