明确甜菜夜蛾 Spodoptera exigua（Hübner）不同龄期幼虫对甲氨基阿维菌素苯甲酸盐和毒死蜱的敏感性及其与羧酸酯酶、多功能氧化酶、谷胱甘肽S-转移酶和乙酰胆碱酯酶活性的相关性。【方法】采用室内生物测定方法检测甜菜夜蛾不同龄期幼虫对药剂的敏感性，并检测了不同龄期幼虫体内羧酸酯酶、多功能氧化酶、谷胱甘肽S-转移酶和乙酰胆碱酯酶的活力。【结果】在所测定的5个龄期中，随龄期增加，敏感性逐渐降低，其中1~5龄幼虫对甲氨基阿维菌素苯甲酸盐的LC₅₀分别为0.1010、0.3561、0.7568、1.4325和8.4390 mg/L，对毒死蜱的LC₅₀分别为27.4632、46.8495、87.5222、129.3217和1 356.6770 mg/L。单头幼虫的羧酸酯酶、多功能氧化酶、谷胱甘肽S-转移酶和乙酰胆碱酯酶活力随虫龄的增加而提高，与龄期间对药剂的敏感性呈负相关（由于外源化合物摄入量减少，5龄单头幼虫的多功能氧化酶活力略有降低）。【结论】甜菜夜蛾不同龄期幼虫对药剂的敏感性存在非常明显的差异，在田间防治中，应选择对杀虫剂敏感性较高的低龄幼虫作为最佳防治时期。

        [Objectives]  The objective of this study is to analyze the susceptibility of different larval instars of the beet armyworm Spodoptera exigua (Hübner) to emamectin benzoate and chlorpyrifos and the correlation of susceptibility with enzyme activity. [Methods]  Bioassay was conducted and activity of esterase, mixed function oxidase, glutathione-S- transferase and acetylcholinesterase in different larval instars of the beet armyworm were tested in the laboratory. [Results] Sensitivity to insecticides decreased continuously as larvae developed from 1st to 5th instar, the LC₅₀ for emamectin benzoate of instars 1 to 5 were 0.1010, 0.3561, 0.7568, 1.4325 and 8.4390 mg/L, respectively, while the LC₅₀ for chlorpyrifos were 27.4632, 46.8495, 87.5222, 129.3217 and 1 356.6770 mg/L, respectively. The activities of esterase, mixed function oxidase, glutathione S-transferase and acetylcholinesterase increased with increasing larval instar (the activity of mixed function oxidase of the 5th instar larvae reduced slightly due to the reduced intake of exogenous compounds). There was a negative correlation between enzyme activity and sensitivity to insecticides. [Conclusion]  The sensitivities of different larval instars of beet armyworm to insecticides were found to be significantly different. The best time to control the beet armyworm is at the early instar larval stage, when sensitivity to insecticides is high.