An entry point for understanding soybean aphid as a pest during the soybean growing season is to be familiar with how this insect alternates between asexual and sexual phases on two different plant hosts, buckthorn and soybeans, over the calendar year.

Soybean aphid overwinters in the egg stage on common buckthorn, an exotic, weedy, shrub common in much of the Midwest north of I-80. Eggs hatch on buckthorn in spring (late March, early April). From each overwintered egg on buckthorn in early spring, a wingless female soybean aphid known as the fundatrix, or “stem mother” hatches. These stem mothers are asexual and give live birth to wingless female aphid nymphs, producing several generations on buckthorn. By late spring/early summer, winged soybean aphid females are produced that leave buckthorn in search of soybean.