Epsilon Class Glutathione S-Transferase Confers Phoxim Tolerance in the Black Cutworm Agrotis ipsilon (Lepidoptera: Noctuidae)

The black cutworm Agrotis ipsilon is a serious crop pest. Phoxim, an organophosphorus insecticide, has been widely used to control A. ipsilon. When phoxim is extensively applied, the susceptibility of A. ipsilon to insecticide is reduced. However, the mechanisms of tolerance of A. ipsilon to phoxim remain unclear. Herein, we report that an epsilon class glutathione S-transferase, AiGSTE1, confers phoxim tolerance in A. ipsilon. Exposure to a sublethal concentration (LC50) of phoxim caused oxidative stress and activated the transcription of AiGSTe1 genes in A. ipsilon larvae. Recombinant AiGSTE1 expressed in Escherichia coli could metabolize phoxim. Furthermore, E. coli cells overexpressing AiGSTE1 displayed significant tolerance to oxidative stress. Knockdown of AiGSTe1 by RNA interference significantly increased the mortality of A. ipsilon larvae to phoxim. These results demonstrate that AiGSTE1 confers phoxim tolerance in A. ipsilon by metabolizing the insecticide and preventing phoxim-induced oxidative stress.