New hope for beetle-killed landscapes

Can native forest fungi combat the West's bark beetle epidemic?

 

From the air, they look like brittle, dead landscapes: millions of acres of scratchy brown pipe cleaners and toothpick logs. Since the 1990s, naturally-occurring bark beetles have multiplied under the effects of drought, climate change and fire-repressed forests, leading to outbreaks that have ravaged forests and left land managers scrambling to deal with a glut of dead trees. But 2015 may prove a turning point. 

The first hopeful news comes from the lab of Richard Hofstetter, a forest entomologist at Northern Arizona University. Working with a private company called Montana BioAgriculture, Hofstetter has identified a deadly strain of the Beauveria bassiana fungus that kills 80 to 90 percent of pine beetles, one of the most destructive bark beetle species of recent years. The fungus is naturally present in the bark of some infected trees; Hofstetter and Montana BioAgriculture’s Cliff Bradley simply collect it, propagate it and dissolve the spores into a liquid that forest managers can spray on trees to help control local outbreaks.

As the journal Entomology Today explains, “The fungus releases white powdery spores, and when the beetles crawl over them the fungus gets into their bodies and takes over.” Once that happens, Hofstetter says, it’s lights out within a day or two, no pesticides necessary. The product may be on the market by the end of the year. 

But the big question for the Intermountain West may be whether Beauveria bassiana or a similar fungus can also be used to treat other bark beetle species, like the spruce beetle. That’s because aerial surveys released this month by the U.S. Forest Service show the mountain pine beetle epidemic is quickly waning: New infestations in Colorado have sunk to levels not seen since the 1990s, and Wyoming and South Dakota show similar downward trends, perhaps because the beetles have exhausted their food supply. 

co-pine-beetles-jpg
U.S. Forest Service
But as mountain pine beetles begin to disappear, spruce beetles are on the rise. In Colorado alone, 253,000 acres were affected last year, and in some places “nearly every mature spruce has been killed,” the Forest Service reports. After Hofstetter perfects his pine-beetle spray, he hopes to look for fungus that can treat spruce beetle outbreaks, too. 

co-spruce-beetles-jpg
U.S. Forest Service

Beyond the region, though, trends are less conclusive. Forest health in the Pacific Northwest is generally improving (see below), but in California, the total number of trees killed by insect, disease and drought more than doubled last year. And while Southwest forest managers haven’t yet released the results of their 2014 aerial surveys, Hofstetter says that if the drought continues, beetle infestations there will also rise, because drought-stressed trees are more susceptible to beetle kill.  

oregon-beetles-jpg
U.S. Forest Service

Though bark beetles are native denizens of the West and their outbreaks naturally cyclical, Hofstetter argues that managers shouldn’t just let them run amuck. “These outbreaks are larger than anything we've seen before, and we need to be aware that ecological impacts are pretty big,” he says. “The forest has changed because of human interference. If humans are altering the environment, we’re responsible for it as well.”

Current efforts to control outbreaks use either pesticides, which affect other wildlife, or chemical pheromones, which aren’t always effective. Fungus, Hofstetter says, is not only environmentally benign, it actually keeps pace with swiftly-evolving beetles: Pesticides have to be reapplied again and again, and insects evolve resistance, while fungus continues to evolve with the beetles after just a single application. 

While a fungal spray to control pine beetles may not be necessary in the Intermountain West right now — forest managers are already changing their tactics from battling outbreaks to clearing out dead trees and re-opening campgrounds — Hofstetter’s work is nonetheless an important step foward. Fungus has been used in agriculture for years, but it’s largely been overlooked as a forest management tool. 

That’s starting to change. Already, a Montana scientist is testing fungi’s ability to fight blister rust in whitebark pine, and there’s a good chance that scientists will find a strain that targets spruce beetles. If current trends continue, that should be welcome news. 


Krista Langlois is a correspondent at
High Country News. Image of Rio Grande National Forest credit Brian Howell/USFS.