NEWS - Aedes aegypti transmits the viruses that cause dengue, yellow fever, Zika and other diseases every year, while Anopheles gambiae transmits the parasite that causes malaria. Their capacity to transmit disease has made mosquitoes the deadliest animals.
%20use%20thermal%20infrared%20to%20navigate%20hosts.webp "Yellow fever mosquito (Aedes aegypti) use thermal infrared to navigate hosts")
Moreover, climate change and global travel have expanded the range of A. aegypti beyond tropical geography. The mosquitoes are now present in subtropical climates that were previously unheard of just a few years ago.
Male mosquitoes are harmless, but females need blood for egg development. There is no single cue that these insects rely on to feed; they integrate information from many different senses across a wide range of distances.
"A. aegypti very adept at finding human hosts. This work provides a new insight into how they achieve this. Once we got all the right parameters, the results were clear and undeniable," says Nicolas DeBeaubien of the University of California at Santa Barbara UCSB.
The researchers added another sense: detecting infrared radiation from sources that are roughly the same temperature as human skin, combined with CO2 and human odors that mosquitoes rely on when searching for blood. Mosquitoes navigate toward these infrared sources.
"Mosquitoes use CO2 from breath, odor, vision, heat from the skin and moisture from the human body. But each of these cues has limitations," says Avinash Chandel of UCSB.
The insects have poor eyesight, and wind or rapid human movement can interfere with the chemical sense's tracking. They detect heat gain from human skin within about 10 centimeters, and they can sense skin temperature immediately after landing.
These two senses relate to two of the three types of heat transfer: convection, carried by a medium such as air, and conduction through direct contact. But heat energy can also travel longer distances when converted into electromagnetic waves, typically in the infrared (IR) range of the spectrum.
The team placed female mosquitoes in cages and measured their activity in two zones. Each zone was exposed to human odor and CO2 at concentrations similar to human exhaled breath. However, only one zone is exposed to IR from the skin temperature source. A barrier separating the source from the room prevents heat exchange by conduction and convection.
Adding thermal IR from a 34C source doubled the host-seeking activity. This makes infrared radiation a newly documented sense that mosquitoes use to find humans, and it remains effective up to a distance of about 70 cm.
"Previous studies have tried to isolate the effect of thermal IR by presenting only infrared signals without other cues. But any single cue does not stimulate host-seeking activity. Only in the context of other cues, such as elevated CO2 and human odor, does IR make a difference," says Craig Montell of UCSB.
Mosquitoes are unlikely to detect thermal IR radiation in the same way they detect visible light. IR is too low in energy to activate the rhodopsin protein that detects visible light in the animal's eyes. Electromagnetic radiation with a wavelength longer than about 700 nanometers will not activate rhodopsin, and IR generated from body heat is about 9,300 nm.
In fact, no known protein is activated by radiation with such a long wavelength. The sun's heat is converted into IR, which travels through the vacuum of space. The IR reaches Earth and hits atoms in the atmosphere, transferring energy and warming the planet.
The IR that comes from the sun has a different wavelength than the IR produced by human body heat. The researchers suspect that the human body heat that produces IR may hit certain neurons in the mosquito and activate the senses. The mosquito detects the radiation indirectly.
"You have heat that is converted into electromagnetic waves and converted back into heat," Montell said.
Scientists had previously known that the tips of mosquito antennae contain heat-sensing neurons, and removing these tips eliminates the mosquito's ability to detect IR. The tip of each antenna has a structure that is well-adapted to sensing radiation.
A hole protects the peg from conductive and convective heat, allowing highly directional IR radiation to enter and warm the structure. The mosquito then uses the protein TRPA1, essentially a temperature sensor, to detect the infrared radiation.
But heat-activated TRPA1 activity doesn't fully explain the IR range. Sensors that rely exclusively on this protein may not be useful at ranges as far as 70 cm. At this distance, there likely isn't enough IR collected to activate TRPA1.
The researchers investigated a protein in the rhodopsin family that is sensitive to small increases in temperature. Proteins in this group are versatile, involved not only in vision but also in taste and temperature sensing. They found that two of the 10 rhodopsins are expressed in the same antennal neurons as TRPA1.
Removing TRPA1 abolished mosquitoes’ IR sensitivity, but insects with defects in either rhodopsin, Op1 or Op2, were unaffected. Even removing both rhodopsins simultaneously did not completely abolish IR sensitivity, although it significantly weakened the sense.
More intense thermal IR directly activated TRPA1. Op1 and Op2, meanwhile, could be activated at lower levels of thermal IR, and then indirectly trigger TRPA1. The constant human skin temperature and sensitivity of TRPA1 effectively extended the mosquitoes’ IR sensing range to about 3 meters.
