For female mosquitoes, finding heat is essential for survival, as they need to feast on warm-blooded prey to produce eggs. At the same time, mosquitoes have to know when something is too hot, so they won't get scorched on an over-heated blacktop, for instance.
Researchers at Rockefeller University have demonstrated that mosquitoes are exquisitely tuned to find heat sources that match the temperature of warm-blooded hosts, including humans. What's more, they uncovered part of the molecular mechanism the insects use to fine-tune their behavior; when a specific gene was blocked, mosquitoes lost the ability to distinguish between different temperatures.
They placed Aedes aegypti mosquitoes--carriers of yellow fever, dengue virus, and other diseases--inside a box lined with metal plates that could be heated up to specific temperatures. Opposite the plates, the researchers placed a tiny camera that captured how many mosquitoes were present on each plate at any given time. The results were obvious, author notes. "The hotter a plate became, the more mosquitoes were attracted to it. But it got to the point when the plate became so hot, most mosquitoes began to avoid it."
The upper limit? Approximately 40 degrees Celsius (104 degrees Fahrenheit), close to the maximum temperature of birds--which are one of the hottest food sources for mosquitoes--and a few degrees warmer than the human body. Once the plates got hotter than that, the mosquitoes avoided them. Given the choice between a plate at 40 degrees and one at 50, the mosquitoes clearly preferred the 40 degrees surface. "The animals could even distinguish between temperature differences as small as 2.5 degrees," notes the author.
They blocked a gene called TRPA1, which is known to help other species seek out appropriate temperatures. Not surprisingly, mosquitoes that didn't express the TRPA1 gene spent equal amounts of time on plates that were either 40 or 50 degrees--in other words, they were unable to fine-tune their ability to seek out the ideal temperature.
Understanding how mosquitoes target temperatures might enable researchers to design better traps. "Just learning how mosquitoes seek out temperatures that resemble hosts, and characterizing this heat-seeking behavior, lets us develop new traps that will capture disease-carrying vectors," author notes.
Mosquitoes use more than just heat to find hosts. They are also attracted to the carbon dioxide we breathe out, as well as body odor and some visual cues.