Tussock moth caterpillars are stripping fir trees throughout the state. To keep our trees healthy, the U.S. Forest Service is fighting back with a spray-on virus straight out of sci-fi.
The tussock moth caterpillar is quite the sight, if you’ve ever seen one hanging around a Douglas fir tree. Its brightly colored body is covered in fuzz, with tufts of hair on its back.
“The caterpillars are really quite attractive,” said Connie Mehmel, a forest entomologist with the U.S. Forest Service. “They’re very colorful. They have a pair of hairs on either side of their heads that look like horns.”
But about every 10 years, Mehmel starts seeing too many of these native insects. Too many can be a bad thing.
These hungry caterpillars can eat Douglas fir and grand fir needles, starting with the new needles that grow as the caterpillars hatch, later munching on older needles high in the treetops.
“These caterpillars, when there are a lot of them in the forest, they really can strip a tree from top to bottom. When a tree loses all of its needles in a single year, that tree will usually die,” Mehmel said.
That can mean a lot of dead standing trees, which could fuel large wildfires, Mehmel said. In that way, the situation is similar to a bark beetle infestation. It can also be dangerous for people recreating in forests, which is why attempts are made to treat outbreaks in high-use areas before the caterpillars damage trees.
To prevent too many trees from dying, the Forest Service sprays goop that’s toxic only to tussock moth caterpillars — it doesn’t even affect other insects, Mehmel said. The mixture is made up of a virus that’s been grown and turned into a powder, combined with water and molasses. (READ MORE)
(Photo by Connie Mehmel/U.S. Forest Service)