A new study suggests that mosquitoes can learn to associate the chemical Deet with a blood meal, potentially making them less repelled by the substance over time. Deet, widely used in insect repellents and recommended by the UK Health Security Agency, may become attractive to mosquitoes if they encounter it while feeding.
Researchers from the University of Tours, France, found that mosquitoes exposed to Deet while feeding on warm blood later showed increased biting attempts when presented with Deet alone. In one experiment, 60% of trained mosquitoes tried to bite a Deet-treated hand, compared to none of the untrained insects.
The study, published in the Journal of Experimental Biology, challenges the long-held belief that repellents work solely through chemical properties. Professor Claudio Lazzari, lead author, said: 'Our findings suggest that the reaction can be modified by experience.'
However, experts caution that the results do not mean Deet is ineffective in normal use. Dr Nina Stanczyk of ETH Zürich noted that the highest risk of association occurs when repellent starts to wear off, emphasising the importance of regular reapplication as per product instructions.
Professor Francesca Romana Dani of the University of Florence added that under normal conditions, it is unlikely mosquitoes would change their response to Deet, as they encounter different repellents across blood meals taken days apart.
