Resistance monitoring and putative biochemical mechanisms of Spodoptera frugiperda to different insecticides in China

BACKGROUND: The control of the fall armyworm (FAW), Spodoptera frugiperda, relies heavily on insecticides, which has accelerated the evolution of resistance; thus it is urgent to monitor the insecticide resistance status of this pest. RESULTS: In this study, insecticide bioassays were conducted using the topical application method on 16 field populations collected in China in 2023. The results showed that FAW in China is susceptible to emamectin benzoate, chlorantraniliprole, tetrachlorantraniliprole and lambda-cyhalothrin, whereas some populations exhibited low-level resistance to indoxacarb, spinetoram, broflanilide, chlorfenapyr and acephate. No mutations were detected in the target genes GluCl, nAChR, RyR, GABAR and VGSC; however, 67.7% individuals displayed mutations at locus F290V of ace-1. Detoxification enzyme activity and synergistic assays suggest that cytochrome P450 enzymes (P450s), glutathione S-transferases (GSTs) and esterases (ESTs) are implicated in the low-level resistance to indoxacarb, spinetoram and acephate. GSTs and ESTs also contributed to broflanilide resistance, whereas only GSTs played a role in chlorfenapyr resistance. CONCLUSION: Our study offers substantial insights for monitoring and managing the development of insecticide resistance in S. frugiperda populations in China. Future research will be needed to further investigate the metabolic mechanisms of related detoxifying enzymes and the resistance mechanisms mediated by ace-1 mutations.