Aphelinus certus: Minnesota's latest invasive species or biocontrol agent?

Aphelinus certus (Hymenoptera: Aphelinidae) is a solitary endoparasitoid of aphids. Native to eastern Asia, the parasitoid was inadvertently introduced into North America. It was first reported in 2005 in Pennsylvania parasitizing the soybean aphid. The soybean aphid, Aphis glycines (Hemiptera: Aphididae), is also native to Asia and is the most serious insect pest in North American soybeans. Interestingly, A. certus was evaluated as a candidate classical biocontrol agent of the soybean aphid prior to its accidental introduction; however, it was ultimately deemed unacceptable for release because of its broad host range and high risk to non-target native aphids. In contrast, a different species of soybean aphid parasitoid with a narrow host range has been intentionally released as a classical biocontrol agent since 2007, but successful establishment of this species has been elusive. Our objectives were to document the distribution of A. certus in Minnesota and investigate the effect of host range on parasitoid establishment. We find that A. certus is established thoughout most of the Minnesota soybean growing region, but may be absent or at low densities in the southeastern part of the state. Moreover, we find that soybean fields adjacent to wheat fields, which provide habitat for alternative aphid hosts, have higher A. certus densities than soybean fields far from wheat (P=0.016). We discuss the implications of the recent A. certus invasion in terms of non-target impact and biocontrol efficacy.