A female mosquito has fed on blood and is ready to lay eggs. How does she decide where to deposit her offspring?

Ring Cardé wants to find out.

The UC Riverside entomology professor hopes to discover what kinds of chemicals and traps work best to lure a female mosquito that's looking for a suitable place to lay eggs.

His results someday could help California health officials do a better job tracking and killing mosquitoes that can spread West Nile virus, which sickened more than 9,500 people nationwide and killed more than 230.

The virus, unknown in North America five years ago, surfaced in Southern California last summer. It is expected to spread statewide this year.

Cardé is part of a statewide research collaboration that includes the Coachella Valley Mosquito and Vector Control District and the University of California, Davis.

Financed by a $3.3 million federal grant, the collaboration will spend the next five years examining better ways to screen and kill particular types of mosquitoes that can spread disease.

"California has the most sophisticated mosquito-control program in the United States," said Greg Lanzaro, head of the Mosquito Research Program at UC Davis. "Despite that, there's a lot of mosquitoes around. They're doing a good job suppressing mosquitoes, but they're not eliminating them."

Some of the researchers will look at how to target insecticides at vegetation where Culex mosquitoes, which transmit West Nile, are known to hide. Others will examine how to better detect and measure mosquito resistance to insecticides used to control them.

"If we lose the chemicals we've got now to resistance, we're going to be in bad shape," said Lanzaro, the project's leader. New compounds are tougher to get approved, he said.

Cardé's role is to study mosquito behavior - "to understand how the trap design influences their willingness to go into the trap," he said.

Existing traps - powered by battery-operated fans - are all-purpose catchers, sucking up any mosquito that flies close enough to get caught in the downdraft. Not all mosquito species are disease carriers, and the traps miss many mosquitoes that buzz nearby but not close enough to get caught.

"These traps are not noted for being highly efficient," Cardé said.

Cardé wants to determine which chemicals work best for attracting a female mosquito prowling for a place to lay her eggs. Such a trap could give a more accurate picture of whether West Nile virus or another worrisome disease is primed to spread, he said. Females mosquitoes need blood before they can lay eggs. That makes them susceptible to spreading diseases like West Nile.

Using a basement wind tunnel and a set of video cameras and infrared lights, Cardé will track individual mosquitoes to determine which chemical attractants and traps work best.

Cardé also has studied what chemicals attract moths. But mosquitoes are more complex. It is harder to discern precisely how carbon dioxide and body odors, for example, affect their decisions, he said. That's one reason why Cardé's wind tunnel must be kept pristine. Even a stray thumbprint or the wrong cleaning agent can affect the mosquito's behavior, he said.