The fall armyworm (FAW) is a serious agricultural pest
and has
developed resistance to multiple insecticides. It is necessary to
introduce novel insecticide(s) for controlling FAW. Isocycloseram
is a completely novel isoxazoline insecticide. However, its activity
and mode of action against FAW have not been reported. In this study,
isocycloseram exhibited a higher insecticidal activity (LC50 = 0.26 mg/kg) than fipronil (LC50 = 7.72 mg/kg) against
FAW. The median inhibitory concentration (IC50) of isocycloseram
(IC50 = 8.52 nM) was almost equal to that of the desmethyl-broflanilide
(IC50 = 7.32 nM) to the SfrRDL1 receptor.
The IC50 of isocycloseram to the SfrRDL2
receptor was 11.13 nM, which was obviously less than that of desmethyl-broflanilide,
dieldrin, fipronil, fluxametamide. Compared with the SfrRDL2 receptor, the SfrRDL1 receptor exhibited higher
sensitivity to GABAergic insecticides. The recombinant SfrGluCl receptor was successfully stimulated by l-glutamate;
however, the currents were low and weakly inhibited by isocycloseram
at 10 μM. In conclusion, our results provided the theoretical
basis for usage of GABAergic insecticides for controlling FAW.