Scientists at the University of California, Santa Barbara discovered that Aedes aegypti mosquitoes use infrared radiation to enhance their host-locating abilities, in addition to cues such as carbon dioxide and odors. This discovery adds to the understanding of mosquito behavior and offers new possibilities for developing methods to control mosquitoes.
Scientists from the University of California, Santa Barbara discovered that Aedes aegypti mosquitoes use infrared radiation, in addition to other cues, to locate hosts. This discovery may lead to improved methods of mosquito control and help reduce the transmission of diseases such as dengue and malaria.
While many see mosquito bites as a temporary nuisance, in some parts of the world they cause serious and even fatal problems. The Aedes aegypti mosquito species spreads viruses that cause more than 100 million cases of dengue, yellow fever, Zika and other diseases each year. Another species, Anopheles gambiae, spreads the parasite that causes malaria. According to WHO estimates, malaria alone causes more than 400,000 deaths a year. The mosquitoes' ability to transmit diseases earned them the title of "the deadliest animal".
While the male mosquitoes are harmless, the female mosquitoes need blood to develop their eggs. For over a century, scientists have been studying the ways in which mosquitoes locate their hosts. Over time, it was discovered that the mosquitoes do not rely on just one clue, but combine information from several different senses located at different distance ranges.
Breakthrough in research on mosquito senses
A new study conducted at the University of California, Santa Barbara has revealed another sense that mosquitoes use to locate their hosts: the detection of infrared radiation. This radiation, which comes from a source at a temperature close to that of human skin, doubled the mosquitoes' search behavior when combined with carbon dioxide and human body odor. The mosquitoes consistently moved towards the infrared source, and the researchers also discovered where the infrared detector is located and how it works morphologically and biochemically. The results of the study were published in the journal Nature.
"The mosquito we're studying, Aedes aegypti, is particularly adept at locating humans," said study co-author Nicolas DuBoin, a former doctoral student and postdoctoral researcher in Prof. Craig Montal's lab at the University of California, Santa Barbara. "This work adds new insights into how they achieve this."
Reliance on infrared radiation
Mosquitoes such as Aedes aegypti use multiple cues to locate hosts from a distance. These include carbon dioxide from our breath, smells, sight, heat coming from our skin and moisture from our bodies. However, each of these cues is limited in its ability. Mosquitoes have poor vision, and rapid host movement or strong wind can disrupt their ability to track chemical cues. The researchers wondered if mosquitoes could detect a more reliable cue, such as infrared radiation.
The mosquitoes can detect the heat emitted from our skin at a distance of about 10 cm, and they can also sense the temperature of the skin when they land on it. These senses correspond to two types of heat transfer: convection (heat transferred by the air) and contact (heat transferred by direct contact). However, heat can travel greater distances when it is converted into waves of electromagnetic radiation, usually in the infrared range. This radiation can heat any bone it hits. The research team wondered if mosquitoes, such as Aedes aegypti, could detect this radiation as well.
Understanding infrared sensing mechanisms in mosquitoes
The researchers placed mosquitoes in a cage and measured their activity in searching for hosts in two areas. In the entire area, the mosquitoes were exposed to the same levels of body odor and carbon dioxide, but only one of the areas was also exposed to infrared radiation from a source at the temperature of human skin. The barrier prevented heat transfer by convection or contact. Adding infrared radiation from a source at a temperature of 34 degrees Celsius doubled the search activity of the mosquitoes. The researchers found that the infrared radiation is effective up to a range of about 70 cm (2.5 feet).
"The thing that surprised me the most about this work was how strong a cue the infrared radiation was," said DeBoyen. "Once we were able to adjust all the parameters, the results were completely clear."
Previous studies have not been able to distinguish the effect of infrared radiation on the behavior of the mosquitoes, but Professor Craig Montal, the lead author of the study, speculates that this is due to the previous research methods. Experiments that test only the effect of infrared radiation without other cues do not induce host-seeking activity. "Only when combined with other cues, such as high levels of carbon dioxide and human body odor, does infrared radiation have an effect," Montal said.
Infrared detection by mosquitoes
Mosquitoes cannot detect infrared radiation the same way they detect visible light, since the infrared energy is too weak to activate the light-sensitive rhodopsin proteins in their eyes. Electromagnetic radiation with a wavelength longer than 700 nm does not activate rhodopsin, and infrared light emitted from our body heat is approximately at a wavelength of 9,300 nm. But there is another way to detect the radiation.
The researchers found that the tips of the mosquitoes' tentacles include neurons that are sensitive to heat, and that removing the tips of the tentacles eliminated the mosquitoes' ability to detect infrared radiation. In addition, it was found that the TRPA1 protein is located at the tips of the tentacles and enables the detection of fluorescence.
Biochemical insights
The activity of the TRPA1 protein does not fully explain the ability to detect infrared radiation at greater distances. The researchers found that the rhodopsin proteins Op1 and Op2, which are located in the same neurons as TRPA1, can increase the sensitivity to detect the radiation, allowing the mosquitoes to detect the radiation even at greater distances.
Implications for public health
Half of the world's population is at risk of mosquito-borne diseases, and about a billion people are infected every year. Climate change and international travel have expanded the distribution areas of Aedes aegypti, and now they are also found in new areas, such as California.
The discovery may improve mosquito control methods. For example, combining infrared radiation in
The discovery may improve mosquito control methods. For example, incorporating infrared radiation into mosquito traps could make them more effective by measuring human skin temperature and attracting mosquitoes more effectively. In addition, the findings help to understand why loose clothing is a good defense against mosquito bites - they not only block access to the skin, but also scatter the infrared radiation emitted by the skin, so that the mosquitoes have difficulty detecting the brown cue.
"Despite their small size, mosquitoes are responsible for more deaths in humans than any other animal," said Debobin. "Our research improves the understanding of how mosquitoes recognize humans and offers new options for controlling mosquito-borne diseases."
For the scientific article in NATURE
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