DEET, chemically known as N,N-diethyl-meta-toluamide, is used in many mosquito repellents. It is supposed to reliably repel them from human skin. But there is a catch. Although, according to several studies, DEET has a negative effect on human health with long-term use, its the repellent effect may not always be clear. Researchers in the US and France have found that mosquitoes can learn to prefer DEET-treated skin over untreated skin.
Researchers from Virginia Polytechnic Institute and State University found that mosquitoes can learn to seek out the smell of DEET under certain circumstancesthe most widely used insect repellent in the world. The study was published in the Journal of Experimental Biology.
During the experiment, the scientists examined mosquitoes of the Aedes aegypti species. First, they were offered a bag of warm sheep’s blood. When the smell of DEET was introduced into the environment, mosquitoes initially moved away from it. Subsequently, researchers linked warm-blooded feeding to the presence of repellent. During three repetitions, mosquitoes received blood for twenty seconds, while the smell of DEET was present at the same time for the last ten seconds. Then they were exposed to the repellent alone.
The result surprised even the scientists themselves. More than 60 percent of the mosquitoes tried to bite into the cloth, even though no blood was present. When one of the researchers offered them two hands — one clean and one treated with DEET — most mosquitoes headed for the hand with the repellent.
“It is commonly assumed that repellents work because of their chemical composition. But we show that the mosquito’s brain can change this response based on experience.” said study co-author Clément Vinauger from the Research Institute of Insect Biology in France.
At the same time, the authors emphasize that similar behavior was observed only under very specific laboratory conditions. That means that the results cannot yet be automatically transferred to common situations in nature.
