Abstract: The responses to deltamethrin and the changes of the detoxification enzymes were compared by bioassay and biochemical method between the susceptible and resistant strains of cotton bollworm Helicoverpa armigera. The results showed that the levels of resistance to deltamethrin were significantly high in the resistant cotton bollwormeither from the field or laboratory selection, and the ratios were 195.8 and 37 375-fold compared with the susceptible one, respectively. The hydrolase and mixed function oxidase might be the important enzymes to cause the high resistance of cotton bollworm todeltamethrin. The tests of inhibition by special inhibitors in vivo and in vitro indicated that there were high levels of acetyleholinesterase in the susceptible and resistantstrains. However, the affinity to the inhibitors between the two strains was significantly different, suggesting that acetylcholinesterase in the susceptible and resistant strains was changed differently. Consequently, the variation of acetylcholinesterase might also be an important factor affecting the resistance of insecticides even if it is a nerve toxin tocentral nervous system such as deltamethrin.

Key words: cotton bollworm, deltamethrin, resistant mechanism, detoxification