Parasitism of Autumnal Morphs of the Soybean Aphid (Hemiptera: Aphididae) by Binodoxys communis (Hymenoptera: Braconidae) on Buckthorn

The soybean aphid, Aphis glycines</it> Matsumura (Hemiptera: Aphididae), is both heteroecious and holocyclic, seasonally alternating between buckthorn (Rhamnus</it> spp.), (the primary, overwintering host) and soybean, Glycine max</it> (L.) Merr. (the secondary host). Recently, a classical biological control program for this invasive pest has been implemented in North America using the Asian aphidiine braconid wasp Binodoxys communis</it> Gahan. Two critical, related questions regarding the overwintering biology of B. communis</it> are 1) does the parasitoid maintain fidelity to A. glycines</it> throughout the aphid life cycle and follow it to its primary host; and, if it does, 2) is parasitoid migration facilitated by phoretic movement within buckthorn-specific winged aphids? In the laboratory, we compared B. communis</it> parasitism on several different autumnal morphs of A. glycines</it>: winged gynoparae (fall migrants) and their oviparous offspring on buckthorn, fourth-instar alatoid nymphs that would form either gynoparae or summer migrants on soybean, and third-instar gynoparous alatoid nymphs on soybean. We also introduced gynoparae and B. communis</it> onto caged buckthorn plants in southeastern Minnesota to examine autumnal parasitism under natural conditions. In both the laboratory and field, parasitism rates of oviparae were much higher than those of gynoparae. In addition, B. communis</it> rarely completed development on fourth-instar alatoid nymphs. Although wasps successfully developed on third-instar gynoparous nymphs, these hosts mummified before forming wings. These results suggest that although at least one buckthorn-specific morph of A. glycines</it> seems suitable for B. communis</it> parasitism, it is unlikely that alate-mediated dispersal of immature parasitoids is an adaptive strategy to locate Rhamnus</it> in this species.