Soybean gall midge is a new pest threatening soybean production in Minnesota and the Midwest. An important knowledge gap about this pest is how it responds to cold temperatures. This information is critically important for predicting how far north the pest might spread and how well its populations might survive from one growing season to the next. From this, growers can be informed about the potential risk that this pest poses for their fields and management practices could be developed to take advantage of cold sensitivity. The work proposed here is for the third of three years on this project to evaluate the cold hardiness of soybean gall midge. Established laboratory methods have been employed to measure the temperatures at which this pest freezes and dies. Further work in this third year will examine how the ability to survive cold might vary among the pest’s life stages. In addition, the data collected over the three-year project will be combined with historic soil temperature data to develop models for predicting pest potential throughout Minnesota, which will be disseminated using informative risk maps.

1. GOAL: To characterize the cold hardiness of soybean gall midge and incorporate this knowledge
into management programs, we propose the following objectives:
OBJECTIVES:
1. Develop actionable models to estimate winter mortality of soybean gall midge
2. Quantify the cold hardiness of different life stages of soybean gall midge

This project will provide several important deliverables that will advance soybean gall midge management in Minnesota. This project is producing foundational knowledge on the effects of cold temperatures on soybean gall midge survival. This knowledge is improving the general understanding of the biology of this pest. Furthermore, this knowledge on the cold hardiness of soybean gall midge will be used in advanced modeling procedures to predict of the potential northward expansion of this pest and year-to-year changes in population size. A very tangible project deliverable resulting from this work will be high-quality maps showing the potential geographic range of soybean gall midge in the Midwest and annual maps that will show predicted mortality induced by the previous winter’s cold temperatures. These maps will be housed on the UMN Extension website and made widely available to farmers and the agricultural community through our extension programming (see communication plan above) and through the communication channels of Minnesota Soybean. Finally, this project will facilitate the training of a graduate student in Entomology, who will gain expertise in pest ecology and integrated pest management.

Updated August 30, 2024:
Reporting period: 1 May 2024 to 30 July 2024

Proposal Objectives & Goal Statements:
To characterize the cold hardiness of soybean gall midge and incorporate this knowledge into management programs, we propose the following objectives:
1. Develop actionable models to estimate winter mortality of soybean gall midge
2. Quantify the cold hardiness of different life stages of soybean gall midge

Specific project achievements during this reporting period:
Goal 1: Data on season-long soil temperatures has been obtained from weather stations in Lamberton and Morris, MN and Fargo, ND. These data are being cleaned and summarized to understand lowest temperatures experienced in the soil where SGM would spend the winter and the durations of exposure to different low temperatures identified as relevant from our previous cold hardiness research on this insect. In addition, we are preparing to perform an additional year of research on the effects of duration of exposure to cold on the survival of SGM. This experiment is critically important to understanding the cold response of SGM and for development of models.
Goal 2: Measures of supercooling points have been collected from larvae and adults of soybean gall midge that were obtained from infested soybean fields. These data are being summarized and analyzed.

Challenges encountered
No problems occurred during this period

Dissemination of data/information during this reporting period
Results of this work will be disseminated to stakeholders in winter extension meetings.

Updated November 25, 2024:
Reporting period: 1 August 2024 to 31 October 2024

Proposal Objectives & Goal Statements:
To characterize the cold hardiness of soybean gall midge and incorporate this knowledge into management programs, we propose the following objectives:
1. Develop actionable models to estimate winter mortality of soybean gall midge
2. Quantify the cold hardiness of different life stages of soybean gall midge

Specific project achievements during this reporting period:

