This project in the second of three years specifically addresses a priority item listed under the category of Soybean Pest Management in the FY2023 request for proposals: ”Soybean farmers need continued research into cultural, chemical and biological control mechanisms for management of soybean insects including, but not limited to, soybean aphid,
Japanese beetle and soybean gall midge.” The methods proposed here were developed and successfully validated in the first year of the project.
Soybean gall midge, Resseliella maxima, is a new devastating pest of soybean in the Midwest (Gagné et al. 2019). Soybean gall midge larvae feed inside the stems of soybean plants near the soil surface (McMechan et al. 2021). Infestations cause wilting, lodging and death of soybean plants, and have resulted in significant yield reductions (McMechan et al. 2021). Currently, this pest is known to occur in Minnesota, Nebraska, Iowa, South Dakota, and Missouri (McMechan et al. 2021). In Minnesota, this pest has already been detected in at least 29 counties in the south and west (soybeangallmidge.org) and it may continue to spread to other areas.
Cold winter temperatures are an important factor, among several, limiting the geographic range and population sizes of insects in temperate regions like Minnesota (Bale 1996). Infestations by soybean gall midge have been more severe in Nebraska than in Minnesota, and the insect has not been detected in northern Minnesota. It remains unknown what role cold winter temperatures play 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. These types of information have proven important for the management of other crop pests (e.g., corn earworm, bean leaf beetle, etc.).
Like related species of gall midges (e.g., the raspberry gall midge (Nilsson 2008)), soybean gall midge larvae drop from the soybean plants in the fall and enter the soil where they construct cocoons. The larvae spend the winter in these cocoons, often in the upper two inches of the soil surface. In spring, as soil temperatures rise, the larvae develop into pupae and then adults, which emerge to restart the life cycle. During the winter months, the larvae must survive extended periods of low temperatures (often around freezing) and occasionally extremely low temperatures.
The cold hardiness of insects is often evaluated by quantification of their supercooling points and lower- lethal temperatures (Sinclair et al. 2015). The supercooling point of an insect is the temperature at which the liquids in its body begin to freeze. Because of freeze-protective chemicals in insect bodies, the temperature at which insects freeze is often below the freezing point of water, hence the term “super”cooling. The lower-lethal temperature is the temperature at which the insect actually dies from cold exposure. By characterizing both the supercooling point and lower-lethal temperature of an insect, an understanding of the insect’s strategies for cold hardiness can be gained.
By acquiring an understanding of the cold hardiness of soybean gall midge, actionable models will be developed to predict the potential geographic range of the pest and levels of survival of the pest from one year to the next. Furthermore, this information will guide development of recommendations for cultural tactics (e.g., tillage, residue management, etc.) that could increase winter mortality of soybean gall midge and result in decreased pest populations.
We are proposing this as the second year of a three-year project to characterize the cold hardiness of soybean gall midge and develop actionable models and recommendations for its management. We are currently making great progress on the first year of the project. We have developed and successfully utilized the necessary methodology obtain initial estimates of cold hardiness (supercooling point and lower-lethal temperature) for soybean gall midge. However, as with other field research projects, we need to replicate this work in additional environments (years) to understand the natural variability in our system.
Our team at the University of Minnesota has extensive experience evaluating the cold hardiness of numerous insect pests and using that information to develop recommendations for farmers and land managers. We will collaborate with Dr. Robert Venette (USDA Forest Service/University of Minnesota) who has state-of-the-art equipment for assessing cold hardiness and considerable technical expertise in this area. This area of research is not being addressed by any of the Midwest researchers working on soybean gall midge; therefore, this project does not duplicate any existing efforts. Furthermore, this proposal has not been submitted to this or any other funding entity.

To characterize the cold hardiness of soybean gall midge and incorporate this knowledge into management programs, we propose 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

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 the
training of a graduate student in Entomology, who will gain expertise in pest ecology and integrated pest management.

