Mosquito brains are wired to spot us

Summer is coming and, with it, those mosquitoes that spoil our evenings. Even our days now. The process by which they can so effectively find us to sting us has long remained a mystery. Today, thanks to the mobilization of several areas of expertise, researchers are finally offering an answer.

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A mosquito bite, it’s annoying. It itches, mostly. But, in some parts of the world, it’s much worse than that. What scientists call Aedes aegypti is now considered the main vector of the dengue fevervirus Zikaof chikungunya and some yellow fever. We understand why scientists are looking for solutions that could save us from its bite.

The problem is that, moreover, this particular mosquito has developed a tendency to bite humans almost exclusively. Does this mean that he knows how to distinguish the smell of a human from that of another mammal? It would seem. And after years of effort, Princeton University researchers (United States) think they have finally understood how, thanks to very high resolution images of brain mosquitoes.

It was not easy. Scientists from different backgrounds got involved. The researchers first had to design genetically modified mosquitoes whose brain lights up when active. Two years of work. Then they had to make them smell human odors — recovered by taking care not to contaminate them with the odors of the fibers of our clothes — and animal — recovered with the greatest precautions from hair in particular, taken here on rats, sheep, guinea pigs or even dogs – in the hope of observing differences in reaction in said mosquitoes. Again, two years of work to develop a system that diffuses these odors effectively. Time, still, to build an imaging system suitable for studying the brain of mosquitoes. But everything seems rewarded today.

An incredibly simple mechanism

To understand, remember that the smells of mammals — including ours — are made up of dozens of different compounds. A complex mix. So to distinguish thehuman smell from that of animals, scientists believed that mosquitoes must have evolved some sophisticated mechanism. That’s why they wanted to dig into their brains.

And surprised! The mosquito actually takes advantage of a surprisingly simple mechanism to target its prey. Of the 60 nerve centers — scientists call them glomeruli — that mosquitoes have, only two are involved. The first acts as a launcher alert, signaling nearby odors, no matter which ones. The second is the one in charge of confirming — or not — that it is a human scent.

Two is also the number of compounds in our smell that seem to interest mosquitoes. And researchers have also identified them: decanal — with the formula CH₃(CH₂)₈CHO — and undecanal — with the formula C₁₀H₂₁CHO. They have already patented a mixture containing decanal which they hope could lead to baits that attract mosquitoes to deadly traps or repellents that interrupt its signal.

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