Evaluating the risks and benefits of Aphelinus certus, an introduced enemy of soybean aphid, in North America

Abstract: Exotic biological control agents under consideration for importation and release are evaluated for risk through the sole use of laboratory-based studies of host range, but ecosystem- and landscape-level effects should be incorporated into the decision-making process as well. The recent invasion of Aphelinus certus (Hymenoptera: Aphelinidae), a generalist Asian parasitoid attacking soybean aphid and native Aphis spp., provides a rare opportunity to investigate the role of a natural enemy in a complex network of interactions – both positive and negative, direct and indirect – throughout the ecological landscape. To address this, we (a) surveyed the distribution and population dynamics of A. certus in agricultural and native habitats and (b) used population models and field studies to determine the potential and actual effect of A. certus on soybean aphid. We found that A. certus readily colonizes or has successfully established in prairies, although the magnitude of its impact on native aphid populations has yet to be quantified. We also show that A. certus has the potential to be a key natural enemy of soybean aphid, although its effectiveness in the field has been more variable. Finally, we discuss the overall impact of A. certus within a risk – benefit framework incorporating its direct effects on soybean aphid and native aphid species as well as potential indirect effects in reducing insecticide applications, which, by extension, aids in conservation of pollinators and other vulnerable insect species. This perspective promotes an environment-based decision-making approach to classical biological control.