Update:
1. Determine if soybean gall midge larvae acclimate to winter conditions by changing cold hardiness over the growing season
Fields in southwest MN with adequate infestations were identified for the research goals proposed here. Methods were refined to produce cocoons throughout the growing season. Preliminary observations suggest that they develop to pupae in the cocoons early in the season, whereas later in the season they remain as third instars within the cocoons, which matches fields observations for the overwintering stage of this insect.
2. Quantify the cold hardiness of fall-collected soybean gall midge larvae that would experience winter conditions
Methods have been refined based on results from last year and collections for this goal will begin in August or September.
3. Develop actionable models to estimate winter mortality of soybean gall midge
Work on this goal has not started. It depends upon completion of other goals.

Update:
see uploaded file

View uploaded report

Update:
Reporting period: 1 November 2023 to 30 January 2024

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 two different acclimation regimes (simulated fall/winter conditions: 1 or 2 months at 37°F with a short day length) and measured their cold hardiness through assessment of their freezing points and lethal temperatures. On average, the supercooling points (freezing points) were around -8 to -9°F. In the lethal temperature experiment, insects were cooled to - 14, 5, -4, -13, or -22°F 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 -4 and -13°F. Overall, the results for freezing points and lethal temperature were very similar between the first two years of this study. An additional component added in this second year was an assessment of lethal time, which examines how the duration of exposure to different low temperatures affects survival. For this study, cocoons were held at 14, 26 and 37°F for 1 or 2 weeks, and in a follow-up experiment at 26 and 37°F for 1, 3 or 5 days. Preliminary results showed high mortality at 14 and 26°F after only 1 week of exposure, and rapidly increasing mortality beginning at 3 days at 26°F.

Goal 3: When we compared these critical temperatures (-4 and -13°F) 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. However, when factoring in longer durations of exposure, it appears that this insect is less likely to survive. More detailed modeling of the response of this insect to cold temperatures will be carried out if the 3rd year of this project is funded.

Challenges encountered
No problems occurred during this period

Dissemination of data/information during this reporting period
Extension presentations:
Koch, RL. 2024, February. Biology and management of two new insect pests of soybean, soybean gall midge and soybean tentiform leafminer. Research Updates for Agricultural Professionals, Institute for Agricultural Professionals, University of Minnesota Extension. (30-minute presentation online with 55 attendees)
Anderson, P. and R.L. Koch. 2023, December. Cold hardiness of soybean gall midge. Prairie Grains Conference. Grand Forks, ND. (15-minute presentation with 30 attendees)

View uploaded report

Updated May 31, 2024:
Reporting period: 1 May 2023 to 30 April 2024

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. Survival of adults was longer when provided with water or honey-water compared to when nothing was provided. Fifty percent of the population survived to about 4 days when provided water or honey-water.

Goal 2: 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 two different acclimation regimes (simulated fall/winter conditions: 1 or 2 months at 37°F with a short day length) and measured their coldhardiness through assessment of their freezing points and lethal temperatures. On average, the supercooling points (freezing points) were around -8 to -9°F. In the lethal temperature experiment, insects were cooled to - 14, 5, -4, -13, or -22°F 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 -4 and -13°F. Overall, the results for freezing points and lethal temperature were very similar between the first two years of this study. An additional component added in this second year was an assessment of lethal time, which examines how the duration of exposure to different low temperatures affects survival. For this study, cocoons were held at 14, 26 and 37°F for 1 or 2 weeks, and in a follow-up experiment at 26 and 37°F for 1, 3 or 5 days. Results showed high mortality at 14 and 26°F after only 1 week of exposure, and rapidly increasing mortality beginning at 3 days at 26°F.

Goal 3: When we compared these critical temperatures (-4 and -13°F) 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. However, when factoring in longer durations of exposure, it appears that this insect is less likely to survive. More detailed modeling of the response of this insect to cold temperatures will be carried out if the 3rd year of this project is funded.

