Excellent news, especially for those living in tropical regions where these mosquitoes carry dangerous pathogens.
Spring is finally here, to the delight of lovers of outdoor walks and picnics. But like every year, it also marks the return of some undesirables that we could do without, starting with those annoying mosquitoes. And American researchers have just identified a mechanism that could explain their propensity to ruin our barbecues.
A team at Princeton University was particularly interested in a species called Aedes aegypti. It is a particularly problematic little animal since it can carry a whole cocktail of pathogens such as malaria, the Zika arbovirus, dengue or yellow fever. And it turns out that in just a few decades, this species has evolved to target a single species almost exclusively: us !
From the point of view of biologists, this is a very interesting transition. In fact, this suggests that in order to survive by relying on a single species, they had to develop Incredibly accurate targeting strategies that researchers have tried to understand. Their ultimate goal: pinpoint the mechanisms that allow mosquitoes to detect humans.
“We went more or less into the brain of mosquitoes to ask them: what do you smell like? What activates your neurons, what lights up differently in your brain when you smell human??” Summarizes Carolyn McBride, professor of evolutionary biology, ecology and neuroscience at Princeton University. “
A Scent-Based Scavenger Hunt
To achieve this, the researchers developed a very visual approach. They produced a genetically modified strain of mosquitoes whose nerve structures selectively light up when activated. They then put these mosquitoes in contact with scents from animals, including humans, to try to see this mechanism more clearly using an imaging system specially designed for the occasion.
The problem is that there are as many human smells as there are people. And for good reason: this smell comes from a very complex cocktail of dozens of organic compounds. However, none of them are of interest to mosquitoes on their own. Therefore, the researchers deduced that the mosquitoes reacted to a very particular combination. But how to find it?
Without any initial clues, they had no choice but to proceed empirically. They began by 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. In fact, most of us regularly use scented hygiene products. Even clothing can significantly alter this smell.
Therefore, some volunteers 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, a member of the research team. They then had to develop a system that would allow them to extract and isolate these odours.
A surprisingly simple process
Precisely which compounds are likely to cause mosquitoes to react remained to be determined. Therefore, the researchers spent many months subjecting the mosquitoes to many combinations of the different compounds identified during collection. They then compared the results to determine the most effective markers.
The researchers expected to discover a very sophisticated tracking system. But the process they identified surprised them because of its simplicity, since apparently it is based solely on two very specific organic compounds: undecanal and decanal, an aldehyde that is also found in buckwheat, coriander essential oil… or the famous Chanel No. 5! To the good understanding…
The other point that surprised the researchers is the reaction that 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 the most of these glomeruli are involved in hunting humans, since this is a vital activity for these mosquitoes; actually there is only… from them.
“When I first saw this brain activity, I couldn’t believe it.”, explains Zhilei Zhao, a doctoral student who played a central role in this study. “There were only two glomeruli involved, which contradicts all our expectations. It’s amazing that this system is so simple.she wonders.
The door is open to very concrete solutions
This discovery will potentially have considerable consequences, some of which are very concrete. Because this work was carried out on mosquitoes known to be vectors of very problematic diseases. Now that researchers have found the chemical compounds that most attract them, it opens the door to a host of countermeasures to combat this public health scourge. It would suffice, for example, to use it to lure into a death trap.
we can also imagine repellants that would specifically block this signal, thus preventing mosquitoes from detecting humans by scent. This is a solution that is even more interesting. Because although they are painful, mosquitoes are still key players in many ecosystems.
For example, many birds or spiders depend directly on mosquitoes, since they represent a substantial part of their diet. Ideally, therefore, it is better to try to keep them away rather than eradicate them, because this could be the start of a catastrophic chain reaction for certain ecological niches.
In short, it will also be very interesting to extend this work to other species. This will allow us to initially see if the mechanism is reserved for these specialized human hunters, or the other way around. universal in all mosquitoes. If necessary, then it would be possible to develop a simple, harmless and eco-friendly solution to avoid serving as a traveling buffet. Good news for lovers of fishing and picnics… but especially for all populations in tropical areas whose life can be completely changed by the simple bite of a mosquito.