Sweetgrass Fights Mosquitoes As Well as DEET

Sweetgrass fights mosquitoes as well as DEET

Long ago, Native North Americans didn’t have insect and mosquito spray to ward off these pests, but they did have a natural remedy called sweetgrass. Now scientists say they have identified the active substances in this Native American answer to mosquito repellent.

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Sweetgrass (Hierochloe odorata) is a fragrant herb that is native to North America and Eurasia. You may also know it as holy grass, vanilla grass, or Mary’s grass.

At the recent 250th National Meeting & Exposition of the American Chemical Society, a team of researchers presented their findings regarding this traditional remedy for warding off mosquitoes and other biting insects. Charles Cantrell, PhD, and his colleagues at the US Department of Agriculture, along with investigators at the University of Mississippi and the University of Guelph conducted the study.

Sweetgrass mosquito study
The study involved two parts. First the team used a common process called steam distillation to extract the essential oil from sweetgrass samples. They evaluated the volatile chemicals in the essential oil to identify which ingredients were responsible for deterring mosquitoes from biting.

The scientists filled vials with a solution that looked like human blood and covered the openings with a thin membrane. Four different solutions were used to coat the membranes: sweetgrass oil, sweetgrass extract not obtained using steam distillation, DEET (N,N-diethyl-m-toluamide, a commonly used chemical mosquito repellent), or ethanol solvent (control).

When the mosquitoes were let loose, the investigators counted how many of the insects tried to bite each of the different membranes. The steam distilled sweetgrass oil and DEET got the fewest number of mosquito bites.

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Next, the team wanted to know which ingredients in sweetgrass are responsible for the mosquito-repelling effect. After purifying the oil into fractions and evaluating them with nuclear magnetic resonance spectroscopy and mass spectrometry, they named coumarin and phytol as the responsible chemicals.

Both coumarin and phytol are known to have mosquito-repelling properties, and the former is found in some mosquito-fighting products on the market. Therefore, while this study did not uncover any new weapons in the fight against mosquito bites, Cantrell noted that “now we understand that there’s a real scientific basis to this folklore” concerning the use of sweetgrass.

DEET is a toxin that works like a paralyzing nerve gas and has been shown to block the activity of an enzyme that is critical for proper functioning of the central nervous system. The Environmental Protection Agency (EPA), however, argues that DEET is safe when used as recommended.

Given that sweetgrass oil was found to be as effective as DEET, the study may also prompt more individuals to consider using this safer, natural method. In the meantime, Cantrell pointed out that more research is necessary since “We don’t know yet what the duration of repellency is. It may work well in our bioassay for three minutes, but how does it work for three hours?”

Also Read Summer Pests Fun Facts

Sources
American Chemical Society meeting, presented 2015 August 18
BBC News. Sweet-smelling secrets of mosquito-repellent grass

Image: "Sweet Grass" by Kodemizer at the English language Wikipedia. Licensed under CC BY-SA 3.0 via Commons

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