Monitoring broflanilide resistance and its synergism with metaflumizone and tetraniliprole against fall armyworm, Spodoptera frugiperda

As an invasive and destructive agricultural pest, the fall armyworm (FAW), Spodoptera frugiperda (Lepidoptera: Noctuidae) has become a major global issue because of its rapid worldwide spread and serious threat to food security. Currently, the control of FAW in China mainly relies on spraying chemical insecticides, which may result in rapid evolution of insect resistance in FAW, ultimately leading to control failure. Application of new insecticides with novel mechanisms of action and their mixtures with insecticides from other classes are effective measures against insecticide-resistant FAW. In this study, we first established the baseline susceptibility of FAW to a new insecticide broflanilide, and then evaluated the resistance status of FAW field populations collected from sixteen different regions in China from 2020-2022. The results revealed that, in 2020, all FAW populations were susceptible to broflanilide. However, low to moderate levels of resis-tance were detected in nine of the sixteen populations in 2021, indicating a potential risk of resistance to broflanilide. The recommended diagnostic dose was 14 mu g/g for future broflanilide resistance monitoring. No mutations were found in the target gene GABAR of broflanilide in all the 2899 tested insects. The synergistic effects of broflanilide with metaflumizone (1:1, co-toxicity coefficient of 149) or tetraniliprole (1:2 and 1:5, co-toxicity coefficient of 296 and 429, respectively) were investigated through laboratory experiments and field investigations, suggesting combining insecticides is promising way to improve FAW control and delay the broflanilide resistance in FAW.