A comparison of the modes of action of novel meta-diamide insecticides and conventional noncompetitive antagonists on the Spodoptera litura RDL GABA receptor

Novel meta-diamides [3-benzamido-N-(4-(perfluoropropan-2-yl)phenyl)benzamides] are a distinct class of RDL GABA receptor antagonists with high larvicidal activity against Spodoptera litura. Genotyping showed that the S. litura RDL GABA receptor subunit (SL-RDL) gene had Ser at its 2' position, which was widely distributed among field S. litura larvae in Japan. We investigated the modes of action of meta-diamides on SL-RDLbd homomers using a membrane potential assay. S2'N and T6'V mutations had profound effects on the inhibitory activities of fipronil and alpha-endosulfan, whereas these mutations had no effect on the inhibitory activities of meta-diamides. In contrast, a G319M mutation abolished the inhibitory activities of meta-diamides, whereas it had only a small effect on the activities of fipronil and alpha-endosulfan. These results suggest that the site of action of meta-diamides is near G319 in the third transmembrane segment of SL-RDL homomers, which is distinct from those of fipronil and a-endosulfan. (C) Pesticide Science Society of Japan