Sweetgrass Chemicals That Keep Mosquitoes At Bay Revealed

Researchers have successfully identified the chemical reason for why sweetgrass keeps pesky bugs at bay. They plan to present their results this Thursday at the 250th National Meeting & Exposition of the American Chemical Society (ACS).

Sweetgrass Chemicals That Keep Mosquitoes At Bay Revealed - Clapway

Sweetgrass has been used for years to ward off insects

Native to North America, sweetgrass (Hierochloe odorata) is a folk-remedy for biting insects, mainly mosquitoes. It gives off a sweet odor and acts as an insect-repellant at once. In addition to being bothersome, insect bites could cause serious, even life-threatening damage. Insects like mosquitoes act as vectors for diseases like malaria and dengue fever. Scientists have long believed that the components that give it the sweet smell could actually be the ones repelling insects.

Chemicals were extracted from sweetgrass using steam

Similar to a process used in making perfumes from flowers, researchers used a method called steam distillation to extract the chemicals in grass that give off the odor. This process involves passing steam though the plant material, and then cooling the temperature to help condense it into a liquid. The liquid then separates into water and oil; the oily fraction is retained as it contains the volatile ingredients of interest. The scientists then tested whether the sweetgrass oil actually worked. They filled a vial with a red colored substance that looks like blood to bait the mosquitoes. The vial was then covered with a thin membrane and laced with either the sweetgrass oil, other extracts of sweetgrass obtained without steam distillation, the gold standard of insect repellants called N, N-diethyl-m-toluamide (DEET) or the solvent alcohol as the negative control. The mosquitoes could either take a bite at the membrane or not. They were then squished onto paper in order to see if they drew ‘blood.’ When counted, they found that the membrane laced with sweetgrass oil had the least bites, matching that of the gold standard.

Chemicals in sweetgrass identified

Upon finding that the sweetgrass oil repelled mosquitoes, scientists wanted to find out what chemicals exactly caused this effect. They separated the oil into 12 sub-fractions, and zeroed in on the components of three of the most effective. Using analytical techniques like Nuclear Magnetic Resonance (NMR) and Mass Spectrometry (MS), they identified the active components to be coumarin and phytol. Coumarin is an ingredient found in insect-repellant and other skin products. Thanks to the study, we now know the scientific basis for this folk-remedy.


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