Goal 1: Data analysis is completed and a scientific paper is being drafted on the response of soybean gall midge to short-term exposure to cold, which includes the freezing points (supercooling points) and the lethal temperatures (survival after short-term exposures). In general, the results indicate that freezing and mortality of soybean gall midge larvae occur between -20 to -25 F. In contrast, the first year of data on the effect of longer durations of exposure to cold temperatures indicated that mortality could occur at warmer temperatures. Such results could have a major impact on predictions of models based on soil temperatures, so we attempted to verify this response through an additional year of data collection in 2024. However, the soybean gall midge population development was unexpectedly more advanced in 2024 and few larvae were available in the fields when we attempted to collect larvae at timings similar to the previous years. Therefore, to ensure robust and valid models, we would like to repeat that experiment looking at the effect of various durations of exposure to cold in 2025. To complement those results, season-long soil temperature data have been obtained to quantify durations of time experienced at different low temperatures at Lamberton and Morris, MN and Fargo, ND. These data will be sued in the predictive model for soybean gall midge survival.

Goal 2: Measures of supercooling points have been collected from larvae and adults of soybean gall midge that were obtained from infested soybean fields. These data will be summarized and analyzed in the next reporting period summarized and analyzed.

Challenges encountered
During this period, we were unable to collect sufficient larvae to perform the experiment assessing the effects of longer durations of exposure to cold temperatures on soybean gall midge survival. We would like to attempt that work in 2025 under a no-cost extension of this project.

Dissemination of data/information during this reporting period
Results of this work were presented at the Entomological Society of America and will be included in presentations at winter extension meetings.

Updated February 22, 2025:
Reporting period: 1 November 2024 to 31 January 2025

Proposal Objectives & Goal Statements:
To characterize the cold hardiness of soybean gall midge and incorporate this knowledge into management programs, we propose the following objectives:
1. Develop actionable models to estimate winter mortality of soybean gall midge
2. Quantify the cold hardiness of different life stages of soybean gall midge

Specific project achievements during this reporting period:
Goal 1: Data analysis is completed and a scientific paper is nearly complete on the response of soybean gall midge to short-term exposure to cold, which includes the freezing points (supercooling points) and the lethal temperatures (survival after short-term exposures). In general, the results indicate that freezing and mortality of soybean gall midge larvae occur between -20 to -25 F. In contrast, the first year of data on the effect of longer durations of exposure to cold temperatures indicated that mortality could occur at warmer temperatures. Such results could have a major impact on predictions of models based on soil temperatures, so we attempted to verify this response through an additional year of data collection in 2024. However, the soybean gall midge population development was unexpectedly more advanced in 2024 and few larvae were available in the fields when we attempted to collect larvae at timings similar to the previous years. Therefore, as mentioned in the previous report, to ensure robust and valid models, we would like to repeat that experiment looking at the effect of various durations of exposure to cold in 2025. A request for a no-cost extension has been submitted to permit this work. To complement those results, season-long soil temperature data have been obtained to quantify durations of time experienced at different low temperatures at Lamberton and Morris, MN and Fargo, ND. These data will be used in the predictive model for soybean gall midge survival.
Goal 2: Measures of supercooling points have been collected from larvae and adults of soybean gall midge that were obtained from infested soybean fields. These data continue to be analyzed.

Challenges encountered
During this period, we were unable to collect sufficient larvae to perform the experiment assessing the effects of longer durations of exposure to cold temperatures on soybean gall midge survival. We would like to attempt that work in 2025 under a no-cost extension of this project.

Dissemination of data/information during this reporting period
Results of this work have been included in presentations at winter extension meetings, such as:
-Koch, R.L. 2025, February. Soybean insect issues and Extension programming for agricultural professionals. Annual Meeting of the Minnesota Independent Crop Consulting Association, St. Cloud, MN (20-minute talk with 55 attendees)
-Koch, R.L. 2025, February. Updates on soybean gall midge and soybean tentiform leafminer. Best of the Best in Wheat and Soybean. North Dakota State University Extension and University of Minnesota Extension. (30-minute talk; Grand Forks: 115 attendees, Moorhead: 86 attendees)
-Koch, R.L. 2025, January. Is agricultural research and extension relevant to highschool agricultural teachers? Educators Network Meeting. Turtle Lake, WI (60-minute talk to 9 attendees)
-Koch, R.L., P. Anderson and A. Ribeiro. 2025, January. Advances in soybean entomology research. Poster presentation. Minnesota Ag Expo, Mankato, MN
-Koch, R.L. 2025, January. Updates on the biology and management of soybean insect pests. Research Updates for Agricultural Professionals, Institute for Agricultural Professionals, University of Minnesota Extension. (50-minute talk; Waseca: 110 attendees, Oronoco: 14 attendees)

