ShareThisThe smell of a volatile chemical exuded by people and birds alike is what draws in the species of mosquito known to carry West Nile Virus, researchers have found.
This discovery at the University of California, Davis could lead to improved efforts to crimp the spread of the disease, said Walt Leal, an entomology professor who led the research over the past three years.
"Now we can call them into a trap," Leal said.
The findings of Leal and his colleague Zain Syed, a UC Davis postdoctoral researcher, appear in the current edition of "Proceedings of the National Academy of Sciences."
The mosquito most likely to harbor West Nile, which is known as the culex, is drawn to both birds and people by the scent of the chemical nonanal, pronounced "no-nan-al," he said.
As fat degrades in birds and people, they excrete the nonanal, Leal said. The chemical has an "unpleasant" smell that Leal said isn't detectable to human senses unless amassed in concentrated amounts.
But the smell is quite an attraction to these specific mosquitoes, which have hypersensitive antennae. In lab tests, Leal and other scientists attached electrodes to tiny hairs on the mosquitoes' antennae to determine what chemicals they found most attractive.
Nonanal was the answer.
Synthetic versions of the simple chemical, which are already available, could be used as lures in traps to lower their population, Leal said.
While scientists have known for 20 years that mosquitoes hone in on the scent of carbon dioxide -- and carbon dioxide emitting dry ice is used as the bait in current mosquito traps -- the discovery about nonanal is specific to the culex mosquito.
Leal said test traps that used a mix of nonanal and carbon dioxide attracted twice as many mosquitoes as traps that used carbon dioxide alone.
One of the leaders of efforts against the culex mosquito, John Albright, a biologist at the Shasta Mosquito & Vector Control District in California, said the discovery opens up a whole new realm of research.
"For people like me, it just gets your mind spinning," he said.
First detected in New York in 1999, West Nile has since spread across the country. It is potentially deadly for the very old and very young.
Along with using nonanal itself as a lure for culex mosquitoes, Albright said scientists could study the possibility of developing chemicals that block or mask a person's nonanal odor output.
But Leal said he doubts that a chemical that blocks the nonanal scent would be effective at deterring culex mosquitoes from their favorite blood meals.
"If we block one compound, they are going to smell another one," Leal said.
He recommends that people use repellents with DEET as an ingredient during mosquito season.
E-mail Redding, Calif., Record Searchlight reporter Dylan Darling at ddarling(at)redding.com.
