Mosquitoes Use Infrared to Track Humans, by Jess Cockerill

 

 

There’s something about us that mosquitoes love. In addition to our smell and breath, our exposed skin acts as a neon sign advertising that this blood bar is open for business.

That’s because mosquitoes use infrared sensing technology in their antennae to locate prey, a new study has found.

In many parts of the world, mosquito bites are more than just an irritation, spreading pathogens such as dengue, yellow fever and Zika virus. Malaria, spread by the Anopheles gambiae mosquito, caused more than 600,000 deaths in 2022, according to statistics from the World Health Organization.

To avoid serious illnesses, or even just an annoying itch, we humans are very careful to find ways to prevent mosquito bites.

Research by scientists at the University of California, Santa Barbara (UCSB) has found that mosquitoes use infrared sensing, along with other cues we already know about, such as sniffing out CO2 in our breath and certain body odors, to search for hosts.

“The mosquito we study, Aedes aegypti, is exceptionally good at finding human hosts,” says UCSB molecular biologist Nicholas Debeabien.

But mosquitoes’ eyesight isn’t very good, and scents can be unreliable if it’s windy or the host is moving. So the team suspected that infrared sensing might offer the insects a reliable aid in finding food.

Only female mosquitoes drink blood, so the researchers presented cages containing 80 female mosquitoes (about 1–3 weeks old) each with a series of fictitious “hosts” represented by combinations of heating pads, CO2 at the concentration of human breath, and human odors, and recorded five-minute videos to observe their host-seeking behaviors.

They defined them as “a mosquito that lands, walks, and extends its proboscis through the cage mesh, reminiscent of a female landing on a human and then walking while feeling the surface of the skin with her labellum.”

Some mosquitoes were presented with a thermoelectric plate set to the average human skin temperature of 34 degrees Celsius (93 °F), which also served as a source of infrared radiation. Others were set to a room temperature of 29.5 °C, a temperature that mosquitoes like but which does not emit infrared.

No single cue—CO2, odor, or infrared—failed to pique the mosquitoes’ interest. But the insect’s apparent bloodlust was doubled when infrared was added to a setup with just CO2 and odor.

“No single signal by itself stimulates host-seeking activity. It’s only in the context of other signals, such as elevated CO2 and human odor, that IR makes a difference,” says UCSB neurobiologist Craig Montell.

The team also confirmed that mosquitoes’ infrared sensors are located in their antennae, where they have a temperature-sensing protein, TRPA1. When the team removed the gene for this protein, the mosquitoes were unable to detect infrared.

The findings help explain why mosquitoes appear to be particularly attracted to exposed skin and why loose clothing, through which infrared radiation is dissipated, provides an effective invisibility cloak against them.

It could also lead to slightly more sophisticated defenses against mosquitoes, such as the ability to create traps that use thermal radiation from skin temperature as bait.

“Despite their small size, mosquitoes are responsible for more human deaths than any other animal,” DeBeaubien says.

“Our research improves understanding of how mosquitoes target humans and offers new possibilities for controlling the transmission of mosquito-borne diseases.”

[This research is published in Nature.]

Source
https://www.sciencealert.com/scientists-discover-mosquitoes-are-using-infrared-to-track-humans-down

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