The secret of mosquito repellent in humans is the aroma of the acid

We have always known that mosquitoes prefer to bite humans than other animals, but we still do not know how these insects distinguish the two.

Aedes aegypti mosquitoes (or yellow fever mosquitoes) have been shown to evolve to bite humans based solely on specific odor molecules that are distinct from odors emitted by other organisms in the environment, according to a new study published in the Journal of Nature.

The mosquito Aedes aegypti, which transmits diseases such as Zika, dengue and yellow fever, strongly prefers the human smell over the smell of animals.

The new study, which involved scientists, including scientists from Princeton University in the United States, applied a new method that requires very high-precision mosquito brain imaging to monitor how annoying insects are. discover their victims.

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To that end, the scientists genetically modified the mosquitoes’ brains to make them ignite when they were active, and released air that smelled of humans and animals in a way that mosquitoes could detect while inside the team’s specially designed camera device.

The researchers tried to distinguish the exact mixture of air components that mosquitoes used to identify human odors.

“We aimed to find out how these mosquitoes seek to distinguish human odor from animal odor, in two ways, what are the distinguishing marks in human odor that insects lead and which part of their brain allows them to process those signals?” . said Caroline (Lindy). McBride, assistant professor of ecology, evolutionary biology and neuroscience.

“We went a little deeper into the mosquito’s brain and asked, ‘What do you smell?’

While the human scent contains dozens of different ingredients, most mammals have slightly different sizes of them.

To compare and test how mosquitoes detect the smell of mammals and humans, the scientists collected samples of hair, wool and wool and used scents taken from 16 people, two mice, two guinea pigs, two quails, a sheep and four dogs.

“For human samples, we had a group of volunteers [الذين قبلوا مشكورين القيام بما طلبناه منهم]Graduate student Jessica Zung said they were asked to “refrain from showering for a few days, then take off their clothes and lie down in a Teflon bag”.

The scientists justified the participants’ request to strip by saying that cotton, polyester and other clothing fibers had their own scents that would deceive the data.

They then collected human and animal scents in a way that prevents any distortion and designed a system that allowed them to pass human scent to mosquitoes in a space prepared for images.

This included creating a wind tunnel to test simple mixtures or single compounds, and raising healthy species of mosquitoes whose brains responded to the tools.

At first, researchers suspected that mosquito brains were likely to contain sophisticated technology that allowed them to distinguish humans from animals, but the study found that the process was much simpler than previously thought.

“We were amazed at the simplicity of the process. Despite the complex nature of the human scent and the fact that it does not actually contain any specific composition for humans, we discovered that mosquitoes developed a surprisingly simple mechanism to identify us,” said Dr. McBride. .

Mosquito brains are known to contain 60 nerve centers called “glomeruli” (a network of capillaries), and researchers initially thought that many, “probably most” of them, would help insects find their favorite food.

But “When I first saw the brain activity, I could not believe it, only two glomeruli were involved,” said Gilly Gao, a graduate student at Princeton University and co-author of the study.

According to Zhaos, “This fact ran counter to everything we expected, so I repeated the experiment several times, with more people and more animals as well. I could not believe it. The process is very simple.”

As they approached the glomeruli used by mosquitoes to monitor humans, the scientists then determined what those nerve centers were discovering.

Scientists have discovered that mosquitoes use these brain centers to detect two chemicals, decane and undechanal, that have an orange flavor, slightly acidic and rich.

“For me, it ‘s a progressive fact: if we do a statistical test to distinguish the human smell, it would be very complicated, but the mosquito does something very simple and simplicity usually pays off when it comes to biological evolution,” Dr. McBride. tha.

Based on the study, scientists have obtained a patent for a mixture containing Decanal, which they hope will lead to the creation of baits that attract mosquitoes to deadly traps, or repellents that block the signal from the human wind to these animals.

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