GRANTS PASS, Ore. – Would a dose of herbal tea slow the march of beetles killing millions of acres of pine trees across the West?
But instead of brewing up a cup, U.S. Forest Service scientists found that sprinkling tiny flakes containing the pheromone verbenone over lodgepole pine forests cut the number of trees attacked by bark beetles by one third.
Verbenone is found in rosemary and walnut husks and approved for use in herbal teas.
It also resembles a pheromone the beetles give off to tell one another that their tree is getting crowded, and it would be better to pick another one.
Forest Service entomologist Nancy Gillette, lead author on the study, said scientists have known for a decade that when bark beetles smell verbenone they tend to disperse.
The problem has been to find a cheap and effective way of distributing it, and Gillette says sprinkling flakes from helicopters is the best way yet.
It costs about $110 an acre, compared to $1,000 an acre or more for thinning. Insecticides are also expensive, and kill lots of beneficial insects.
Gillette said she could foresee the technique being used around campgrounds, visitor centers and ski resorts, where it would be desirable to save trees.
Andy Stahl, director of Forest Service Employees for Environmental Ethics, said it would be fruitless to use across large areas, because the beetles infest only mature trees weakened by factors such as drought, and the infestations are part of a natural cycle that replaces lodgepole pine forests every 100 years.
“All you are doing is saving (commercially) worthless trees in order that they burn next year,” he said.
The beetles have killed millions of acres of pine forests, touching every state in the West.
Warming temperatures have meant winters no longer get cold enough to routinely kill the insects, so more of them survive to bore into trees, which fight them off by oozing sap.
In Colorado alone, a survey found nearly 2 million acres of forests killed by beetles. The biggest outbreak in North America is in British Columbia, where 23 million acres have been killed.