甜菜夜蛾不同世代对氯氟氰菊酯抗性减退及多功能氧化酶系活性变化

在室内用人工饲料连续饲养和未用药剂筛选条件下，测定了采自田间对氯氟氰菊酯产生高水平抗性甜菜夜蛾Spodoptera exigua (Hübner)种群的抗药性及其多功能氧化酶系活性的变化情况。用点滴法测定不同世代3龄幼虫抗性结果为：室内F₁代LD₅₀值为 0.9672 μg/头，抗性倍数为4 836.0倍，以后各世代逐渐降低，至F₄₃代LD₅₀值为0.0325μg/头，抗性倍数为162.5倍，抗性水平下降了29.8倍。用浸叶法测定不同世代3龄幼虫抗性结果为：室内F₁代LC₅₀值为185.6 mg/L，抗性倍数为964.7倍，以后各世代也逐渐降低，至F₄₃代LC₅₀值为9.2 mg/L，抗性倍数为47.8倍，抗性水平下降了20.2倍。与敏感品系相比，该田间种群室内饲养至F₄₃代仍处于较高的抗性水平，抗性减退缓慢，很难恢复到敏感水平。测定甜菜夜蛾田间种群室内F₂、F₂₀和F₄₁代及敏感品系5龄幼虫中肠微粒体甲氧试卤灵-O-脱甲基酶、乙氧试卤灵-O-脱乙基酶、芳香基羟基化酶及艾氏剂环氧化酶活性，结果表明：与敏感品系相比，田间种群甲氧试卤灵-O-脱甲基酶和艾氏剂环氧化酶的活性仅F₂代显著较高，F₂₀和F₄₁代差异不显著，乙氧试卤灵-O-脱乙基酶和芳香基羟基化酶的活性F₂、F₂₀和F₄₁代均显著较高。结果提示甜菜夜蛾抗性水平可能与其体内微粒体多功能氧化酶系活性有密切关系。

Resistance reduction to lambda-cyhalothrin and activity change of multifunction oxidases in the beet armyworm, Spodoptera exigua,under non-selection pressure in the laboratory

Larvae of the beet armyworm, Spodoptera exigua (Hübner), originally collected from the field of sugar beet, were reared on artificial diet and evaluated for resistance to lambda-cyhalothrin for 43 generations under laboratory condition without exposure to any insecticide (under non-selection). Lambda-cyhalothrin showed LD₅₀ value of 0.9672 μg/larva at F₁ generation and decreased gradually in onward generations,  resulting in LD₅₀ value of 0.0325 μg/larva at F₄₃ generation by using topical application, and the resistance level of the non-selected strain decreased from 4 836.0 fold to 162.5-fold compared with the susceptible strain. In leaf dipping bioassay, lambda-cyhalothrin exhibited LC₅₀ value of 185.6 mg/L at F₁ generation and decreased gradually to onward generations with LC₅₀ value of 9.2 mg/L at F₄₃ generation. Correspondingly, the resistance level of the non-selected strain decreased from 964.7-fold to 47.8-fold compared with the susceptible strain. Though decreased 29.8-fold (topical application) or 20.2-fold (leaf dipping bioassay) from F₁ to F₄₃ generation, the resistance levels of F₄₃ generation was still quite high,  and this indicated that it was very difficult for the beet armyworm to recover the sensitivity to lambda-cyhalothrin. Activities of four monoxygenases,  i.e., methoxyresorufin O-demethylase (MROD), ethoxyresorufin O-deethylase (EROD),  arylhydrocarbon hydroxylase (AHH) and aldrin epoxidase (AE), of F₂, F₂₀ and F₄₁ generation were compared with that of the susceptible strain, respectively. Compared with the susceptible strain, the activities of MROD and AE in midguts in the 5th instar larvae of F₂ generation was significantly higher, but those of F₂₀ and F₄₁ generations showed no significant difference. Similarly,  the activities of EROD and AHH of F₂,  F₂₀ and F₄₁ generation were also significantly higher compared with the susceptible strain. The results suggested that the resistance of S. exigua to lambda-cyhalothrin was closely correlated with multi-function oxidase which may play different roles at different resistant levels.