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March 16, 2006
UC Chemical Ecologist Makes Offers that Mosquitoes Can't Refuse
And he does. He makes offers that the mosquitoes can’t refuse. Leal, an entomology professor at the University of California, Davis and a newly elected fellow of the American Association for the Advancement of Science (AAAS), draws gravid mosquitoes—or females ready to deposit their eggs—to his chemically scented oviposition traps set in Sacramento, Fresno, Shasta and Los Angeles counties. Culex mosquitoes, the principal carriers of West Nile virus, buzz excitedly around Leal’s traps, drawn by the tantalizing smell, the whirring movement of battery-operated fans, and the water-filled tray. “The smell is offensive to us, but the mosquitoes like it,” said Leal, who has been perfecting the “stinky” chemical compound mixture for the past four years as part of a federally funded grant. Once sucked into the traps, the mosquitoes can be tested for the presence of West Nile virus (WNV), which last year killed 18 people in California and infected some 900 others throughout the state. Leal’s ovitraps work much better than the host-seeking standard traps, said medical entomologist Anthony Cornel, director of the Mosquito Research and Control Laboratory at the UC Kearney Agricultural Center, Parlier. During the height of the WNV epidemic last year in Fresno County, as many as 18 percent of the Culex pipiens s.l. collected in Leal’s ovitraps tested positive for the virus, said Cornel, who also serves as associate director of the UC Davis Center for Vectorborne Diseases and an associate professor of entomology at UC Davis. “Arbovirus surveillance conducted using oviposition traps is more efficient than collections based on host-seeking methods as they (ovitraps) contain predominately gravid females,” Cornel said. An arbovirus is an arthropod-borne virus transmitted to humans through the bite of mosquitoes. To the outsider, the ovitrap resembles a metal tool box nestled in a water-filled tray. Generally, female mosquitoes consume a blood meal and later—after the.blood is digested and nutrients converted to egg yolk—look for a place to “ovipost” or lay their eggs. With the onset of mosquito season, “we’ll be collecting mosquitoes where the WNV outbreaks occurred last year, and then they will be tested for WNV infections,” said Leal, who heads the UC Davis Chemical and Olfaction Group. The ovitraps, to be placed in Sacramento, Los Angeles, Fresno and Redding beginning in late May or early June, are like sentinel chickens in that entomologists can alert the public to an outbreak of WNV. Last year 1,053 sentinel chickens from 31 California counties tested positive for West Nile/St. Louis encephalitis antibodies, indicating they were infected with the mosquito-borne disease. The ovitraps are also somewhat like the canaries in coal mines that alert the miners of the presence of dangerous underground gases. Sacramento County, which tallied 175 cases of WNV infections last year, proved to be the nation’s hot spot for the virus, according to the Centers for Disease Control and Prevention. Leal is partnering with Cornel and mosquito abatement district officials in Sacramento, Fresno, Redding and Los Angeles to combat West Nile virus in California. They are part of a 16-member team of scientists, mosquito abatement experts and industry partners involved with “Control of Urban and Peri-Urban Culex Mosquitoes,” a five-year, $3.7 million grant from the National Institutes of Health. Principal investigator of the grant, which continues through December 2008, is UC Davis medical entomologist Greg Lanzaro, director of the UC California Mosquito Research Program and director of the UC Davis Center for Vectorborne Diseases. One of the grant’s three aims is to optimize trap efficacy through the development of better lures, Lanzaro said. “Walter is an internationally recognized expert on the chemical ecology of insects,” Lanzaro said. “I was delighted when he agreed to participate with the UC Mosquito Research Program in this project. His work represents a significant contribution to our ability to monitor and manage mosquito-transmitted diseases.” Already the ovitrap has proved more efficient, effective and user friendly than the infusion traps that are standard in the industry, Leal said. “With these ovitraps, we attract more gravid mosquitoes, the traps are easier to operate and they don’t stink as much.” The infusion traps smell like a plugged-up toilet. The ovitraps also serve another purpose: they indicate the size of mosquito populations. “Last year when the mosquito abatement district was night-spraying pesticides in Sacramento County, we saw a decrease in mosquito populations and more dead ones—the mosquitoes were dead or dying in our traps,” Leal said. “So we could tell right away that the spraying was working well.” At the end of California’s mosquito season last September, Leal tested the ovitraps in his native Brazil for six months. “It’s summer there in September,” he said, “and we had a six-month window of nice weather.” His trips to Brazil resulted in highly successful catches. On one weeklong trip in February, he averaged 20 Culex quinquefasciatus mosquitoes a night. “They have Culex mosquitoes, but fortunately, they don’t have West Nile yet,” he said. Culex mosquitoes are found worldwide except in Antarctica. Leal specializes not only in what attracts mosquitoes, but what repels them, both important in controlling mosquitoes and the diseases they transmit. He has studied the sense of smell of insects, including scarab beetles, bees, cockroaches, moths and mosquitoes, for more than two decades. West Nile virus, first discovered in West Nile district of Uganda in 1937, was reported in New York in 1999 and in California in 2002. Last year health officials found WNV in all of California’s 58 counties. Related NewsSidebar: Walter Leal's Research on Insects' Sense of Smell Leads to Worldwide Honor |
