 Soybean aphids are tiny, soft-bodied insects that pierce a plant and feed on the sap. They reproduce rapidly, and in large enough numbers, aphids can reduce yield and quality. Soybeans are susceptible to aphid injury till the crop reaches full seed. Bruce Potter is an Extension Integrated Pest Management Specialist with the University of Minnesota. He says not every field is going to have aphids, and infestation levels can even vary within a field.