By Susan Milius
Fruit flies actually have a love-hate relationship with the smell of fruit. And a new insight into the chemistry of that attraction and repulsion could lead to novel repellents for other insects, researchers say.
Carbon dioxide is a known turn-off to fruit flies when it emanates from stressed peers. “Drosophila sniff CO2 and avoid it like crazy,” says neurobiologist Anand Ray of the University of California, Riverside. But ripe fruit puffs out the gas and still attracts plenty of flies. In this case, compounds released by the fruit block the flies’ CO2 receptors, Ray and Riverside colleague Stephanie Turner report online August 26 in Nature.
Mosquitos, in contrast, outright love CO2. They hunt down blood meals by following plumes of the exhaled gas. But as in fruit flies, a fruit compound can jam CO2 receptors in the notorious mosquito Culex quinquefasciatus, the researchers say. This species spreads West Nile fever and the parasites that cause the huge limb swellings of the tropical disease filariasis. Ray proposes that compounds that could keep the mosquito detectors from sensing those plumes might render people hard to find. With a grant from the Bill and Melinda Gates Foundation, he’s starting to test the strategy.
In fruit flies, the aversion to CO2 turned up when researchers shook the insects or zapped them with a little electric shock. The stressed flies released an odor with CO2 as a key component, and unharmed flies fled from that odor.
“There was this paradox,” Ray says. The same fruit flies that avoid stressed flies and even unripe CO2-exhaling fruit, crowd around ripe fruit as well as other strong CO2 sources such as beer.