Bassianolide, a cyclodepsipeptide insecticide produced by the fungal species B. bassiana and V. lecanii, demonstrates significant biological activity. Upon oral administration, it induces atony in B. mori silkworms at a concentration of 4 ppm and becomes lethal when concentrations exceed 8 ppm. Remarkably, atony in silkworm larvae can also be triggered by doses as low as 2 µg/larva. Further studies reveal that bassianolide (0.01-1 µM) specifically targets muscarinic receptors to inhibit contractions in isolated guinea pig smooth muscle tissue, elicited by acetylcholine, without affecting nicotinic receptor-induced contractions.