Soybean aphid, Aphis glycines, causes both direct and indirect effects on soybean that can lead to yield loss and reduced seed quality. Direct feeding damage (plant sap removal) results in subsequent plant stress, stunting and yield loss. Indirectly, soybean aphids have been found to reduce photosynthetic rate in soybean (Macedo et al. 2003). Winged soybean aphid morphs occur early in the growing season as females migrate from the primary (overwintering) host, buckthorn (Rhamnus spp.), to the secondary host, soybean, for the asexual development phase (Zhang and Zhong 1982). A summer winged morph develops later in the growing season as females respond to crowding and decreased host quality by dispersal flight to uncolonized plants and fields (Steffey 2003). It is the winged soybean aphids that are capable of transmitting viruses to soybean (alfalfa mosaic virus, soybean mosaic virus) as they probe and feed between infected and uninfected plants in the process of movement between fields. Because soybean viruses can be transmitted rapidly by winged aphids, there are no thresholds to control this indirect damage (yield loss and seed mottling effects) caused by soybean aphid (Grau 2003).