Mosquitoes use infrared detection to help find people

Mosquitoes use infrared detection to help find people

Mosquitos have a fine-tuned ability to find and bite people. This includes Aedes aegypti, which can transmit viruses that cause deadly diseases such as dengue, yellow fever, and Zika.

Female mosquitoes use a range of cues to hunt us for our blood, including odor molecules from our skin and carbon dioxide released when we breathe. But these can disperse through air and be affected by wind. Up close, Ae. aegypti can also sense body heat transferred through air. But they must be very close-within four inches-of a person to perceive this.

Scientists have thought that the ability to detect thermal infrared radiation (IR) which can be detected at greater distances, might help mosquitoes home in on people. IR, sometimes called infrared light, is released by heat sources and is outside the range human eyes can detect. Previous research had suggested that mosquitoes can't detect IR, either. However, such studies only looked at IR in isolation, not combined with other cues that mosquitoes use to find their prey.

In a new study, researchers led by Dr. Craig Montell from the University of California, Santa Barbara, tested whether IR emanating from skin could play a role in helping mosquitoes home in on people. The team built a special testing chamber that allowed them to manipulate the levels of odor, heat, and carbon dioxide. They enabled it to block conductive and convective heat to make sure mosquitoes were sensing thermal IR to orient towards their prey.

When female mosquitoes land, they start probing around to find a vein for a blood meal. The team also designed a computer program to identify this host-seeking behavior from collected videos. Results were published on August 21, 2024, in Nature.

As observed previously, IR alone did not draw Ae. aegypti to a surface and trigger host-seeking behavior. However, adding IR to human odor and carbon dioxide doubled the number of mosquitoes drawn to a surface to start probing.

Since Ae. aegypti prefer to bite people around dawn and dusk, the researchers looked at whether sensitivity to IR changed with shifts in environmental temperature. They found that mosquitoes were more attracted to thermal IR from a source at skin temperature when the environmental temperature was lower than that of human skin. When the environment heated up to match the temperature of human skin, as it would in midday, the mosquitoes lost their ability to sense thermal IR.

The team also found that mosquitoes could sense IR while in flight at a distance of more than two and a half feet away.

To better understand how Ae. aegypti senses IR, the researchers used imaging and genetic manipulation to examine mosquito antennae. They found that a heat-activated protein called TRPA1, found in neurons at the tips of antennae, was necessary for IR sensing. At lower intensities of thermal IR, such as when a target is further away, TRPA1 received help from two proteins called opsins. Opsins are specialized proteins that are used to detect light. At the end of the antenna, they function to help detect thermal IR.

"Despite their diminutive size, mosquitoes are responsible for more human deaths than any other animal," says Dr. Nicolas DeBeaubien, who helped lead the study. "Our research enhances the understanding of how mosquitoes target humans and offers new possibilities for controlling the transmission of mosquito-borne diseases."

IR sensing, for example, could potentially be exploited in large-scale mosquito control, such as by adding IR emitters to mosquito traps.

-by Sharon Reynolds

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