Original research
Chandel, A., DeBeaubien, N.A., Ganguly, A. et al. Thermal infrared directs host-seeking behaviour in Aedes aegypti mosquitoes. Nature (2024). DOI:10.1038/s41586-024-07848-5
%20use%20thermal%20infrared%20to%20navigate%20hosts.webp "Yellow fever mosquito (Aedes aegypti) use thermal infrared to navigate hosts")
Moreover, climate change and global travel have expanded the range of A. aegypti beyond tropical geography. The mosquitoes are now present in subtropical climates that were previously unheard of just a few years ago.
Male mosquitoes are harmless, but females need blood for egg development. There is no single cue that these insects rely on to feed; they integrate information from many different senses across a wide range of distances.
"A. aegypti very adept at finding human hosts. This work provides a new insight into how they achieve this. Once we got all the right parameters, the results were clear and undeniable," says Nicolas DeBeaubien of the University of California at Santa Barbara UCSB.
The researchers added another sense: detecting infrared radiation from sources that are roughly the same temperature as human skin, combined with CO2 and human odors that mosquitoes rely on when searching for blood. Mosquitoes navigate toward these infrared sources.
"Mosquitoes use CO2 from breath, odor, vision, heat from the skin and moisture from the human body. But each of these cues has limitations," says Avinash Chandel of UCSB.
The insects have poor eyesight, and wind or rapid human movement can interfere with the chemical sense's tracking. They detect heat gain from human skin within about 10 centimeters, and they can sense skin temperature immediately after landing.
These two senses relate to two of the three types of heat transfer: convection, carried by a medium such as air, and conduction through direct contact. But heat energy can also travel longer distances when converted into electromagnetic waves, typically in the infrared (IR) range of the spectrum.
The team placed female mosquitoes in cages and measured their activity in two zones. Each zone was exposed to human odor and CO2 at concentrations similar to human exhaled breath. However, only one zone is exposed to IR from the skin temperature source. A barrier separating the source from the room prevents heat exchange by conduction and convection.
Adding thermal IR from a 34C source doubled the host-seeking activity. This makes infrared radiation a newly documented sense that mosquitoes use to find humans, and it remains effective up to a distance of about 70 cm.
"Previous studies have tried to isolate the effect of thermal IR by presenting only infrared signals without other cues. But any single cue does not stimulate host-seeking activity. Only in the context of other cues, such as elevated CO2 and human odor, does IR make a difference," says Craig Montell of UCSB.
Mosquitoes are unlikely to detect thermal IR radiation in the same way they detect visible light. IR is too low in energy to activate the rhodopsin protein that detects visible light in the animal's eyes. Electromagnetic radiation with a wavelength longer than about 700 nanometers will not activate rhodopsin, and IR generated from body heat is about 9,300 nm.
In fact, no known protein is activated by radiation with such a long wavelength. The sun's heat is converted into IR, which travels through the vacuum of space. The IR reaches Earth and hits atoms in the atmosphere, transferring energy and warming the planet.
The IR that comes from the sun has a different wavelength than the IR produced by human body heat. The researchers suspect that the human body heat that produces IR may hit certain neurons in the mosquito and activate the senses. The mosquito detects the radiation indirectly.
"You have heat that is converted into electromagnetic waves and converted back into heat," Montell said.
Scientists had previously known that the tips of mosquito antennae contain heat-sensing neurons, and removing these tips eliminates the mosquito's ability to detect IR. The tip of each antenna has a structure that is well-adapted to sensing radiation.
A hole protects the peg from conductive and convective heat, allowing highly directional IR radiation to enter and warm the structure. The mosquito then uses the protein TRPA1, essentially a temperature sensor, to detect the infrared radiation.
But heat-activated TRPA1 activity doesn't fully explain the IR range. Sensors that rely exclusively on this protein may not be useful at ranges as far as 70 cm. At this distance, there likely isn't enough IR collected to activate TRPA1.
The researchers investigated a protein in the rhodopsin family that is sensitive to small increases in temperature. Proteins in this group are versatile, involved not only in vision but also in taste and temperature sensing. They found that two of the 10 rhodopsins are expressed in the same antennal neurons as TRPA1.
Removing TRPA1 abolished mosquitoes’ IR sensitivity, but insects with defects in either rhodopsin, Op1 or Op2, were unaffected. Even removing both rhodopsins simultaneously did not completely abolish IR sensitivity, although it significantly weakened the sense.
More intense thermal IR directly activated TRPA1. Op1 and Op2, meanwhile, could be activated at lower levels of thermal IR, and then indirectly trigger TRPA1. The constant human skin temperature and sensitivity of TRPA1 effectively extended the mosquitoes’ IR sensing range to about 3 meters.
Original research
Chandel, A., DeBeaubien, N.A., Ganguly, A. et al. Thermal infrared directs host-seeking behaviour in Aedes aegypti mosquitoes. Nature (2024). DOI:10.1038/s41586-024-07848-5