Mosquitoes Can Learn to Love DEET: Study Shows Repellent Could Become Attractive Through Conditioning
Lab experiments suggest that Aedes aegypti mosquitoes can be conditioned to seek out DEET-treated skin, raising questions about long-term repellent effectiveness.
Background
For eight decades, N,N-diethyl-meta-toluamide (DEET) has been the gold standard in insect repellents, recommended globally to ward off mosquitoes that transmit fatal diseases such as dengue, malaria, Zika, and yellow fever. Although its exact mechanism remains debated, DEET is thought to be unpleasant to mosquitoes or to block their ability to detect humans.
Pavlovian conditioning
A study published in the Journal of Experimental Biology demonstrates that the yellow fever mosquito Aedes aegypti can learn to associate DEET’s odor with a blood meal. Researchers from the University of Tours and Virginia Tech used a classical conditioning setup: female mosquitoes were allowed to feed on warm blood while simultaneously exposed to DEET vapour. After four training sessions, more than 60% of the insects attempted to bite when later exposed to DEET alone, compared with only 17% of untrained mosquitoes. In a choice test, nearly 60% of conditioned mosquitoes tried to bite a DEET-treated hand, while untrained individuals universally avoided it.
- No training
- 17 %
- DEET only
- 13 %
- Blood only
- 17 %
- Blood then DEET (separate)
- 23 %
- Blood with DEET (simultaneous)
- 60 %
Expert reactions
For a long time, it was believed that repellents worked solely because of their chemical properties, either by being toxic or unpleasant to mosquitoes and driving them away, or by blocking their ability to detect humans. However, our findings suggest that the reaction can be modified by experience.
DEET is still the gold standard of mosquito repellents. Our work is an important reminder to carefully read the manufacturer’s recommendations regarding dosage and application frequency to ensure these products are as effective as possible.
Implications for public health
While the study does not challenge DEET’s immediate efficacy, it raises concerns that improper use—such as allowing the repellent to wear off—could teach local mosquito populations to overcome their natural aversion. Researchers stress that DEET remains the most effective tool available but urge users to follow instructions meticulously to avoid suboptimal concentrations that might facilitate learning. The duration of the learned association in mosquitoes is still unknown and requires further investigation.
