In the News

March 26, 2006
Sacramento Bee

UC Davis team takes swat at mosquitoes Researchers try to improve response to West Nile virus with better traps. By Edie Lau -- Bee Staff Writer Published 2:15 am PST Sunday, March 26, 2006 Story appeared in Metro section, Page B1 Zain Syed, a researcher at UC Davis, works in Walter Leal's entomology lab, where mosquitoes are studied in an effort to isolate what chemical compounds they find attractive. (Sacramento Bee Photo by Jay Mather) Supposing you wanted to build a better mosquito trap. How would you begin? If you were a chemical ecologist like Walter Leal, you'd start with a mosquito's antenna. The quest for a better trap is why Leal and the researchers in his laboratory at the University of California, Davis, have electrodes hooked up to the antennae of live mosquitoes. Tapping directly into the mosquitoes' "noses," the scientists can see on a computer screen whether the bugs react to any of a sampling of scents wafted over them. Big squiggles on the monitor mean the chemical source of the scent may make a good lure - the equivalent of cheese in a mousetrap. Leal is part of a team of scientists at UC Davis trying to improve the nation's ability to detect and respond to West Nile virus, a disease spread by the bite of mosquitoes. The researchers have a grant of $3.7 million from the National Institutes of Health over five years to assess the effectiveness of spraying pesticides to kill adult mosquitoes; to monitor insecticide resistance; and to improve mosquito trapping. The work is especially relevant in California's Central Valley, which was the epicenter of West Nile virus last year, and has the makings of another tough season this year. California logged 929 cases in 2005, more than any other state. While most people exposed to West Nile virus don't get sick, infection can cause crippling neurological disease and, occasionally, death. The virus killed 18 people in California last year. Leal, an expert in insect pheromones, aims to invent a trap that does a better job than standard equipment at attracting the kinds of mosquitoes that carry West Nile virus - and at a stage in life when the mosquitoes are most likely to be infected. "If you're going to spray (pesticides to control mosquitoes), you want the most reliable information," said Leal. Recalling the public outcry last summer when the Sacramento-Yolo Mosquito and Vector Control District treated by aircraft 110,000 acres of urban Sacramento County, Leal said he understands why the district felt obligated to act. He said he also understands why some people objected to the widespread spraying. For his part, Leal would like to help refine the information that officials use to decide mosquito control measures. "We don't have enough information because the trapping is not good enough," Leal said. Mosquito agencies use an array of traps. The Sacramento-Yolo district, for example, employs four different models that use a variety of attractants, including carbon dioxide, heat and light. Some draw mosquitoes that are hungry for blood; another draws "gravid" mosquitoes, which bear ripe eggs. Some are better at attracting one species of mosquito than another. Some traps hold the mosquitoes live; in others, they die. This image of a mosquito's head and antenna is magnified 120 times. The tiny hairlike strands sticking out from the antenna are the sensilla, through which the mosquito smells its targets. Scanning electron microscope photo/ Zain Syed and Walter Leal Zeroing in on the West Nile virus carriers requires more than simply trapping and testing skeeters. First, only the females are targets because only females drink blood, taking the protein they need to develop their eggs. Next, you want to catch the species that are known to carry the virus - not all do. Finally, notes Leal, the ones that have fed on blood and are ready to lay their eggs are more likely than those with empty bellies to have picked up the virus. So, what do expectant mother skeeters need? They favor standing water, and all the better if it's fetid with decaying bits of vegetation that larvae can eat. A trap to catch gravid mosquitoes exists already, but to Leal's eye, it is less than ideal. Informally, it's known as a "stinky-water trap," which is a big clue to why he finds fault with it. "It's not user-friendly," Leal said. Consider this recipe for making the stinky water: 9 grams of dry Bermuda grass 0.54 grams of lactalbumin hydrosylate (protein) 0.54 grams of brewer's yeast 2 liters of water Mix and leave at room temperature for seven to 10 days. Filter through a No. 100 mesh wire filter. "Then," Leal said, making fun, "wait for the moon to align with the sun." He likens the laborious process to growing your own plants for medicine. "It's not acceptable in this age," he said. "You go to a pharmacy." At the Sacramento-Yolo mosquito district, officials are planning to deploy 27 stinky-water traps this year, more than triple the number they used last year. David Brown, district general manager, said he has confidence in his agency's trapping system, but welcomes improvements. "Obviously, anything that would make our trapping schemes easier to implement are a benefit to everybody," he said. Leal's goal is to develop a lure that can be packaged in vials. You'd simply open a vial, pour it into standing water and wait for the mosquitoes to arrive. Coming up with the right potion requires understanding the fine details of a mosquito's chemical sensory system. In Leal's lab, images of mosquito heads and antennae enlarged 100 times or more hang on the walls. Each of the short hairs on an antenna, the scientist explains, detects and receives chemical signals in the air. The chemicals enter each hair, or sensillum, through pores. Those compounds that mean something to the mosquito make contact with nerve receptors inside the sensillum, stimulating the bug to act. Researchers test compounds by measuring mosquitoes' reactions with tiny electrodes inserted into the insects' sensilla. The tough little bugs can endure five or six hours of testing, even though their wings and legs are removed and their bodies are taped to a slide to keep them from escaping. Leal said the scientists can do tests with just the antennae, too. For a couple of hours after it's removed from a live mosquito, an antenna will still respond as if it's attached. That hardiness apparently is characteristic of many bugs. "Insects are amazing," Leal said. "You can decapitate a moth and it will still mate." Leal and his colleagues will test several candidate mosquito lures in Sacramento as the weather warms and the bugs begin, once again, to swarm. The Bee's Edie Lau can be reached at (916) 321-1098 or elau@sacbee.com. News ~ News Tips ~ Related News Contact: Kathy Keatley Garvey Communications UC Mosquito Research Program Department of Entomology 396 Briggs Hall University of California, Davis Davis, CA 95616 Phone: (530) 754-6894 E-mail: kegarvey@ucdavis.edu