No more big stink: scent lures mosquitoes, but humans can'...(s are less likely to be infected than th...)

"The gravid traps are more important for surveillance," Leal said, "as they capture mosquitoes that have had a blood meal and thus, more opportunity to become infected."

By monitoring gravid traps containing West Nile virus-infected mosquitoes, mosquito and vector control districts and health officials can determine when it is time to spray.

Leal said that another advantage of the gravid traps is that with the capture of one female mosquito, that eliminates not only her, but hundreds of her would-be offspring. "Each female mosquito has the potential to produce about 200 eggs, and she can have as many as five cycles. So when we capture a gravid mosquito, that can remove as many as 500 females."

UC Davis research entomologist William Reisen said sampling Culex species in urban environments can be challenging, but the gravid trap work is crucial.

Because the Southern house mosquito, Culex quinquefasciatus, feeds on the blood of a wide variety of hosts, the West Nile virus can move rapidly through bird and human populations, according to Reisen.

"Sampling the species in urban environments has been a challenge until studies on its oviposition cues allowed the development of gravid female traps that collect mostly females that previously have blood-fed and, therefore, had a chance to become infected," Reisen.

Leal said the compounds used in the research are "simple and inexpensive" and would be of great benefit "to not only us, but third-world countries where Culex quinquefasciatus is a problem."

The researchers began preliminary field tests in Davis and Sacramento but when aerial sprays mitigated the levels of West Nile virus-infested mosquitoes, they set up traps in Recife, Brazil, a city endemic for lymphatic filariasis.

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