Millions of pine trees are dying in western North America, all due to a beetle about the size of a grain of rice. The mountain pine beetle uses pheromones, a chemical that attracts other mountain pine beetles, to successfully overwhelm a tree's defenses and kill it. Dr. Ken Raffa at the University of Wisconsin-Madison and Dr. Gary Blomquist at the University of Nevada, Reno are studying the beetle and how climate change is impacting its spread. Changing Planet is produced in partnership with the National Science Foundation.
Bark Beetle Outbreaks
ANNE THOMPSON, reporting:
From northwest Canada, to Colorado, Nevada, and other parts of the United States, the beautiful natural landscape of the West looks in some areas like a killing field. Hundreds of millions of ponderosa, lodgepole and other pine trees, dead, the worst outbreak of its kind in recorded history. And it's all due to an insect about the size of a grain of rice, the mountain pine beetle.
Dr. KEN RAFFA (Entomologist, University of Wisconsin-Madison): It's killed about forty-seven million hectares. That's an unprecedented event.
THOMPSON: Dr. Ken Raffa is a professor of Forest Entomology at the University of Wisconsin-Madison whose research is partly funded by the National Science Foundation. He studies the mountain pine beetle, a species of bark beetle. The beetle is not an invasive species, it's native to North America and has always been an important part of the health and life cycle of the forest ecosystem. But this current outbreak is ten times greater than any other previous outbreak on record. And Raffa and other scientists believe the real culprit is climate change.
RAFFA: Warming temperatures benefit the beetle because it over-winters in higher numbers, it reproduces more quickly, maybe one generation per year rather than one generation per two years in some areas.
THOMPSON: In addition to a warmer climate increasing the beetle population, the beetle's unique method of attacking trees can annihilate an entire forest. It begins when a single female is looking for a home to start her family.
RAFFA: The female lands on the tree. And she tastes the bark and decides whether or not to enter, and she's gaining chemical information during that period.
THOMPSON: Once the beetle begins to burrow, the pine tree quickly reacts by throwing an arsenal of natural defenses at it.
RAFFA: When trees are attacked they respond viciously. They start producing insecticides that kill the beetle. They produce compounds that kill the beetle's eggs.
THOMPSON: But some beetles can still make it through. That's when they use their own secret weapon.
RAFFA: She starts boring her way through. And as she is doing that, she produces a pheromone.
THOMPSON: A pheromone is a chemical produced by certain animals that can attract, alarm, or communicate with other members of the same species. Many insects, like bees, ants, and also the mountain pine beetle, use pheromones to survive and prosper.
Dr. GARY BLOMQUIST (Entomologist, University of Nevada, Reno): A pheromone is a chemical produced by a beetle. It's a mixture of two or three components, terpenoid components, that are produced primarily in the mid-gut of beetles. It's excreted in their frass, and then it's the chemical signal that other beetles cue in on, and then can attack the same tree.
THOMPSON: Dr. Gary Blomquist at the University of Nevada-Reno, another researcher funded by the National Science Foundation, studies beetle pheromones. He says the mountain pine beetles use their pheromones as an aggregator, a chemical signal telling hundreds of beetles to converge on a single tree in a coordinated attack.
BLOMQUIST: If a single beetle attacks the tree, the tree always wins. It's when you get the mass attack that results in the death of the tree.
THOMPSON: Within a period of about just three to four days, the beetles exhaust the defenses of the mighty tree and it dies. Just under the bark, the beetles' eggs hatch and larvae emerge. When they're grown, they leave the tree and attack another tree.
BLOMQUIST: This is a tree that was infested last summer, probably July or August. And you can see it's been heavily attacked. What you see here, each of these pitch tubes is where a male and female beetle have entered the tree. The tree has tried to literally pitch them out with oleoresin.
THOMPSON: Blomquist believes that one possible solution to save North America's forests may rely on unlocking the secrets of pheromone production in the hope of preventing devastating outbreaks in the future.
BLOMQUIST: Our goal is to understand the chemical reactions, the enzymes and the molecular biology that goes in producing pheromones, such that the more we understand it, the better our chances of coming up with something that would prevent pheromone production.
THOMPSON: Many of the answers to controlling the beetles' pheromones, Blomquist says, can be found in the genes that produce the pheromones. He and his team have been focusing much of their research on identifying the sequences of those genes.
BLOMQUIST: We've got eight or ten of the genes characterized. And we have a much better picture of how the pheromone is made which is necessary for the further work for control.
THOMPSON: As the pheromones help the beetles overwhelm the trees through sheer numbers, the warmer and drier climate also plays a continuing role in the devastation.
RAFFA: What we’re seeing now is much more frequent outbreaks, larger outbreaks. Climate change is what has driven spread.
THOMPSON: Until solutions can be found, the landscape of the American West could lose many of its most enduring symbols, the mighty and majestic pine trees.
COLLEGE PARK, Md. — When J.D. Rinehart noticed brownish, depressed areas on his orchards’ apples and peaches about five years ago, he thought the fruit was low in calcium. But spraying the fruit with calcium didn’t help.
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