Predator-prey interactions involving the soybean aphid (Hemiptera : Aphididae) in Missouri

In Missouri, there is a unique predator complex that suppresses soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), populations prior to reaching economic threshold. Preliminary research has shown that when soybeans were infested with soybean aphids under normal field conditions, populations did not become well established. However, when plants were caged to exclude predators, soybean aphid populations grew rapidly. To determine which predator is most responsible for suppression of soybean aphid populations in Missouri, soybean plants were caged using different size meshes. Three sizes of mesh were used; one which excludes all insects, one which excludes insects larger than thrips and one which excludes insects larger then Orius insidiosus (Say) (Hemiptera: Anthocoridae), a principal predator. As a control, cages were placed over soybean without mesh. Caged plants were infested with soybean aphid at the plant growth stages V5, R1, and R3. Fifteen aphids were transferred using a fine camel’s hair brush to the uppermost expanded trifoliate. Soybean aphids used were colony reared and of the same ages (<48 hours). Sampling consisted of weekly visual observations of the caged plants for soybean aphids and aphidophagous predators; in particular, O. insidiosus (nymph and adult) and coccinellids (Coleoptera: Coccinellidae) (larvae and adult). Information gained from this study will allow us to assess the key soybean aphid predators at different soybean phenologies.