Updated May 31, 2025:
Final report – May 2025
Proposal Objectives & Goal Statements:
To characterize the cold hardiness of soybean gall midge and incorporate this knowledge into management programs, we propose the following objectives:
1. Develop actionable models to estimate winter mortality of soybean gall midge
2. Quantify the cold hardiness of different life stages of soybean gall midge

Specific project achievements during this reporting period:
Goal 1: Soybean gall midge passes the winter as a mature (third instar) larva inside a cocoon in the soil. To examine the response of soybean gall midge to cold temperatures, we had to obtain this overwintering stage of this insect. Through this project, we developed laboratory methods for reliably producing this overwintering stage of the soybean gall midge from field-collected insects. Briefly, larvae were dissected from soybean stems and placed into vials containing moistened sand. These vials were then held in a growth chamber for an adequate amount of time to allow them to produce cocoons and were then transferred to different acclimation conditions (combinations of lower temperatures and durations of time). Across the acclimation conditions, 75-83% of larvae produced cocoons and did not continue to develop to pupae, which indicates they were in their overwintering dormant state.

Two standard measures of cold hardiness were measured from the cocooned larvae held at the different acclimation conditions. First, the supercooling point, which is the temperature at which the insect begin to freeze, was measured using contact thermocouple thermometry. Overall, 87% of cocooned larvae began to freeze at temperatures colder than -20°C, and 58% began to freeze between -20 and -25°C. Mean supercooling points ranged from -24.3 to -21.9°C across acclimation conditions, with an overall mean of -22.9°C. Second, lower lethal temperature, which is the temperature at which the insect actually dies from cold exposure (short duration exposure to cold). Overall, cocooned larvae showed low mortality (~4.9%) with exposure to -10 to -20°C, followed by a rapid increase in mortality between -20°C and -25°C. No individual across any set of acclimation conditions survived exposure to -30°C. As the exposure temperature decreased, a greater proportion of cocooned larvae died. The acclimation conditions generally had no effect on the supercooling points or lower lethal temperatures of the insects. Overall, the measures of supercooling points and lower lethal temperature suggest that soybean gall midge is extremely resistant to short-term exposures to cold temperatures, as soil temperatures at Lamberton, Morris or Fargo rarely if ever reach these critical temperatures.

An additional measure of cold hardiness called lethal time was also examined to quantify the effects of different durations of time on the mortality of cocooned larvae. Maintaining cocooned larvae at 3°C caused little mortality over 2 weeks; however, those maintained at -3 or -10°C experienced nearly complete mortality within 1 week. These results suggested that cocooned larvae are not as resistant to cold implied by the initial experiments. Such results could have a major impact on predictions of models based on soil temperatures, so we attempted to verify this response through an additional year of data collection under the project in 2024-2025. However, the soybean gall midge population development was unexpectedly more advanced in 2024 and few larvae were available in the fields when we attempted to collect larvae at timings similar to the previous years. Therefore, to ensure robust and valid models, we need to repeat that experiment looking at the effect of various durations of exposure to cold in 2025. These will be critical data for the modeling of how the pest’s mortality can be affected by cold temperatures and allow predictions of pest potential based on winter temperatures. A no-cost extension was granted to allow us to perform this work later in 2025.

