Nav: Home

How mosquitoes smell human sweat (and new ways to stop them)

March 28, 2019

Female mosquitoes are known to rely on an array of sensory information to find people to bite, picking up on carbon dioxide, body odor, heat, moisture, and visual cues. Now researchers reporting in the journal Current Biology on March 28 have discovered how mosquitoes pick up on acidic volatiles found in human sweat.

The key is an olfactory coreceptor known as Ir8a. Mosquitoes lacking a functional version of the Ir8a gene were much less attracted to people, the researchers found. The findings potentially suggest new approaches for designing new and improved mosquito repellents.

"Removing the function of Ir8a removes approximately 50 percent of host-seeking activity," says senior author Matthew DeGennaro (@MattDeGennaro), a mosquito neurobiology researcher at Florida International University in Miami. "Odors that mask the IR8a pathway could be found that could enhance the efficacy of current repellents like DEET or picaridin. In this way, our discovery may help make people disappear as potential hosts for mosquitoes."

On the flip side, the Ir8a pathway also could be used to design new mosquito attractants, he adds. Those attractants could lure mosquitoes away from people and into traps.

The inspiration for the new work came from previous work DeGennaro conducted as a postdoctoral student in Leslie Vosshall's lab at The Rockefeller University. In those studies, the team disrupted another olfactory coreceptor, called Orco, and watched to see how it changed mosquitoes' behavior.

They found that those mosquitoes had more trouble telling the difference between people and other animals. The mosquitos also lost their interest in nectar and their aversion to DEET. But, they still were attracted to vertebrate animals including people. It meant that there were more receptors still to find.

In the new study, DeGennaro and his colleagues looked to another group of receptors broadly known as ionotropic receptors and specifically Ir8a, which is expressed in the antenna. They used the CRISPR/Cas9 gene-editing system to disrupt Ir8a in Aedes aegypti mosquitoes. Then, they tested the coreceptor's relative contribution in human odor detection and its genetic interaction with other olfactory receptor pathways that had been implicated previously in Ae. aegypti host-seeking behavior.

The studies show that mosquitoes carrying a mutant version of Ir8a weren't attracted to lactic acid and couldn't detect other acidic components of human odor. In comparison to wild-type controls in membrane blood-feeding assays, Ir8a mutants showed reduced responses to human odor, but not heat or CO2. Ir8a mutants also were less responsive to humans and human odor than were wild-type controls in another set of experiments.

Their findings further suggest that genetic interactions among various receptors are important, with CO2 sensitizing mosquitoes to human odors. They also highlight the importance of detecting human acidic volatiles in the insects' ability to hunt and feed on humans.

"The Ir8a phenotype was not modulated by carbon dioxide, but required the function of the carbon dioxide receptor," DeGennaro explains. "This suggests that carbon dioxide is necessary to activate the IR8a response to acidic volatiles in human odor, but not sufficient to rescue the mutant phenotype. Our results strongly suggest that host odor detection by IR8a is an indispensable component of the mosquito's host detection system."

DeGennaro says their ultimate goal is to develop a life-saving perfume to protect people from mosquito bites, and this new study is an important step along the way.

"The transmission of diseases like dengue, yellow fever, Zika, and malaria can be blocked if we stop these mosquitoes from biting us," DeGennaro says. "In order to find new solutions to prevent mosquito bites, we need to focus on understanding the molecular basis of mosquito behavior."

The researchers now hope to gain an even more detailed view of the IR8a pathway. Next, they'll begin chemical screens, using the identified genes to lead them to potentially new mosquito attractants and repellents.
-end-
This work was supported by the National Institute of Allergy and Infectious Diseases of the National Institutes of Health and startup funds from Florida International University.

Current Biology, Raji et al.: "Aedes aegypti Mosquitoes Detect Acidic Volatiles Found in Human Odor Using the IR8a Pathway" http://www.cell.com/current-biology/fulltext/S0960-9822(19)30215-5

Current Biology (@CurrentBiology), published by Cell Press, is a bimonthly journal that features papers across all areas of biology. Current Biology strives to foster communication across fields of biology, both by publishing important findings of general interest and through highly accessible front matter for non-specialists. Visit: http://www.cell.com/current-biology. To receive Cell Press media alerts, contact press@cell.com.

Cell Press

Related Mosquitoes Articles:

Mosquitoes are drawn to flowers as much as people -- and now scientists know why
Despite their reputation as blood-suckers, mosquitoes actually spent most of their time drinking nectar from flowers.
Mosquitoes engineered to repel dengue virus
An international team of scientists has synthetically engineered mosquitoes that halt the transmission of the dengue virus.
Engineered mosquitoes cannot be infected with or transmit any dengue virus
Genetically engineered mosquitoes are resistant to multiple types of dengue virus (DENV), according to a study published Jan.
Researchers identify that mosquitoes can sense toxins through their legs
Researchers at LSTM have identified a completely new mechanism by which mosquitoes that carry malaria are becoming resistant to insecticide.
Mated female mosquitoes are more likely to transmit malaria parasites
Female mosquitoes that have mated are more likely to transmit malaria parasites than virgin females, according to a study published Nov.
In Baltimore, lower income neighborhoods have bigger mosquitoes
Low-income urban neighborhoods not only have more mosquitoes, but they are larger-bodied, indicating that they could be more efficient at transmitting diseases.
Mosquitoes more likely to lay eggs in closely spaced habitats
Patches of standing water that are close together are more likely to be used by mosquitoes to lay eggs in than patches that are farther apart.
Why do mosquitoes choose us? Lindy McBride is on the case
Most of the 3,000+ mosquito species are opportunistic, but Princeton's Lindy McBride is most interested in the mosquitoes that scientists call 'disease vectors' -- carriers of diseases that plague humans -- some of which have evolved to bite humans almost exclusively.
Biting backfire: Some mosquitoes actually benefit from pesticide application
The common perception that pesticides reduce or eliminate target insect species may not always hold.
What makes mosquitoes avoid DEET? An answer in their legs
Many of us slather ourselves in DEET each summer in hopes of avoiding mosquito bites, and it generally works rather well.
More Mosquitoes News and Mosquitoes Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Climate Mindset
In the past few months, human beings have come together to fight a global threat. This hour, TED speakers explore how our response can be the catalyst to fight another global crisis: climate change. Guests include political strategist Tom Rivett-Carnac, diplomat Christiana Figueres, climate justice activist Xiye Bastida, and writer, illustrator, and artist Oliver Jeffers.
Now Playing: Science for the People

#562 Superbug to Bedside
By now we're all good and scared about antibiotic resistance, one of the many things coming to get us all. But there's good news, sort of. News antibiotics are coming out! How do they get tested? What does that kind of a trial look like and how does it happen? Host Bethany Brookeshire talks with Matt McCarthy, author of "Superbugs: The Race to Stop an Epidemic", about the ins and outs of testing a new antibiotic in the hospital.
Now Playing: Radiolab

Speedy Beet
There are few musical moments more well-worn than the first four notes of Beethoven's Fifth Symphony. But in this short, we find out that Beethoven might have made a last-ditch effort to keep his music from ever feeling familiar, to keep pushing his listeners to a kind of psychological limit. Big thanks to our Brooklyn Philharmonic musicians: Deborah Buck and Suzy Perelman on violin, Arash Amini on cello, and Ah Ling Neu on viola. And check out The First Four Notes, Matthew Guerrieri's book on Beethoven's Fifth. Support Radiolab today at Radiolab.org/donate.