and their mutants toward pyrethroid insecticides were not determined in vitro. However, 271L mutation has been reported to be capable of increasing the hydrolysis activity of other insect esterases, like L. cuprina E3, D. melanogaster EST23, and three H. armigera esterases, toward some pyrethroid isomer insecticides in vitro [18] and [19]. Therefore, in this study, insecticide resistance was investigated by comparing the carboxylesterase activities and resistance levels to four OP insecticides and one pyrethroid insecticide between (1) wild-type and mutant esterase transgenic lines and (2) between transgenic lines and non-transgenic lines. The evolutionary fitness characteristics of the two resistance mechanisms were discussed.