The voltage-gated sodium channel mutation and detoxification enzymes associated with the resistance of Grapholita molesta (Busck) (Lepidoptera: Tortricidae) to lambda-cyhalothrin

The oriental fruit moth , Grapholita molesta (Busck) (Lepidoptera: Tortricidae), a major fruit pest, is primarily controlled with pyrethroid insecticides such as lambda-cyhalothrin and resistance has emerged as a serious threat to management. In this study, we compared a lambda-cyhalothrin-resistant strain (RS) with a susceptible strain (SS) of G. molesta . Sequencing of the voltage-gated sodium channel (VGSC) gene revealed the L1014F mutation exclusively in RS individuals, strongly associated with knockdown resistance. Bioassays showed that the RS exhibited a 13.1-fold cross-resistance to deltamethrin and a 6.0-fold cross-resistance to bifenthrin, as well as moderate cross-resistance to chlorantraniliprole, abamectin, and emamectin benzoate. While showing only low or negligible cross-resistance to other insecticides tested. Synergist assays indicated that piperonyl butoxide (PBO) increased lambda-cyhalothrin toxicity by 1.72-fold in RS, implicating cytochrome P450 as key contributors. Biochemical assays confirmed significantly elevated activities of glutathione S-transferase (GST) and P450 in RS relative to SS. Transcriptomic analysis identified 758 differentially expressed genes, including 13 P450s, 5 GSTs, and 2 carboxylesterases (CarEs), with qRT-PCR validating strong up-regulation of CYP333B121 (14-fold), CYP6B230 (15-fold), CYP6AB117 (13-fold), and GSTs2 (5-fold). These findings suggest that the target-site resistance conferred by the L1014F kdr mutation, together with metabolic resistance mediated by overexpressed P450 and GST genes, jointly contribute to the resistance of G. molesta to lambda-cyhalothrin.