Scientists research plant-based insect repellent

What do the US Department of Agriculture and the Department of Defense have in common? Besides being government departments, both want to improve technologies for killing pathogen-transmitting insects.

Mosquitoes, sand flies, ticks, and other biting bugs can cause some of the most devastating diseases like malaria, dengue fever, and yellow fever. These arthropods pose a particular problem not only for native populations, but also for military troops that are located where these illnesses are endemic.

To combat the issue, the Deployed War-Fighter Protection (DWFP) research program was implemented to prevent and defend against insect attacks on troops. USDA receives $3 million from Congress each year to develop public-health insecticides, improve personal protection for troops, and devise improved application technologies to kill insects.

USDA scientists can be credited with the discovery of DEET, which remains the primary defense for troops against biting insects. "DEET is still the best topical repellent we’ve got," says U.S. Air Force Lieutenant Colonel Douglas Burkett, research liaison officer with the Armed Forces Pest Management Board (AFPMB). "It has a long safety track record, but some soldiers don't like the odor and feel, and they prefer to have other options."

So scientists are looking for more natural, plant-derived compounds that will have the same abilities to deter insects.

Researchers are currently exploring compounds from plants such as the American beautyberry after a farmer started using the plant to keep pests away from his livestock in 1930. Scientists say the compound callicarpenal, which is found in the plant has significant repellency against mosquitoes and ticks.

Following up on a practice in Africa and India who burn Jatropha curcas seed oil in lamps to keep insects away, researchers have also identified which of the oil's components are responsible for mosquito repellency.

To further test the compounds, smoke was extracted from burning J. curcas oil and analyzed. Fatty acids and triglycerides were found and were determined to be effective at preventing mosquitoes from biting.

"Fatty acids are well known to have insect repellency," says chemist Charles Cantrell. "We identified the triglycerides as also having repellent activity, the first such report, to my knowledge."

Another possible source of repellents is breadfruit, which contains compounds similar to those in Jatropha sp. Cantrell hopes to combine the two sources into a more effective product.

Finding natural sources of insect repellents will not only be beneficial to our troops but will be useful to those in developing countries that can obtain these plant materials from their own backyards.