Chemical ecologist Walter Leal, professor and former chair of the UC Davis Department of Entomology, and his postdoctoral researcher Zain Syed have done it again.
In August of 2008, they discovered the secret mode of the insect repellent, DEET. In groundbreaking research published in the Proceedings of the National Academy of Sciences (PNAS), they found that DEET doesn't mask the smell of the host (that would be you and me), nor does DEET jam the insect's senses.
Mosquitoes CAN indeed smell DEET. They avoid it because they don't like the odor.
Then on Monday, Leal and Syed published more groundbreaking research, also in PNAS. They identified the dominant compound that attracts Culex mosquitoes to both birds and humans.
It's a compound called nonanal, naturally produced in birds and humans. This not only explains the host shift from birds to humans, but paves the way for key developments in mosquito and disease control.
Infected Culex mosquitoes transmit life-threatening diseases, including West Nile virus. Since 1999, the Centers for Disease Control and Prevention has recorded 29,397 human cases and 1,147 fatalities in the United States alone.
“Nonanal is how they find us,” Leal said. “The antennae of the Culex quinquefasciatus are highly developed to detect even extremely low concentrations of nonanal.”
Researchers from throughout the country this week praised their work.
Yale University professor John Carlson, a leading scientist in insect olfaction, described the study as “exciting with important implications for the intriguing question of how mosquitoes find the humans they bite.”
“Leal and Syed have identified a human odor that is detected with great sensitivity by the antennae of mosquitoes that transmit West Nile virus,” Carlson said. “In addition to its scientific interest, the study may have important practical applications in the control of these mosquitoes and the diseases they carry.”
Chemical ecologist Coby Schal, a professor at North Carolina State University, described the research as representing “some of the best research on insect olfaction that I have ever read. By combining trapping experiments in the field with careful characterization of the response profiles of antennal and maxillary sensilla of Culex mosquitoes, Syed and Leal show not only that the combination of carbon dioxide and nonanal is an important beacon for blood-seeking mosquitoes, but also that a large fraction of the sensilla on the mosquito’s nose (antennae) is dedicated to the detection of nonanal at incredibly low concentration.
“Such high sensitivity of olfactory receptor neurons to nonanal – rivaling the response characteristics of pheromone responsive neurons – suggests that nonanal has played an important role in the evolution of host-finding and host-preferences in Culex mosquitoes,” Schal said. “This is a truly exceptional achievement by the outstanding Syed/Leal team, but in step with their previous outstanding contributions on a wide range of arthropods.”
More information on the Leal lab research is on the Department of Entomology Web page.
Leal, a newly elected Fellow of the Entomological Society of America (he's one of 10 entomologists to be so honored this year) and Syed, named one of the top post-doctoral researchers at UC Davis this year, have indeed done it again.
When you think of all the havoc that mosquito-borne diseases have wreaked, this is the kind of research that definitely deserves a round of applause.
Dr. Leal and Dr. Syed are a highly efficient and effective SWAT team.
Chemical ecologist Zain Syed of the Walter Leal lab, University of California, Davis, knows just where to find mosquitoes for his research.
He's been collecting up to 3000 mosquitoes a night along the Yolo Causeway, located on Interstate 80 between Davis and West Sacramento. The Yolo basin is home to the Vic Fazio Yolo Wildlife Area.It's easy to catch mosquitoes.
Syed is using carbon-dioxide traps to capture host-seeking mosquitoes. The female skeeters are seeking a blood meal (you, if you're around there). His traps entice them to "come on in."
"Once mosquitoes are lured to the vicinity," Syed says, "a suction fan traps them and sends them to the sleeve, a mesh bag that holds mosquitoes."
The mesh bag below holds 2000 mosquitoes. They are mostly Culex tarsalis, but also some Culex pipiens.
Culex mosquitoes are known for transmitting West Nile virus.
Syed and Leal are known for uncovering the mode of action for DEET, the chemical insect repellent used by more than 200 million people worldwide. Their groundbreaking research last year found that DEET doesn't jam a mosquito's senses or mask the smell of the host, as scientists previously thought for some 50 years. Mosquitoes avoid DEET because it smells bad to them.
Syed recently won one of two coveted campuswide awards for excellence in postdoctoral research from a field of 800 postdocs.
But other fields--rice fields--have always drawn his attention.
That's where the skeeters are.
The San Diego County Health and Human Services Agency (HHSA) announced today that a 76-year-old man contracted WNV, but "he did not acquire the virus locally."
The HHSA, along with other agencies, is urging folks to avoid outdoor activity at dawn and dusk, when mosquitoes are the most active. If you must be outside at that time, they say, use an insect repellent with DEET, Picaridin, oil of lemon eucalyptus or IR3534.
It goes without saying that if you're camping, don't sleep outside unprotected.
Among the other good tips:
- Wear long sleeves and pants when outdoors
- Make sure your windows and doors have tight-fitting screens without holes or tears
- Check your property weekly to eliminate any standing water sources, where mosquitoes can breed.
- Keep your eye on any foreclosed homes in the neighborhood to ensure that swimming pools do not go unattended and containers do not contain water.
Meanwhile, the ground-breaking research (Aug. 18, 2008) of UC Davis chemical ecologists Walter Leal and Zain Syed on why mosquitoes avoid DEET continues to draw attention. It's one of the most downloaded and cited articles from the Proceedings of the National Academy of Sciences (PNAS).
Be careful out there.
The competition was fierce.
We're talking 800 postdoctoral scholars on the UC Davis campus, 12 finalists and two winners.
