Newswise — COLUMBUS, Ohio – Hotter temperatures may render natural insect repellents less effective against mosquitoes, according to a new study.
Researchers found that a pain receptor called TRPA1 becomes less sensitive in mosquitoes when exposed to heat, meaning that the chemical cues that typically trigger insect avoidance behaviors are prevented from activating as strongly.
TRPA1, also known as the “wasabi receptor,” helps animals detect noxious heat and harmful chemicals. In humans, this receptor can induce eye and skin irritation. In mosquitoes, it influences which hosts the insects find most alluring – specifically, those unprotected by repellents that drive them away, said , co-author of the paper and a .
“What we found was that the chemicals were not able to activate the mosquito wasabi receptor as effectively when temperatures exceeded the heat activation threshold,” said Piermarini. “So the mosquito would find certain repellents less irritating in hotter weather.”
Typical insect repellents create a chemical barrier that discourages proximity and prevents mosquitoes from reaching their target. Yet because their receptors are desensitized in warmer temperatures, natural substances like citronellal and catnip oil, known for their repellent properties, would be less effective.
“Products with those ingredients may be less effective if you’re using them at temperatures that are considered extreme heat events,” said Piermarini. Additionally, as the climate warms, more per season the spread of mosquito-borne disease.
The study was recently published in the journal
Piermarini and co-author of the study and a graduate student in , discovered the changes by removing TRPA1 mosquito receptors and injecting them into frog egg cells, a technique often used for making receptor proteins in the lab.
Then, they tested how the receptors would react to citronellal and catnip oil under normal and high temperatures. The receptors were activated, but were less sensitive to the substances at higher temperatures. “It was very close to what we predicted,” said Piermarini.
In a second experiment, the researchers studied how fully grown female mosquitoes reacted when confronted with either repellent at different temperatures. When temperatures exceeded 32 degrees Celsius, the mosquitoes were less likely to avoid the substances, suggesting they might behave similarly in the wild.
Still, there is some defense against mosquito bites. When the team tested a synthetic mosquito repellent called DEET, they found that because it does not interact with the wasabi receptor to repel mosquitos, its efficacy was not impacted by higher temperatures.
“This suggests that during the hottest days of the year you’d probably want to stick with a more conventional synthetic repellent and avoid using a natural product with citronella or catnip oil,” said Piermarini.
Piermarini said the team will continue to investigate the specific mechanisms behind temperature-induced desensitization of the TRPA1 receptor, and they hope to study the phenomenon in a more comprehensive manner, potentially with the help of human participants.
“The more we learn about the mechanisms by which these natural products work, it can help us determine which ones might be better to use under certain conditions,” said Piermarini. “Understanding these limitations can potentially save lives.”
This research was supported by Ohio State, the Sigma Xi Grants in Aid of Research (GIAR) program, and the National Institutes of Health.
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Contact: Peter Piermarini, [email protected]
Written by: Tatyana Woodall, [email protected]
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