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
"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
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