UC students are studying ways to combat tick-borne illness in Professor Joshua Benoit's lab.
Photo Credit: Joseph Fuqua II/UC
Scientific Frontline: Extended "At a Glance" Summary: Pesticide-Induced Cross-Tolerance in Ticks
The Core Concept: Exposure to nonlethal doses of broad-spectrum insecticides inadvertently increases the cold tolerance of dog ticks, allowing them to withstand dangerous winter temperatures that would otherwise be lethal.
Key Distinction/Mechanism: The survival mechanism relies on a phenomenon known as "cross-tolerance." Pesticides act as intense physiological stressors, prompting surviving ticks to activate broad, protective cellular pathways. Because the biological mechanisms for chemical tolerance and cold tolerance share overlapping pathways, exposure to the pesticide fortifies the tick against freezing temperatures.
Major Frameworks/Components:
- Physiological stress response: The activation of broad, protective biological pathways in an organism following chemical exposure.
- Cross-tolerance: The overlapping evolutionary mechanisms that allow resistance to one stressor (pesticides) to confer resilience against an unrelated stressor (extreme cold).
- Vector range expansion: The geographical spread of disease-carrying organisms due to increased environmental resilience and shifting climatic conditions.
Branch of Science: Entomology, Physiology, Ecology, and Epidemiology.
Future Application: This research guides the development of highly targeted vector control strategies. Instead of deploying broad-spectrum chemicals that inadvertently trigger cross-tolerance, future advancements will focus on exploiting specific physiological vulnerabilities, such as interrupting a tick's ability to sense environmental humidity.
Why It Matters: Cold winters have historically acted as a reliable, natural barrier against the northern migration of cold-sensitive ticks. Enhanced cold tolerance removes this backstop, allowing ticks to establish permanent populations in previously tick-free regions and expanding the geographical risk zone for debilitating tick-borne illnesses, including Lyme disease, Rocky Mountain spotted fever, and ehrlichiosis.
Ticks that survive less-than-lethal doses of pesticides are able to withstand dangerous cold, which could help them spread tick-borne diseases farther north.
Biologists with the University of Cincinnati (UC) and the US Department of Agriculture (USDA) examined the effects of pesticides on two common species of dog ticks.
Ticks were exposed to two broad-spectrum insecticides and then exposed to two hours of intense cold between −16 and −28 degrees. About half the ticks survived exposure to −16 degrees, while virtually none survived temperatures of −28 degrees.
UC students also mimicked overwintering conditions typical of the West and Midwest, where dog ticks are common. They buried ticks 10 centimeters underground in enclosures in Crooks, South Dakota, and Cincinnati, Ohio, between September and April.
Researchers expected that ticks exposed to pesticides would be more susceptible to cold, but they found the opposite.
"This study highlights an unintended consequence of pesticide exposure," said coauthor and UC College of Arts and Sciences professor Joshua Benoit. "Chemicals designed to suppress tick populations may increase tick cold tolerance."
How do pesticides make ticks more resistant to cold?
"Many pesticides act as physiological stressors. When ticks survive exposure, they may activate broad pathways that help protect against multiple forms of stress," Benoit said. "Because some of these protective mechanisms are shared between pesticide tolerance and cold tolerance, exposure to pesticides may produce a phenomenon known as cross-tolerance, where surviving ticks become better able to withstand low temperatures."
Benoit and his students study ticks, mosquitoes, and other disease vectors in his biology lab.
Ticks can carry diseases such as Rocky Mountain spotted fever, Lyme disease, and ehrlichiosis, which can be debilitating and persistent.
Benoit said cold winters have been a reliable backstop against the northern spread of cold-sensitive ticks.
"If pesticide exposure increases the ability of ticks to survive winter conditions, populations may establish and persist in areas that were previously too cold," he said.
This could lead to exposures to tick-borne illnesses in regions that until now have been tick-free, he noted.
The study was led by former UC postdoctoral researcher Kennan Oyen, who is now at the USDA. UC students Thomas Arya, Benjamin Davies, and Elise Didion also contributed to the study.
Benoit and UC students Kosisochukwu Onyeagba and Joshua Tompkin spoke to Spectrum News about how some tick species are expanding their ranges and what UC is doing to find ways to prevent tick-borne illnesses.
"In the last few years, we are starting to see more black-legged ticks, which carry Lyme disease," Benoit said.
Benoit also noted that Gulf Coast ticks are showing up in new places. They are known to carry spotted fever.
Benoit said students in his lab are learning more about tick physiology to develop better ways to prevent exposure to tick-borne illnesses without deploying dangerous pesticides. Onyeagba is studying ways to interrupt the tick's ability to sense environmental humidity, which is key to its survival.
Published in journal: British Ecological Society’s Journal of Applied Ecology
Authors: Kennan J. Oyen, Thomas Arya, Benjamin Davies, Elise M. Didion, and Joshua B. Benoit
Source/Credit: University of Cincinnati | Michael Miller
Edited by: Scientific Frontline
Reference Number: ent071926_01
.jpg)