Tackling mosquito-borne diseases with next-generation insect repellents
At the 256th ACS National Meeting and Exhibition (19–23 August 2018), Iowa State University researchers report a new class of insect repellents that could help combat mosquito-borne diseases.
Research carried out at Iowa State University (IA, USA) suggests a new class of mosquito repellents based on naturally occurring compounds could be effective at repelling mosquitos with fewer environmental side effects. The findings, presented at the 256th ACS National Meeting and Exhibition (19–23 August 2018; MA, USA), report compounds that are variations of natural products, designed to be long-lasting and highly repellent.
Mosquito-borne diseases, including West Nile virus, malaria, Zika and dengue fever, affect approximately 700 million individuals each year and result in over 1 million deaths. Furthermore, many species of mosquito are thought to be resistant to popular pyrethroid-based insecticides, so there is a great need for new and effective repellents.
“Our new repellents are based on how nature already works,” remarked corresponding author Joel Coats. “For example, citronella, a spatial repellent that comes from lemongrass, contains naturally occurring essential oils that have been used for centuries to repel mosquitoes. But citronella doesn't last long and blows away easily. Our new, next-generation spatial repellents are variations of natural products that are longer-lasting and have greater repellency.”
The researchers from Coats’ lab at Iowa State University synthesized and tested hundreds of compounds to find those effective against mosquitos. It was previously known that sesquiterpenoids, which occur naturally in many plants, are effective insect repellents; however, these molecules are very large, making them hard to both isolate and synthesize and purify in the lab.
The team designed repellents using monoterpenoids and phenylpropanoid alcohols. These are smaller, less complex molecules that are more easily obtainable than sesquiterpenoids and are known to have short-term repellent activities against insects.
The compounds were chemically modified to produce novel potential repellents with higher molecular weights, which should make them less volatile and last for longer. More than 300 compounds were synthesized, and the most effective were found to be α-terpinyl isovalerate, citronellyl cyclobutanecarboxylate and citronellyl 3,3-difluorocyclobutanecarboxylate.
The effectiveness of each repellent was tested against Culex pipiens, Aedes aegypti and Anopheles gambiae mosquitos; species of mosquito known to transmit West Nile virus, Zika and dengue virus, and malaria, respectively. Mosquitos were introduced to a tubular chamber, containing filter paper at each end. One filter paper was blank, while the other had the novel repellent applied. The mosquitos were monitored for 2.5 hours post-introduction to determine if they migrate away from the candidate repellent.
“We think the mechanism of our terpene-based repellents, which try to mimic what nature does, is different from that of the pyrethroids,” commented Coats.
“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.”
Source: Coats JR. Next-gen biorational spatial repellents. ACS National Meeting and Exposition 2018 (19–23 August; MA, USA)