Challenges encountered
No problems occurred during this period

Dissemination of data/information during this reporting period
Extension presentations:
Anderson, P., R. Venette, B. Potter, A. Hanson and R.L. Koch. 2024, April. Updates on cold tolerance of soybean gall midge. 2024 Midwest Soybean Gall Midge Discussion Series (10-minute presentation with 120 attendees)
Koch, RL. 2024, February. Biology and management of two new insect pests of soybean, soybean gall midge and soybean tentiform leafminer. Research Updates for Agricultural Professionals, Institute for Agricultural Professionals, University of Minnesota Extension. (30-minute presentation online with 55 attendees)
Anderson, P. and R.L. Koch. 2023, December. Cold hardiness of soybean gall midge. Prairie Grains Conference. Grand Forks, ND. (15-minute presentation with 30 attendees)

Scientific presentations:
Anderson, P., R.C. Venette, B. Potter, Anthoy Hanson and R.L. Koch. 2024, March. Assessing the cold tolerance of soybean gall midge. Meeting of the North Central Branch of the Entomological Society of America. Fort Collins, CO.
Anderson, P. and R.L. Koch. 2023, November. Adult longevity of soybean gall midge. Meeting of the Entomological Society of America. National Harbor, MD.

Soybean gall midge, Resseliella maxima, is a new devastating pest of soybean in the Midwest. Soybean gall midge larvae feed inside the stems of soybean plants near the soil surface. 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, North Dakota and Missouri.
Cold winter temperatures are an important factor, among several, limiting the geographic range and population sizes of insects in temperate regions like Minnesota. Infestations by soybean gall midge have been more severe in Nebraska than in Minnesota, and the insect has not been detected in northern Minnesota. It remains unknown what role cold winter temperatures play 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. These types of information have proven important for the management of other crop pests (e.g., corn earworm, bean leaf beetle, etc.).

Like related species of gall midges (e.g., the raspberry gall midge), soybean gall midge larvae drop from the soybean plants in the fall and enter the soil where they construct cocoons. The larvae spend the winter in these cocoons, often in the upper two inches of the soil surface. In spring, as soil temperatures rise, the larvae develop into pupae and then adults, which emerge to restart the life cycle. During the winter months, the larvae must survive extended periods of low temperatures (often around freezing) and occasionally extremely low temperatures.
The cold hardiness of insects is often evaluated by quantification of their supercooling points and lower- lethal temperatures. The supercooling point of an insect is the temperature at which the liquids in its body begin to freeze. Because of freeze-protective chemicals in insect bodies, the temperature at which insects freeze is often below the freezing point of water, hence the term “super”cooling. The lower-lethal temperature is the temperature at which the insect actually dies from cold exposure. By characterizing both the supercooling point and lower-lethal temperature of an insect, an understanding of the insect’s strategies for cold hardiness can be gained.

Through this research, 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 two different acclimation regimes (simulated fall/winter conditions: 1 or 2 months at 37°F with a short day length) and measured their coldhardiness through assessment of their freezing points and lethal temperatures. On average, the supercooling points (freezing points) were around -8 to -9°F. In the lethal temperature experiment, insects were cooled to - 14, 5, -4, -13, or -22°F 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 -4 and -13°F. Overall, the results for freezing points and lethal temperature were very similar between the first two years of this study. An additional component added in this second year was an assessment of lethal time, which examines how the duration of exposure to different low temperatures affects survival. For this study, cocoons were held at 14, 26 and 37°F for 1 or 2 weeks, and in a follow-up experiment at 26 and 37°F for 1, 3 or 5 days. Results showed high mortality at 14 and 26°F after only 1 week of exposure, and rapidly increasing mortality beginning at 3 days at 26°F.
When we compared these critical temperatures (-4 and -13°F) 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. However, when factoring in longer durations of exposure, it appears that this insect is less likely to survive. More detailed modeling of the response of this insect to cold temperatures will be carried out if the 3rd year of this project is funded.

By acquiring an understanding of the cold hardiness of soybean gall midge, actionable models will be developed to predict the potential geographic range of the pest and levels of survival of the pest from one year to the next. Furthermore, this information will guide development of recommendations for cultural tactics (e.g., tillage, residue management, etc.) that could increase winter mortality of soybean gall midge and result in decreased pest populations.

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, but 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 of 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 recommendation are being developed to help farmers protect their crop from this pest.