Moths an indicator of budworm infestation in forests

By Mona Mattei

Millions of moths infesting the forests in the Boundary region could threaten key lumber sources for the area.

 

The Western Spruce Budworm has made areas of the Boundary and Okanagan regions home for many years, but a current population explosion could be the largest ever seen in the area, reaching as far as the West Kootenays. Moths in the thousands invading businesses around Grand Forks are the hatched larvae that have been feeding on the host trees for the past several months.

 

While thousands are dying as they fail to find new host trees, Entomologist Art Stock with the Ministry of Forests, Lands and Natural Resources in Nelson says they are just a drop in the proverbial bucket.

 

“It’s been percolating in the area in the last three years, and then it just exploded,” Stock said. “The last time there was any budworm at all was in the early ‘80’s. This is much bigger. I think it was here, and it blew up. It could have been augmented from some moths blown in from the Okanagan.”

 

While Stock says the infestation could last only a short while, it’s possible it will go on for as much as 10 years and damages are expected on many of the trees that forestry companies rely on as a source for lumber.

 

“Last year we didn’t map any defoliation from the air,” said Stock. “Currently, our estimate is 10,000 hectares. That’s just visible from the Phoenix area to the Okanagan. We even have them in Nelson.”

 

Forester and Woodlot Owner Fred Marshall, explained that these pests are found throughout most of Canada and the northern United States. In B.C., all age classes of Douglas-fir, true firs, and spruce in multi-level stands are preferred by the worm, but larch, hemlock and pine could be attacked. 

 

“All kinds of environmental conditions converge and conspire to make a flush happen – an overabundance of food, or low predation by its natural predators,” added Gary Smith of Gaia Principles Intergrated Pest Management in Grand Forks. “They can fly quite a distance in search of places to lay eggs.”

 

The worms in the initial stages of life feed on new foliage only and the tree is usually able to survive the attack unless the worms attack repeatedly or feed on the old foliage.

 

“The moths are about 13 millimetres (mm) long, with a 15-25 mm wingspan. Fore-wings are grey to brown and overlaid with similarly colored bands, spots and blotches. Hind-wings are buff or light to dark grey. Male and female moths are similar in appearance, but females are more robust than males. Both sexes fly,” Marshall explained. “Moths emerge from mid-July to early August, mate, oviposit and die within two weeks and fly mainly at dusk. Females each deposit about 150 eggs in flattened shingle-like masses on the undersides of needles.”

 

Stock added that the moths seen right now are in the process of finding mates to propagate. The Ministry can use a naturally occurring bacteria specific to moths and butterflies, called BTK, to spray for the budworm. If they determine that higher value forest stands are at risk they may treat them.

 

“It’s far less aggressive than the Tussock moth – you’re not going to see a lot of tree mortality for two years assuming they don’t get a whole lot worse. It takes a very intense population to really kill the trees. Unless they get really intense in numbers, then they will feed on old foliage because that’s what’s left. When that starts to happen you’ll get dead trees,” said Stock.

 

Local homeowners are not likely to be impacted by the infestation, but may see the occasional tree die as a result over the next few years. With a potential province-wide ban on pesticides in non-commercial settings, there will be few options for containing the worm, Smith commented.

 

But the impact in the local forests could be quite high, Stock added.

“We’re going to go out and do an egg sampling (in the fall) to assess what kind of defoliation we can expect next year,” said Stock. “We’re seeing more intense infestations and longer so it could be in the Boundary for 10 years. Right now based on what we’ve seen we have a lot of defoliation, extensive but moderate damage on average with a few areas of severe. We’ll find out where it’s going to go.”