Dec. 2, 1997 Who says you can't fool Mother Nature?
It certainly isn't Dezene Huber, a PhD student in Simon Fraser University's department of biological sciences. He's part of a research team investigating the secret scent life of two of British Columbia's most destructive forest insect pests.
His goal? To fool the insects into bypassing vulnerable trees.
For the past two years, Huber has been studying how two species of bark beetle - the Douglas fir beetle and the mountain pine beetle - find the trees they need to survive in a mixed forest environment. The answer is in the air - in natural scents given off by the beetles, and, surprisingly, by the trees themselves.
These two species of bark beetle are tiny, about half a centimetre long, and attack their preferred host trees - Douglas firs and lodgepole pines - by tunnelling under the bark and laying eggs. They eventually girdle and kill the trees, destroying billions of dollars worth of commercial timber in B.C. every year. It's long been known that bark beetles use chemical signals, or pheromones, to attract others of their kind to a suitable host tree. It's also known that they can detect the scent of host trees. But Huber's work reveals that the beetles are doing much more. They're smelling other trees in the forest, too.
Every type of tree, says Huber, releases signature compounds, or 'volatiles,' into the air. And just as we can smell the fragrance of a nearby pine or fir, a bark beetle can sort through the scent bouquet of a mixed forest to find the tree that it wants.
The beetles can't afford to make a mistake. Burrowing into the wrong tree not only wastes time, but the strong defences of non-host trees, such as toxic resin, can kill adult beetles and their young.
"We think that, as a beetle flies through the forest, it smells a non-host tree before it even gets to it, and the message is to keep on going," says Huber, who has hacked down trees such as birch, aspen and maple to extract key volatiles.
"We now know that there are perhaps 20 different compounds that the beetles can detect from non-host trees," he says. "There must be a reason for this, and we think it's because it improves their search efficiency."
Ironically, the bark beetle's superb sense of smell may soon be used against it. Researchers plan to use the non-host scents to disguise trees that the beetles would normally attack.
"In an area where we know bark beetles are present, we'd, say, make a Douglas fir smell like a cottonwood," says Huber. "Instead of attacking the tree, the beetles would fly on by."
Huber is now analysing and testing various non-host compounds to see which, if any, are better beetle deterrents than others. He divides his time between an SFU lab, and the woods near Princeton and Lytton, where there are current bark beetle outbreaks.
"We challenge them to find traps baited with various combinations of scents, so there are a lot of confused little beetles out there," he grins. The results are promising. This past summer, he found that single trees can be protected "quite well" using non-host volatiles, along with other compounds that the beetles avoid.
Huber believes the method has huge potential as a control agent.
"I don't think it'll be the only method used, because there are so many other aspects of bark beetle biology that we can tweak for our own purposes," he says. "But if we can get this developed, I think it's going to be a very important part of a pest manager's portfolio of weapons."
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