DEET could attract, not repel, mosquitoes in a warmer world

DEET, or the chemical N,N-diethyl-meta-toluamide, is considered the most effective tool to deter insects. That’s particularly true of mosquitoes that carry serious diseases such as Zika, chikungunya, and dengue, whose incidence may increase as the world warms because of climate change. 

Though the synthetic ingredient has been used widely and successfully for decades, questions remain about the mechanisms that make it so unappealing to mosquitoes. Previous research suggests that DEET confuses a mosquito’s olfactory sensors and masks human body odor. The chemical likely tastes and smells terrible too, so if a mosquito lands on treated skin, it flies away before biting.

But new research published in the Journal of Experimental Biology suggests instead, under certain conditions, at least one mosquito species can learn to associate the substance with meals and can shift their avoidance toward attraction (J. Exp. Biol. 2026, DOI: 10.1242/jeb.251935).

“Our study aimed at better understanding what makes DEET a repellent,” says study coauthor Clément Vinauger, associate professor in biochemistry at Virginia Tech.

“Is it something intrinsic to its chemical structure, or is it about how mosquitoes interpret the molecule in a way that can be modified by their prior experiences?” he says. Turns out, it’s more of the latter.

Making DEET delectable

Over 3,500 mosquito species cover the globe, but not all suck blood. In the new study, researchers worked with Aedes aegypti, also known as the yellow fever mosquito, whose bite transmits diseases that affect tens of millions of people worldwide each year.

Using classical conditioning—the same principle behind the famous Pavlov’s dog experiment—the scientists confined more than 250 female mosquitoes in small mesh-covered tubes, with an artificial feeder containing warm sheep blood behind a thin membrane just out of reach. The insects could smell the blood and sense its warmth, but could not eat it. Researchers developed a measurable feeding behavior—the biting-attempt response—that could be used as a way to gauge the mosquitoes’ motivation to feed.

When mosquitoes were allowed to feed on the blood through the membrane for up to 20 s, researchers introduced DEET-scented air into the tubes. The exposure to the chemical didn’t prevent the mosquitoes from feeding, and after only four trials, the mosquitoes learned to associate DEET with a food reward. Nearly 60% of the trained mosquitoes displayed a biting-attempt response when they were exposed only to the scent of DEET—even when blood wasn’t present.

The results dovetail with the team’s previous research that shows individual mosquitoes can learn. “Mosquitoes can learn associations between many odors, either punishment or reward, and remember these associations for a couple of days,” says Vinauger.

In the study’s second phase, researchers gave the trained mosquitoes a chance to respond to DEET on human skin. “When given a choice between the two arms of a human volunteer, with one arm treated with DEET and the other left untreated, mosquitoes actually preferred to attempt to bite the DEET-treated arm,” Vinauger says.

Researchers even conducted the same trials with sugar instead of blood, and mosquitoes performed the same way: mosquitoes trained to associate DEET with a food reward became attracted to the chemical.

“Prior work also showed that preexposing mosquitoes to DEET lowered its effectiveness during subsequent encounters. We were not surprised that [mosquitoes] could learn that DEET isn’t so bad when it is associated with a food reward, but we found the extent to which they learned to like DEET and become attracted to it to be remarkable,” says Vinauger.

Don’t toss the DEET

So what does the study mean for people looking to enjoy their summers without getting bitten?

For one, it suggests DEET itself—created by the US Army in the 1940s—might not be inherently harmful to mosquitoes. Instead, the chemical carries information that insects can learn to interpret, says Ali Afify, assistant professor of biology at Drexel University, who was not involved in the new study.

The study’s results also don’t mean people should switch to repellents, such as picaridin. In the wild, mosquitoes don’t seek out and bite people who are wearing DEET-based repellents. This is why the study’s backward-conditioning method—mosquitoes encounter DEET while feeding, not before—is unlikely to occur in nature.

“This type of learning, mosquitoes becoming attracted to DEET, would only happen if mosquitoes succeed in biting a person who has applied DEET to their skin several hours earlier, and the concentration of the repellent is not high enough to repel the mosquito,” Afify says.

The compound is highly effective in repelling untrained mosquitoes, and following universal guidelines for applying DEET—such as not overapplying the product—remains a strong line of defense, Vinauger says.

Still, the study brings up questions about how mosquitoes may adapt and behave in the future—concerns that are especially important as climate change intensifies mosquito populations, as well as potentially the diseases they carry.

“If a mosquito manages to bite someone wearing a low concentration of DEET, could it then learn to seek out the smell of DEET in the future? The study suggests the answer may be yes,” Afify says.