July 01, 2005
Friday

Massive Alaska yellow-cedar trees contain natural preservatives that repel mosquitoes, kill ticks, and prevent diseases from attacking other trees.

Alaska yellow-cedar has the strongest wood of any in the state, and grows on coastlines from Prince William Sound to northern California. In recent years, yellow-cedar have been dying of causes other than old age on more than 500,000 acres of Southeast Alaska, and scientists aren't yet sure why. Some think it may be warm winters and springs that are limiting snowfall accumulation, exposing shallow root systems to blasts of lethal cold air. As the trees' cause of death is investigated, scientists have come up with an innovative way to utilize the dead trees.

When Alaska yellow-cedars die, they often remain standing for more than a century. Rick Kelsey and Nick Panella are two scientists who are finding uses for the mass of dead trees, beyond lumber and firewood.

Kelsey, who works for the U.S. Forest Service in Corvallis, Oregon, traveled with Paul Hennon of the Forest Service in Juneau to collect heartwood samples from live and dead yellow-cedar trees in Southeast Alaska. From those samples, Kelsey and others looked at 16 compounds within the trees' essential oil. They tested a few of those compounds, nootkatin and carvacrol, in the lab and found they killed spores of Phytophthora ramorum, the fungus that causes sudden oak death. Sudden oak death has killed thousands of oak trees in California.

The anti-fungal compounds in Alaska yellow-cedar persist in the heartwood for up to a quarter-century after the trees die. Kelsey thinks that shavings or chips of Alaska yellow-cedar could prevent the spread of sudden oak death in some areas. He envisions spreading the chips over pathways in recreational areas where hikers and bicyclists pick up the spores that cause sudden oak death and carry them without knowing it. The chipped pathways might kill the spores before the disease can get established in a new area.

Panella is a biologist with the Centers for Disease Control and Prevention's Division of Vector-borne Infectious Diseases, based out of Fort Collins, Colorado. He and his coworkers' search for all-natural pesticides led them to check out the virtues of dead Alaska yellow-cedar. In a lab where his agency raises about 10 different species of mosquitoes for use in experiments, Panella coated the inside of bottles with the essential oils from yellow-cedar heartwood and dropped 25 to 50 mosquitoes into each bottle. He found that the compounds carvacrol, nootkatone, and valencene-13-0L were effective at killing Aedes aegypti mosquitoes, and that the compound nootkatol was a repellant. Both compounds did the job in many cases after being in the bottles for up to six weeks. Aedes aegypti don't occur in Alaska, but the mosquitoes carry dengue and yellow fever in other parts of the world.

Panella and his colleagues have mixed up a repellant from the Alaska yellow-cedar compounds and it has worked for several hours. Yellow-cedar compounds also work against ticks and fleas, Panella said, and have low toxicity to mammals. The researchers have filed patents on their mixtures as repellants and insecticides, and are talking with businesspeople who are interested in developing and selling the final products. Some day in the near future, Alaska's most valuable lumber export may also repel its worst summer pest.

This column is provided as a public service by the Geophysical Institute, University of Alaska Fairbanks, in cooperation
with the UAF research community.
Ned Rozell [nrozell@gi.alaska.edu] is a science writer at the institute.

 

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