A Granddad’s Advice May Help Thwart Mosquitoes

Regional wisdom passed on long ago to a boy who grew up to be an Agricultural Research Service (ARS) scientist could lead to the next breakthrough against mosquitoes.

The scientist, Charles T. Bryson, was told by his grandfather John Rives Crumpton that fresh, crushed leaves of American beautyberry, Callicarpa americana, helped keep biting insects away from draft animals such as horses and mules.

According to Bryson, a botanist in ARS’ Southern Weed Science Research Unit at Stoneville, Miss., it was known among folks in northeastern Mississippi during the early 20th century that placing the crushed leaves under an animal’s harness would mash out a repellant oil. Eventually, some people there started mashing the leaves and rubbing the residue on their own skins.

Bryson later shared this knowledge with colleagues in ARS' Natural Products Utilization Research Unit at Oxford, Miss, where chemist Charles Cantrell studied the American beautyberry to see what it is about it that mosquitoes don't like.

Cantrell, working with entomologist Jerome Klun of ARS’ Chemicals Affecting Insect Behavior Research Unit in Beltsville, Md., and Oxford plant physiologist Stephen Duke, isolated several insect-repelling compounds from the plant.

Among these was callicarpenal, which may represent ARS’ next important anti-mosquito compound. ARS recently developed SS220, a repellent that’s just as effective as DEET, the world’s most-used insect repellent. DEET was developed by ARS and the U.S. Army decades ago.

According to Cantrell, isolated callicarpenal was as effective in laboratory tests as SS220 in preventing mosquito bites. Those tests were conducted by Klun against the mosquito species Aedes aegypti, which is best known as the yellow-fever mosquito, and Anopheles stephensi, which spreads malaria in Asia.

Cantrell said that a provisional patent application has been submitted for callicarpenal, and that toxicity trials will precede any testing on humans.