Variation in the cold physiology of Tetanops myopaeformis between fields in North Dakota

Tetanops myopaeformis, the sugarbeet root maggot, is a freeze-tolerant crop pest native to North America. The species range increased over the past 10 years, establishing in locations with variable thermal profiles. To determine if populations differ in their response to low temperatures, populations from a northern (St. Thomas, ND) and southern location (Buxton, ND) were compared. We hypothesized that the southern population would be less resilient to low temperatures. To compare the two populations, we measured lower lethal temperature, supercooling point, body mass, and water content in both populations in late October and early November. Larvae were exposed for 24 hours to one of four treatments: 0, -10, -20, and -30°C. Survival was determined 3 days after cold exposure. Body mass and water content did not differ between populations or among temperature treatments. Supercooling points differed by up to 4°C among the treatment groups, but not with population. For both populations, the -30°C treatment group was lethal to all individuals. However, the post-treatment survival differed by roughly 10% between the two populations. This indicates that survival is not inherently dependent on the temperature to which the larvae are exposed. Another mechanism, likely independent of cold exposure, led to the variation in survival. Surprisingly, the southern population was more resilient to treatment. This study highlights the variation in cold tolerance within a species. Future work, expanding the range and sampling from newly identified populations, could lead to understanding this species' ability to spread.