Mosquitoes are 'loving' insect repellents, scientists warn it’s not good

For decades, DEET has been considered the gold standard in mosquito repellents, helping protect millions of people from mosquito-borne diseases such as dengue, Zika, chikungunya and malaria.

However, a new study suggests that mosquitoes may be capable of learning something scientists did not fully expect: they can associate the smell of DEET with a food reward and, under certain circumstances, become attracted to it rather than repelled by it.

The findings, published in the Journal of Experimental Biology, are prompting researchers to rethink how repellents work and how mosquitoes adapt to their environment.

What is DEET?

DEET stands for N,N-Diethyl-meta-toluamide (also known as N,N-Diethyl-3-methylbenzamide). It is one of the world's most widely used and studied insect repellents and has been used since the 1940s.

More from Lifestyle

What does DEET do?

DEET does not kill mosquitoes. Instead, it works by interfering with their ability to detect and locate humans. Mosquitoes rely on cues such as body odour, carbon dioxide and heat to find a host, and DEET disrupts these sensory signals, making it harder for them to identify and bite people.

What did the study discover?

The research focused on Aedes aegypti, the mosquito species responsible for spreading diseases such as dengue, yellow fever, chikungunya and Zika.

Scientists from the University of Tours in France and Virginia Tech in the United States found that mosquitoes exposed to DEET while feeding could learn to associate the repellent's smell with a rewarding food source.

In laboratory experiments, many of these trained mosquitoes later responded positively to DEET alone, despite the chemical's usual repellent properties.

The researchers described the process as a form of associative learning, similar to the well-known Pavlovian conditioning observed in other animals.

How did mosquitoes learn to like DEET?

During the experiments, mosquitoes were exposed to blood meals while simultaneously detecting DEET. Over time, some insects learned to link the smell of the repellent with feeding opportunities.

Researchers reported that nearly 60 per cent of mosquitoes trained under these conditions later attempted to feed when exposed only to DEET, a significantly higher proportion than among untrained groups.

Additional experiments found that trained mosquitoes were more likely to attempt to bite DEET-treated skin compared with mosquitoes that had not undergone the conditioning process.

Why experts find the findings significant

The study challenges the traditional assumption that mosquito repellents work solely because their smell or taste is inherently unpleasant to insects.

Researchers say the findings suggest mosquito responses can be shaped by experience and learning. This is particularly important because Aedes aegypti mosquitoes are expanding into new regions and mosquito-borne diseases remain a major public-health concern in many parts of the world.

Understanding how mosquitoes process environmental information could help scientists develop more effective control strategies in the future.

Does this mean DEET no longer works?

No. Scientists involved in the research have emphasised that the findings should not be interpreted as evidence that DEET has stopped being effective.

The experiments were conducted under highly controlled laboratory conditions specifically designed to investigate mosquito learning behaviour.

Researchers noted that real-world environments are far more complex, with mosquitoes encountering multiple sensory cues and varying repellent concentrations. DEET continues to be regarded as one of the most effective and widely recommended mosquito repellents available.

Experts also stress the importance of applying repellents correctly and reapplying them according to product instructions, particularly as protection can diminish over time.

What could this mean for future mosquito control?

While the findings do not undermine current recommendations on DEET use, they highlight the remarkable learning abilities of mosquitoes and the need for continued research into insect behaviour.

Scientists believe a better understanding of how mosquitoes interpret smells, visual cues and environmental signals could lead to the development of more sophisticated repellents and vector-control strategies.

As insecticide resistance becomes an increasing challenge worldwide, behavioural research may play a growing role in disease prevention efforts.