Female mosquitoes are known to use a wide array of sensory information, such as pick up on carbon dioxide, body odor, heat, moisture and visual cues, to find people to bite. Now researchers have discovered how mosquitoes pick up on acidic volatiles found in human sweat. The study was published in the international journal Current Biology on March 28.
The key is Ir8a, a co-receptor related to the sense of smell. Researchers discovered that mosquitoes lacking a functional version of the Ir8a gene were much less attracted to people. These findings can help find new approaches for designing improved mosquito repellents.
“Removing the function of Ir8a removes approximately 50 percent of host-seeking activity,” said Matthew DeGennaro , senior author and a mosquito neurobiology researcher at Florida International University in a statement.
“Odors that mask the Ir8a pathway 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,” he added.
On the other hand, the Ir8a pathway could also be used to design new mosquito attractants which could lure mosquitoes away from people and into traps.
According to the statement, the inspiration for this study came from work DeGennaro had conducted as a postdoctoral student at The Rockefeller University. During the study, they had disrupted another olfactory coreceptor called Orco to see how it changed the behavior of the mosquitoes.
They found that such mosquitoes had more trouble telling people and other animals apart. The mosquitos also lost their interest in nectar and their aversion to DEET. However, they still were attracted to vertebrate animals including people which meant that there were more receptors still to find.
In the new study, DeGennaro and his colleagues used the CRISPR/Cas9 gene-editing system to disrupt Ir8a in Aedes aegypti or the yellow fever 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 Aedes 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.
These 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.
DeGennaro said, “Our results strongly suggest that host odor detection by Ir8a is an indispensable component of the mosquito’s host detection system.” He added that their ultimate goal is to develop a life-saving perfume to protect people from mosquito bites, and this new study is an important step.
“The transmission of diseases like dengue, yellow fever, Zika, and malaria can be blocked if we stop these mosquitoes from biting us,” said DeGennaro. “In order to find new solutions to prevent mosquito bites, we need to focus on understanding the molecular basis of mosquito behavior.”
In the future, the researchers hope to gain a detailed view of the Ir8a pathway. They’ll begin chemical screens, using the identified genes to lead them to potentially new mosquito attractants and repellents.