Five contemporary strains of the bollworm Helicoverpa armigera Hubner from China, Pakistan and India, all with high resistance to pyrethroids, were compared with a standard susceptible strain that originated from the Cote D Ivoire in the 1970s (SCD). Two of the Chinese strains (YGF and YGFP) were derived by laboratory selection from a third, field collected strain (YG). The strain YG exhibited 7-, 14- and 21- fold resistance to fenvalerate, cypermethrin and deltamethrin, respectively. After selection with fenvalerate for 14 generations (YGF), this increased to 1690-, 540- and 73-fold. Selection with a mixture of fenvalerate and piperonyl butoxide (PBO) for 14 generations (YGFP) resulted in resistance ratios of 2510, 2920 and 286. The synergistic ratios to fenvalerate that resulted from pre-treatment of PBO were 5-, 462- and 12-fold in YG, YGF and YGFP strains, respectively. Resistance ratios for a Pakistani strain (PAK) were 2320-, 4100- and 223-fold to fenvalerate, cypermethrin and deltamethrin, respectively. The synergistic ratio of PBO to these pyrethroids was 450-, 950- and 11-fold. The strong synergism of pyrethroids by PBO implied that an oxidative metabolism could be involved in pyrethroid resistance in these resistant strains. The activities of cytochrome P450 monooxygenases from midguts of final instar larvae to p-nitroanisole (PNOD), ethoxycoumarin (ECOD), methoxyresorufin (MROD) significantly increased in all the resistant strains when compared with the susceptible strain. This further implies that cytochrome P450 monooxygenases are involved in pyrethroid resistance in Asian H. armigera. Comparative in vitro studies of the metabolism of 14C-deltamethrin by midgut microsomes of the resistant PAK and susceptible SCD strains showed that the resistant strain had a much greater capacity than the susceptible strain for the metabolic degradation of deltamethrin. This enhanced metabolic degradation occurred in the presence of NADPH which suggested an oxidative detoxification. In the resistant strains, minor increases in glutathione S-transferase activity to the substrates (CDNB and DCNB), and esterase activity (to the substrate a-naphthyl acetate) further suggested that, of the putative metabolic mechanisms, oxidases are the most important. This study provides the first evidence that cytochrome P450 monooxygenases are a major metabolic mechanism responsible for pyrethroid resistance in H. armigera from Asia.

通过RT-PCR克隆了烟粉虱Bemisia tabaci（Gennadius）南京种群（B2生物型）的钠离子通道结构域ⅡS4-6CDNA段，证实了与拟除虫菊酯抗性相关的是位于第925位亮氨酸到异亮氨酸的突变（L925I），并建立了L925I突变的PASA检测技术。与SUD-S 敏感品系相比，2002 年采自南京棉花上的烟粉虱种群对氯氰菊酯具有77倍的抗性，用氯氰菊酯对该种群进行多次筛选后，该种群对氯氰菊酯的抗药性提高到227倍。PASA检测结果表明筛选后的南京种群中100%个体都具有L925I突变（6111%的个体为L925I突变纯合子，3819%的个体为杂合子），而未筛选的南京种群只有75%个体具有L925I突变（35%个体为L925I突变纯合子，40%的个体为杂合子，25%的个体为野生型）。该结果表明了烟粉虱钠离子通道L925I突变与对拟除虫菊酯抗性密切相关。还讨论了烟粉虱对拟除虫菊酯抗性的代谢机理。

A mutation, leucine to isoleucine at position 925 (L925I) in the Ⅱ S 4-6 linker of the para type sodium channel protein from the Nanjing strain (B2biotype) of the tobacco whitefly, Bemisia tabaci (Gennadius) was identified to be associated with pyrethroid resistance. The DNA2based genotyping technique PASA (PCR amplification of specific allele) for rapid detection of the L925I mutation was established. The Nanjing strain collected from cottons in Nanjing in 2002 showed 772 fold resistance to cypermethrin compared with the susceptible SUD2S strain. The resistance to cypermethrin in the selected Nanjing strain increased to 2272 fold after several selections with cypermethrin. PASA genotyping results indicated that 100% individuals from the selected Nanjing strain had L 925I mutation (61.1% homozygotes and 38.9% heterozygotes), whereas only 75% individuals from the unselected Nanjing strain had L925I mutation (35% homozygotes, 40% heterozygotes and 25% wild type). Our results indicated that L925I mutation was tightly associated with pyrethroid resistance in the tobacco whitefly from Nanjing. Possible metabolic mechanisms for pyrethroid resistance in this strain were discussed.

A laboratory strain (GY) of Helicoverpa armigera (Hubner) was established from surviving larvae collected from transgenic cotton expressing a Bacillus thuringiensis var. kurstaki insecticidal protein (Bt cotton) in Gaoyang County, Hebei Province, People's Republic of China, in 2001. The GYBT strain was derived from the GY strain through 28 generations of selection with activated Cry1Ac delivered by diet surface contamination. When resistance to Cry1Ac in the GYBT strain increased to 564-fold after selection, we detected high levels of cross-resistance to Cry1Aa (103-fold) and Cry1Ab (>46-fold) in the GYBT strain with reference to those in the GY strain. The GYBT strain had a low level of cross-resistance to B. thuringiensis var. kurstaki formulation (Btk)(5-fold) and no cross-resistance to Cry2Aa (1.4-fold). Genetic analysis showed that Cry1Ac resistance in the GYBT strain was controlled by one autosomal and incompletely recessive gene. The cross-resistance pattern and inheritance mode suggest that the Cry1Ac resistance in the GYBT strain of H. armigera belongs to "mode1," the most common type of lepidopteran resistance to B. thuringiensis toxins. A cadherin gene was cloned and sequenced from both the GY and GYBT strains. Disruption of the cadherin gene by a premature stop codon was associated with a high level of Cry1Ac resistance in H. armigera. Tight linkage between Cry1Ac resistance and the cadherin locus was observed in a backcross analysis. Together with previous evidence found with Heliothis virescens and Pectinophora gossypiella, our results confirmed that the cadherin gene is a preferred target for developing DNA-based monitoring of B. thuringiensis resistance in field populations of lepidopteran pests.