We now know how these mosquitoes follow us

Excellent news, especially for the inhabitants of tropical areas where these mosquitoes carry dangerous pathogens.

Spring is finally here, much to the delight of lovers of outdoor walks and picnics. But like every year, it also marks the return of a few unwanted things we could be missing out on, starting with those pesky mosquitoes. And American researchers have just discovered a mechanism that could explain their propensity to ruin our barbecues.

A team from Princeton University was particularly interested in a species called Aedes aegyptian† It is a particularly problematic animal because it can carry a whole cocktail of pathogens, such as malaria, the Zika arbovirus, dengue or yellow fever. And it turns out that this species evolved in a few decades to target almost exclusively a single species: we

From the point of view of biologists, this is a very interesting transition. Indeed, this suggests that they had to evolve in order to survive depending on a single species incredibly accurate targeting strategies that researchers have tried to understand. Their ultimate goal: to determine exactly the mechanisms by which mosquitoes can spot people.

We kind of delved into the brains of mosquitoes to ask them: What do you smell? What activates your neurons, what lights up differently in your brain when you smell a human being??” summarizes Carolyn McBride, professor of evolutionary biology, ecology and neuroscience at Princeton University. †

A scent-based treasure hunt

To achieve this, the researchers developed a highly visual approach. They produced a genetically modified strain of mosquitoes of what? nerve structures selectively light up when activated† They then introduce these mosquitoes to animal odors, including those of humans, to see this mechanism more clearly with an imaging system designed especially for the occasion.

The problem is, there are just as many human scents as there are humans. And for good reason: this fragrance comes from a very complex cocktail of dozens of organic compounds. However, none of them are of interest to mosquitoes by themselves. The researchers therefore concluded that the mosquitoes reacted to a very special combination. But how to find it?

Without any initial clues, they had no choice but to proceed empirically. They started collecting scents from rats, guinea pigs, quail, sheep and dogs. But for humans it was more complicated; harvesting a “pure” human scent is less obvious than it seems. Indeed, most of us regularly use perfumed hygiene products. Even clothing can significantly alter this smell.

Some volunteers therefore had to give of themselves. †We asked them not to shower for several days, to undress and then to lie down in a large Teflon bag.”, laughs Jessica Zung, member of the research team. They then had to develop a system that would allow them to extract and isolate these odors.

This work could make it possible to develop repellents that are much more effective and less annoying than the famous burning spirals and other citronella sprays. © Ronald Langeveld

A surprisingly simple process

It still remained to determine exactly which compounds are likely to make mosquitoes react. The researchers therefore subjected the mosquitoes to numerous combinations of the different compounds identified during the collection for months. They then compared the results to determine the most effective markers.

The researchers expected to discover a highly sophisticated tracking system. But the process they identified surprised them with its simplicity, as it is apparently based on only two very specific organic compounds: undecanal and decanal, an aldehyde also found in buckwheat, coriander essential oil… or the famous Chanel No. 5! On good terms…

The other point that surprised the researchers is the response these compounds cause in the nervous system. The “brain” of mosquitoes is a structure made up of about 60 substructures called glomeruli. The researchers expected that the majority of these glomeruli are involved in the hunting of humans as this is a vital activity for these mosquitoes; there are really only… theirs

When I first saw this brain activity, I couldn’t believe it”, explains Zhilei Zhao, a PhD student who played a central role in this research. †Only two glomeruli were involved, which contradicts all our expectations. It’s amazing that this system is so simple‘, she wonders.

Repellents based on this work could reduce the spread of pathogens carried by these mosquitoes. In particular, we can cite Plasmodium as the origin of malaria. © Frevert en. para.

The door is open for very concrete solutions

This discovery will potentially have significant implications, some of which are very concrete. Because this work was performed on mosquitoes that are known to be carriers of very problematic diseases. Now that researchers have found the chemical compounds that most attract them, it opens the door to a whole host of countermeasures to combat this public health scourge. It would be enough to use it for example for: to lure into a deadly trap.

We can also introduce ourselves repellents that would specifically block this signal, which prevents mosquitoes from spotting people by smell. This is a solution that is even more interesting. Because even if they are painful, mosquitoes remain important players in many ecosystems.

For example, many birds or spiders depend directly on mosquitoes, as they make up a substantial part of their diet. Ideally, therefore, it is better to try to keep them away rather than eradicate them, as this is the start of a catastrophic chain reaction for certain ecological niches.

Eventually it will also be very interesting to extend this work to other species. This will initially allow us to see if the mechanism is reserved for these specialized human hunters, or vice versa. universal in all mosquitoes† If necessary, a simple, harmless and ecosystem-friendly solution could then be developed to avoid serving as a traveling buffet. Good news for fishing and picnic lovers… but especially for all populations of the tropical zones whose lives can be completely changed by a simple mosquito bite.

The text of the survey can be found here.

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