Bark beetles were flitting around Rich Hofstetter’s lab at Northern Arizona University on Thursday morning, escapees from one of several ponderosa pine logs sitting in plastic tubs stacked in the corner.
Though harmless inside the lab’s walls, the species, ips lecontei, has a deadly history — it was the biggest killer of ponderosa pine trees during the state’s 2002 drought.
The tiny bugs are test subjects in Hofstetter’s most recent project: a quest to find a fungus strain that will kill the beetles that have wreaked havoc on trees throughout the West.
The NAU forest entomology professor is one of world's top bark beetle experts. His past research has focused on using sound — from rock music to amplified versions of the beetles’ own calls — to control the beetles’ tree munching.
The specific fungal strain that Hofstetter is testing now penetrates the beetles’ exoskeleton and grows inside the bug, eventually killing it. Then the fungus grows out of the dead insect's body and produces spores that can be picked up by other beetles.
“The fungus is already (in the forest), all we're doing is increasing its ability and its success,” Hofstetter said. “It's not going to eliminate bark beetles but it may prevent some of the catastrophic events.”
So far, the fungus is producing 70 percent to 80 percent mortality rates in the beetles after two days, he said.
Hofstetter makes a liquid formula with the fungal spores that he sprays onto trees, so it gets picked up by beetles as they exit the tree. Eventually, he wants to try injecting the fungus directly into the tree. If that works, forest managers could begin to protect a forest even before beetles arrive.
Hofstetter is currently conducting the experiments in his lab. This spring though, he’ll move the experiment outside to NAU’s Centennial Forest, a 400-acre plot dedicated to research, teaching, and demonstration, to see how the fungus works on living trees and to monitor whether it harms other bugs and fungi in the tree.
But Hofstetter’s bark beetle tests are only one part of the equation. The other is finding the fungal strains that target only the aggressive types of bark beetle scientists want to go after. That’s the job of Montana BioAgriculture, a company based in Missoula that develops biological pesticides using fungus and bacteria. Fungal insecticides are already being used in agriculture, but no one has developed an equivalent product to be used in forests, said Clifford Bradley, the company’s president.
The company cultivates beetle-killing fungal spores that it has collected from forests around Montana and Arizona, then sends them off to Hofstetter for testing. The work has already uncovered some strains that hold promise to become commercial products, Bradley said. The next step after that is to go through the testing required for Environmental Protection Agency approval, he said.
While spraying fungal insecticide might not be a practical solution for hundreds of acres of forest, it could be used to protect trees in high-value areas like campgrounds, ski resorts and riparian areas, Bradley said.
The U.S. Forest Service considers 15 bark beetle species as threats to trees in the West. One species alone — the mountain pine beetle — has killed pines on more than 40 million acres in the western United States and Canada.
Pine beetles are a natural part of the conifer ecosystem, but warmer and drier climate trends have allowed the beetles to survive in greater numbers through the winter and to develop at faster rates. Drought, another symptom of climate change, is also good news for beetles because it weakens trees’ defenses and allows the insects to penetrate the bark and reproduce easier.
The current options to control the pine beetles are limited to chemical pesticides, which can be toxic to other bugs as well, repellent pheromones that tend to protect only individual trees, and forest health treatments like forest thinning and prescribed fire, Bradley said.
And though the larger forces of climate change will continue to threaten the long term viability of the region’s trees, controlling bark beetles will at least help those trees hang on for a bit longer, Hofstetter said.