The Evolution and Mechanisms of Multiple-Insecticide Resistance in Rice Stem Borer, Chilo suppressalis Walker (Lepidoptera: Crambidae).

The emergence of insecticide resistance in the rice stem borer, Chilo suppressalis, is a growing threat to the sustainable control of this important insect crop pest. Thus, monitoring of C. suppressalis populations for insecticide resistance and characterization of the underlying genetic mechanisms is essential to inform rational control decisions and the development of resistance management strategies. Here, we monitored 126 C. suppressalis field populations from China for resistance evolution to four major insecticides: 53 for chlorantraniliprole, 50 for abamectin, 74 for triazophos, and 76 for spinetoram. Moderate to high levels of resistance were observed to all four insecticides. Investigation of the underlying resistance mechanisms revealed multiple mutations in the ryanodine receptor (RyR) and acetylcholinesterase 1 (AChE1), leading to target-site resistance to chlorantraniliprole and triazophos, respectively. In contrast, the absence of mutations in the glutamate-gated chloride channel (GluCl) and α6 nicotinic acetylcholine receptor (nAChR α6) subunit suggested that nontarget site mechanisms contribute to the multiple-insecticide resistance phenotypes observed in C. suppressalis. In this regard, we revealed overexpression of the uridine 5'-diphospho-glycosyltransferase UGT33AF1 and cytochrome P450 CYP6AB45 in C. suppressalis field populations. Functional characterization using transgenic Drosophila demonstrated that UGT33AF1 confers resistance against multiple insecticides in vivo, whereas CYP6AB45 does not appear to contribute to resistance. Collectively, our findings reveal the current status of resistance of C. suppressalis to insecticides in China and uncover a diverse profile of resistance mechanisms in this species. These findings provide a foundation for the development of sustainable strategies to effectively manage and control this pest.