Characterization of the thioredoxin peroxidase gene and its role in lambda-cyhalothrin tolerance in Agrotis ipsilon (Lepidoptera: Noctuidae)

Exposure to insecticides can cause abnormally high accumulation of reactive oxygen species (ROS) and oxidative stress in insects. Thioredoxin peroxidases (TPXs) play critical roles in protecting insects from insecticide-induced oxidative injury. The black cutworm, Agrotis ipsilon (Hufnagel) (Lepidoptera: Noctuidae), is an important agricultural pest. Lambda-cyhalothrin (LCT) is a pyrethroid insecticide used to control A. ipsilon. However, whether LCT causes oxidative stress and whether TPXs are involved in the antioxidant defense in A. ipsilon remain unknown. In this study, a TPX gene, AiTPX6, was identified from A. ipsilon. AiTPX6 consists of five exons and four introns and encodes a protein of 227 amino acid residues. The AiTPX6 protein has characteristic features of TPXs, including the peroxidase active site motif PVCTTE with a conserved catalytic cysteine residue. Phylogenetic analysis revealed that AiTPX6 belongs to the “1-Cys” TPX group. The mRNA transcripts of AiTPX6 were most abundant in the larval midgut and at the fifth- and sixth-instar larval stages. Exposure to a sublethal concentration (LC₅₀) of LCT significantly increased the H₂O₂ and malondialdehyde (MDA) concentrations and elevated the mRNA level of AiTPX6, suggesting that LCT-induced oxidative stress activates AiTPX6 transcription. Recombinant AiTPX6 expressed in Escherichia coli displayed potent antioxidant activity, protecting the cells against oxidative stress. Knockdown of AiTPX6 via RNA interference (RNAi) significantly increased the mortality rate of A. ipsilon following LCT exposure. These findings revealed that AiTPX6 contributes to LCT tolerance via antioxidant defense and could therefore be used as a potential target for RNAi-based control of A. ipsilon.