http://www.ens-newswire.com/ens/jul2004/2004-07-16-04.asp

Cinnamon Oil Kills Mosquitoes Better Than DEET

TAIPEI, Taiwan, July 16, 2004 (ENS) - Cinnamon oil can be used as an environmentally friendly pesticide, with the ability to kill mosquito larvae more effectively than DEET, new research shows. The cinnamon  oil can be derived from a tree that grows in Taiwan's natural hardwood forests.

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 say scientists at the National University of Taiwan.

Cinnamon leaves (Photo credit unknown) Supported by funding from the Council of Agriculture of the Executive Yuan, a government agency, natural products chemist Peter Shang-Tzen Chang, a professor in the School of Forestry and Resource Conservation at National Taiwan University, led a team of researchers in testing compounds in cinnamon leaf oil.

Chang and his coworkers tested 11 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.

The researchers also expect that cinnamon oil could be a good mosquito repellant, though they have not yet tested it against adult mosquitoes.

The findings are reported in the July 14 edition of the "Journal of Agricultural and Food Chemistry," a peer-reviewed journal of the American Chemical Society.

Mosquitoes carry deadly agents such as malaria, yellow fever, dengue,  and West Nile virus. While conventional pesticides are often effective in controlling mosquito larvae before they hatch, repeated use of these pesticides has raised serious environmental and health concerns.

Aedes aegyti feeding. This mosquito is one of the most important vectors of arbovirus infections, especially dengue and yellow fever, throughout the tropics. (Photo courtesy Wellcome Trust) DEET is a chemical (N,N-diethyl-meta-toluamide) used as the active ingredient in many insect repellent products. First developed by the U.S. Army in 1946, it is now widely used around the world, but may have toxic effects.

"Some persons who used products containing a high concentration such as 50 or 75 percent of DEET or who were exposed to excessive amounts of DEET experienced rashes, blisters, and skin and mucous membrane irritation. In a few cases of overdose and misuse, brain effects (encephalopathy) and seizures occurred in children," says the U.S. Agency for Toxic Substances and Disease Registry.

A recent study by Duke University pharmacologist Mohamed Abou-Donia details a list of neurological harms caused by DEET and other conventional insecticides, from memory loss to tremors to slurred speech. The study also found DEET caused brain cell death and severe behavioral changes in rats.

"These problems have highlighted the need for new strategies for mosquito larval control," says Chang, adding that scientists are increasingly turning to more benign natural chemicals to ward off mosquitoes and other pests.

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.

By comparison, the LC50 of DEET - a popular pesticide and mosquito repellant - is more than 50 ppm.

Mixed deciduous and broad-leaved evergreen forest in Taiwan. (Photo by David E. Boufford, Arnold Arboretum of Harvard University)Bark oil from the Cinnamomum cassia tree is the most common source of cinnamaldehyde, but the tree used in this study, indigenous cinnamon, Cinnamomum osmophloeum, is 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 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 also should prove 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.

Other common essential oils, such as catnip, have shown promise in  fighting off mosquitoes, but Chang says that this is the first time  researchers have demonstrated cinnamon's potential as a safe and  effective pesticide.

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