Soybean Aphid Egg Hatch Nearly Complete

May 11, 2022
ICM News

Iowa’s most significant soybean insect pest, the soybean aphid, has host-alternating biology. Its primary host 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. For many aphids that overwinter as an egg, hatching often happens when the host resumes spring growth. This makes biological sense because the aphids feed on phloem from actively growing tissue. If egg hatch happens too soon, they can suffer mortality from starvation.

We can track soybean aphid development using growing degree days (GDD), and research has confirmed 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 2022 (Figure 1), egg hatch is nearly complete in northern Iowa, where most of the buckthorn in Iowa is located.

Growing degree days map.
Figure 1. Accumulated growing degree days (base 50) in Iowa from January 1 to May 11, 2022. Map courtesy of the Iowa Environmental Mesonet, Iowa State University Department of Agronomy.

After soybean aphid eggs hatch, they go through a few asexual generations on buckthorn before leaving in search of soybean. Soybean aphid may colonize plants as early as the beginning of June, but these infestations are typically short-lived due to natural enemy activity and environmental factors. However, infestations are sporadic and change quickly, so scouting throughout the growing season is the best way to understand how populations are changing and whether management is required. Begin scouting soybeans for soybean aphid in June and continue to scout every seven to 10 days. Learn more about soybean aphid identification, biology, scouting, and management in this encyclopedia article.

Links to this article are strongly encouraged, and this article may be republished without further permission if published as written and if credit is given to the author, Integrated Crop Management News, and Iowa State University Extension and Outreach. If this article is to be used in any other manner, permission from the author is required. This article was originally published on May 11, 2022. The information contained within may not be the most current and accurate depending on when it is accessed.


Ashley Dean Agriculture and Natural Resources Extension Specialist II

Ashley is an education extension specialist for field crop entomology at Iowa State University. She coordinates the Iowa Moth Trapping Network, the Regional Corn Rootworm Monitoring Network, and the Iowa Pest Alert Network. She also develops educational resources for field crop pests in Iowa and ...

Erin Hodgson Professor

Dr. Erin Hodgson started working in the Department of Entomology, now the Department of Plant Pathology, Entomology, and Microbiology, at Iowa State University in 2009. She is a professor with extension and research responsibilities in corn and soybeans. She has a general background in integrated...