Mosquitoes are believed to use infrared light from body heat to find humans.
- Mosquitoes detect infrared body heat to locate humans.
- However, they need other elements such as smell or carbon dioxide emissions to detect humans accurately.
- This new study could help develop new repellents.
Annoying noises, bites, disease vectors… there are many reasons to avoid mosquitoes. For over 100 years, scientists have taken turns trying to understand how these insects find their hosts. Today, we know that mosquitoes, like Aedes aegypti use multiple signals to detect hosts: CO2 exhaled air, odors, the heat of our skin and the humidity of our bodies. Thanks to researchers at the University of California, Santa Barbara, another element can be added to the list: infrared radiation from body heat.
Their work was published in the journal Nature, August 21, 2024.
Mosquitoes: infrared helps them guide themselves
Some animals, such as vipers, can detect thermal infrared radiation emitted by their prey. The researchers wanted to know if female mosquitoes had the same ability. They placed a few specimens in a cage with two separate areas. While both had been exposed to human odors and CO2 at the same concentration as we exhale, only one part had also been exposed to infrared radiation from a source at skin temperature (i.e. about 34 °C). The team then counted how many mosquitoes began to probe each area as if they were looking for a vein.
“Infrared radiation from a source roughly equal to human skin temperature doubled the overall host-seeking behavior of insects when combined with CO2 and human odor.”note the authors in their press release. They also found that infrared radiation detection was effective up to about 70 cm. “What struck me most about this work was how powerful the detection of infrared radiation ended up being,” says co-lead author Nicolas DeBeaubien. “Once all the parameters were perfectly set, the results were undeniably clear.”
While infrared helps mosquitoes navigate, it is not their only “navigation” feature. “A single signal does not stimulate host-seeking activity on its own. It is only in the context of other signals, such as increased CO2 and human odor, that infrared makes a difference.”explains Craig Montell of UC Santa Barbara. Subsequent tests confirmed that infrared alone has no impact and does not allow insects to find their prey.
How do mosquitoes detect infrared body heat?
The researchers suggest that our body heat, which generates infrared, could reach certain neurons in the mosquito, activating them by warming them. “Indeed, another lab discovered the temperature-sensitive protein, TRPA1, at the tip of their antennae. And the UCSB team observed that animals lacking a functional trpA1 gene, which encodes the protein, could not detect infrared.”the authors explain. “The tip of each antenna has peg structures that are well suited to detecting radiation. The pit shields the peg from conductive and convective heat, allowing highly directional infrared radiation to penetrate and warm the structure. The mosquito then uses TRPA1 – essentially a temperature sensor – to detect the infrared radiation.”
Loose clothing is effective in preventing bites
Furthermore, the ability to detect infrared light would also be supported by the presence of certain proteins from the rhodopsin family that are sensitive to light in the mosquito organism.
For the team, their findings could lead to new types of mosquito repellents. “The results also help explain why loose clothing is particularly effective at preventing bites. Not only does it prevent the mosquito from reaching our skin, it also allows infrared rays to dissipate between our skin and the clothing, preventing mosquitoes from detecting them.”