Soybean Aphid Egg Hatch Predicted in Northern Iowa

May 8, 2018
ICM News

Iowa’s most significant soybean insect pest, soybean aphid, has host-alternating biology. This species has multiple, overlapping generations on soybean in the summer and moves to buckthorn in the winter. Fall migration to buckthorn is based on senescing soybean, and decreasing temperatures and photoperiod. For the majority of the year, soybean aphids are cold-hardy eggs near buckthorn buds (Photo 1). As spring temperatures warm up, soybean aphid eggs hatch and produce a few generations on buckthorn before moving to soybean (Photo 2). Tilmon et al. (2011) goes into more detail about the life cycle and biology of soybean aphid.

soybean aphid on buckthorn
Photo 1. Sexual females deposit eggs near buckthorn buds in the fall. Photo by David Voegtlin.

soybean aphid on buckthorn
Photo 2. There are a few wingless generations produced on buckthorn before the spring migration to soybean every year. Photo by Chris DiFonzo (

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. Research has confirmed soybean aphid egg hatch happens around buckthorn bud swell. Bahlai et al. (2007) developed a model to predict soybean aphid egg hatch based on accumulating degree days. They adjusted the model to include ambient air temperatures and solar radiation. 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 2018, we expect egg hatch is occurring in northern Iowa, where most of the buckthorn in Iowa is located (Figure 1).

degree days for soybean aphid egg hatch
Figure 1. Accumulated growing degree days (base 50°F) in Iowa from January 1 – May 7, 2018. Map courtesy of Iowa Environmental Mesonet, ISU Department of Agronomy.


Bahlai, C. A., J. A. Welsman, A. W. Schaafsma, and M. K. Sears. 2007. Development of soybean aphid on its primary overwintering host. Environmental Entomology 36: 998-1006.

Tilmon, K. J., E. W. Hodgson, M. E. O’Neal, and D. W. Ragsdale. 2011. Biology of the soybean aphid in the United States. Journal of Integrated Pest Management 2: A1-A7.

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 8, 2018. The information contained within may not be the most current and accurate depending on when it is accessed.


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...