Sweetgrass, Hierochloe odorata, has been known to repel mosquitoes for centuries. Native Americans first used the plant as an insect repellent. The chemicals that produce the insect repelling effect in sweetgrass have never been identified. Dr. Charles Cantrell and his team at the U. S. Department of Agriculture and colleagues from the University of Guelph and the University of Mississippi found the chemicals that make mosquitoes avoid sweetgrass. The discovery and the method were presented at the annual meeting of the American Chemical Society.
The chemists used steam distillation to separate the organic oils in sweetgrass into 12 different fractions. The fractions were tested to determine what component repelled mosquitoes. The researchers found phytol and coumarin. Coumarin is used in many commercially available mosquito repellents. Phytol has previously been reported as having mosquito repellent properties.
The researchers compared mosquito aversion to the extracts from sweetgrass to DEET (N,N-diethyl-m-toluamide) and found an equivalent if not superior repellent action from sweetgrass extracts. Sweetgrass was used by the majority of Native American groups across the United States and Canada. The plant provided fibers for making baskets and the coumarin was used as a meditative state inducer in many rituals.
The researchers acknowledge that they did not find anything new in sweetgrass that repels mosquitoes. The plant extract could be used as a viably commercial insect repellent that has no known detrimental effects based on the centuries of use by a huge population of Native Americans. The researchers also acknowledge that verifying folk medicine was one of their goals in this project.
