Molecular identification of four novel cytochrome P450 genes related to the development of resistance of Spodoptera exigua (Lepidoptera: Noctuidae) to chlorantraniliprole.

Abstract

The beet armyworm, Spodoptera exigua, is an omnivorous insect that damages a variety of crops worldwide. Chlorantraniliprole is a new diamide insecticide that acts on the ryanodine receptors in insects. The aim of this study was to explore key genes related to the development of chlorantraniliprole resistance in S. exigua. Transcriptomes were compared between beet armyworms from a susceptible laboratory strain (Sus-Lab) and Sus-Lab screened with LC25 sublethal doses of chlorantraniliprole for six generations (SE-Sel). Ten of 11 cytochrome P450 genes with upregulated expression verified by quantitative reverse transcription polymerase chain reaction (qRT-PCR) in SE-Sel strains were detected in SE-PZ16 and SE-ZY16, two extremely resistant field populations. In addition, expression of four new cytochrome P450 genes, CYP9A21v1, CYP9A21v2, CYP9A21v3 and CYP9A21v4, was shown in the two field populations and was significantly higher in the SE-Sel strain than in the Sus-Lab strain (P < 0.05). Their full-length and protein tertiary structures were also cloned and predicted. The function of CYP9A21v3 was analysed by RNA interference, and the relative expression of CYP9A21v3 in the SE-ZY16 population after feeding on dsRNA was lower than in the control group. Moreover, mortality rates in insects treated at the LC50 of chlorantraniliprole after dsRNA feeding were significantly higher than in the control group 24 h after treatment (P < 0.05). Overexpression of CYP9A21v3 may be a primary factor in the development of chlorantraniliprole resistance in beet armyworms. © 2018 Society of Chemical Industry.