Mosquito-borne diseases kill around one million people every year. One of the few tools available to reliably ward off these blood-sucking insects is the repellent chemical N, N-diethyl-meta-toluamide (DEET).
DEET also repels ticks and flies, but some researchers have suggested that it loses its effectiveness after repeated exposure. Now, scientists have taken this idea one step further, showing that mosquitoes can even learn to love the chemical if it is associated with food rewards.1 In new research published in the Journal of Experimental Biology, these trained mosquitoes actually bit people who were soaked in DEET more than those who wore no repellent at all. Claudio Lazzari, a biologist at the University of Tours and coauthor of the study, said in a statement that DEET likely mimics natural insect repellents released by plants and that the spray remains society’s best hope for repelling the bugs. The new study, he said, could offer hints about how best to apply DEET to minimize the chance of getting bitten.
Mosquitoes Get the Munchies
Lazzari and his team developed a series of experiments inspired by the foundational behavioral work of physiologist Ivan Pavlov, who trained dogs to associate food with the noise of a bell. While Pavlov recorded how the bell made his dogs drool, the mosquito scientists instead measured how strongly the insects reached for a blood reward by sticking their probosces through a fabric mesh. This jabbing motion was termed the biting attempt response (BAR).
The team offered the mosquitoes blood while pumping air laced with DEET into their test chamber. At first, this put the bugs off their meal. The team then shook things up by offering blood to the insects for 30 seconds and only pumping in DEET for the last 10 seconds.
After just three rounds of this sequenced exposure, the smell of DEET alone sent the insects into a food frenzy. Now, 60 percent of mosquitoes exposed to DEET showed the BAR. In comparison, just 17 percent of bugs that hadn’t gone through the training procedure showed biting responses.
When DEET Stops Working
To see whether DEET-fan mosquitoes would change their responses to repellent-soaked humans, the team offered them a choice between two hands. One was covered in DEET, while the other wasn’t. While 100 percent of the untrained insects steered clear of the DEET hand, more than half of the trained insects opted for a meal of blood and insect repellent.
The association wasn’t specific to human blood. A separate experiment trained the mosquitoes to link DEET to a sugar reward. The results were identical: Trained mosquitoes performed BAR in the presence of DEET.
The results could be instructive outside the lab. People who want to avoid being bitten should be careful about how they apply DEET, said Lazzari. “If a mosquito bites someone who applied DEET to their skin several hours earlier and the concentration of the repellent is too low to repel the mosquito, but still strong enough for the insect to smell it, the mosquito may be more likely to bite people who smell of DEET.”
- Lazzari CR, et al. Associative learning switches DEET valence from aversive to appetitive in Aedes aegypti. J Exp Biol. 2026;229:jeb251935.
