Biophysical drivers of tick exposure risk due to climate change in Maine

Climate change is an ongoing global issue, and in Maine, increased annual mean temperatures, decreased snowfall, and warmer winters are being recorded. These changes in climate have likely contributed to the increased densities of blacklegged ticks (Ixodes scapularis) and expansion into novel areas in Maine, resulting in an increase in reported cases of tickborne diseases such as of Lyme disease, anaplasmosis, and babesiosis across the state. In a changing climate, understanding temperature variance in relation to overwinter tick survival is crucial in understanding their expansion limitations. The goals of this study were to conduct a field study to determine which winter month ticks experience the highest level of mortality due to fat resource depletion and conduct a lab study to investigate the interactions between temperature variance and mean temperature on tick mortality. We monitored an outdoor tick overwintering enclosure in Orono from November – May 2021 to assess monthly nymphal mortality and hourly temperatures and used indoor temperature-controlled experiments to explore the effects of temperature variance on tick mortality. In the outdoor enclosure, the highest tick mortality compared to other months occurred in May and we hypothesize that these ticks had lower fat content compared to months when mortality was lower. Moreover, ticks exposed to more frequent temperature variance and colder temperatures were faster to die compared to ticks exposed to less frequent temperature variance and milder temperatures. Collectively, these findings provide insight for more accurate tick expansion prediction models to reduce tickborne disease cases.