There are few creatures as annoying as the humble yet deadly mosquito. These pesky pests seem to always be on search-and-destroy missions, sparing none but a lucky few who release body odors that mosquitoes don’t like. If you’ve ever walked outside and found yourself swarmed by mosquitoes, you might have asked yourself: how do these damn things find me so fast?
You may be aware that mosquitoes track carbon dioxide and other chemicals found in body odor and breath. However, a new study found that mosquitoes have another trick up their sleeve. Although their vision is terrible, experiments suggest that the malaria-spreading insects can sense infrared radiation, which doubles their ability to find a human host.
These experiments showed that mosquitoes overwhelmingly chose heat sources matching human skin temperature over other cues, such as body odor and CO2.
The Science Behind Mosquito Attraction
The study focused on the mosquito species Aedes aegypti, known for transmitting viruses like Zika, yellow fever, and dengue fever, causing over 100,000 cases annually. Another species, Anopheles gambiae, spreads malaria, which kills over 400,000 people each year, according to the World Health Organization.
Only female mosquitoes attack people and suck their blood, which they require for egg development. Researchers have long understood that mosquitoes rely on a combination of cues — CO2 from breath, body odors, visual signals, heat, and humidity. However, these cues often have limitations. Poor vision and environmental factors like wind can disrupt a mosquito’s tracking ability, for instance.
The University of California, Santa Barbara (UCSB) team suspected that mosquitoes might use a more reliable method: infrared radiation (IR). IR is part of the light spectrum and can travel longer distances than heat carried by air. Some animals, like pit vipers, use infrared to sense warm prey. Could mosquitoes do the same?
To test their hypothesis, scientists placed female mosquitoes in a controlled environment with two zones. Both zones had human odors and CO2, but only one included IR at a temperature similar to human skin — 93 degrees Fahrenheit (33 degrees Celsius). The results were striking. The presence of IR doubled the mosquitoes’ host-seeking activity, indicating that heat detection significantly enhances their ability to find humans.
A surprisingly strong sense
But how do mosquitoes develop this IR-homing ability? Researchers identified that the tips of mosquito antennae have specialized structures adept at detecting IR. These structures, shielded from conductive and convective heat, allow mosquitoes to sense directional IR radiation. A temperature-sensitive protein, known as TRPA1, helps them detect this radiation, effectively extending their range to about 2.5 feet (75 centimeters).
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“What struck me most about this work was just how strong of a cue IR ended up being,” DeBeaubien said. “Once we got all the parameters just right, the results were undeniably clear.”
With climate change and increased global travel, Aedes aegypti mosquitoes are spreading beyond tropical regions. They are now found in parts of the United States, including Florida, Texas, and California, as well as surprising places like Washington DC, New York, and Indiana.
Half the world’s population is at risk for mosquito-borne diseases, and about a billion people get infected every year.
“Despite their diminutive size, mosquitoes are responsible for more human deaths than any other animal,” DeBeaubien said. “Our research enhances the understanding of how mosquitoes target humans and offers new possibilities for controlling the transmission of mosquito-borne diseases.”
Understanding their advanced host-seeking mechanisms is more important than ever as we face a growing threat from mosquito-borne diseases. For instance, incorporating thermal sources at skin temperature into traps might improve their effectiveness. The study also explains why loose-fitting clothing helps prevent bites by allowing IR to dissipate before mosquitoes can detect it.
The findings appeared in the journal Nature.
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