By Ashley Dean & Erin Hodgson
Iowa’s most significant soybean insect pest, the soybean aphid, alternates between two hosts to complete its development. The primary host of soybean aphid is buckthorn, an invasive shrub often found in hedgerows and roadside ditches, and its secondary host is soybean. For most of the year, soybean aphids exist as cold-hardy eggs on buckthorn branches near leaf buds. Overwintering eggs hatch around the same time buckthorn resumes growth in the spring, which allows them to synchronize their life cycle with availability of their host plant to limit death by starvation.
We can track soybean aphid development using growing degree days (GDD), and research has shown that eggs hatch around the time buckthorn buds swell. Soybean aphid egg hatch occurs between 147-154 degree days (base 50°F) and buckthorn bud swell happens shortly after that (165-171 degree days). Based on air temperatures in 2024 (Figure 1), egg hatch is complete in northern Iowa, where most of the buckthorn in Iowa is located.
