Competitive interactions between a native and an introduced parasitoid of the soybean aphid, Aphis glycines (Homoptera: Aphididae)

Binodoxys communis (Gahan) (Hymenoptera: Braconidae) has been recently released as a biological control agent against the soybean aphid, Aphis glycines Matsumura(Homoptera: Aphididae), in six north central U.S. states. Relatively little attention has been paid to potential interactions of B. communis with native parasitoids with which it may directly or indirectly compete. Although the soybean aphid natural enemy community in North America has a very small number of parasitoid species, the insertion of an exotic parasitoid into these communities will likely change host-parasitoid relationships. One outcome may be competitive displacement of either the native or the recently introduced parasitoid. Our objectives are to determine and characterize the interactions between B. communis and the native species Lysiphlebus testaceipes (Cresson) (Hymenoptera: Braconidae), a common parasitoid of soybean aphid in Wisconsin soybean fields. Experiments on competitive interactions between the two adult parasitoids on soybean aphid suggest that under laboratory conditions B. communis is a better competitor than L. testaceipes. We will discuss the implications of these results and the potential effects of parasitoid competition on the population dynamics of the soybean aphid.