We now know how these mosquitoes haunt us

Excellent news, especially for residents of tropical regions where these mosquitoes transmit dangerous pathogens.

Spring has finally arrived, to the delight of lovers of walks and picnics in the great outdoors. But like every year, a few unwanted ones return that we could do without, starting with the pesky mosquitoes. And American researchers have just identified a mechanism that could explain their propensity to ruin our grills.

A team from Princeton University was particularly interested in a species called Aedes aegypti. It is a particularly problematic little animal because it can transmit 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 almost exclusively target a single species: weather !

From the perspective of biologists, this is a very interesting transition. Indeed, this suggests that they had to evolve to survive dependent on a single species incredibly precise targeting strategies the researchers have tried to understand. Their ultimate goal: to determine the precise mechanisms that allow mosquitoes to recognize humans.

We more or less penetrated 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 someone??” summarizes Carolyn McBride, professor of evolutionary biology, ecology and neuroscience at Princeton University. “

A smell-based treasure hunt

To achieve this, the researchers developed a very visual approach. They produced one genetically modified strain of mosquitoes, whose Nerve structures selectively light up when activated. They then brought these mosquitoes into contact with animal scents, including human ones, to try to see this mechanism more clearly using an imaging system specially developed for the occasion.

The problem is that there are as many human smells as there are people. And with 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. From this, the researchers concluded that the mosquitoes reacted to a very specific combination. But how do you find it?

Without initial clues, they had no choice but to proceed empirically. They began 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.

Some volunteers therefore had to sacrifice themselves. “We asked them not to shower for several days, to undress, and then to put themselves 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 has yet to be determined exactly which compounds are likely to cause mosquitoes to respond. The researchers therefore spent many months exposing the mosquitoes to many combinations of the different compounds identified during the collection. They then cross-referenced the results to determine the most effective markers.

Researchers expected to discover a very sophisticated tracking system. But the process they identified surprised them with its simplicity since it appears to be based on just two very specific organic compounds: undecanal and decanal, an aldehyde also found in buckwheat, coriander essential oil… or the famous one Channel #5! On good terms…

The other thing that surprised the researchers was the response these compounds elicited 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 these glomeruli are involved in hunting humans as this is a vital activity for these mosquitoes; there is really only… from them.

When I first saw this brain activity, I couldn’t believe it‘ explains Zhilei Zhao, a graduate student who played a central role in this study. “Only two glomeruli were involved, contrary to all our expectations. It’s amazing how simple this system is“, 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 and Abs.

The door is open to concrete solutions

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

Can we introduce ourselves too? Repellents that would specifically block this signal, which prevents mosquitoes from detecting people by smell. This is an even more interesting solution. Because even if they are painful, mosquitoes remain important players in many ecosystems.

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

Ultimately, it will also be very interesting to extend this work to other species. This will first allow us to see if the mechanism is reserved for these specialized human hunters or if the opposite is true universal in all mosquitoes. If necessary, a simple, harmless and ecosystem-friendly solution could then be developed in order not to serve as a traveling buffet. Good news for fishing and picnic enthusiasts… but especially for all population groups in the tropical zones, whose lives can be completely changed by a simple mosquito bite.

The text of the study can be found here.

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