A rich guild of predators and parasitoids prey upon the soybean aphid (Aphis glycines Matsumura), leading to potentially complex ecological interactions which may vary with time, region, local and landscape factors. It is clear from a number of studies that natural enemies are a significant source of mortality and control for the soybean aphid. Less clear is the relative importance of different species of natural enemies under different conditions. This question is relevant for the refinement of IPM approaches and the development of conservation biocontrol strategies, but is difficult to tease apart in the field. Field cage studies have limitations, but they allow us to investigate the nature of some of these interactions under controlled conditions. In this experiment we studied the impact of Harmonia axyridis (Pallas) and Orius spp., acting both separately and in combination, on soybean aphid populations already at outbreak levels in large field cages.