This project will provide several important deliverables that will advance soybean gall midge management in Minnesota. This project will produce foundational knowledge on the effects of cold temperatures on soybean gall midge survival. This knowledge will improve 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 training of a graduate student in Entomology, who will gain expertise in pest ecology and integrated pest management.

Determine if soybean gall midge larvae acclimate to winter conditions by changing cold hardiness over the growing season:

Soybean stems infested with soybean gall midge larvae will be collected every 2-3 weeks from fields of a cooperating farmer from June until larvae are no longer present in the stems (September-October). The stems from each collection date will be brought to a laboratory and placed into emergence cages maintained at “summer” conditions (warm temperatures and long day length) to allow the larvae to complete development and drop to the soil substrate within the cages. After the mature larvae construct their cocoons in the soil substrate, they will be collected from the soil substrate and tested for cold hardiness. Two laboratory assays will be used to assess cold hardiness. First, the supercooling points (i.e., temperature at which the body fluids freeze) will be measured. A subset of the larvae collected from the emergence cages will be attached to small thermocouples and placed in glass vials inside a cooling bath. The thermocouples will record the temperature of the larvae as the cooling bath cools at a slow and constant rate of about 1°C per minute. With this methodology, the supercooling point is visualized as a sudden increase in temperature (release of energy) caused when the liquids in the bodies freeze. To complement the supercooling point data, the lower-lethal temperatures of the larvae will also be measured. A subset of the larvae collected from the emergence cages will be randomly assigned to different targeted low temperatures. The cooling bath described above, will be used to cool the larvae to the targeted low temperatures. After reaching the targeted temperatures, the larvae will be removed and placed into Petri dishes for assessment of survival. By collecting data on the supercooling points and lower-lethal temperatures over the growing season, we will be able to determine if the soybean gall midge acclimates to winter conditions by changing its cold hardiness as winter approaches.

Quantify the cold hardiness of fall-collected soybean gall midge larvae that would experience winter conditions:

Similar to the experiment described above, soybean stems infested with soybean gall midge larvae will be collected about every 2 weeks from fields of a cooperating farmer, but for this experiment the collections will occur from September to October. The stems will be brought to a laboratory and placed into emergence cages maintained under “fall” conditions (moderate temperature and moderate day length) in a growth chamber to allow the larvae to complete development and drop to the soil substrate within the cages. The cages will then be transferred to a growth chamber at “winter” conditions (low temperature and short day length). Then, at monthly intervals throughout the winter, larvae will be collected from the soil substrate and their cold hardiness measured using the laboratory assays for supercooling points and lower-lethal temperatures.

Develop actionable models to estimate winter mortality of soybean gall midge:

Based on previous research, we know the proportion of the soybean gall midge population spending the winter at different depths in the soil. To predict winter mortality, the cold hardiness data collected in the above mentioned experiments need to be compared to actual temperatures experienced at those depths in soybean fields. Utilizing the network of Research and Outreach Centers of the U of MN, we will monitor soil temperatures in soybean fields over the winter at Lamberton, Morris, Crookston, Rosemount and Waseca. Data loggers will be deployed in two fields at each location to record soil temperatures soil depths of 0.5, 2 and 4 inches, which will span the likely depths at which soybean gall midge spends the winter. These temperature data will be used to inform modeling efforts for predicting the winter survival of soybean gall midge.

Communication plan:

Results of this research will be disseminated through a multi-media outreach effort. Koch, Potter and Hanson have formal extension responsibilities and interact with growers and agricultural professionals (crop consultants, industry and agency staff, etc.). We can leverage Extension’s large, integrated outreach system, which is well-suited for the distribution of agricultural information, forecasting for pests based on weather and climate data. An example is field days held at research and outreach centers, at which we will present results of this research. Furthermore, results of the project proposed here will be delivered at agricultural professional and producer meetings during winter months, and published on Extension’s crop news blog. In particular, we will communicate project results through Minnesota Soybean communication program events such as Ag-Expo, the MN Soybean tent at Farmfest, the MN Soybean Booth at Big Iron and/or Minnesota Soybean Minne-Line articles. Research results will be presented at scientific conferences and published in peer-reviewed scientific journals, which will provide scientific validity to the research.

Updated May 18, 2023:
Proposal title: Cold hardiness of soybean gall midge: Foundations for pest forecasting and cultural control

Reporting period: 1 February 2023 to 30 April 2023

Proposal Objectives & Goal Statements:
Characterize the cold hardiness of soybean gall midge and incorporate this knowledge into management programs through the following objectives:
1. Determine if soybean gall midge larvae acclimate to winter conditions by changing cold hardiness over the growing season
2. Quantify the cold hardiness of fall-collected soybean gall midge larvae that would experience winter conditions
3. Develop actionable models to estimate winter mortality of soybean gall midge

Specific project achievements during this reporting period:

Goal 1: As described in a previous report, multiple measures of larval and adult supercooling points (temperatures at which they freeze) were recorded over the growing season. Analyses of these data suggested a possible trend for an increase in freezing point as the season progresses. This could be due to changes in host quality as the infested plants deteriorate over time. In addition, we performed some preliminary longevity experiment with excess adult insects from this work.

