The Aedes aegypti mosquito likes human blood, which is a problem because it carries many diseases (yellow fever, dengue fever, Zika…). (Photo: Joao Paulo Burini/Getty Images)
BZZZZ – Crawl into your bed, you suddenly hear the buzzing in your ear. This characteristic sound is never appreciated, as it is the sign of a possible bite. However, not everyone seems to be in the same boat. Indeed, mosquitoes do not strike humans randomly, while some species have even specialized in tracking us down.
But how do mosquitoes concentrate to track humans so accurately? This is the question a new study published this Wednesday, May 4 in the journal Nature† The latter specifically focused on one species, the Aedes aegypti mosquito.
Indeed, these animals show an overwhelming preference for humans over other animals, as explained in the study Zhilei Zhao, a postdoctoral researcher in neurobiology and behavior at Cornell University.
Distinguish humans from other animals
It has now been established that mosquitoes use their sense of smell to strike. Every animal (including us) gives off a tasty bouquet of scents for these insects. It could be bacteria (Brevibacterium sheets) on our feet, specific compounds (such as lactic acid) that we expel when we sweat, or even carbon dioxide that we exhale.
While scientists know the importance of these chemical signals to mosquitoes, most of them occur in many animals. So how do they manage to differentiate them and target them specifically at people? The answer lies in the tiny brains of mosquitoes, according to this new study.
To do this, the researchers used a technique that roughly consists of flashing the mosquito’s neurons using a fluorescent aid (CRISPR) when a nerve cell is activated. They then exposed the mosquitoes to an odor sample from various animals, including humans, to see which parts of the brain lit up in response to different smells.
open brain surgery
To observe what happened in the mosquitoes’ brains, the team had to operate on the insects alive by opening their skulls. The task here is much more difficult than a simple “mad doctor”, since the brains of these animals are about 0.5 millimeters in diameter.
Photo of the skull of an Aedes aegypti mosquito, which is no larger than 0.5 millimeters in diameter. (Photo: Joao Paulo Burini via Getty Images)
Analysis showed that a spherical nerve bundle known as the glomerulus reacted strongly to human odors (and weakly to animal odors). Of these human scents, two appeared to be particularly attractive to mosquitoes: decanal and undecanal, which have a sweet, lemony scent, similar to orange peel.
These discoveries allowed researchers to develop chemical formulas that would reduce or even block the activity of glomerulus H, making mosquito repellents more effective. Another application would be to use the scents that attract mosquitoes to make bait that would keep them away from humans.
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This article originally appeared on The HuffPost and has been updated.