Sublethal pesticide exposure increases tick overwintering survival

Pesticides are the primary tool for pest control throughout the world. Although most organisms are likely to encounter pesticides in the environment, little is known about the effect of these persistent chemicals on the physiology of off-target species. We measured the effect of sublethal pesticide exposure on two common tick species. We predicted that sublethal pesticide exposure would make ticks more sensitive to extreme temperatures. In contrast, we found that exposure to sublethal pesticides has the opposite effect. Sublethal pesticide exposure decreased the LT₅₀ (lethal temperature at which 50% mortality is observed) of adult and nymphal Dermacentor variabilis from -16° C. To investigate the impact of this physiological shift in cold tolerance, we developed a novel approach for incorporating physiological survival data into spatially explicit species distribution models. Using this approach, we demonstrate that pesticide-induced increases in cold tolerance may permit faster northward range shifts of Dermacentor variabilis. We also demonstrate that incorporating physiological data into species distribution models modulates the estimate of climate change impacts and according to model validation methods, provides more accurate predictions of species responses to changing environments. Although our study is limited to ticks, other studies have shown effects of pesticides on thermal tolerance traits in diverse species. Our work demonstrates that broad usage of pesticides may drive complex interactions between species and their environments and leading to altered thermal tolerance traits and establishment in new habitats.