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Spruce budworm boom not yet cause for concern, says entomologist

Provincial entomologist says insects natural part of forests and are monitored
MVT Spruce budworm
A western spruce budworm caterpillar. Photo courtesy of Natural Resources Canada

SUNDRE — A forest entomologist for the provincial government understands why residents are worried about a sudden boom of spruce budworms that have been feasting on evergreens.

“I understand people’s concerns, because it is scary, and people see that those trees are losing their needles,” Caroline Whitehouse said on July 7 during an interview.

But the trees are not at immediate risk of death, Whitehouse told The Albertan.

“We know research shows us that it takes multiple years for severe defoliation for spruce budworm to actually put that tree at risk of dying,” she said. “We are not at that stage yet.”

An infestation of the insect, which is a natural part of Alberta's forest ecosystem, would have to endure for several years and cause widespread defoliation before being considered a substantial threat.

So far, however, she said reports are primarily indicating a sudden increase of the bug this season, although Bragg Creek has been experiencing a surge for the past couple of years.

“The word invasive would be incorrect,” she said. “Because it’s actually a native insect to our forests. So, it’s basically present at low levels all the time throughout all of the range of white spruce in Alberta.”

Of course it can still be disconcerting for property owners to see their trees being defoliated, leading people to assume the evergreens won’t regrow their needles and eventually die off, she said.

“I think they equate it with mountain pine beetle, which is really aggressive and kind of acts invasively and kills trees within a year,” she said.

“But this is not the same situation with spruce budworm, as unpleasant as the defoliation might appear to be.”  

Asked whether trees affected by the insect might yet bounce back, she promptly replied, “Absolutely.”

Natural cycle

“The white spruce is really quite resilient to defoliation by spruce budworm because they evolved together. This is a natural cycle in spruce budworm’s life history," she said.

Every so often, a variety of factors can play a role in setting the stage for the bugs’ population to suddenly multiply, she said, calling the spruce budworm an “eruptive species.”

Yet while the population can spontaneously explode, their numbers will tend to subsequently collapse quite quickly, she added.

“It goes through these cycles,” she said.

Generally more of a problem in northern Alberta where the forests have an abundance of white spruce trees with fewer aspen in the mix, she said the bug does not spread as easily when there isn’t a monoculture of older spruce trees.

A mix of not only tree varieties but also different life stages — young, middle age and old trees — also helps to maintain a much healthier forest, she said.

“That is basically the most resilient forest you could find," she said.

In southern Alberta, there hasn’t been any outbreaks that she could recall from her 10 years of past experience with the province. Prior to that, she said there had been large outbreak in the early 2000s that involved using a targetted spray. The insect's numbers collapsed shortly afterward, although other factors such as extreme temperatures and diseases that spread easily among dense populations can also contribute to sudden die-offs, she said.

“A really important regulator of spruce budworm feeding is when the trees burst bud,” she elaborated.

The spruce budworm overwinters as small caterpillars, and essentially lie in wait for the buds to burst, she said.

“If we have a long cool spring, and it takes a long time for the spruce trees’ buds to burst, that’s going to cause some of those larvae that are waiting, to die,” she said.

Conversely, she said an early, hot spring will likely prompt a sooner burst in spruce tree buds, subsequently triggering the insects to wake up from their winter slumber and start feasting.

“Warmer, drier temperatures, definitely support higher populations,” she said, adding there are limits when it comes to extreme hot or cold conditions.

Monitoring efforts ongoing

Whitehouse said monitoring efforts, which include aerial overview surveys, will continue and encourages people not to worry for the time being.  

“We have thresholds and we have a strategy in the province for dealing with spruce budworm because of those historic outbreaks, and so we have a plan and we can provide advice to municipalities and be there to help support them to help them understand what’s going on, and some of the best tactics," she said.

Before determining any management strategies, she said the first step is to properly evaluate and understand what the bug’s population is doing.  

“What is the spatial extent of it, and what is the severity of the defoliation,” she said. “That effort is underway.”

