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In many parts of the world, a mosquito bite is more than just an annoying itch—it can be deadly. The Aedes aegypti species, for example, spreads viruses responsible for over 100 million cases of dengue, yellow fever, Zika, and other diseases each year. Another species, Anopheles gambiae, transmits the malaria-causing parasite, which the World Health Organization estimates leads to more than 400,000 deaths annually. Mosquitoes’ ability to transmit such diseases has earned them the notorious title of the deadliest animal on Earth.
While male mosquitoes are harmless, female mosquitoes need blood to develop their eggs, making them relentless in their search for human hosts. Over a century of research has revealed that these insects use multiple sensory cues to locate their targets. Now, a new study led by researchers at UC Santa Barbara has uncovered an additional sense that mosquitoes use to find humans: infrared detection.
Guided by Infrared Radiation
Mosquitoes like Aedes aegypti are already known to use a variety of cues, such as carbon dioxide (CO2) from exhaled breath, human odors, vision, heat from the skin, and body humidity to track their hosts. However, each of these cues has limitations. For instance, mosquitoes have poor vision, and strong winds or rapid human movements can disrupt their tracking abilities. This led researchers to explore whether mosquitoes could also detect a more reliable directional cue—infrared radiation (IR).
The study, detailed in the journal Nature, involved placing female mosquitoes in a controlled environment where they were exposed to human odors and CO2 at concentrations similar to those in exhaled breath. The researchers then introduced infrared radiation from a source at skin temperature into one of the zones. Remarkably, the presence of IR doubled the mosquitoes’ host-seeking behavior. The insects overwhelmingly navigated toward the infrared source, even when it was separated from the chamber by a barrier that prevented heat exchange through conduction and convection. The team found that infrared radiation remained effective up to a distance of about 70 centimeters (2.5 feet).
“What struck me most about this work was just how strong of a cue IR ended up being,” said Nicolas DeBeaubien, co-lead author and former graduate student and postdoctoral researcher at UCSB. “Once we got all the parameters just right, the results were undeniably clear.”
Unveiling the Infrared Detection Mechanism
To understand how mosquitoes detect IR, the team examined the morphology and biochemistry of mosquito sensory organs. Previous research had identified heat-sensing neurons at the tips of mosquito antennae, but this study took it further by revealing that these neurons are crucial for infrared detection. When the researchers removed the tips of the antennae, the mosquitoes lost their ability to sense IR.
The study also highlighted the role of a temperature-sensitive protein, TRPA1, located in the mosquito antennae. This protein, along with certain rhodopsins—proteins usually associated with light detection—enables mosquitoes to sense infrared radiation. The researchers discovered that at closer ranges, intense thermal IR directly activates TRPA1, while at lower levels, rhodopsins help trigger TRPA1, extending the mosquito’s IR detection range to about 2.5 feet.
Implications for Mosquito Control
The discovery of infrared detection in mosquitoes opens up new avenues for controlling mosquito-borne diseases. The research suggests that incorporating IR into mosquito traps could make them more effective. Additionally, the findings provide insight into why loose-fitting clothing is particularly effective at preventing mosquito bites, as it allows IR to dissipate between the skin and the clothing, making it harder for mosquitoes to detect their target.
“Despite their diminutive size, mosquitoes are responsible for more human deaths than any other animal,” DeBeaubien said. “Our research enhances the understanding of how mosquitoes target humans and offers new possibilities for controlling the transmission of mosquito-borne diseases.”
As the range of mosquito species like Aedes aegypti continues to expand due to climate change and global travel, understanding their sensory mechanisms becomes increasingly important. This study not only advances our knowledge of mosquito behavior but also provides practical insights that could help reduce the global burden of mosquito-borne diseases.
The research was a collaborative effort, with contributions from Vincent Salgado, formerly at BASF, and his student, Andreas Krumhotz, along with the Montell team at UCSB.
