Behold and cower at the sight of a human arm as seen by a mosquito. That’s right: the bloodsuckers rely on thermal infrared to find a good spot to bite, leaving you itchy and potentially sick.
In research published this week in Nature, a team of biologists described the infrared detector of the mosquito Aedes aegypti and its affiliated morphological and biochemical structures. “These include CO2 from our exhaled breath, odors, vision, [convection] heat from our skin, and humidity from our bodies,” said Avinash Chandel, a biologist at UC Santa Barbara and co-lead author of the study, in a press release. “However, each of these cues have limitations.”
Itchy welts aside, mosquito bites can transmit diseases including dengue, yellow fever, and Zika. The recent team wanted to explore exactly what functions the animals use when seeking out a host for their blood-sucking shenanigans.
Mosquitos don’t have great vision, so they rely on a combination of senses to find an animal to bite. Their senses also protect them from danger; one 2022 paper in Scientific Reports found that mosquitos respond to visual and mechanical indicators that they’re facing a threat while feeding (namely, an open hand ready to swat).
Within about 4 inches (10 centimeters) from human skin, mosquitos can detect heat rising from it. Once the insects land on our skin, they can directly sense its temperature. But according to the new research, the animals also detected thermal infrared.
The researchers measured the way female mosquitos sought out hosts in two zones, both of which were exposed to human odors and carbon dioxide at the same concentration that we exhale. But one of the zones was exposed to thermal infrared from a skin-temperature source, which the researchers found doubled the mosquitoes’ host-seeking activity. With the infrared source active, the mosquitoes’ sensitivity to heat seemed to jump up to about 2.5 feet (70 centimeters).
“Any single cue alone doesn’t stimulate host-seeking activity,” said Craig Montell, a biologist at UCSB and the study’s senior author, in the release. “It’s only in the context of other cues, such as elevated CO2 and human odor that IR makes a difference.”
The team believes that loose-fitting clothing may be a particularly good defense against mosquitoes, because it leaves space between the skin and clothing for thermal IR to dissipate, making it harder for the insects to find hosts.
In recent years, A. aegypti‘s footprint has broadened from its historical range in tropical and subtropical climes. The species’ range now stretches to California as well as a few other parts of the United States. Better understanding the ways mosquitoes seek us out will help researchers discovers ways to deter the pests, in turn reducing the spread of mosquito-borne diseases.
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