Abstract: By applying bioassays and biochemical analyses, the reactions to endosulfan and deltamethrin of two cotton bollworm Helicoverpa armigera (Hübner) populations, the susceptible one (collected from Xinjiang) and resistant one (by indoor selection using endosulfan and deltamethrin ),and the activity dynamics of their α-naphthylacetate esterase and acetylcholinesterase (AChE) were tested. The results showed that the resistance ratios to endosulfan and deltamethrin were 13 and 66 folds in Xinjiang cotton bollworm after selection. ΑNaphthylacetate esterase and aceylcholinesterase activities of the resistant populations were higher than that of the susceptible. Pretreated with corresponding insecticides the activity of α-naphthylacetate esterase was inhibited. The affinity of α-naphthylacetate esterase to the substrate was higher in the 2 resistant populations than the susceptible, while the maximum velocity (V_max) was lower. But the affinity of AChE to the substrate was lower and V_max was higher. It was found on the PAGE profiles that the 2 resistant populations possessed a special band and the immigration rate of this band was similar. In the resistance and susceptible populations the activity of this enzyme band can be inhibited by the inhibitor methyl paraoxon of aceylcholinesterase. These results suggested that α-naphthylacetate esterase had involved in hydrolysis and sequestration and AChE played an important role in the resistance mechanism of cotton bollworm to the 2 insecticides.

Key words: cotton bollworm, resistance, endosulfan, deltamethrin, biochemical mechanism