Widespread high-level resistance to emamectin benzoate and chlorantraniliprole and associated resistance mutations in Spodoptera exigua across China.

BACKGROUND

The beet armyworm, Spodoptera exigua, is a polyphagous pest with long-distance migration capabilities. It has been a major crop pest in southeastern China since the 1980s, but only emerged as a significant pest in northwestern China (Xinjiang) over the past decade. As a consequence of intensive insecticide use, this pest has developed serious resistance. Although insecticide resistance has been documented in southeastern populations, data on the current resistance status, particularly in Xinjiang populations, remain limited.

RESULTS

We evaluated resistance in 13 southeastern populations collected in 2023 and five Xinjiang populations collected in 2024 to four insecticides by comparing their median lethal concentrations (LC50s) with those of the reference WH-S strain. All 18 field populations exhibited high-level resistance to emamectin benzoate (EB; 711- to 8790-fold) and chlorantraniliprole (103- to 1422-fold) relative to a susceptible laboratory strain, whereas resistance to broflanilide and chlorfenapyr was absent or limited. Genotyping identified high frequencies of the CYP9A186 F116V (0.55-1.00) and RyR I4743M/K (0.92-1.00) mutations, which are associated with resistance to EB and chlorantraniliprole, respectively. Resistance magnitudes and resistance-allele frequencies were similar in Xinjiang and southeastern China. Furthermore, resistance to EB and chlorantraniliprole has markedly increased over time (from 2009 to 2024) in southeastern populations.

CONCLUSION

Our results demonstrate widespread, high-level resistance to EB and chlorantraniliprole in S. exigua across China and near-fixation of two major resistance alleles. Although broflanilide and chlorfenapyr currently remain effective alternatives, they should be used judiciously given the ≈10-fold existing variation in susceptibility to both insecticides. Coordinated geographical resistance monitoring and management are needed for S. exigua in China and elsewhere, given its strong migratory and dispersal capabilities. © 2026 Society of Chemical Industry.