Piericidin B is a bacterial metabolite that has been found inS. mobaraensisand has insecticidal and antimicrobial activities.1,2,3It inhibits NADH oxidase activity in isolated bovine heart mitochondria and inhibits respiration in isolated rat liver mitochondria and isolated cockroach (P. americana) muscle mitochondria.2,3Topical application of piericidin B (4 microg/insect) induces mortality in 87.5% of houseflies (M. domestica).1It induces 93.3, 100, and 100% mortality in rice stem borer (C. simples), silkworm (B. mori), and green caterpillar (P. rapae) larvae, respectively, when applied at respective concentrations of 60, 4.8, and 96 microg/larva. Piericidin B is active against the fungiT. asteroides,T. rubrum,M. gypseum, andC. neoforms(MICs = 20, 10, 20, and 2 microg/ml, respectively), as well as the bacteriaM. luteusandP. vulgaris(MICs = 50 and 100 microg/ml, respectively).