The characteristics of voltage-gated sodium channel and the association with lambda cyhalothrin resistance in Spodoptera exigua

Spodoptera exigua has developed very high resistance to pyrethroid insecticides; however, the mode-of-action target of pyrethroids has not been studied, and the mechanism for target resistance remains elusive in this insect. In this study the resistance level of a field collected population from Huizhou, China was assayed with leaf-dip method and further selected in laboratory. The transcripts of voltage-gated sodium channel gene from S. exigua were cloned and analyzed for the structural characteristics, the relative expression levels of transcripts were measured by quantitative RT-PCR. Finally, detection of the point mutations was performed. The bioassay indicated that Huizhou population had developed 309.5-fold resistance to lambda-cyhalothrin, and the selection in laboratory led to the resistant strain (HZ14-sel) with increased resistance of 423-fold. Nine transcripts of sodium channel with 4517–6149 bp nucleotides were identified from S. exigua, among which only one transcript (SeNav4) encode the functional protein with complete domains, and other eight transcripts were observed to lost some transmembrane segments. The L834F mutation in IIS6 corresponding for the typical kdr mutation “L1014F”, was detected in 50% individuals of HZ14-sel strain. These results suggested that lambda-cyhalothrin resistance is associated with point mutations and expression level changes of sodium channel transcripts in HZ14-sel strain.