Abstract

BACKGROUND Previous field-based resistance monitoring and indoor selection studies by the present authors indicated significant cross-resistance between the sulfoximine insecticide sulfoxaflor and neonicotinoid insecticides in the brown planthopper, Nilaparvata lugens. However, the mechanism of cross-resistance has remained unclear. RESULTS In this study, we investigated the involvement of cytochrome P450 monooxygenases in cross-resistance between neonicotinoids and sulfoxaflor with a particular focus on overexpression and qualitative changes to CYP6ER1. Real-time quantitative PCR results show that the mRNA and DNA levels of CYP6ER1 in the sulfoxaflor-resistant (SFX-R) strain (G120) were 46.71- and 2.93-fold higher than in the sulfoxaflor-susceptible (SFX-S) strain, respectively. Meanwhile, the toxicity of sulfoxaflor and four neonicotinoids (nitenpyram, clothianidin, dinotefuran, and thiamethoxam) was synergized by the inhibitor piperonyl butoxide in SFX-R (G120). Transcript abundance of CYP6ER1 was induced by sulfoxaflor and by each tested neonicotinoid. RNA interference reduced CYP6ER1 expression and significantly increased susceptibility of SFX-R to sulfoxaflor and the four neonicotinoids. Three CYP6ER1 transcripts were identified in SFX-R, including two novel transcripts. Heterologous overexpression of each variant reduced sensitivity of Drosophila melanogaster to sulfoxaflor, nitenpyram, clothianidin, dinotefuran, and thiamethoxam. Further molecular modeling studies showed that the ligand binding pockets of CYP6ER1vM, CYP6ER1vM1, and CYP6ER1vK are similar, and they exhibit high binding activity with all five insecticides. CONCLUSION