Forestry scientists are working to find out why a devastating tree predator from the B.C. Interior and Alberta is relatively harmless on the South Island.
The Western spruce budworm is capable of great defoliation and has a lengthy criminal record that should make Douglas fir trees itch uncomfortably in their presence.
“One thing we are looking at is why the budworm, which loves Douglas fir trees, is relatively dormant in our climate,” said forestry centre research scientist Brian Van Hezewijk.
“We know they were quite prominent here in the early part of the century.”
The budworm is on record for killing large swaths of canopy in 1909 and 1929 from Sooke to Saanich.
But its random patterns of attack, especially in the South Island where it was once active, has Pacific Forestry Centre researchers looking for a logical answer.
“It’s normal for it to have a bumper season every 30 to 40 years, but we’ve had nothing here since 1929,” Van Hezewijk said. “Nature has figured out a solution to this problem and we’re trying to find that out.”
A native species, the Western spruce budworm is a natural defoliator of trees and is healthy in Merritt, Lilloet and the Cariboo and Okanagan regions.
In Alberta, the tiny worms took down 36,771 hectares in 2006 and 142,832 hectares in 2007. Across B.C., the budworm has ruined approximately 1,598,500 hectares of trees between 1916 to 2002.
There are likely a few contributors to the neutralized bugs, but one leading theory and area of study is the effect of earwigs on the worm population.
An invasive species, earwigs came to the West Coast around 1919, Van Hezewijk believes.
On Vancouver Island, earwigs are prolific predators of budworm larva.
“Earwigs do reside in the interior, but perhaps it’s too cold or dry for them, we’re not sure,” he said.
Another predator that’s happy to lunch on the Western spruce larva is the parasitic wasp, which is also used to prey on gypsy moth eggs in the B.C. Interior.
In the meantime, the province has a regular spraying program that it will likely continue to limit the spread of the Western spruce budworm in affected areas each summer.