【目的】 阐明小菜蛾Plutella xylostella (L.)对乙基多杀菌素的代谢抗性机理，为延缓小菜蛾对乙基多杀菌素抗药性发展及抗性治理技术提供支持。【方法】 通过酶动力学方法测定了小菜蛾对乙基多杀菌素高抗、中抗和敏感种群的谷胱甘肽-S-转移酶、羧酸酯酶、乙酰胆碱酯酶和多功能氧化酶4种代谢解毒酶的比活力。【结果】 乙基多杀菌素高抗小菜蛾种群的谷胱甘肽-S-转移酶、羧酸酯酶、乙酰胆碱酯酶的比活力分别为15.38、3.15和7.30 OD·min^-1·mg^-1pro，显著高于敏感种群；但乙酰胆碱酯酶在中抗种群和敏感种群中比活力差异不显著；多功能氧化酶在高抗、中抗和敏感种群中的比活力分别为4.97、4.08和4.23 OD·min^-1·mg^-1pro，差异不显著。【结论】 谷胱甘肽-S-转移酶、羧酸酯酶和乙酰胆碱酯酶的酶活随着小菜蛾对乙基多杀菌素抗性的增强而增强，而多功能氧化酶的酶活在抗性种群与敏感种群间差异不显著，因此小菜蛾对乙基多杀菌素的代谢抗性机理研究应重点关注这3种酶。

      [Objectives]  To clarify the metabolic mechanisms underlying the resistance of Plutella xylostella (L.) to spinetoram. [Methods]  The activity of glutathione-S-transferase, carboxylesterase and acetylcholinesterase and multifunctional oxidase were measured using the enzyme kinetic method in a highly resistant, moderately resistant and a susceptible strain of P. xylostella. [Results]  The specific enzyme activities of glutathione-S-transfer enzyme, acetylcholinesterase and carboxylesterase were significantly higher in the highly resistant strain than in the susceptible strain. Specific activity to these insecticides were, respectively, 15.38, 3.15 and 7.30 OD·min^-1·mg^-1pro in the highly resistant strain. There was, however, no significant difference in acetylcholinesterase activity between the moderately resistant and susceptible strains, or in multifunctional oxidase activity among all three strains. The specific enzyme activity of multifunctional oxidase activity was 4.97 in the highly resistant strain、4.08 in the middle resistant strain, and 4.23 OD·min^-1·mg^-1pro in the susceptible strain, respectively. [Conclusion]  The glutathione-S-transferase, carboxylesterase, and acetylcholinesterase, activity increased with the level of resistance. There was no significant difference in multifunctional oxidase activity among the three strains. Further investigation of the metabolic mechanism underlying spinetoram resistance in P. xylostella should therefore focus on glutathione-S-transferase, carboxylesterase, and acetylcholinesterase.