Mosquitoes have always preferred to feast on humans over other animals, but exactly how they distinguish between the two has remained a mystery until now.
The mosquitos Aedes aegypti they have evolved to sting humans by relying on odor molecules other than those exuded by other creatures in the surrounding environment, a new study, published in Nature, reveals.
These mosquitoes, which act as vectors for diseases such as Zika, dengue fever and yellow fever, prefer the human scent over that of animals, according to research retrieved by The Independent.
The new study, involving scientists from Princeton University in the United States, applied a novel approach by imaging mosquito brains at very high resolution to see how they identify their next victims.
Scientists genetically engineered mosquitoes to make their brains light up when active and delivered human- and animal-flavored air to them in ways they could detect while inside the team’s custom imaging equipment.
The researchers sought to understand the exact mix of components in the air that mosquitoes used to recognize human scent.
Carolyn McBride, assistant professor of ecology and evolutionary biology and neuroscience, noted, “We dove into the mosquito brain and asked, ‘What can you smell? What lights up your brain? What activates your neurons, and how does your brain activate differently when you smell human versus animal odor?’”
While human scent is made up of dozens of different compounds, these are also present in most mammals in slightly different proportions. To compare and test how mosquitoes detected odors from mammals and humans, the scientists collected hair, skin, and wool samples and used odor from 16 humans, two rats, two guinea pigs, two quail, one sheep, and four dogs.
“For the human samples, we had a group of volunteers. They were not allowed to shower for a few days, then stripped naked and lay down in a Teflon bag,” explained graduate student Jessica Zung.
The participants were naked since cotton, polyester and other fibers have their own odors that would distort the data, the scientists said.
At first, the researchers suspected that mosquito brains probably had a highly advanced technique for distinguishing humans from other animals, but the study found that the process was much simpler than previously thought.
“The simplicity surprised us. Mosquitoes have evolved a surprisingly simple mechanism for recognizing us,” McBride said.
Mosquito brains have 60 nerve centers called glomeruli, and researchers initially thought that many, “maybe even most,” would help them find their favorite food.
“When I first saw the brain activity, I couldn’t believe it, only two glomeruli were involved,” said study co-author Zhilei Zhao.
That contradicted everything we expected, so I repeated the experiment several times, with more humans, more animals. I just couldn’t believe it. It’s very simple,” he added.
Narrowing down to the glomeruli that mosquitoes use to detect humans, the scientists found that they use these brain centers to detect two chemicals, decanal and undecanal, which smell slightly orange and citrusy and are enriched with that of humans.
“To me, it’s an evolutionary story: If we create a statistical test to differentiate human scent, it would be very complex, but the mosquito does something very simple, which works quite well for it,” McBride added.
Based on the study, scientists have patented a mix with decanal that they hope could lead to baits that lure mosquitoes into lethal traps or signal-disrupting repellents.
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