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Cinnamon oil kills mosquitoes
Cinnamon oil shows promise as a great-smelling, environmentally friendly pesticide, with the ability to kill mosquito larvae, according to a new study published in the July 14 issue of the Journal of Agricultural and Food Chemistry, a peer-reviewed journal of the American Chemical Society, the world's largest scientific society.
The researchers also expect that cinnamon oil could be a good mosquito repellant, though they have not yet tested it against adult mosquitoes.
Besides being a summer nuisance, mosquitoes pose some major public health problems, carrying such deadly agents as malaria, yellow fever and West Nile virus. While conventional pesticide application is often effective in controlling mosquito larvae before they hatch, repeated use of these agents has raised serious environmental and health concerns.
"These problems have highlighted the need for new strategies for mosquito larval control," says Peter Shang-Tzen Chang, a professor in the School of Forestry and Resource Conservation at National Taiwan University and lead author of the paper. Scientists are increasingly turning to more benign natural chemicals to ward off mosquitoes and other pests.
Chang and his coworkers tested eleven compounds in cinnamon leaf oil for their ability to kill emerging larvae of the yellow fever mosquito, Aedes aegypti. "Four compounds - cinnamaldehyde, cinnamyl acetate, eugenol and anethole - exhibited the strongest activity against A. aegypti in 24 hours of testing," Chang says.
Larvicidal activity is judged with a measurement called LC50. "The LC50 value is the concentration that kills 50 percent of mosquito larvae in 24 hours," Chang explains. Lower LC50 translates into higher activity, because it takes a lower concentration to kill larvae in the same amount of time. All four compounds had LC50 values of less than 50 parts per million (ppm), with cinnamaldehyde showing the strongest activity at an LC50 of 29 ppm.
Other common essential oils, such as catnip, have shown similar promise in fighting off mosquitoes, but this is the first time researchers have demonstrated cinnamon's potential as a safe and effective pesticide, according to Chang.
Cinnamaldehyde is the main constituent in cinnamon leaf oil and is used worldwide as a food additive and flavoring agent. A formulation using the compound could be sprayed just like a pesticide, but without the potential for adverse health effects - plus the added bonus of a pleasant smell.
Bark oil from the Cinnamomum cassia tree is the most common source of cinnamaldehyde, but the tree used in this study - indigenous cinnamon, or Cinnamomum osmophloeum - has been of interest to researchers because the constituents of its leaf oil are similar to those of C. cassia bark oil. The leaves of C. osmophloeum, which grows in Taiwan's natural hardwood forests, could be a more economical and sustainable source of cinnamon oil than isolating it from bark, Chang says.
Though the team only tested the oil against the yellow fever mosquito, cinnamon oil should prove similarly lethal to the larvae of other mosquito species, the researchers say. In further studies they plan to test cinnamon oil against other types of mosquitoes as well as different commercial pesticides.
"We think that cinnamon oil might also affect adult mosquitoes by acting as a repellant," Chang says. The researchers haven't yet tested this theory, but they plan to find out in the near future.
The Council of Agriculture of the Executive Yuan, a government agency in Taiwan, provided support for this research.
- Jason Gorss