Download high-resolution photos of Larry Zweibel and Anopheles mosquitos and a female mosquito feeding.
NASHVILLE, Tenn. – Today, we know a little bit more about one of
mankind’s deadliest enemies, the mosquito. Scientists have taken an
important step toward understanding the mosquito’s sense of smell, an
avenue of research that may lead to better ways to repel the deadly
insect.
In a joint effort reported in the Jan. 15 issue of the journal
Nature, researchers at Vanderbilt and Yale universities have verified
that the antennae of female Anopheles mosquitoes that prey on humans
contain receptors that respond to one of the chemical compounds found
in human sweat.
"This validates our hypothesis that the olfactory system of
mosquitoes-and other insects-consists of an array of different
receptors, each of which responds to a very narrow range of odorants,"
says Laurence J. Zwiebel, associate professor of biological sciences at
Vanderbilt, who participated in the study. His co-authors were
Vanderbilt graduate student A. Nicole Fox along with Yale colleagues
Elissa A. Halem, a graduate student, and professor John R. Carlson.
Confirmation of this hypothesis means that it should be possible to
identify the specific human odorants and the protein receptors that
allow female mosquitoes to identify their hosts when they need blood to
satisfy their reproductive needs. In addition to cataloging the human
odorants that attract mosquitoes, it also will allow the researchers to
go further and search for additional chemicals that either attract or
repel these highly selective insects.
"Looking at attractants is only half of the picture. There is
no evidence that mosquitoes find some human odorants repellent, but
we’re interested in exploring this," says Zwiebel. Such discoveries
might lead to new and more effective repellants that could play a major
role in reducing the death toll from diseases spread by mosquitoes,
including malaria, encephalitis, West Nile, dengue, hemorrhagic and
yellow fevers.
Previous studies have shown that human sweat contains about 350
different aromatic compounds, but not much research has been done on
them. For example, researchers do not know much about the individual
variations in these odorants, not even how greatly the odorants of men
and women differ. However, recent data from researchers in the
Netherlands suggests that mosquitoes use a blend of many odorants in
targeting prey. "This is a very complex system," Zwiebel observes.
The Nature paper reports another important advance. The researchers
were able to get a mosquito olfactory gene to work in Drosophila, the
fruit fly that has become the "white lab rat" of genetic research. This
provides the researchers with a wealth of tools they can use to explore
the nature of the mosquito’s olfactory system at the genetic and
molecular level.
The researchers created fruit flies with Anopheles’ olfactory genes
and then tested their sensitivity to different compounds found in human
sweat. They identified one particular compound, 4-methylphenol,
strongly activated an odorant receptor that is expressed in female
mosquitoes but not in males. Previous studies had shown that the
production of this protein is suppressed in female mosquitoes
immediately following a blood meal when they are no longer responsive
to human odors. The new finding strengthens the argument that female
Anopheles use 4-methylphenol to seek out hosts.
The fact that the mosquito gene works properly in the fruit fly has
another significant ramification. It means that the fundamental nature
of the olfactory system in other insects must be extremely similar to
that of the mosquito. "As a result, our research should have a direct
bearing not only on the mosquito, but also on other insects that carry
disease and act as agricultural pests," Zwiebel says.
For more news about Vanderbilt research, visit Exploration, Vanderbilt’s online research magazine, at www.exploration.vanderbilt.edu.
Media contact: David Salisbury, (615) 343-6803
David.Salisbury@vanderbilt.edu