Goal 2: As mentioned in a previous report, we developed methods to successfully “trick” filed-collected larvae to develop into the overwintering stage (third instar larvae in cocoons). We then subjected these cocoons to four different acclimation regimes (simulated fall/winter conditions: 1 or 2 month at 3 or 13 degrees Celsius with short day length) and measured their coldhardiness through assessment of their freezing points and lethal temperatures. On average across regimes, the supercooling points (freezing points) were around -25 degrees Celsius. In the lethal temperature experiment, insects were cooled to -10, -15, -20, -25 or -30 degrees C (with additional insects maintained at room temperature as a control) and immediately rewarmed to assess survival. This experiment assess survival after an acute (short term) exposure to cold. Survival decreased greatly between -20 and -25 degrees C. In year two of this project, we will repeat the above mentioned research and try to add a component to look at longer term exposure to temperatures.

Goal 3: When we compared these critical temperatures (-20 and -25 degrees C) to soil temperatures experienced across a south-north gradient in Minnesota, we found it to be very unlikely that soil temperatures would reach these critical values.

Challenges encountered
No problems occurred during this period

Dissemination of data/information during this reporting period

Scientific presentations:
-Anderson, P., R. Venette, B.D. Potter and R.L. Koch. 2023, April. Initial assessment of cold tolerance of soybean gall midge. 10-minute presentation. Meeting of the North Central and Soutwestern Branches of the Entomological Society of America. Oklahoma City, OK.

Extension presentations:
-Koch, R.L. 2023, March. Soybean insects update: soybean aphid, soybean gall midge and soybean tentiform leafminer. Minnesota Winter Region Conference, Winfield United. Mankato, MN (60-minute talk with 200 attendees)
-Anderson, P., R. Venette, B. Potter, A. Hanson and R.L. Koch. 2023, February. Initial research into cold tolerance of soybean gall midge. 2023 Midwest Soybean Gall Midge Discussion Series (7-minute presentation with 230 attendees)
-Koch, R.L. 2023, February. Biology & Management of new pests of soybean. Advanced Crop Advisors Workshop, Fargo, ND. (45-minute co-presentation with 46 attendees)
-Koch, R.L. 2023, February. Mortality factors affecting soybean gall midge: predators, parasitic wasps and cold. Best of the Best. University of Minnesota Extension and North Dakota State University Extension. (30-minute talk; Grand Forks, ND: 170 attendees; Moorhead, MN: 132 attendees).
-Anderson, P., B.D. Potter, A. Hanson and R.L. Koch. 2023, January. Cold tolerance of soybean gall midge. Poster presentation. Minnesota Ag Expo, Mankato, MN
-Koch, RL. 2023, January. Updates on the status and management of new insect pests of soybean. Research Updates for Agricultural Professionals, Institute for Agricultural Professionals, University of Minnesota Extension. (45-minute presentation; Lamberton: 20 attendees [co-presented by B. Potter]; Morris: 29 attendees; Willmar: 32 attendees)
-Koch, R.L. 2022, December. Soybean gall midge update. Crop Pest Management Short Course. Minnesota Crop Production Retailers and University of Minnesota Extension. Minneapolis, MN (two 50-minute talks with 8 and 9 attendees).

ONE-PAGE PROJECT DESCRIPTION (May 2023)

Cold hardiness of soybean gall midge: Foundations for pest forecasting and cultural control
Robert Koch, Bruce Potter and Anthony Hanson (University of Minnesota)

Soybean gall midge is a new devastating pest of soybean in the Midwest. Infestations cause wilting, lodging and death of soybean plants, and have resulted in significant yield reductions. Currently, this pest is known to occur in Minnesota, Nebraska, Iowa, South Dakota, and Missouri.

Cold winter temperatures are an important factor, among several, limiting the spread and population growth of insects in northern states, like Minnesota. Infestations by soybean gall midge have been more severe in Nebraska than in Minnesota. It remains unknown what role cold winter temperatures in northern areas may be playing in limiting populations of this pest. 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. The ability of organisms to survive exposure to cold temperatures is referred to as their cold hardiness. Because the soybean gall midge is such a new pest, there is no knowledge about its cold hardiness, and therefore we are limited in our abilities to predict how widespread it may become in Minnesota and to predict spring populations based on winter temperatures.

Research performed in 2022 was successful for development of methods for assessing the cold hardiness of this pest. The main focus of the project was on late-season cold hardiness, which is more relevant to real-world overwintering survival of a pest. An exciting first outcome of this work is that we developed methods to successfully “trick” filed-collected larvae to develop into the overwintering stage (third instar larvae in cocoons). We then subjected these cocoons to four different acclimation regimes (simulated fall/winter conditions: 1 or 2 month at 3 or 13 degrees Celsius with short day length) and measured their cold hardiness through assessment of their freezing points and lethal temperatures. On average across regimes, the super-cooling points (freezing points) were around -25 degrees Celsius. In the lethal temperature experiment, insects were cooled to -10, -15, -20, -25 or -30 degrees C (with additional insects maintained at room temperature as a control) and immediately rewarmed to assess survival. This experiment assess survival after an acute (short term) exposure to cold. Survival decreased greatly between -20 and -25 degrees C. A question remained about what temperatures the pest could experience in the soil under the snow in winter months. Therefore, we compared these critical temperatures (-20 and -25 degrees C) to soil temperatures experienced across a south-north gradient in Minnesota. We found it to be very unlikely that soil temperatures would reach these critical values, suggesting that winter temperatures might not impact the survival of this pest. In year two of this project, we will repeat the above mentioned research and try to add a component to look at longer term exposure to cold temperatures, which is more relevant to what insects experience in the field.