Abstract: By using the leaf-dip method,effects of sublethal concentrations of chlorantraniliprole on insecticide susceptibility and detoxifying enzyme activity in the larvae of diamondback moth (DBM),Plutella xylostella,were investigated.After continuous treatment with sublethal concentrations (LC10 and LC25) of chlorantraniliprole for five generations,the susceptibility of DBM to chlorantraniliprole and spinosad decreased by 57.3%,67.7% and 60.2%,51.5% respectively,compared to the untreated control,but kept susceptible to chlorpyrifos and beta-cypermethrin.When the 3rd instar larvae were treated with chlorantraniliprole at concentration of LC10 and LC25 for 24,48 and 72 h,the specific activity of carboxylesterase (CarE) was induced,but the specific activity of cytochrome P450 O-deethylase (ECOD),glutathione S-transferase (GSTs) and aryl amidase were significantly inhibited.After continuous treatment with LC10 and LC25 of chlorantraniliprole for 5 generations,the CarE and ECOD activity of the DBM were increased significantly to 1.16-,1.40-fold and 1.65-,1.56-fold respectively,whereas the specific activity of GSTs and aryl amidase was decreasedby 11.0%,27.5% and 43.6%,52.5% respecitively,comparing to those of the untreated control.These results suggested that the diamondback moth may have high risk of developing resistance to chlorantraniliprole,and the carboxylesterase and mixed function oxidase may be involved in the resistance of the DBM to chlorantraniliprole.