The soybean gall midge is a new destructive pest of soybean. Because this pest is so new, very little is known about its biology and management. Cold winter temperatures are an important factor limiting the geographic range and population sizes of insects in temperate regions like Minnesota. Two standard indices of cold hardiness were measured from the overwintering stage (cocooned larvae) held at the different acclimation conditions.

First, the supercooling point, which is the temperature at which the insect begins to freeze, was measured. 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. Second, lower lethal temperature, which is the temperature at which the insect actually dies from cold exposure (short duration exposure to cold) was measured.

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 individuals across any set of acclimation conditions survived exposure to -30°C. Overall, these measures of supercooling points and lower lethal temperature suggested 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. Cocooned larvae maintained at 3°C experienced 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 indicated by the initial experiments. Additional data on the lethal time for this pest will be collected 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. 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.