Chemical ecologist Zain Syed, who helped discover the mode of action for the insect repellent DEET in the Walter Leal lab, UC Davis Department of Entomology, emerged as one of the two winners.
The occasion: the sixth annual postdoctoral scholar research awards, sponsored by the UC Davis Postdoctoral Scholars’ Association and the Office of Graduate Studies.
Syed and fellow recipient Izumi Maezawa of the Department of Pathology and Laboratory Medicine, UC Davis Health System, each received a certificate and a $500 cash prize.
So, the next time you’re applying DEET to ward off mosquitoes, you can thank Leal and Syed for why mosquitoes won’t go near you. For the past 50 years, scientists assumed that DEET jams the senses of a mosquito or masks the smell of the host.
Not so. Mosquitoes can smell DEET and they avoid it because it smells bad to them. No jamming. No masking. Just a smell that's not in their comfort zone.
The chemical ecologists identified the olfactory receptor neuron in the antenna that detects the repellent. Their work led to one of the most popular research articles ever published in the Proceedings of the National Academy of Sciences (PNAS). The research paper has been loaded 9317 times from August 2008 through April 2009.
What this research means is we may see a whole new direction in the development of novel and promising insect repellents.
Syed, a native of
“Zain has an an encyclopedic knowledge of the literature and he designs well-thought experiments,” said Leal, also praising him as “a good mentor to students in the department, college and elsewhere on campus.”
“Zain is the type of postdoc that every principal investigator dreams about one day having in their own laboratory,” wrote professor Gabrielle Nevitt of Neurobiology, Physiology, and Behavior,
Entomology professor Penelope Gullan, who supported the nomination, said: "As a faculty member in the same department as Dr. Syed, I have watched his research progress and accomplishments over the past four years. His recent achievements have been truly outstanding in terms of significant research findings and publications in highly rated journals."
A dynamo, a maverick and an inspiration: mosquitoes beware!/st1:place>/st1:placename>/st1:placetype>/st1:place>/st1:country-region>/st1:city>/st1:country-region>/st1:place>/st1:country-region>/o:p>/o:p>/o:p>/o:p>/o:smarttagtype>/o:smarttagtype>/o:smarttagtype>/o:smarttagtype>/o:smarttagtype>
Chemical ecologists at the University of California, Davis, are changing their navel-orangeworm research direction after an elementary school student’s science project found that the major agricultural pest prefers pistachios over almonds and walnuts.
Gabriel Leal, 11, a sixth grader at Willet Elementary School, Davis, prefers pistachios over all other nuts so he figured that the navel orangeworm (NOW) would, too.
“Pistachios taste better,” reasoned Gabriel, whose family says he can eat an entire bag of pistachios at one sitting. Pistachios have long been his favorite nut, so why wouldn’t the navel orangeworm prefer pistachios over almonds and walnuts, too?
So the sixth grader hypothesized that the insect would lay more eggs in pistachios than in almonds and walnuts, contrary to widely published research that indicates an almond preference.
“Everybody knows that navel orangeworms prefer almonds,” said his father, Walter Leal, a chemical ecologist and professor of entomology at UC Davis. Research published recently in the California Agriculture journal also indicates the preference.
“But in science,” Leal said, “we should believe what we see, not what others tell us. I know that Gabriel prefers pistachios, but I assumed the navel orangeworm’s taste receptors were different.”
Wrong. Gabriel’s research showed that the insects preferred pistachios, just like him.
The findings led to a report at the Almond Board of California’s 32nd Almond Industry Conference, held Dec. 1-2 in Modesto, and launched a new direction of navel orangeworm chemical ecology research at UC Davis
Gabriel performed his research in his father’s UC Davis lab, under the volunteer supervision and mentoring of chemical ecologist Zain Syed.
“It was a ‘choice’ experiment where Gabriel placed mated and gravid (egg-filled) females in a cage,” Syed said. “He used four commercially available navel orangeworm traps (Ovitraps). One trap was filled with 50 grams of shelled pistachios, another with 50 grams of almonds, and the third with 50 grams of walnuts. The empty trap served as the control to check if the trap itself had any effects on attracting egg-laying moths. The eggs laid in the ovitraps were counted for two consecutive nights.”
Said Leal: "Gabriel got enough replicates to demonstrate that female orange navelworms do prefer pistachios over walnuts and almonds. We are very excited with our little scientist’s discovery. I reported ‘our’ findings at the state almond industry conference in Modesto. And these findings changed our research direction, because we are now interested in determining what chemistry in pistachios attracts female navel orangeworms.”
“Oviposition (egg-laying) attractants derived from almond oil are used to monitor female populations in the field,” Leal explained, “but during hull split, the chemical from the natural source (crop) competes with the synthetic material in traps. If we use pistachio-derived attractants in the almond field there will be no competition throughout the flight season.”
So how significant a pest is the navel orangeworm?
According to research entomologist Brian Higbee of Paramount Farming, Bakersfield, "it is the primary and most destructive pest on almonds and pistachios." California has some 152,000 acres planted in pistachios, while the state's almond acreage totals more than 700,000.
"The economic impact of NOW damage varies from year to year, but it can easily reach $10-15 million for our company and much higher statewide," Higbee said.
The take-home message? "Well, in science we should never underestimate anyone's idea,” Leal said. “That's why the academic environment is so enriching: students come with new ideas, but I never imagined we would benefit so much from a science project for elementary school."
For more, see news story on the UC Davis Department of Entomology Web site.