Broflanilide prolongs the development of fall armyworm Spodoptera frugiperda by regulating biosynthesis of juvenile hormone

Broflanilide, a novel meta-diamide insecticide, has been registered worldwide to control agricultural pests, and cause negative influence to insects under not only lethal but also sublethal levels in the field. Fall armyworm (FAW), Spodoptera frugiperda, is a worldwide distributed insect frequently controlled by using insecticides. The molecular mechanisms by which broflanilide acts have yet to be fully characterized. In the present study, we exposed FAW larvae to sublethal dose (LD5), low lethal doses (LD10 and LD30) and median lethal dose (LD50) of broflanilide and measured various subsequent physiological sublethal effects. FAW larvae body length became shorter (LD5-LD50), the larvae and pupae duration were increased by 0.96-4.63 days (LD5-LD50), and the juvenile hormone (JH) titer significantly increased up to 134.46% (LD10-LD30). Meanwhile, the JH acid methyltransferase (JHAMT) and farnesyl diphosphate synthase 1 (FPPS1), which are critical enzymes of JH biosynthesis, respectively increased by 2.07- and 2.18- fold in the LD10 broflanilide-treated group, and by 2.22- and 1.78- fold in LD30 broflanilide-treated group in 3(rd) day larvae of FAW. In the 12-hour-old adults, SfrFPPS1 increased to 1.92-fold in the LD30 broflanilide-treated group. Broflanilide induced multiple physiological sublethal effects on the biosynthesis of JH by regulating the expression of SfrFPPS and SfrJHAMT genes in FAW and likely in other insects (both pests and non-target organisms). Therefore, its potential for Integrated Pest Management should be further assessed.