Research HighlightsStudying the Cold-Hardiness of the Soybean Gall Midge
By Carol Brown
Since the soybean gall midge first appeared in Nebraska fields in 2018, researchers across the Midwest have been studying this pest to learn all they can. Entomologists and agronomists are conducting research funded by state and regional soybean boards to learn about this new insect.
Justin McMechan, assistant professor of entomology at the University of Nebraska, led the first soybean gall midge research project in 2018. Funded by the North Central Soybean Research Program, the project began with determining its emergence timing and crop infestation abilities. One outcome of this ongoing project is the Soybean Gall Midge Alert Network website.
Other scientists, including soybean entomologist Robert Koch, are studying the soybean gall midge’s life cycle, habits, habitat and insecticide resistance. Koch is leading a new project at the University of Minnesota focused on the insect’s cold hardiness.
“Being in the northern states, one of the early biological questions we typically have for new pests is what effect the cold, winter conditions might have on such a pest,” Koch says. “We know that cold temperatures can limit the ability of some insects to establish and spread. That is the impetus behind this research project.”
Koch’s research, supported by the Minnesota Soybean Research and Promotion Council, is focused on two main aspects: how cold-hardy the midges are, and once that is established, how to incorporate this knowledge into soybean gall midge management.
“Knowing the soybean gall midge’s relationship to cold could help us figure out how far north they could establish and be problematic,” says Koch. “It could also be useful for predicting pest severity from one year to the next, based on the kinds of cold temperatures experienced each winter.”
The soybean gall midge is a fly species that can cause major damage to a soybean field. The adult midge lays eggs on the soybean stem near the base. The hatched larvae feed on the plant’s stem, then drop off the plant and burrow into the soil where they pupate. The adult midge emerges from the soil in the summer and repeats the process. A midge infestation usually starts at the field’s edge and works toward the center.
Koch’s research includes conducting laboratory assessments that determine the lowest temperature the soybean gall midge larvae can withstand while overwintering in the soil. Many insects have certain compounds in their blood that keep them from dying even at temperatures lower than 32 degrees Fahrenheit, the freezing point of water, Koch explains. He calls this phenomenon super-cooling. Eventually, the insect gets to a temperature cold enough where they die, which is their lethal temperature.
“To determine the soybean gall midge’s lethal temperature, our laboratory work exposed the larvae to temperatures ranging from 14 degrees to –22 degrees Fahrenheit. We then warmed them back up to see how many survived,” he explains. “At temperatures from 14 to –4 degrees, they survived fairly well. However, when exposed to –13 and –22 degrees, most or all of those insects died. Our preliminary data, after just one year of study, is showing that this insect is not surviving below about –9 degrees Fahrenheit.”
Koch has been looking at soil temperatures over the last decade in various areas around Minnesota to see if and where the soil got cold enough to kill the soybean gall midge larvae. But it may take temperatures colder than –9 degrees to be lethal.
“If the air temperature gets to –9 degrees or colder, it doesn’t mean that the insects are going to be exposed to that,” says Koch. “The gall midge larvae are spending the winter in the soil inside of a silken cocoon that they make. The soil can provide some insulation and then the snow on top of that provides even more. So far, it looks unlikely that soil temperatures at 2-inches deep get cold enough to kill these insects.”
Finding the soybean gall midge lethal temperature is only the first part of Koch’s research. His next step is to mimic actual winter soil conditions to see how long the larvae can survive.
“This coming year, we will be looking at holding the larvae at those targeted temperatures for an extended period of time because that is more realistic of what’s happening in the field,” Koch explains. “Just because the larvae survived from a short exposure to those cold temperatures, it doesn’t mean they’ll survive if they are held there longer.”
With the research being conducted by Koch and other entomologists, he hopes they can bring all the results together to paint a complete picture of this pest.
“There is a coordinated approach to study this insect so we aren’t duplicating our efforts,” says Koch. “My colleague, Bruce Potter at the University of Minnesota Southwest Research and Outreach Center, is also looking at seasonal activity such as when the adult midges emerge. Erin Hodgson at Iowa State University and Justin McMechan are leading projects on other aspects of the midge including conducting surveys to find out how widespread it is, tillage effects on its survival, and finding out how deep the larvae are found in the soil.”
Once the researchers answer these questions about the biology of the soybean gall midge, management strategies can be fine-tuned to combat this pest in soybean fields across the Midwest. Koch says the soybean checkoff funding from Minnesota, other states, and the NCSRP have provided the opportunity for a rapid response to research this pest.
SRIN information page: Soybean Gall Midge
Soybean Gall Midge Alert Network
Published: Apr 10, 2023
This project was funded by the soybean checkoff. To find research related to this research highlight or to see other checkoff research projects, please visit the National Soybean Checkoff Research Database.