Monitoring and mechanisms of insecticide resistance in Spodoptera exigua (Lepidoptera: Noctuidae), with special reference to diamides.

The beet armyworm, Spodoptera exigua, is a major lepidopteran pest of global importance in cultivation of numerous crops including cotton, maize, soybean, onion, cabbage, and ornamentals. It has evolved resistance to different insecticides. However, the current status of insecticide resistance in S. exigua has not been well examined in China. In this study, concentration-mortality responses of S. exigua to seven insecticides, including chlorantraniliprole, tetraniliprole, methoxyfenozide, indoxacarb, chlorfenapyr, emamectin benzoate and beta-cypermethrin were evaluated. The results showed that most of the tested populations had developed moderate to high resistance to chlorantraniliprole, with resistance ratios ranging from 6.3 to 2477.3-fold. Our results also showed that chlorantraniliprole have cross-resistance with tetraniliprole in S. exigua. The AY19 population collected from Anyang in Henan Province in 2019 exhibited a high resistance level to beta-cypermethrin (RR = 277.5). Methoxyfenozide and chlorfenapyr were highly effective against all of the tested populations with resistance ratios (RR) ranging from 0.1 to 2.2-fold. One of the tested populations showed moderate resistance to indoxacarb and emamectin benzoate. We detected the known ryanodine receptor target site resistance mutation, I4743M, in the field populations of S. exigua with different levels of diamide resistance.