Efforts to protect our skin from mosquitoes on a summer night may work for a while, but not forever. The pests use visual, olfactory, and thermal cues to home in on their human hosts.
When an adult female mosquito needs a blood meal to feed her young, she searches for a host—often a human. Many insects, mosquitoes included, are attracted by the odor of the carbon dioxide (CO2) gas that humans and other animals naturally exhale. However, mosquitoes can also pick up other cues that signal a human is nearby: they use their vision to spot a host and thermal sensory information to detect body heat.
But how do the mosquitoes combine this information to map out the path to their next meal?
They found that mosquitoes showed a preference for the warm object. But contrary to the mosquitoes’ visual attraction to objects, the preference for warmth was not dependent on the presence of CO2.
“These experiments show that the attraction to a visual feature and the attraction to a warm object are separate. They are independent, and they don’t have to happen in order, but they do often happen in this particular order because of the spatial arrangement of the stimuli: a mosquito can see a visual feature from much further away, so that happens first. Only when the mosquito gets closer does it detect an object’s thermal signature,” van Breugel said.
Elegant Females
Information gathered from all of these experiments enabled the researchers to create a model of how the mosquito finds its host over different distances. They hypothesize that from 10 to 50 meters (32 to 164 feet) away, a mosquito smells a host’s CO2 plume. As it flies closer—to within 5 to 15 meters (16 to 52 feet)—it begins to see the host. Then, guided by visual cues that draw it even closer, the mosquito can sense the host’s body heat. This occurs at a distance of less than a meter.
“Understanding how brains combine information from different senses to make appropriate decisions is one of the central challenges in neuroscience,” Dickinson said.
“Our experiments suggest that female mosquitoes do this in a rather elegant way when searching for food. They only pay attention to visual features after they detect an odor that indicates the presence of a host nearby. This helps ensure that they don’t waste their time investigating false targets like rocks and vegetation. Our next challenge is to uncover the circuits in the brain that allow an odor to so profoundly change the way they respond to a visual image.”
Published in the journal Current Biology, the work provides researchers with exciting new information about insect behavior and may even help companies design better mosquito traps in the future. But it also paints a bleak picture for those hoping to avoid mosquito bites.
“Even if it were possible to hold one’s breath indefinitely,” the authors noted toward the end of the paper, “another human breathing nearby, or several meters upwind, would create a CO2 plume that could lead mosquitoes close enough to you that they may lock on to your visual signature.
“The strongest defense is therefore to become invisible, or at least visually camouflaged. Even in this case, however, mosquitoes could still locate you by tracking the heat signature of your body. ... The independent and iterative nature of the sensory-motor reflexes renders mosquitoes’ host seeking strategy annoyingly robust.”
Researchers from the University of Washington contributed to the work, which was funded by the National Institutes of Health.
This article was originally published by Caltech. Republished via Futurity.org under Creative Commons License 4.0.
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