University of California researchers have discovered why mosquitoes like to feast on the blood of humans.
They have identified a dominant odor naturally produced in humans and birds that attracts the blood-feeding Culex mosquitoes, which transmits West Nile virus and other life-threatening diseases.
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Entomology professor Walter Leal and postdoctoral researcher Zain Syed, UC Davis Department of Entomology, found that nonanal (pronounced "no-nan-al") is the powerful semiochemical that triggers the mosquitoes' keen sense of smell, directing them toward a blood meal. A semiochemical is a chemical substance or mixture that carries a message.
"Nonanal is how they find us. The antennae of the Culex quinquefasciatus are highly developed to detect even extremely low concentrations of nonanal," Leal said.
Mosquitoes detect smells with the olfactory receptor neurons of their antennae.
Birds, the main hosts of mosquitoes, serve as the reservoir for the West Nile virus, Leal said.
When infected mosquitoes take a blood meal, they transmit the virus to their hosts, which include birds, humans, horses, dogs, cats, bats, chipmunks, skunks, squirrels and domestic rabbits.
During the study, the researchers tested hundreds of naturally occurring compounds emitted by people and birds. They collected chemical odors from 16 adult human subjects, representing multiple races and ethnic groups.
"We then determined the specificity and sensitivity of the olfactory receptor neurons to the isolated compounds on the antennae of the mosquitoes," Syed said.
The researchers found that nonanal acts synergistically with carbon dioxide, a known mosquito attractant.
"We baited mosquito traps with a combination of nonanal and carbon dioxide and we were drawing in as many as 2,000 a night in Yolo County, near Davis. Nonanal, in combination with carbon dioxide, increased trap captures by more than 50 percent, compared to traps baited with carbon dioxide alone," Syed said.
The research has been published this week in the early online edition of the Proceedings of the National Academy of Sciences.
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