Provincial lands are categorized into green and white areas — the former being forest and public land while the latter represents private property such as agricultural land. And although the forestry department is responsible for green areas, she said “we’re going to expand our surveys this year” to cover portions of white category lands “to provide municipalities and people with some understanding of the damage that’s being observed at higher level.”

Depending on the situation next spring, and whether the population continues to grow significantly, more labour-intensive ground surveys could be conducted. But that step is generally reserved until multiple years of the bug’s sustained spread has been observed, she said.

Damage looks worse than it is

Although the spruce budworm becomes a moth, it’s the caterpillar stage of the insect’s life that causes damage by gorging itself on needles, leaving trees looking “red and ragged and terrible,” she said.

That might motivate some property owners to spray insecticides, even though the trees are not in immediate danger. However, that course of action must be carefully considered, and even the forestry department won’t immediately resort to applying chemicals, she said.

“The benefit has to exceed the cost,” she said.

Broad spectrum insecticides that are more readily available to consumers “kill everything indiscriminately, and it soaks into the ground and then filters into our beautiful water systems,” she said.

“So, people need to be very careful when they’re using that," she said.

There is an alternative spray that is more targetted, using bacteria that attack only larvae of moths and butterflies — which are important pollinators — causing the insects to basically explode from the inside, she said.  

“It’s not very pleasant for the insect. But it is more specific, so it wouldn’t kill a bee or a bird,” she said.

Furthermore, there is a limited window of opportunity when using that spray is even an effective method to control the insect’s spread, she added.

“That time has passed for this year. So, there’s no management options for this year,” she said.

“You also have to spray at a very specific life stage, because not every life stage of that insect is equally susceptible. So, you could spray and have no effect at all, but then kill all these other lovely insects that are beneficial to us."

Despite the damage done, she said people should be able to find some comfort in the fact the larvae are now done feeding and that the level of defoliation at this point has reached its peak for the season.

Timber values not at risk

Over at West Fraser — Sundre Forest Products, general manager Bruce Alexander said he had not heard any alarm bells about the bug, which can create havoc in high numbers, but conceded that did not necessarily mean the insect isn’t spreading.  

However, he added that as the pest can cause problems for the logging sector, the industry would get a heads up if a rampant infestation was spreading out of control.  

In such an event involving a problem unfolding on public lands where industry has forest management agreements with the Alberta government, Alexander said their operation would seek to engage with the province’s forestry department and applicable stakeholders to determine whether they could play a role in managing the insect’s population.

“We know our trees are not at risk. Timber values are not at risk at this point,” said Whitehouse.

Alfred Schmutz, a professional tree pruner with a background in forestry, said he is concerned by the situation in Sundre, which he called something that might well be unprecedented.

“After the mountain pine beetle in some areas has attacked the pines, now we have a pest which attacks the spruce, and I’m very concerned,” said Schmutz.

However, the insect's presence does not appear widespread, as he said he had not seen any of the bugs in the James River area during a recent visit to a quarter section featuring a mix of spruce, pine and poplars.

“There’s not a single moth to be seen in the entire tree stand,” he said.  

Although he had not yet had the chance to extensively observe the trees in Sundre, he added the insects did appear to be “prevalent.”

Compounding the situation, he said, is low subsurface moisture that has already placed the trees under stress.

“In spite of these rains we’ve had, we’re still running way, way below average for moisture,” he said.

Responding to people calling for emergency action to spray with provincial help, he said, “Like with any chemical application, that would have to be used with discretion. Don’t forget, the spray going onto those trees, it has a certain amount of toxicity to humans.”

Resorting to such a course of action would have to be a targetted, last ditch resort, he said,.

“I’m not 100 per cent against (using chemicals), but it should be used very much with discretion,” he said, adding such substances should also be handled only by people qualified in their application.



Simon Ducatel

About the Author: Simon Ducatel

Simon Ducatel is the editor of the Sundre Round Up and a longtime columnist for other publications of Mountain View Publishing.
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