Carlos Solis
Gaby
Repellents are a primary line of defense against mosquitoes and the diseases those insects carry. The most common active ingredient in mosquito products is N,N-diethyl-m-toluamide, better known as DEET. Effective, relatively long-lasting (about five hours), and inexpensive to produce, DEET is the “gold standard” of repellents.
DEET doesn’t kill mosquitoes; it masks you. Mosquitoes find hosts by sensing the carbon dioxide and lactic acid your body emits. A repellent blocks the insects’ receptors, making you “invisible” to them.
Researchers recently found a small fraction of mosquitoes that are insensitive to DEET, and that insensitivity is inherited. Another study showed that repeated exposure to DEET for three hours made mosquitoes temporarily less sensitive — as if they’d habituated.
New study — mosquitoes can learn to associate DEET with a blood meal
Researchers developed a behavioral test: they kept mosquitoes in small containers and brought a food target (a warm tube of blood) close to them, recording proboscis movements as the insects approached. They called that motion the “probing response.” Then they ran an experiment pairing an unconditioned stimulus (heat), a conditioned stimulus (a short puff of DEET), and a reward (a brief chance to sip blood).
The result was surprising: if mosquitoes received a puff of DEET while they were already feeding, they later showed a much stronger probing response when they encountered DEET again. In other words, DEET that accompanied food became a cue for available nourishment.
By contrast, when researchers sprayed DEET before offering blood, none of the mosquitoes attempted to bite the blood source.
In the next stage, a researcher volunteered her hand: one hand was treated with DEET, the other left clean. Among mosquitoes trained with the “DEET + blood” program, about 50% tried to bite the DEET-covered hand. In the untrained control group, all the mosquitoes avoided the DEET hand and went for the clean one.
What this means
Mosquitoes can learn and remember, and what they pick up about hosts and the environment can change how diseases spread. The study shows DEET’s effect isn’t purely physiological — it has a cognitive side: mosquitoes can learn to link the smell of DEET with food.
The authors propose that if a DEET concentration is too low to repel a mosquito, but the insect experiences it while feeding, the compound could become a cue that makes people wearing DEET more attractive to mosquitoes.
The experiments took place under controlled laboratory conditions, and the training programs may not reflect typical real-world scenarios. Follow-up studies should model more realistic conditions to see whether these results hold outside the lab.
At a time when mosquito-borne diseases (malaria, dengue, chikungunya, Ross River virus, Japanese encephalitis, and others) spread through travel, urbanization, and climate change, DEET remains an effective protective tool. This new study doesn’t overturn that — it deepens our understanding of how repellents work and points toward ways to improve them.
This article is based on material from The Conversation.
