Identification and Functional Characterization of a Sigma Glutathione S-Transferase CpGSTs2 Involved in λ-Cyhalothrin Resistance in the Codling Moth Cydia pomonella.

The codling moth, Cydia pomonella (L.), is a quarantine pest of global significance impacting pome fruits and walnuts. It has evolved resistance to many commonly used insecticides including λ-cyhalothrin. Glutathione S-transferases (GSTs) are multifunctional enzymes playing a crucial role in the detoxification of insecticides in insects. However, the role of specific GST gene in λ-cyhalothrin resistance in C. pomonella is unclear. In this study, we identified three sigma-class genes (CpGSTs1, CpGSTs2, and CpGSTs3). These genes were ubiquitously expressed at all developmental stages, and of these, the expression level of CpGSTs2 in the larval stage was significantly higher than in the egg, pupal, and adult stages. Moreover, CpGSTs2 was predominantly expressed in the fat body while lower levels in the cuticle. In addition to exposure of larvae to LD10 of λ-cyhalothrin elevating the expression level of CpGSTs2, mRNA levels of CpGSTs2 in a field population (ZW_R) from northeast China, which has developed moderate level resistance to λ-cyhalothrin, was significantly higher than that of susceptible strains. In vitro inhibition assays demonstrated that λ-cyhalothrin inhibited the conjugating activities of recombinant CpGSTs2, and metabolic assays indicated that λ-cyhalothrin could be depleted by recombinant CpGSTs2. These results bring evidence for the involvement of CpGSTs2 in C. pomonella in resistance to λ-cyhalothrin.