Abstract: The toxicities of imidacloprid and phoxim against cotton aphids fed on transgenic Bt cotton for different generations were measured by leafdip bioassay in the laboratory and compared with those on parental cotton variety. Activities of esterase, carboxylesterase and acetylcholinesterase of cotton aphids fed on Bt cotton were detected with microtiter plate reader. The results indicated that the susceptibility of cotton aphids to either imidacloprid or phoxim was not affected by Bt cotton. For both kinds of insecticides, there was no significant difference of LC₅₀ among cotton aphids fed on Bt cotton for 1 generation, on Bt cotton for over 60 generations, and on parental cotton continuously. For all three detoxification enzymes tested, there was no significant difference of enzyme activities among cotton aphids fed on Bt cotton for 1 and 21 generations, and those on parental cotton. It was so concluded that transgenic Bt cotton had no significant effects on the susceptibility to insecticides and detoxification enzyme activities of cotton aphids.

Key words: Transgenic Bt cotton, Aphis gossypii, insecticide susceptibility, detoxification enzyme, acetylcholinesterase