Mosquitoes that transmit Zika, malaria, and dengue disease, Aedes aegypti, have evolved to bite people nearly exclusively.
A team has now figured out how they can target us so precisely.
Mosquitoes looking for a blood meal utilize several cues to locate us, including our body heat and carbon dioxide in our breath.
According to new research, a specific olfactory receptor in their antennae also serves as a human detector, responding to smelly chemicals in our sweat.
How do mosquito brains encode such odor as humans?
JONATHAN NACKSTRAND/AFP via Getty Images
Most mosquitos on the planet are promiscuous, meaning they will take blood from any surrounding source.
However, in some areas, Aedes aegypti, the mosquito that transmits Zika, dengue, and yellow fever, has evolved to bite people nearly exclusively.
To flourish as a specialized feeder, relying on only one species like ours for survival, they must have evolved highly accurate targeting tactics.
Carolyn "Lindy" McBride, an associate professor of ecology and evolutionary theory and cognitive science, said, "We set out to try to understand how these mosquitoes make a distinction between human and animal odor, including both terms of what that is regarding human smell that they help in guiding in with and what portion of their brain means allowing them to cue in on such signals," as per ScienceDaily.
Her team has uncovered answers to both portions of this equation after years of hard labor and innumerable scientific and technical hurdles.
Zhilei Zhao, a 2021 Ph.D. alumna currently at Cornell, pioneered their innovative method of visualizing mosquito brains at very high resolution to see how the mosquito determines its next victim.
To do this, he had to first genetically modify mosquitos so that their brains lighted up when they were active, and then the team had to provide human- and animal-flavored air in manners that the mosquitos could sense while within the team's custom-built imaging equipment.
Human odor is made up of dozens of distinct chemicals, and most animal scents include the same molecules in slightly varying ratios.
Because none of these molecules are appealing to mosquitos on their own, the task was to identify the precise combination of components that mosquitos utilize to distinguish human odor.
According to Matthew DeGennaro, a neurogeneticist at Florida International University in Miami, they discovered a receptor for human perspiration and discovered that acidic volatiles that comes off of humans are particularly important for mosquitoes to detect people.
Lindy McBride, a Princeton University scientist who studies mosquito behavior and was not part of the research team, said, "I think what's fascinating about it is that we now have proof that there is some type of route, in the sense of smell, that is essential for mosquitoes to like people," as per NPR.
DeGennaro and his collaborators genetically modified mosquitos to inhibit the activation of an olfactory receptor known as Ir8a.
As a result, female mosquitos that suck blood were no longer attracted to lactic acid, an important component of human perspiration.
Furthermore, the researchers conducted a series of laboratory studies to see if blocking this receptor might make mosquitos less receptive to people.
The scientists encouraged participants to place their hands inside an "olfactometer," which allowed mosquitos to smell them from a distance.
Mosquitoes kept in captivity may fly through the device to get near, but not close enough to bite.
Experiments revealed that genetically modifying mosquitos to block this olfactory receptor rendered bugs substantially less inclined to fly near people's skin.
