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Plan beats back bark beetle

Number of affected Douglas fir trees crashes by 90 per cent

by Laura Walz Officials from BC’s ministry of forests, lands and natural resource operations have successfully quelled a tiny insect that could have a devastating impact on the Sunshine Coast Forest District. But the war on the bark beetle, a cousin of the mountain pine beetle that attacks Douglas fir trees, isn’t over.

Forest district officials first detected the Douglas fir beetle outbreak in 2008. They believe populations increased due to wind storms in 2006 and 2007, which resulted in an unusually high volume of wind-thrown trees, coupled with consecutive dry summers.

In 2010, an assessment determined that the district was experiencing a higher level endemic outbreak. Forest officials and industry representatives responded by developing a strategy to reduce the beetle population. The plan included public education, district wide placement of trap trees and using funnel traps with pheromones.

Martin Plewak, the ministry’s forest health coordinator in the district, said that as a result of the strategy, the Sunshine Coast is back to experiencing normal and expected population levels, compared to 2010’s endemic levels. “Based on our detailed flights of 2010 versus 2011, I could say that the beetle population of affected Douglas fir trees has crashed by 90 per cent,” he said. “During our 2011 detailed flights, we really struggled to find any affected trees and I safely say that throughout my flight, I only counted approximately 200 to 250 affected individual trees between here and Sechelt.”

In 2010, officials saw around 800 individual pockets in areas that are considered high risk to further spread the outbreak, Plewak said. Each pocket contained anywhere from five to 25 affected trees.

“We don’t exactly know why we had such a dramatic drop in the populations and we can only speculate why,” Plewak said. “Generally these sorts of things tend to linger for about three years and we experience more gradual population declines, even with the best of mitigation effort. Regardless, I think it’s safe to say that we are back to normal and we will continue to monitor the situation for future outbreaks.”

Favourable weather last summer helped with reducing the beetle’s population, Plewak said. “Our temperatures weren’t very high and also the temperatures were fickle,” he said. “The Douglas fir beetle doesn’t actually do very well in our climate.”

Ministry officials are continuing the trap tree, funnel trap and education programs this year.

Adult beetles, which are about the size of a grain of rice, fly and attack trees in spring and early summer. The female beetle burrows under the bark, releasing a chemical, called a pheromone, to attract males. One beetle will attack, signal it’s a suitable host, then a mass attack follows.

The burrowing adult beetles bring with them a fungus that clogs the conductive tissue of the tree, helping to overcome tree resistance. After mating, the female tunnels upward and lays eggs in the long galleries, which are constructed parallel to the grain of the inner bark. The small white eggs hatch in about two weeks and the second life stage, the larvae, emerge to feed on the tree’s inner bark. This, combined with the growth of the fungus, kills the tree.

Foliage of killed trees turns from green to pale yellow-green to red by the spring of the year following the attack. Red needles may remain on the tree for up to two years after an attack and aerial spotting of these “redtops” helps to determine the extent of an outbreak.

The ministry advises the public to leave trap trees in the forest alone.