Les tiques qui survivent aux pesticides peuvent résister à des hivers plus froids.

Ticks that survive less-than-lethal doses of pesticide appear to develop increased resistance to cold, potentially enabling them to expand their geographic range further north, according to a study conducted by researchers at the University of Cincinnati and the U.S. Department of Agriculture. The findings, published in the Journal of Applied Ecology, suggest that pesticide exposure may inadvertently enhance the cold tolerance of certain tick species, allowing them to endure harsher winter conditions and thrive in previously inhospitable climates. In laboratory experiments, scientists tested the effects of two broad-spectrum insecticides on two common species of dog ticks. After exposing the ticks to these chemicals, they subjected them to extreme cold, ranging from -16°F to -28°F, for two hours. While nearly all ticks perished at the lowest temperature, approximately half survived the milder -16°F exposure. This resilience was unexpected, as researchers had anticipated that pesticide-treated ticks would be more vulnerable to freezing conditions. To simulate real-world scenarios, the team also recreated overwintering conditions in the Midwest and Western United States. Ticks were buried 10 centimeters underground in controlled enclosures located in Crooks, South Dakota, and Cincinnati, Ohio, between September and April. These trials aimed to mimic the environmental challenges ticks face during hibernation. Researchers observed that ticks exposed to pesticides exhibited greater survival rates under cold conditions compared to unexposed counterparts. Professor Joshua Benoit, who leads the research group at the University of Cincinnati, explained that many pesticides function as physiological stressors. Surviving exposure to these substances may trigger adaptive responses within ticks that bolster their defenses against various stresses, including extreme cold. He noted that some of the biological pathways responsible for resisting pesticides overlap with those that aid in enduring low temperatures, a phenomenon referred to as cross-tolerance. “This study highlights an unintended consequence of pesticide exposure,” Benoit stated. “Chemicals designed to suppress tick populations may increase tick cold tolerance.” His comments underscore the complex interplay between human interventions and ecological outcomes. The implications of this discovery are significant, as it suggests that current pest control strategies might inadvertently contribute to the spread of tick-borne diseases into new regions. Tick-borne illnesses such as Rocky Mountain spotted fever, Lyme disease, and ehrlichiosis pose serious health risks to humans and animals. As climate change alters seasonal patterns, the potential for ticks to extend their range becomes increasingly relevant. Benoit emphasized that cold winters have historically acted as a barrier preventing ticks from establishing themselves in northern latitudes. If pesticide-induced cold tolerance enables ticks to overcome this limitation, public health concerns could rise in areas previously free of tick infestations. The study was led by Kennan Oyen, a former UC postdoctoral researcher now affiliated with the USDA. Contributions came from UC students Thomas Arya, Benjamin Davies, and Elise Didion. Additional insights were provided by Benoit and UC students Kosisochukwu Onyeagba and Joshua Tompkin, who discussed the growing presence of blacklegged ticks and Gulf Coast ticks in new locations. Both species are known carriers of pathogens linked to severe illness. The research underscores the need for a nuanced approach to pest management, one that considers both immediate efficacy and long-term ecological impacts. As tick populations continue to shift due to changing environmental factors, understanding the mechanisms driving their adaptability will be crucial in developing effective prevention strategies.