Comparative effects of two plant secondary metabolites on host-parasitoid association.

Two plant-derived allelochemicals, berberine and α-terthienyl (α- T), were tested for their effects on the European corn borer,Ostrinia nubilalis, and its endoparasitoidDiadegma terebrans. The compounds were administered to the host insect in meridic diets, and the responses of the host larvae and parasitoids reared from treated hosts were measured in terms of growth parameters and survival. InO. nubilalis, survival to pupation and adult emergence were reduced significantly by the inclusion of berberine and α-T in larval diets at a concentration of 100 μg/g. However, in the parasitoid, adverse effects were much more apparent with the α-T treatment than with the berberine treatment. α-T and one of its metabolites were found in host larvae and in emerged adult parasitoids and their cocoons. Berberine residues were not detected. The implications of these responses to compounds of widely differing physiological properties are discussed with reference to host-plant resistance and biological control.