Body odour attracts mosquitoes

The study paves the way for key developments in mosquito and disease control. Walter Leal, entomology professor and postdoctoral researcher Zain Syed at the University of California-Davis (UC-D), found that nonanal is the powerful semiochemical that triggers the mosquito's keen sense of smell, directing them towards a blood meal.

A semiochemical is a chemical substance or mixture that carries a message.

"Nonanal is how they find us," Leal said. "The antennae of the Culex quinquefasciatus are highly developed to detect even extremely low concentrations of nonanal." 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. Since 1999, the US Centre for Disease Control and Prevention (CDC) has recorded 29,397 human cases and 1,147 fatalities in the US alone.

Researchers tested hundreds of naturally occurring compounds emitted by people and birds. They collected chemical odours from adult human subjects, representing multiple races and ethnic groups.

Leal and Syed found that nonanal acts synergistically with carbon dioxide, a known mosquito attractant, an UC-D release said.

"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," Syed said.  "Nonanal, in combination with carbon dioxide, increased trap captures by more than 50 percent, compared to traps baited with carbon dioxide alone," Syed added.

These findings were published this week in the early online edition of the Proceedings of the National Academy of Sciences.