Pesky mosquitoes on the hunt for a blood meal may find the smell of a common repellent alluring rather than repulsive.
Yellow fever mosquitoes (Aedes aegypti) exposed to the insect repellent DEET can learn to associate the off-putting chemical with food, researchers report May 28 in Journal of Experimental Biology. The finding suggests that mosquitoes can link unpleasant odors with rewards — turning a negative experience into a positive one — although it’s unclear what might happen outside the lab.
Although DEET has been a “gold standard” in insect repellent for decades, it’s still unclear exactly how it works, says Clément Vinauger, a neuroethologist at Virginia Tech in Blacksburg. Some studies suggest that mosquitoes don’t like the way DEET smells or tastes. Others hint that the repellent scrambles mosquito senses so that the insects can’t detect the otherwise enticing body odors that would lure them in for a blood meal.
The new results offer a clue that mosquitoes detect DEET, Vinauger says, and that their behavior can change depending on prior experience.
Vinauger and colleagues housed mosquitoes in a central container connected to two flasks: One contained clean air, and the other contained DEET. The team allowed the mosquitoes to feed on blood from an artificial feeder while exposed to only clean air for 10 seconds. The researchers then cranked up the DEET dial, aiming to train the mosquitoes to associate the repellent with a meal.
To test the association, the researchers put trained and untrained mosquitoes in narrow tubes. A team member held an untreated hand a few centimeters from one end of the tube and a hand sprayed with a DEET-containing repellent at the other end. Trained mosquitoes attempted to bite the repellent-treated hand, while untrained mosquitoes steered clear.
The findings suggest that mosquitoes are smelling DEET and that the chemical is not masking our scent, says Anandasankar Ray, a neuroscientist at the University of California, Riverside, who was not involved in the work. “And [mosquitoes] can be trained to be attracted to it by offering a reward with it.”
But the mosquitoes also smell with their legs, Ray notes, and they couldn’t land on the repellent-treated hand in the experiments. Because the insects land on the skin to take blood, DEET should rebuff the mosquitoes before they can even start to feed. “You’d be getting the smell of DEET being paired with a bitter touch contact,” Ray says. “It would be a punishment for them rather than a reward.”
Vinauger suspects that mosquitoes could learn to associate DEET with a meal when its repellent effects have largely worn off, perhaps hours after people apply it to their skin. “There might still be some traces of DEET on the skin, but maybe not enough to create that repellency effect,” Vinauger says. “Mosquitoes might still land, drink some blood and not be repelled.” If they manage to snag blood, the insects may learn to link the smell with the meal and begin hunting for a combination of human odor and DEET.
The results certainly don’t suggest that people shouldn’t use DEET, Vinauger says. “It’s still the gold standard in terms of protection.” But the chemical is sold by different manufacturers at varying concentrations, and each product may come with unique instructions. “Flipping that bottle and reading the label,” he says, “is important.”
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