New research suggests that mosquitoes can learn to associate the insect repellent Deet with a blood meal, potentially making the chemical attractive to them under certain conditions. The study, published in the Journal of Experimental Biology, challenges the long-held belief that repellents work solely due to their chemical properties.
Researchers from the University of Tours in France observed that 60% of mosquitoes that fed on warm blood while exposed to Deet subsequently attempted to bite when presented with Deet alone. In contrast, only 17% of untrained mosquitoes showed similar behaviour. In a further test, nearly 60% of trained mosquitoes tried to bite a researcher's Deet-treated hand, while untrained mosquitoes universally avoided it.
Professor Claudio Lazzari, lead author of the study, said: 'For a long time, it was believed that repellants worked solely because of their chemical properties... However, our findings suggest that the reaction can be modified by experience.' He emphasised that this represents a significant change in understanding repellents.
Experts caution that the findings do not mean Deet is ineffective in normal use. Dr Nina Stanczyk of ETH Zürich noted that mosquitoes have impressive learning abilities, but stressed that travellers should continue using repellents as directed. 'The most important point for travellers is to regularly reapply repellant as instructed by the product label,' she said.
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 and take blood meals only every few days.
