How do you control mountain pine beetles, which are killing vast stretches of lodgepole pine forests in the West and Canada? Invite the bugs to tea.
When pine beetles first invade a stand, they release a chemical that attracts males and females so they can mount a massive attack on the host trees to overwhelm their defenses. Then, when the infestation is established, they produce a pheromone called verbenone that is also found in herbal tea and a variety of plants, including rosemary and sage.
The substance, which other beetles sense with their antennae, amounts to a "no vacancy" sign, signaling them to stay away and avoid overcrowding. Some research indicates that verbenone may also slow the insects' flight muscles, hindering their spread.
When verbenone flakes were scattered by helicopter across research plots in Northern California and Idaho, the treatment reduced mountain pine beetle attack rates to about a third of that observed in untreated forest plots, according to a paper published in the February issue of Forest Ecology and Management.
Rising temperatures, drought and, in some places, forest overcrowding, are aiding the spread of the beetles, which have killed 23 million acres of forest in British Columbia and left parts of the Rocky Mountains gray with dead trees.
While not that commercially valuable, lodgepole pines are the dominant tree in many higher-elevation areas of the West.
Nancy Gillette, a U.S. Forest Service research entomologist in California who led the study, said verbenone treatments could be used "in special situations," for example, to preserve pine stands around campgrounds or ski resorts or near homes. It is now being applied in a Washington national forest to protect spotted owl habitat.
The treatments last for one season and cost $110 to $300 an acre, depending on how heavy the application. That is less expensive than using insecticides or thinning the forests.
For the research, helicopters dropped plastic flakes embedded with verbenone resin on lodgepole plots northeast of Mt. Shasta in California and in Idaho's Bitterroot Mountains. The flakes were laminated to hinder evaporation, but Gillette said biodegradable materials are now being tested for large-scale field applications.
— Bettina Boxall
Photo: Mountain pine beetle Credit: U.S. Forest Service