The Role of Detoxification in Abamectin resistant Plutella xylostella (L.)

Tests were conducted to determine the activity of detoxification enzyme systems, including carboxylesterase (CarE), gluthione S-transferase (GST) and mixed-function oxidase (MFO) in the abamectin susceptible (ABM-S) and-resistant (ABM-R) strains. There were significant differences in CarE activities at various developmental stages except the first and the second instars between the two strains. The differences increased when the age of instar increased. The CarE specific activity of ABM-R strain at the late fourth instar was 2.25-fold higher than that of the ABM-S strain. Kinetics studies showed that change of CarE molecular play a key role in the earlier instar. Quantitative differences might gradually replace the role within lately instar. Esterase isozyme upon isoelectric focusing eletrophores demonstrated that the high levels of total esterase activity in ABM-R was due to the increased activities of E7, E13 and E15 isozymes. The biggest difference of GST activities between ABM-S and ABM-R strain was at earlier stage, which was 2.09-fold. However, the differences reduced with the increase of larval age. And no difference was observed at the late fourth instar. It was unexpected that there was no significant difference in O-demethylase activity of the monooxygenases between the two strains. Four possible reasons were discussed.