Scientists are zeroing in on what makes mosquitoes so good at zeroing in on humans to bite. As this ScienCentral News video reports, the goal of the research is new ways to stop the spread of human diseases like malaria and West Nile virus.
Ever wonder while you're scratching your latest mosquito bite how that bug was able to zero in on you?
"They can find a human from at least a hundred yards off, which is quite a long distance if you're a mosquito," says John Carlson, professor of molecular, cellular and developmental biology at Yale University. "A mosquito seems to be able to smell us sort of the way we can find a pie in a bakery way down the street. I guess we smell just as good to the mosquito as the pie smells to us."
Carlson is working on figuring out exactly how these biting bugs find us by homing in on their sensitive sense of smell, which is concentrated in their antennae. "They have 79 receptors in their antennae," he says. "Their antennae are sort of the equivalent of their nose. And they use these receptors to actually detect odors in the air. But we know very little about which receptors are used or which odors they're actually most sensitive to."
Now, Carlson and Elissa Hallem have found a substance in the antennae of female mosquitoes—the only ones that bite us—that responds to a specific odor in human sweat. "We've developed a new way of trying to understand how it is that insects find the humans that they bite and this could lead to new ways of controlling those insects," says Carlson.
Carlson and Hallem have discovered many genes for smell and taste in fruit flies They bred flies with antennae that couldn't smell, gave the flies a gene from a female mosquito, and tested the genetically engineered flies' new sense of smell by hooking up tiny electrodes to their antennae.
An electrode is attached to a fly's antenna. image: Yale University
"We tested it with a whole panel of different odors," says Carlson, "and it didn't respond to anything we tried, which got us very disappointed until we tried 4-methylphenol," a compound found in human sweat. "Then it started responding like crazy. It was just an extremely strong response. So we concluded from this that this mosquito receptor is an exquisitely sensitive detector for 4-methylphenol, this component of human sweat."
Carlson found this receptor in Anopheles mosquitoes, which kills over a million people a year worldwide by spreading malaria, and has been called the most dangerous mosquito in the world. Mosquitoes also carry West Nile virus.
The researchers are now testing compounds that target the odor receptor, hoping to use them to make more effective and safer insect repellents and traps, something that will help both humans and crops. "We think that if we can identify the receptors which are most sensitive to human sweat compounds that we may be able to find compounds that block those receptors and these compounds could be very useful in mosquito repellants," says Carlson. "Alternatively, if we can find compounds that excite those receptors very strongly, those compounds could be useful in designing a new generation of mosquito traps—in other words, put these compounds in a trap, and mosquitoes will fly into the trap rather than towards humans."