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.
They're as long and thin as darning needles. And, sometimes they’re as difficult to find as a needle in the proverbial haystack.
These slender, frail-looking insects (below) are damselflies. They fly around ponds and streams and perch on plants near the shoreline. As adults, they prey on flying insects such as mosquitoes and gnats, and in turn, they're preyed upon by dragonflies, other insects, and birds. Occasionally a spider snares one in its web.
Anglers consider them good luck, especially when these brightly colored insects touch down on their fishing lines.
Like dragonflies, damselflies are members of the Odonata order. Their suborder is Zygoptera--in case anybody asks!
Retired entomologist Jerry Powell of UC Berkeley estimates California has about 40 species of damseslflies.
I saw one damselfly, probably the common bluet, checking out our backyard fish pond last weekend before perching on a tower-of -jewels leaf.
Another one was flitting about the Yolo Causeway last year while a UC Davis researcher was trapping mosquitoes.
Neither looked like a damsel in distress. In fact, they looked quite predaceous.
Especially to skeeters.
Plain as day. And they’re not going away.
The estimated ratio of insects to humans is 200 million to one, say Iowa State University entomologists Larry Pedigo and Marlin Rice in their newly published (sixth edition) textbook, Entomology and Pest Management. Rice is the 2009 president of the Entomological Society of America.
Rice is the 2009 president of the Entomological Society of America.
There's an average of 400 million insects per acre of land, they say.
“The fact is, today’s human population is adrift in a sea of insects,” they write in their introduction.
Well, what about biomass? Surely we outweigh these critters?
No, we don't. The
There you go. The insects are the land owners; we are the tenants. “They are the chief consumers of plants; they are the major predators of plant eaters; they play a major role in decay of organic matter; and they serve as food for other kinds of animals,” Pedigo and Rice write.
Insects represent the good, the bad and the ugly.
Insects represent the good, the bad and the ugly.
The good: they give us honey and pollinate our crops. They spin our silk. They serve as natural enemies of pests. They provide food for wildlife (not to mention food for some of us humans). They are scavengers. They provide us with ideas for our art work. They are fodder for our horror movies.
And what scientist hasn't benefitted from the inheritance studies of the fruit fly, Drosophila melanogasta? What ecologist hasn't studied water pollution by examining the mayfly population? Mayflies are the counterpart of canaries in the coal mine.
The bad: they eat our food crops, forests and ornamental plants. They devour or spoil our stored grain. They chew holes in our clothing. They pester us. They annoy our animals, too.
The ugly: They can—and do—kill us. Think mosquitoes. Think malaria,
But wait, there's more! Many more. Scientists have described more than 900,000 species of insects but there could be seven times as many out there, the authors point out.
Ironically, despite the huge numbers of insects, many people don't know the meaning of the word, entomology, the science of insects. They should. Insects outnumber us and always will. They've lived on the earth longer than us (400 million years) and adapt to changes better than we do. Most are tiny. Most can fly. And most reproduce like there's no tomorrow.
"Based solely on numbers and biomass, insects are the most successful animals on earth," the authors claim.
You can't argue with that.
So, you want to become an entomologist...
Entomologists, future entomologists and others interested in science are looking forward to the fall seminars sponsored Oct. 1 through Dec. 3 by the Department of Entomology, University of California, Davis.
All seminars are held on Wednesdays from 12:10 to 1 p.m. in 122 Briggs Hall. Individual faculty members will host the seminars.
You'll learn about fungus-farming ambrosia beetles, the invasive brown marmorated sting bug, argentine ants, thrips, and Culex mosquitoes, to name a few.
The UC Davis entomology faculty do a fantastic job lining up speakers. The key word here is "passion." (The best advice I ever received in a fortune cookie involved passion: "Nothing great in the world has ever been accomplished without passion.")
Bring on the bugs!
Oct. 1: Jiri Hulcr of Department of Entomology, Michigan State University, East Lansing, “Evolution and Ecology of Fungus-Farming Ambrosia Beetles. Host: entomology professor Phil Ward
Oct. 8: Anne Nielsen, Department of Nematology, UC Davis, “Population Ecology and Damage Estimates of the Invasive Brown Marmorated Stink Bug, Halyomorpha halys.” Host: nematology and entomology professor Ed Lewis
Oct. 15: Urs Wyss, Institute of Phytopathology, Kiel University, Kiel, Germany, “Biological Control of Greenhouse Pests with Natural Arthropod Enemies.” Host: entomology and nematology professor Harry Kaya
Oct. 22: Greg Crutsinger, Department of Ecology and Evolutionary Biology, University of Tennessee, “Linking Plant Genetic Variation to Foliage- and Litter-Based Arthropod Communities.” Host: entomology professor Rick Karban
Oct. 29: Kris Godfrey, California Department of Food and Agriculture, Sacramento "Pest Management of Invasive Insect Pests in California.” Host: nematology and entomology professor Ed Lewis
Nov. 5: Neil Tsutsui, Department of Environmental Science, Policy and Management, UC Berkeley, “Exploring the Genetic and Chemical Basis of Argentine Ant Behavior.” Host: entomology professor Phil Ward
Nov. 12: Le Kang, Institute of Zoology, Chinese Academy of Sciences, Beijing, China Chemical Communications Between Plants, Leafminers and Parasites.” Host: Michael Parrella, associate dean of the Division of Agricultural Sciences, College of Agricultural and Environmental Sciences, and entomology professor
Nov. 26: Chris Barker, Department of Entomology, UC Davis, “Environmental Drivers of Large-Scale Spatial and Temporal Patterns in Mosquito Abundance and Virus Transmission in California.” Host: Bruce Eldridge, emeritus professor of entomology
Dec. 3: Lisa Chanbusarakum, Department of Entomology, UC Davis, “Exploring the Microbial World of Frankliniella occidentalis, the Western Flower Thrips.” Host: Diane Ullman, associate dean for undergraduate academic programs at the College of Agricultural and Environmental Sciences and entomology professor