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

Abstract

The codling moth, <i>Cydia pomonella</i> (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 <i>C. pomonella</i> is unclear. In this study, we identified three sigma-class genes (<i>CpGSTs1</i>, <i>CpGSTs2</i>, and <i>CpGSTs3</i>). These genes were ubiquitously expressed at all developmental stages, and of these, the expression level of <i>CpGSTs2</i> in the larval stage was significantly higher than in the egg, pupal, and adult stages. Moreover, <i>CpGSTs2</i> 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 <i>CpGSTs2</i>, mRNA levels of <i>CpGSTs2</i> 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 <i>CpGSTs2</i>. These results bring evidence for the involvement of <i>CpGSTs2</i> in <i>C. pomonella</i> in resistance to λ-cyhalothrin.