Mosquitoes Are Learning to Love Bug Spray, New Study Finds

For decades, DEET has been one of the best tools people have to keep mosquitoes away. But new research out of Virginia Tech suggests the bugs might not stay repelled forever.

Researchers found they could train mosquitoes to link the smell of DEET with a blood meal, essentially teaching them to like the very thing that's supposed to drive them off. Clement Vinauger, an associate professor at Virginia Tech, worked with researchers at the University of Tours in France on the project.

"They were really excited about it and became really attracted by DEET," Vinauger said.

The team used a method similar to Ivan Pavlov's classic dog experiments, where an animal learns to associate one thing with another through repeated exposure. In the lab, mosquitoes fed on a bag of warm blood behind a mesh barrier. Each time they fed, researchers introduced the smell of DEET alongside it.

"We did that only four times, and that was sufficient for them to learn the association in such a way that a few minutes later when you give them only the smell of DEET, they're really excited about it," Vinauger said. "So instead of being repelled and going away, they go towards DEET and try to pierce through that membrane, even though the blood is not here anymore and there's just the smell of DEET."

Afterward, researchers gave mosquitoes a choice between two human hands, one coated in DEET and one left untreated. Mosquitoes that hadn't gone through the training avoided the treated hand as expected. The trained mosquitoes, though, went straight for it, suggesting their brains could essentially get rewired based on what they'd experienced.

Despite the findings, researchers say DEET is still the best option people have for avoiding bug bites this summer. The real takeaway, they say, is about how it's used. Applying too little, too rarely, or letting it wear off could create the exact conditions that led to the mosquitoes' shift in behavior in the lab.

The study, published in the Journal of Experimental Biology, focused on the yellow fever mosquito, a species known for spreading dengue, Zika and yellow fever. Researchers say the findings could help scientists better understand how mosquitoes adapt to the tools used against them.