Just before the Inks Lake turnoff south of Kamloops, a reddish-brown blotch of trees is visible in the hills. It is the result of defoliation from a certain type of moth larvae, which eats coniferous tree needles.
That moth — the Western hemlock looper — is more prevalent this year in British Columbia, including in the Kamloops and the Thompson-Okanagan area, resulting in patches like the one visible near Inks Lake.
Residents in all parts of Kamloops have likely noticed more moths than usual this year.
But this year isn’t the concern. The moth is expected to procreate to levels deemed an “outbreak” by next summer.
“This summer was their building year, so these moths that you’re seeing, they’re all mating and laying eggs,” Ministry of Forests regional forest entomologist Lorraine Maclauchlan told KTW.
“If you do the math, every pair of moths will produce a lot of larva or offspring. So, next summer, we anticipate that we’ll see a lot more feeding on the trees, that reddy-brown stripping. We’ll probably see some tree mortality, as well.”
Looper moth outbreaks are normal and occur about every 10 years. What’s unusual, however, is the targeted tree. Outbreaks typically occur in hemlock trees, found more commonly in the back country, but surveying suggests an outbreak amongst Douglas fir, which are prevalent around the city in lower elevations, in yards and predominantly in recreational areas.
“They typically go into outbreak mode in hemlock [trees], but we do occasionally have outbreak modes in Douglas fir and we’ve had them around Kamloops,” Maclauchlan, said. “But it seems this one, judging by all the moths, it’s quite extensive and can be quite severe next summer.”
The province is concerned about impact of the outbreak on Douglas fir. Maclauchlan said it can have a local impact, particularly in the forest, where there is higher tree concentration. Homeowners should not be overly concerned, but are advised to watch their trees for damage around June and July of next year, when larvae hatch and begin to eat the needles through early August. Damage would potentially be seen in July.
“Just keep a lookout,” Maclauchlan said.
She said homeowners can spray the larvae, which are, essentially caterpillars, with a power hose when they are eating the tree needles. Homeowners can also call a professional at a garden store for advice.
Maclauchlan and her staff have been surveying and discovered the moths in Kamloops, Heffley Creek, Inks Lake, Cache Creek, Salmon Arm, the Shuswap area and Okanagan. Forestry staff are looking at key areas where moths lay their eggs, typically on lichen hanging from trees or at the base of a stand. The province is considering treatment with biological insecticide.
“We don’t want this insect to kill our trees,” Maclauchlan said. “Even if it’s a few hundred or thousand hectares, it does impact our timber supply, the health of the forest and everything else. We’re just in that evaluation phase right now.”
Maclauchlan said the reasons for an outbreak in Douglas fir are related to weather — drought-like conditions in recent years may have impacted the trees to the point where they are stressed and more susceptible to being eaten by the larvae — and a phenomenon she dubbed “erupted insect,” wherein an insect grows its population very quickly.
“Explosive,” Maclauchlan said. “But they don’t usually last long in that high, severe outbreak mode. They only last usually a couple of years and then they crash just as quickly.”