Two plant-derived allelochemicals, berberine and alpha -terthienyl ( alpha -T), were tested for their effects on the European corn borer, Ostrinia nubilalis , and its endoparasitoid Diadegma terebrans . In O. nubilalis , survival to pupation and adult emergence were reduced significantly by the inclusion of berberine and alpha -T in larval diets at a concentration of 100 mu g/g. However, in the parasitoid, adverse effects were much more apparent with the alpha -T treatment than with the berberine treatment. alpha -T and one of its metabolites were found in host larvae and in emerged adult parasitoids and their cocoons. none