Scientists trained mosquitoes to love repellent, but don't throw away your bug spray yet

Scientists have discovered that mosquitoes can be trained to associate the smell of the world's most widely used insect repellent with a rewarding meal and can even develop a preference for biting people who have applied it. Despite the striking findings, lead study author Claudio Lazzari was quick to reassure the public that the results, obtained under highly controlled laboratory conditions, do not undermine the effectiveness of DEET (N,N-diethyl-m-toluamide). The chemical compound has been in use since the 1940s and is considered the gold standard in repellents, recommended by the World Health Organisation in the fight against mosquito-borne illnesses.

However, Lazzari, a professor emeritus at the University of Tours in France, noted that the world still needs newer, more environmentally friendly alternatives that cause fewer allergic reactions — and that requires a deeper understanding of why existing repellents work at all.

To investigate, an international research team applied a conditioning method similar to the one made famous by Pavlov's dog, the subject of classical conditioning. Aedes aegypti mosquitoes carriers of dengue fever, Zika, yellow fever, and chikungunya were placed in a mesh enclosure and exposed to warm blood alongside the scent of DEET in repeated sessions. Initially, the insects retreated from the repellent as expected. But after just a few rounds of conditioning, more than 60 percent attempted to bite a DEET-scented surface even when no blood was present. When given a choice between a clean hand and one coated in DEET, the trained mosquitoes consistently preferred the treated one. Similar results were observed using sugar instead of blood.

The researchers concluded that DEET's repellent effect is not purely chemical but depends on how mosquitoes interpret and remember the scent. Co-author Clement Vinauger of Virginia Tech described this as a paradigm shift in understanding repellent behavior. The findings were published in the Journal of Experimental Biology.