Goal 2: Supercooling points were measured on various life stages (larvae, cocooned larvae and pupae, and adults) of soybean gall midge to compare their relative cold hardiness. Cocooned larvae and pupae had the lowest supercooling points, which were around -23°C. Larvae and adults had generally higher precooling points, which were around -17 and -20°C, respectively, and were much more variable than those of the cocooned individuals. Separate measures of larval supercooling points over the course of the season showed no evidence for acclimation (increasing cold hardiness) toward the end of the season.

Challenges encountered
As described above, we were unable to collect sufficient larvae to perform the experiment assessing the effects of longer durations of exposure to cold temperatures on soybean gall midge survival. We will perform this work under a no-cost extension.

Dissemination of data/information during this reporting period
Results of this work have been presented at extension meetings as summarized in previous reports.

Soybean gall midge is a new pest of soybean in the Midwest. Infestations cause wilting, lodging and death of soybean plants, and have resulted in significant yield reductions. Cold winter temperatures are an important factor, among several, limiting the geographic range and population sizes of insects in temperate regions like Minnesota. Understanding how a new pest like soybean gall midge responds to cold temperatures is foundational information for understanding its pest potential and for developing pest management programs. Soybean gall midge passes the winter as a mature (third instar) larva inside a cocoon in the soil. To examine the response of soybean gall midge to cold temperatures, we developed laboratory methods for reliably producing this overwintering stage of the soybean gall midge from field-collected insects. Two standard measures of cold hardiness were measured from the cocooned larvae held at the different acclimation conditions. First, we measured the supercooling point, which is the temperature at which the insects begin to freeze. Mean supercooling points ranged from -24.3 to -21.9°C across acclimation conditions, with an overall mean of -22.9°C. Second, we measured lower lethal temperature, which is the temperature at which the insect actually dies from cold exposure (short duration exposure to cold). Overall, as the exposure temperature decreased, a greater proportion of cocooned larvae died. Cocooned larvae showed low mortality with exposure to -10 to -20°C, followed by a rapid increase in mortality between -20°C and -25°C. No individual across any set of acclimation conditions survived exposure to -30°C. Overall, the measures of supercooling points and lower lethal temperature suggest that soybean gall midge is extremely resistant to short-term exposures to cold temperatures, as soil temperatures at Lamberton, Morris or Fargo rarely if ever reach these critical temperatures. An additional measure of cold hardiness called lethal time was also examined to quantify the effects of different durations of time on the mortality of cocooned larvae. Overall, much more mortality was experienced when larvae were held for increasing durations at low temperatures. Maintaining cocooned larvae at 3°C caused little mortality over 2 weeks; however, those maintained at -3 or -10°C experienced nearly complete mortality within 1 week. These results suggested that cocooned larvae are not as resistant to cold implied by the initial experiments. A no-cost extension was granted to allow us to repeat this work to obtain robust parameters for cold hardiness to be used in modeling.

Soybean gall midge is a new pest that poses a significant threat to soybean production. Currently, farmers in Minnesota do not know how widespread this pest will become nor how the pest population might change from one year to the next. This limits their ability to prepare for and respond to the pest. Investment in this project will enable us to provide research-based forecasting to inform farmers about their risk for this pest. More specifically, we will clarify which regions of Minnesota are at more or less risk for infestation by soybean gall midge. In addition, we will provide forecasts about the impact of winter on the coming year’s pest infestation. This information will be important for helping farmers determine if and what actions to take against soybean gall midge. Furthermore, understanding how cold affects the survival of this insect, recommendations for cultural control (e.g., tillage or residue management) could be developed to increase winter mortality of the pest.
Indirectly, the proposed work rearing this insect in the laboratory should advance our abilities for maintaining year-round colonies of this insect. To date, no researchers in the Midwest have been able to successfully maintain such laboratory colonies of this pest. Having the ability to produce soybean gall
midge in the laboratory year-round would advance all aspects of soybean gall midge research and greatly increase the rate at which management recommendations are being developed to help farmers protect their crop from this pest.