It’s summertime and the pungent scents of barbecue, sunscreen, and sweaty humans fill the air. Body odor may be a turnoff to us, but it is especially attractive to some types of mosquitoes. And that inclination may save many lives: HHMI investigator Leslie Vosshall recently created a strain of mosquitoes that has a hard time telling the scent of people and animals apart.
Some mosquitoes are happy to feed on any animal they encounter. Aedes aegypti, however, prefer humans, which makes them a dangerously efficient vector of yellow fever and dengue fever. Intrigued by this partiality, Vosshall, whose lab is at the Rockefeller University, surmised that body odor may lead mosquitoes to their preferred meal. To test this theory, she and her colleagues created a strain of A. aegypti that lacks the orco gene—which encodes a protein necessary to build working mosquito odorant receptors.
“We knew this gene was important for flies to be able to respond to the odors they respond to,” says Vosshall. “And we had some hints that mosquitoes interact with smells in their environment, so it was a good bet that something would interact with orco in mosquitoes.”
As the researchers report in the June 27, 2013, issue of the journal Nature, not only did the mutant mosquitoes have no activity in neurons linked to odor sensing, they were unable to sniff out their favorite food. When given the choice between a guinea pig and a human, A. aegypti would normally go straight for the human. Mosquitoes lacking orco, on the other hand, showed much reduced preference for humans. “By disrupting a single gene, we can fundamentally confuse the mosquito from its task of seeking humans,” explains Vosshall.
The biggest surprise, however, came when the scientists discovered that the mutant mosquitoes couldn’t detect the insect repellent DEET. When presented with two human arms—one covered in 10 percent DEET and the other untreated—the mosquitoes were impartial. Once they landed on the DEET arms, however, instead of settling in for a meal, they quickly flew away. “This tells us that there are two totally different mechanisms that mosquitoes are using to sense DEET,” explains Vosshall. “One is what’s happening in the air, and the other only comes into action when the mosquito is touching the skin.”
Vosshall and her collaborators are searching for the second contact receptor. If they succeed, it could pave the way for a new super-repellent that inhibits both pathways. And that could help stop the spread of mosquito-borne illnesses.