Next-Gen Insect Repellents Could Combat Mosquito-Borne Diseases

Photo credit: Anest/Shutterstock.com

Because of the challenges of synthesizing sesquiterpenoids, Coats’ team designed their repellents using smaller, less complex, easily obtainable molecules — monoterpenoids and phenylpropanoid alcohols with known, short-term repellent activities against insects. By modifying these compounds chemically, they produced new potential repellents with higher molecular weights, making them less volatile and longer-lasting. Klimavicz has synthesized more than 300 compounds, the most effective of which are α-terpinyl isovalerate (a natural compound), citronellyl cyclobutanecarboxylate and citronellyl 3,3-difluorocyclobutanecarboxylate.

To determine the compounds’ effectiveness as repellents against mosquitoes, Corona tests them in a tubular chamber developed in the Coats laboratory. The chamber has filter papers at either end. One filter paper has nothing on it; the other has the synthesized repellent applied. Then mosquitoes — raised in the Iowa State University medical entomology lab — are introduced into the chamber. Corona uses time-lapse photography and in-person monitoring over 2.5 hours to document whether the mosquitoes migrate away from the candidate repellents. The researchers are currently exploring computer tracking of mosquitoes using video footage to gain a better understanding of mosquito repellency and behavior when exposed to these compounds.

With this method, the researchers tested the repellents with Culex pipiens, the northern house mosquito, which is most closely linked to West Nile transmission in the Midwestern U.S.; Aedes aegypti, the yellow fever mosquito which is also known to transmit the Zika and dengue viruses; and Anopheles gambiae, which transmits malaria.

“We think the mechanism of our terpene-based repellents, which try to mimic what nature does, is different from that of the pyrethroids,” which many mosquito species have become resistant to, Coats says. “We believe these ‘next-gen’ spatial repellents are new tools that could provide additional protection against mosquitoes in treated yards, parks, campgrounds, horse stables and livestock facilities. Our next step is to understand more precisely how the repellents biologically affect the mosquitoes.”

The researchers acknowledge support from the U.S. Department of Defense(Deployed War Fighter Protection Program). The industry partner on the grant is ISCA Technologies, which will be testing the efficacy of the repellents in the tropics using their proprietary slow-release technology.The researchers presented their results at the 256th National Meeting & Exposition of the American Chemical Society (ACS). ACS, the world’s largest scientific society, is holding the meeting here through Thursday. It features more than 10,000 presentations on a wide range of science topics.

Contacts and sources:
Katie Cottingham, Ph.D.
The American Chemical Society