Interactions of a "risky" biological control agent with target and non-target aphids

Importation ("classical") biological control entails risks to non-target species as well as the potential benefit of target pest supression. Typically, prior to the release of a classical biological control agent (BCA), host range tests are performed to predict non-target risk, and generalist BCAs are precluded from release. Little is known, however, how host range may impact efficacy of BCAs. The parasitoid Aphelinus certus (Hymenoptera: Aphelinidae) was considered for release against the invasive soybean aphid (Hemiptera: Aphididae) which was found in North America in 2000. Tests revealed broad parasitism by A. certus within Aphididae, therefore release of the parasitoid was considered to great a risk to native aphid species. Unfortunately, A. certus, was inadvertently introduced - first recorded in Pennyslvania in 2005 - and it has since been found through much of the Canadian and US soybean growing region. Interestingly, this accidental introduction presents an opportunity to explore the interaction between risk and efficacy of a introduced BCA. We designed a field experiment to explore the direct and indirect effects of A. certus on the target soybean aphid in soybean, and on non-target grain aphids in wheat. Implications for risk-benefit analysis in biological control are discussed.