Black-tusked tussock moth caterpillars are munching fir trees along Colorado’s Front Range, spreading across 25,000 acres in one year and forcing a $293,000 helicopter chemical assault to stop them.
The U.S. Forest Service and Colorado Springs launched the aerial attack to hammer the bugs over five days in June. They’re relying on a new power granted by Congress to act quickly, without full environmental review, against insect invasions. A chopper sprayed a biological insecticide, Foray 48B, steering clear of endangered species and waterways.
Caterpillar infestation of normally deep-green Douglas firs — fading to gray-brown now near Colorado Springs, Boulder and Larkspur — has raised concerns about catastrophic wildfires, recreation and tourism, and water supplies.
“The purpose is to minimize the spread and intensity” of the outbreak, Forest Service spokesman Lawrence Lujan said. “The Forest Service is committed to ecological restoration, which includes maintaining and restoring healthy and diverse landscapes in the face of climate change and other stressors.”
These fuzzy green tussock moth caterpillars are voracious defoliators, the latest in a series of insects attacking Colorado’s ailing forests.
But unlike the mountain pine beetle, which ravaged 3.4 million acres of Western forests from 1996 to 2013, tussock caterpillars infest Front Range forests near cities where more people see the wilting brown trees.
And those cities, expanding in a semi-arid region, increasingly need healthy forest watersheds.
“Our goal is to protect our backyard. Aesthetically, we want to keep trees alive. From a natural resources perspective, a healthy forest has got trees in it,” Colorado Springs city forester Jay Hein said. “When it’s right in your backyard, it is a big deal. Watershed problems will be the biggest issue. Without that tree canopy to intercept rainfall, we’re going to have a lot more sediment running into our water.”
The caterpillars spread swiftly, from 1,000 acres in 2014 to 26,000 acres in 2015, Colorado State Forest Service data from aerial surveys show. Data from a new survey is due in January.
In some areas west of Colorado Springs, caterpillars have eaten all the needles off trees. Defoliated trees initially turn brownish red. This invites other insect invaders, including mountain pine beetles and western spruce budworm.
“We see groups of trees dying along the foothills that face Colorado Springs and communities such as Perry Park and Larkspur. You can see the mortality, the defoliated trees,” state entomologist Dan West said. “All that’s left is just the branches. These caterpillars have eaten all the needs off some of the trees. The needles are 100 percent completely eaten.”
Fattened caterpillars turn into tussock moths in July. While tussock moth outbreaks have hit forests since the 1930s or earlier, this recent surge ranked among the fastest ever recorded, state forest officials said. A previous outbreak, afflicting the South Platte River Basin from 1993 to 1996, killed trees across 18,000 acres.
A warming climate, droughts and wildfire suppression in Colorado and the West have created conditions that favor insect epidemics, putting 81 million acres of forests at risk, Forest Service maps show. This weakening of forests has, in turn, raised the risk of intense wildfire on 58 million acres. And as Colorado developers build commercial structures and houses near forests, authorities increasingly must gird for disasters.
“The huge outbreaks of mountain pine beetle in the north-central Colorado mountains and the spruce bark beetle in southwestern Colorado have left their marks on the landscape and increased tremendously the risk of fire,” said Tom Thompson, a former deputy director of the U.S. Forest Service who lives in Colorado.
“Currently, the Douglas fir tussock moth outbreak on the Front Range is also changing the condition of the forest and will result in increased wildfire risk,” Thompson said.
The chemical spraying is over for now. City and federal crews are inspecting forests, hoping to see caterpillars dead on the ground.
“The insects have to physically feed on the chemical for it to be effective,” Hein said.
Federal land managers acted under a Farm Bill provision that changed the Healthy Forest Restoration Act to give a “categorical exclusion” from required environmental assessments and impact studies to fight insect invasions. An expedited review allows faster Forest Service action. U.S. Sen Michael Bennet pushed through that change.
“Colorado’s forests are too important to our state’s economy and way of life to allow bureaucracy to stand in the way of effective coordination to protect them from invasive species like the tussock moth,” Bennet said.
“The moth is already a growing concern in El Paso County. We’re glad the Forest Service is using its expedited authority … to work with local communities and treat the forests now before it’s too late.”
Yet less than 15 percent of the caterpillars have been hit with helicopters spraying Foray 48B on 455 acres of federal land near Cheyenne Canyon and on 3,700 acres of private and city-owned forest. Entomologists are monitoring the Front Range to try to understand long-term effects on moth-infested firs, including observation of a parasite that is a natural enemy of the moths.
Colorado Springs residents expressed concerns about Foray 48B. Forest Service supervisor Erin Connelly weighed those concerns and considered potential health risks in helping to design the counterattack.
Colorado Springs’ role, ramping up city forestry to battle tussock moth invaders, shows the rising importance of “urban forests” near cities, Colorado State Forester Mike Lester said.
“Whether it’s for clean air, clean water, or the beauty,” Lester said, “healthy forests are an important municipal asset.”
