Delta-Class Glutathione S-Transferase Modulates the Susceptibility of Myzus persicae to λ-Cyhalothrin

Glutathione S-transferases (GSTs) constitute a critical enzyme superfamily responsible for xenobiotic detoxification in insects. The green peach aphid, Myzus persicae, is a globally significant agricultural pest that has exhibited declining field susceptibility to λ-cyhalothrin (LCT), a widely applied pyrethroid insecticide. While elevated GST activity has been correlated with LCT tolerance in various aphid populations, the precise molecular mechanisms driving this process have not been fully elucidated. In this study, we functionally characterized a delta-class GST gene (designated MpGSTd1) from M. persicae. The encoded protein possesses hallmark structural motifs of the GST family, including distinct glutathione-binding (G-site) and hydrophobic substrate-binding (H-site) pockets. Transcriptional profiling revealed maximal MpGSTd1 expression during the late nymphal to adult stages, and its transcript levels were markedly induced following LCT challenge. Biochemical analysis of the recombinant MpGSTd1 protein confirmed its catalytic competency toward the model substrate CDNB, exhibiting a V_max of 0.91 µmol/min/mg and a K_m of 2.73 mM. Notably, LCT exposure inhibited the enzyme's activity in vitro with an IC₅₀ of 0.02 mM, and high-performance liquid chromatography (HPLC) assays demonstrated that MpGSTd1 can directly deplete LCT by 11.4%. Furthermore, RNA interference (RNAi)-mediated suppression of MpGSTd1 in vivo significantly elevated aphid mortality upon subsequent LCT exposure. Collectively, these findings delineate an essential role for MpGSTd1 in modulating LCT susceptibility in M. persicae and underscore its potential utility as a molecular target for future aphid management strategies.