Bassianolide is a cyclodepsipeptide insecticide synthesized by the fungal species B. bassiana and V. lecanii.1,2 In vivo, the oral administration of bassianolide induces atony in the silkworm B. mori at a concentration of 4 ppm and is lethal at doses exceeding 8 ppm. Atony is similarly induced in silkworm larvae at oral doses as low as 2ug/larva.1 In isolated guinea pig smooth muscle tissue, bassianolide (0.01-1uM) specifically inhibits the muscarinic, but not nicotinic, receptor-induced contractions in response to acetylcholine.3,4