The goal of this project is to evaluate whether host plant resistance and biological control could be used as compatible tools to suppress soybean aphid throughout the North Central region.
Aphelinus glycinis adult female parasitoid wasp laying an egg inside a soybean aphid. Photo (c) Matt Kaiser
Soybean aphid (Aphis glycines) is currently managed primarily by individual farmer decisions about the use of insecticide seed treatments and foliar applications each year. While the benefits of treating an aphid outbreak in a given field are large and immediate for that farmer, any attempt to reduce the likelihood of soybean aphid outbreaks across a wider area and slow the evolution of insecticide resistance will require a different approach. Two tools that may be useful against soybean aphid in such a manner are host plant resistance and biological control. Host plant resistance takes advantage of conventionally-bred traits in soybean plants which result in suppressed aphid population growth, called Rag genes for “resistant to Aphis glycines.” Biological control involves the consumption of aphids by other predatory or parasitic organisms, called natural enemies or biological control agents.
In 2016, a new biological control agent for soybean aphid was introduced to central Iowa. Matt O’Neal and Matt Kaiser released the aphid parasitoid Aphelinus glycinis at 11 ISU-affiliated research farms among both aphid-susceptible and aphid-resistant soybean plants, as part of this USDA-backed project aiming to combine biological control and host-plant resistance to provide area-wide suppression of the soybean aphid.
The parasitoid is a minute, specialist stingless wasp that attacks soybean aphids, originally collected in the aphid’s native range in northeastern China. Adult female wasps lay their eggs in live aphids, eventually killing them, while killing and eating additional aphids to gain nutrients for energy and egg development. After extensive host-range testing at the USDA Beneficial Insect Introductions Research Unit in Newark, DE, it was cleared for release in 2013. Small scale releases occurred in Minnesota in 2014 and 2015, but 2016 saw the first releases in Iowa and the largest releases to date, with an estimated 126,000 wasps released in Iowa alone. The wasps successfully attacked aphids in the field and were recovered up to 5 weeks after release. Next spring and summer, O’Neal and Kaiser will look for the wasps in soybean fields to determine if they survived the winter. External collaborators on the project include Keith Hopper with USDA-ARS, George Heimpel and Kelton Welch at the University of Minnesota, and Andy Michel at Ohio State University. Additional field help on the project came from Joshua Rhoades from the University of Delaware and Emily Manthei, an undergraduate student at ISU, as well as other Soybean Research lab members.
Parasitoid release bucket within a soybean field (L). Inside a parasitoid release bucket (R). The tiny black specks inside the bucket are the parasitoid wasps, beginning their search for aphids to parasitize and consume. Photos (c) Matt Kaiser