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StumbleUponPosts Tagged: Culex quinquefasciatus
The SWAT Team
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.
Walter Leal and Zain Syed
Culex Mosquito
Heaven-Scent
Whew, that stinks!
If you've ever smelled a mosquito gravid trap, you know it's not heaven-scent. This isn’t about the aroma of summer roses or the whiff of freshly baked cinnamon rolls or the fragrance of vanilla-laced skin cream.
No. This is something that stinks to high heaven. Probably low heaven, too.
It’s s-o-o bad (how b-a-d is it?) that you just want to distance yourself from the stench: you hold your nose, mutter “P.U.” and make like a Lightening Bolt (Olympic gold-medal sprinter Usain Bolt).
Said UC Davis chemical ecologist Walter Leal: “It smells like a latrine."
So he and his researchers set out to find a synthetic mixture that attracts mosquitoes but is odorless to humans. And they have. Their mixture, containing the compounds trimethylamine and nonanal in low doses, lures Culex mosquitoes just as effectively as the current gravid trap attractants. But look, ma, no smell!
They did it with what Leal calls "reverse chemical ecology."
The results are published in the current edition of the Public Library of Science Journal or PLOS One.
This research could play a key role in surveillance and control programs for Culex species, which transmit such diseases as
What are gravid traps? They're chemical- and water-infused traps, sometimes called oviposition traps or ovitraps. They're meant to attract blood-fed mosquitoes searching for places to lay their eggs. Scientists monitor these traps to determine the presence of West Nile-infected mosquitoes.
“The gravid traps are more important (than carbon-dioxide traps) for surveillance,” Leal said, “as they capture mosquitoes that have had a blood meal and thus, more opportunity to become infected.”
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.”
The compounds used in the research, Leal said, 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 did preliminary field testing in
Other scientists involved in the study included UC Davis researchers Wei Xu, Yuko Ishida,
(See more information on the UC Davis Department of Entomology Web site).
Culex quinquefasciatus laying eggs
Water for mosquito gravid trap
The Secret's Out
We know it works, but how?
Just how does DEET work? Does it jam the senses of a mosquito? Does it mask the smell of the host?
You spray the chemical repellent on your arm and thankfully, those darn skeeters leave you alone. They need a blood meal to develop their eggs, so off they buzz to find another host, one that’s not so inhospitable.
But why do mosquitoes avoid DEET?
Well, they avoid it because it smells bad to them. Yes, they can smell it--that's why they avoid it.
The groundbreaking research, the work of UC Davis chemical ecologist Walter Leal and researcher
The research contradicts a Science article published in March by researchers at
The Leal-Syed research solidly establishes the real mode of action.
Noted entomologist James "Jim" Miller of
Said Miller: "For decades we were told that DEET warded off mosquito bites because it blocked insect response to lactic acid from the host -- the key stimulus for blood-feeding. Dr. Leal and co-workers escaped the key stimulus over-simplification to show that mosquito responses -- like our own -- result from a balancing of various positive and negative factors, all impinging on a tiny brain more capable than most people think of sophisticated decision-making.”
“This new work corrects long-standing erroneous dogma, and shows that recent work on DEET mode-of-action published in the flagship journal, Science, apparently was flat-out wrong,” Miller said. “One of the great attributes of science is that, over time, it is self-correcting."
Leal, past president of the International Society of Chemical Ecology and former chair of the UC Davis Department of Entomology, said previous findings of other scientists showed a “false positive” resulting from the experimental design.
Now that we know that skeeters can smell it, this will no doubt lead to better methods of insect control. Or, as
Those darn female mosquitoes, always in a “Let-us-prey” mood, have clearly met their match: the "why" behind "Let us spray."
(For more information and a video,access this page.)
Culex quinquefasciatus
Spraying DEET
