As mountain pine beetles ravage pine forests across the West, leaving in their wake stands of devastated trees bearing the telltale signs of "pitch tubes" and brown or rusty orange needles, botanists are re-discovering a remedy that may rescue these trees.
Mountain pine beetle infestation is the direct result of climate change, according to one author, who explains that - in Colorado, as elsewhere across the West - winter temperatures no longer drop low enough to kill the beetles or their eggs. As an example, she cites daytime Denver temperatures on February 6 as hovering in the mid-60s, with February averages in the high 40s. Winter snowfall, so far, is also at a record low, or one-tenth of an inch in February - a record not seen since 1882. On March 2 and 3, meteorologists recorded more record temperatures of 74 and 75 degrees respectively in Colorado's mile-high capital.
However, according to research released in February, 2009 by the National Forest Service's Pacific Southwest Research Station, a pheromone used in herbal tea may curtail the mountain pine beetle's ravages.
Called verbenone, and occurring naturally in the herb rosemary and the husks of walnuts, a special, flaked formulation - sprinkled over lodgepole pine forests - appears to cut infestations by two-thirds.
Verbenone is also found in a pheromone these beetles excrete to inform other beetles that a tree is supporting its maximum population. This verbenone signaling phenomenon, reported by James W. Hanson in his 2007 book, Chemistry in the Garden (published by the Royal Society of Chemistry), has been known to horticultural scientists for at least a decade.
Using it was another matter. According to Forest Service entomologist Nancy Gillette, the lead author on the Forest Service study (which appeared in the February issue of Forest Ecology and Management), the problem was finding a cost-effective yet efficient way to disperse the verbenone. The use of flaking was the first step, allowing the verbenone to "stick" (unlike liquid spraying). The second step is aerial dispersal via helicopter.
Costing about $110 an acre - a bargain compared to $1,000 per acre for thinning - the method was shown to effectively reduce insect attack rates three-fold, compared to areas where it was not applied. And while thinning is still the preferred method to reduce a forest's susceptibility, the flakes offer salvation to dense, old growth forests essential to wildlife habitat or essential to recreation.
The study, conducted primarily in California and Idaho, shows verbenone flakes superior to insecticides because insecticides also kill beneficial insects. Gillette foresees the technique being especially useful in visitor areas in national parks.
The director of Forest Service Employees for Environmental Ethics, Any Stahl, notes that beetles only attack mature trees already debilitated by environmental stresses like lack of moisture - a natural cycle which Stahl says is designed to replace lodgepole pines every 100 years. Unfortunately, climate change is not natural.
Mountain pine beetles, Dendroctonus ponderosae Hopkins, are native to North America and range from the Pacific Ocean to the Black Hills of South Dakota, as far north as northern British Columbia and as far south as the northwestern coast of Mexico. Members of a larger genus called bark beetles, the Mountain pine beetle completes most of its life cycle under the bark, emerging only as an adult to infest new trees.
Its prey includes lodgepole, ponderosa, sugar, and western white pine, though most infestations occur in stands of mature, well-spaced lodgepole pine or dense stands of ponderosa. Infestations kill millions of acres of trees, allowing such inferior species as subalpine fir or aspen to take over, and alter the makeup of indigenous wildlife by changing food, shelter and water parameters. Stands of dead and dying trees promote the spread of wildfires, further impacting wildlife by altering the ecology to grasslands. In Colorado alone, 2 million acres of forests have been decimated. Currently, the largest outbreak of Mountain pine beetle infestation is happening in British Columbia, which has seen 30 million acres infested (and 22 million destroyed) in the last decade.
Using verbenone is known as a "push-pull" strategy. These strategies rely on the integration of natural stimuli to manipulate the behavior of insect pests by moving them from valuable locations (push) to ones less integral to forest health and wildlife survival (pull). This strategy, highly preferable to harmful insecticides, has been used to manage many kinds of pests, in everything from forest management to agriculture, and including animal husbandry. Hopefully, its use in conjunction with verbenone will rescue enough of Western forests to insure these sometimes ancient stands of trees are not lost forever.