Mosquitoes May Be Learning to Associate DEET with Food: Study

**Mosquito Repellent DEET May Lose Effectiveness Through Repeated Exposure, Study Finds**

A new study has revealed that mosquitoes can develop a taste for the popular insect repellent DEET (N,N-diethyl-meta-toluamide) after being exposed to it on multiple occasions. This research, published in the *Journal of Experimental Biology*, suggests that the common perception of DEET as an unfailing deterrent against mosquito bites may need reconsideration.

The study was led by researcher Claudio Lazzari from the University of Tours in France, who noted, “If mosquitoes are repeatedly exposed to DEET, it becomes less effective as a repellent.” The findings are significant in the context of Aedes aegypti mosquitoes, known carriers of serious diseases such as yellow fever and Zika virus.

In conducting the study, researchers employed techniques echoing the classical conditioning methods pioneered by Ivan Pavlov, who famously trained dogs to associate the sound of a bell with feeding. Similarly, the researchers exposed Aedes aegypti mosquitoes to the scent of DEET while they fed on blood, training the insects to associate the chemical’s smell with a food reward. Remarkably, after just three exposures, around 60% of the mosquitoes attempted to bite a person wearing the repellent when they detected its scent.

Clément Vinauger, an associate professor at Virginia Tech and co-author of the study, highlighted the implications of these findings. He explained that when DEET’s concentration diminishes over time, mosquitoes may begin to associate the lingering scent with their blood meal. This could prompt them to seek out humans wearing the repellent even when its effectiveness has diminished.

In a controlled experiment involving two hands — one treated with DEET and the other left untreated — the mosquitoes consistently chose to bite the hand coated in the repellent. This behavioural response indicates that, in some instances, a reduced concentration of DEET may enhance mosquitoes’ likelihood of biting human hosts.

Lazzari further elaborated on this phenomenon, noting that if a mosquito bites a person who applied DEET several hours prior and the repellent’s concentration falls below effective levels, the insect could still retain a preference for the smell of DEET. This could lead to increased vulnerability to bites for individuals whose skin still carries the scent of the chemical.

Despite these alarming revelations, experts stress that DEET remains the most effective ingredient in insect repellents. According to the Agency for Toxic Substances and Disease Registry, DEET has a robust track record of effectiveness and minimal side effects when used as directed. The Aedes aegypti mosquito, which poses a significant public health risk due to its role in the transmission of various viruses, underscores the need for effective preventive measures against bites.

While the implications of the study raise important questions about the long-term efficacy of DEET as a repellent, researchers argue that it is premature to discard its use entirely. Lazzari reassured users that DEET continues to save lives and emphasised the importance of regular reapplication when outdoors.

As concerns surrounding mosquito-borne diseases grow, this research compels individuals and public health officials to remain vigilant about the use of insect repellents. The dynamics of mosquito behaviour are complex and adaptive, and understanding these can improve personal protection strategies.

In light of this study, it might be prudent for users of DEET-based products to reapply regularly and consider additional protective measures, such as wearing long sleeves and employing physical barriers like nets. This multifaceted approach will be crucial in combatting the threats posed by Aedes aegypti and other mosquito species.

As the fight against mosquito-borne diseases continues, ongoing research into these adaptative behaviours will be vital in shaping effective public health strategies that safeguard communities against these prolific pests.