Can DEET attract mosquitoes? Lab study offers clues

Annoying mosquitoes looking for a blood meal may find the smell of a common repellent more alluring than repellent.

Yellow fever mosquitoes (Aedes aegypti) exposed to DEET insect repellent can learn to associate the off-putting chemical with foodreport the researchers on May 28 in Journal of Experimental Biology. The results suggest that mosquitoes can associate unpleasant odors with rewards, turning a negative experience into a positive one, although it is unclear what might happen outside the laboratory.

Although DEET has been the gold standard in insect repellent for decades, it’s still unclear exactly how it works, says Clement Vinauger, a neuroethologist at Virginia Tech in Blacksburg. Some studies suggest that mosquitoes don’t like the way DEET smells or tastes. Others suggest that the repellent confuses mosquitoes’ senses so that insects cannot detect otherwise enticing body odors that would attract them for a blood meal.

The new results suggest that mosquitoes detect DEET, Vinauger says, and that their behavior may change based on their previous experience.

Vinauger and his colleagues housed the mosquitoes in a central container connected to two vials: one contained clean air and the other contained DEET. The team allowed the mosquitoes to feed on blood from an artificial feeder while exposing them only to clean air for 10 seconds. The researchers then turned up the dial on DEET, aiming to train the mosquitoes to associate the repellent with a meal.

To test this association, the researchers placed trained and untrained mosquitoes in narrow tubes. A team member held an untreated hand a few inches from one end of the tube and a hand sprayed with DEET-containing repellent at the other end. Trained mosquitoes attempted to bite the repellent-treated hand, while untrained mosquitoes avoided it.

The results suggest that mosquitoes smell DEET and that the chemical doesn’t mask 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 him by offering him a reward.

But mosquitoes also smell with their legs, Ray notes, and they weren’t able to land on the hand treated with the repellent during the experiments. Since the insects land on the skin to draw blood, DEET should repel mosquitoes before they can even begin feeding. “You would experience the smell of DEET combined with a bitter touch,” says Ray. “It would be a punishment for them rather than a reward.”

Vinauger suspects that mosquitoes might learn to associate DEET with a meal when its repellent effects have largely worn off, perhaps a few hours after people apply it to their skin. “There may still be some traces of DEET on the skin, but perhaps not enough to create that repellent effect,” says Vinauger. “Mosquitoes can still land, drink blood and not be repelled.” If they can collect blood, the insects can learn to associate the smell with the meal and begin to seek out 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 for protection.” But the chemical is sold by different manufacturers in varying concentrations, and each product may come with unique instructions. “It’s important to turn that bottle over and read the label,” he says.