Biotic interference of parasitoid biological control agents by resident species can severely hamper biological control efforts. In aphid biological control, where intraguild predators of parasitoids such as coccinellids are often abundant, the risk of biotic interference may be very strong. The myriad of possible ecological interactions a classical biological control agent may be faced with in the field makes pre-release evaluations of biotic interference problematic. However, simulating a release using a surrogate biological control agent may aid in making predictions about the biotic interference that will occur during the actual release. In 2005, we simulated a parasitoid release against the soybean aphid and found that biotic interference of an introduced parasitoid was likely, but that interference would not be strong enough to render the release unworthwhile. In 2007, a permit for releasing Binodoxys communis, the actual biological control agent of soybean aphid, was obtained and B. communis was released in North America. We examined biotic interference against B. communis using a cage study that excluded B. communis, resident natural enemies, or both from soybean aphid infestations, and compared our assessment of B. communis with our 2005 simulation. We also assessed temporal interactions with resident predators, hypothesizing that interference would be strongest late-season, when resident enemies are generally abundant. Finally, we conducted a molecular gut-contents analysis, to determine which predator species / life stages caused biotic interference of B. communis. We present these results, and discuss the implications this work has for soybean aphid biological control.