抗胆碱酯酶剂亚致死剂量对棉铃虫毒力的影响及对乙酰胆碱酯酶的诱导作用

辛硫磷、马拉硫磷和灭多威3种抗胆碱酯酶剂亚致死剂量（LD10）预处理棉铃虫Helicoverpa armigera 3龄幼虫24 h后，对辛硫磷、马拉硫磷、灭多威、溴氰菊酯和高效氯氰菊酯5种杀虫药剂的毒力影响有明显差异。酶动力学研究表明：在48 h内，辛硫磷亚致死剂量对棉铃虫乙酰胆碱酯酶比活力有一定的抑制作用，24 h仅为对照组的0.56倍；马拉硫磷、灭多威则可以诱导乙酰胆碱酯酶的比活力增加，诱导最大值时间分别为3 h和12 h。通过对米氏常数（K_m）值分析表明，辛硫磷诱导48 h内对乙酰胆碱酯酶与底物亲和力的影响不大，马拉硫磷、灭多威诱导48 h内乙酰胆碱酯酶对底物亲和力有所下降，其中灭多威诱导组最为明显。3种药剂亚致死剂量处理24 h后，通过蔗糖密度梯度离心表明5%蔗糖梯度层乙酰胆碱酯酶分布百分数明显高于对照组，而20%蔗糖梯度层却明显低于对照组，说明亚致死剂量处理可能引起乙酰胆碱酯酶分子型及不同分子型分布比例的变化。

Effects of sublethal doses of anticholinesterase agents on toxicity of insecticides and their induction to acetylcholinesterase(AChE) activity in Helicoverpa armigera

Effects on toxicity of insecticides by sublethal doses of anticholinesterase agents (phoxim, malathion and methomyl) and their induction of AChE specific activity, the Michaelis constants(K_m) were investigated in the larvae of the cotton bollworm, Helicoverpa armigera(Hübner). The results indicated that toxicity of five insecticides had significant differences at 24 hours after treatments. The AChE specific activity of cotton bollworm was moderately depressed at 24 hours after treatment with LD₁₀ of phoxim. The time course study revealed that the maximum induction of AChE specific activity by malathion and methomyl was observed at 3 h and 12 h after treatment, resulting in a 1.45 fold and 1.92 fold increase of AChE activity, respectively. The sublethal dose of phoxim had no effect on the affinity of AChE toward acetylthiocholine in 48 hours after treatment, but AChE affinities were significantly reduced after treatment with LD10 of malathion and methomyl. The density gradient centrifugation showed that the distribution of AChE activity in the 5% gradient layer was higher than the control at 24 hours after treatment with sublethal doses of anticholinesterase agents, but lower in the 20% gradient layer. It was inferred that treatment of sublethal doses may cause the changes in molecular forms and the distribution of different molecular forms of AChE.