Mosquitoes might outsmart humans by liking DEET

Ever heard of Pavlov’s dogs? Now we have Pavlov’s mosquitoes.

A study published Thursday in the Journal of Experimental Biology showed that mosquitoes can learn to like the smell of DEET, an ingredient used in most insect repellents, and even associate it with eating. The method used in the study was similar to how Russian physiologist Ivan Pavlov trained dogs to associate the sound of a bell with meal time in the 1890s.

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According to a press release from Virginia Tech, the researchers there and the University of Tours in France trained yellow fever mosquitoes using Pavlovian conditioning.

Clément Vinauger, a professor at Virginia Tech, said they found that “if someone applies DEET and the concentration fades over time, but a mosquito still manages to feed, the insect may begin associating that smell with a reward,” per the press release.

Why repellents work — or so we thought

Vinauger explained in the press release that repellents were thought to be effective because of the ingredients’ chemistry. For example, DEET smells bad to mosquitoes or the smell of DEET masks the smell of a person, he said. People assumed the insects couldn’t do anything to fight that chemistry.

“But what we are showing is that the mosquito’s brain can rewrite that response based on experience. What the insect has learned matters just as much as what the chemical does,” he said.

In the study, “mosquitoes were restrained behind fabric mesh with a bag of warm blood positioned just out of reach.” Then, the researchers allowed the insects to feed on the blood and “introduced the smell of DEET.”

After feeding on the blood with the added smell, the team presented the mosquitoes with only the smell of DEET. “More than 60 percent of the insects tried to feed when presented with only the smell of DEET,” the press release said.

The researchers then presented the mosquitoes with two choices: one human hand coated with DEET, and another without. Untrained bugs chose the untreated hand, but the mosquitoes who were accustomed to the smell of DEET chose the hand covered in it.

Are bug bites inevitable?

If mosquitoes are smart enough to know that the smell of DEET is only masking a delicious meal, what can be done? Are we doomed to be subject to the insects’ appetites all summer?

The researchers say there is no need to panic.

The findings do not mean people should stop using DEET, but rather change how they use it, per the press release.

“Instead of applying a lot at once,” Vinauger said, “you may want to reapply regularly so it’s always active and providing continuous protection.”

Other studies at Vinauger’s lab show that mosquitoes can retain more than just the smell of DEET. According to another Virginia Tech press release from a 2018 study, mosquitoes remember the scent of people who swat at them and will avoid those hosts.

Vinauger said mosquitoes are “remarkable” creatures, and his lab will continue to study them in the name of public health.