Mosquito-borne diseases, such as dengue, malaria and Zika, cause more than 600,000 deaths worldwide per year. Mosquitoes are increasingly becoming resistant to current insecticides, leading to a pressing need for new methods to prevent mosquito bites - and the potential transmission of disease.
New research by an international team, including researchers at the University of Washington, provides insight into how an organic compound common in plant-based mosquito repellents affects mosquitoes. The study, published Feb. 20 in Nature Communications, reveals that Aedes aegypti mosquitoes use a specific sensory receptor to detect and avoid borneol (pronounced "bor-nee-ohl"), an organic compound found in several aromatic plants, including camphor trees, rosemary and other aromatic herbs.
"We were surprised by how sensitive the mosquitoes were to this repellent," said co-author Jeffrey Riffell, a UW professor of biology. "By identifying the odorant receptor, we can now develop and test repellents that are even more effective than borneol, in that they last longer and are more repellent."
The researchers discovered that Aedes aegypti mosquitoes, which are the major carrier of dengue and yellow fever viruses, have a single odor receptor, called OR49, that is highly tuned to detect borneol.
When a mosquito encounters this compound, OR49 activates a specific nerve cell in a mosquito's maxillary palp, one of its primary organs for detecting odors and locating human hosts. That signal then travels from the nerve cell to a distinct region of the mosquito's brain, triggering avoidance behavior.
To test how critical this receptor is, the researchers disabled the Or49 gene. Without OR49, the repellent signal essentially disappeared. The mosquitoes' neurons no longer responded to borneol and the insects were far less likely to avoid it.
Researchers at the UW were instrumental in collecting neural recordings from the mosquito brains to identify how the mosquito olfactory system processes borneol and other similar compounds and repellents.
"Because the repellency through the OR49 receptor is so strong, we might be able to identify other volatile odors that activate the same receptor to 'push' mosquitoes away from people," said co-senior author Jason Pitts, associate professor of biology at Baylor University. "The new compounds might be easier and cheaper to produce, or safer and more acceptable to the human nose than existing repellent formulations."
This research bridges basic neuroscience and public health, offering fresh insight into how tiny sensory signals can have life-saving implications. That is central to the premise of the team's larger research goal: understanding the genetic basis for how Aedes aegypti is attracted to sources of nectar. The team hopes to create a new generation of mosquito attractants that can be used in traps for enhancing mosquito surveillance and control.
"The knowledge gained in these studies will inform similar studies in mosquitoes that transmit malaria, plus other biting insects that continue to exert negative impacts on human flourishing on a global scale," Pitts said.
Carlos Ruiz, a UW postdoctoral scholar in the biology department, is a co-author on this paper. A full list of co-authors is included with the paper. This research was funded by the Israel Science Foundation; the National Institutes of Health; the National Science Foundation; the Bill and Melinda Gates Foundation; the Science and Technology Development Plan Project of Jilin Province, China; and the Ministry of Science & Technology, Israel.
