The interaction of nicotinic acetylcholine receptor subunits Ld & alpha;3, Ld & alpha;8 and Ld & beta;1 with neonicotinoids in Colorado potato beetle, Leptinotarsa decemlineata

The Colorado potato beetle (CPB), Leptinotarsa decemlineata (Say), is an extremely destructive notifiable quarantine pest. Over the last two decades, neonicotinoid insecticides, particularly thiamethoxam and imidacloprid, have been used to control it in Xinjiang, and local field populations have developed different levels of resistance in consequence. However, the contributions of nicotinic acetylcholine receptors (nAChRs) to neonicotinoid resistance are currently poorly understood in CPB. Previous studies have shown that nAChR & alpha;1, & alpha;3, & alpha;8 and & beta;1 are major target subunits for neonicotinoids in some model and important agricultural insects including nAChR & alpha;1 subunit of L. decemlineata (Ld & alpha;1). In this study, the expression levels of Ld & alpha;3, Ld & alpha;8 and Ld & beta;1 following 72 h of treatments with median lethal doses of thiamethoxam and imidacloprid were compared using real-time quantitative PCR. These genes were then individually and simultaneously knocked down with Ld & alpha;1 by RNA interference (RNAi) using a double-stranded RNA (dsRNA) feeding method for six days to explore their roles in CPB susceptibility to imidacloprid and thiamethoxam. The results showed that the expressions of Ld & alpha;3, Ld & alpha;8 and Ld & beta;1 were significantly decreased by 36.99-74.89% after thiamethoxam and imidacloprid treatments, compared with the control. The significant downregulation of the target genes resulting from RNAi significantly reduced the mortality of adults exposed to thiamethoxam and imidacloprid by 34.53% -56.44% and 28.78%-43.93%, respectively. Furthermore, the adult survival rates were not affected by every dsRNA-feeding treatment, while the body weight of the test adults significantly deceased after four and six days of individual gene RNAi. This study showed that Ld & alpha;3, Ld & alpha;8 and Ld & beta;1 are down-regulated by thiamethoxam and imidacloprid and play important roles in the tolerance of CPB to neonicotinoids.

Automated summary

In this study, it was found that the expression levels of Ld & alpha;3, Ld & alpha;8 and Ld & beta;1 were significantly decreased after treatments with thiamethoxam and imidacloprid. Furthermore, RNA interference also reduced the susceptibility of Colorado potato beetles to these insecticides.