New research reveals that mosquitoes can adapt to — and even seek out — the scent of popular insect repellents, challenging long-held assumptions about protection against bites.
TheDigger Intelligence Unit
In a startling twist, scientists have discovered that mosquitoes—nature’s most notorious bloodsuckers—can actually learn to be attracted to the very scent millions rely on to keep them away.
DEET—short for N,N-diethyl-meta-toluamide—is the world’s leading insect repellent and the top recommendation of the UK Health Security Agency for preventing bites.
However, a new study by American and French scientists published in the Journal of Experimental Biology found that mosquitoes can, under certain conditions, learn that the presence of DEET signals the possibility of a blood meal.
The experiment began with a swarm of insects placed in a fabric-mesh enclosure, then presented with a bag of warm sheep’s blood to observe how keen they would be to feed on it.
The Aedes aegypti mosquitoes were quick to feast on the blood, but initially, when the smell of DEET was introduced, they moved away.
Next, the scientists fed the insects warm blood for 20 seconds, releasing DEET during the last 10 seconds.
That part of the experiment was repeated three times before the mosquitoes were exposed to solely the scent of the repellent.
This time, more than 60 per cent of the insects tried to bite the fabric – even though there was no blood.
Then, one of the scientists offered up their hands – one clean, the other coated with DEET – to the trained mosquitoes to see which one they would bite.
And the mosquitoes almost unanimously flocked to the hand covered in repellent, in results which were described as ‘beyond doubt’.
The scientists had similar results when they repeated the experiment using sugar instead of blood, because mosquitoes mostly feed on plant nectar in the wild.
Co-author of the study, Clement Vinauger, said: ‘The common assumption has always been that repellents work because of their chemistry.’
However, the scientist said that his latest study reveals that ‘it’s not the chemistry of the molecule itself which is toxic’ to the insects, but instead they are repelled by how they ‘interpret the chemical information’.
Mr Vinauger, who works with Virginia Tech in the United States, added: ‘What we are showing is that the mosquito’s brain can rewrite that response based on experience.
‘What the insect has learned matters just as much as what the chemical does. That, I think, is the paradigm shift.’
The other author, Claudio Lazzari of the Insect Biology Research Institute in France, however, insisted that ‘very specific conditions’ would be required to reproduce the findings outside the lab.
He added that DEET, which was developed in the US around 80 years ago, remains ‘the absolute gold standard for repellents’ – and said that his study’s findings do not ‘call into question the effectiveness’ of the repellent.
Meanwhile, Doctor Nina Stanczyk of ETH Zurich University said the findings showed mosquitoes’ impressive capacity for learning.
She said: ‘Mosquitoes have been shown to have impressive learning abilities, but the fact they can associate such a strong repellent smell with their food and are then attracted to it afterwards is remarkable, and important for us to be aware of for the future.’
She nevertheless also emphasised that travellers should not ditch their DEET supplies.
‘People should understand that DEET does not lose its effectiveness through normal use, but only under specific laboratory conditions designed to reveal how it works on mosquitoes,’ the doctor added.