Colorado turns to beetles to fight invasive tamarisk
Grand Junction correspondent
Aspen, CO Colorado
GRAND JUNCTION, Colo. ” Tamarisk-munching beetles are eating their way across Mesa County’s waterways in western Colorado.
By this time next year, once-healthy, fluffy green and lavender stands of tamarisk choking riverbanks in Mesa County and elsewhere will begin to brown ” thanks to the tiny striped beetles from Asia that feed exclusively on the invasive plant species.
Tamarisk throughout Colorado is thought to drink up to 100,000 acre feet of Colorado’s river water annually ” enough to supply half the population of Denver, said Tim Carlson, executive director of the Tamarisk Coalition, based in Grand Junction.
Tamarisk also chokes out native plants, and local wildlife species prefer native plants to the tamarisk, Carlson. said.
“When it really gets dense, it really is very poor wildlife habitat,” Carlson said. “From the birds’ and bunnies’ standpoint, they would really much prefer the cottonwood willow.”
In Mesa County, tamarisk beetles have been released in Horsethief Canyon, below Loma on the Colorado River. They’re also in Flume Canyon and Devil’s Canyon in the McInnis National Conservation Area; in No Thoroughfare Canyon; along the Dolores and Gunnison rivers; and along Parachute Creek in Garfield County, Carlson said.
They’ve also been released in northwest Colorado, along the South Platte River and on the Arkansas River, primarily downstream of Pueblo Reservoir.
Already, tamarisk stands along the Dolores River have begun to brown, said Dan Bean, director of biological pest control and manager of the Colorado Department of Agriculture’s Palisade Insectary.
Next year, the Bureau of Land Management and Insectary staff expect complete defoliation of tamarisks from Loma to Utah and “major beetle movement into the Grand Valley,” the BLM said.
By June next year, boaters, hikers and walkers along the Colorado and Gunnison rivers and their tributaries will begin to notice the tamarisk beetles’ work, Bean said.
“The people in Grand Junction will see the plants start getting hammered,” Bean said. “It’s all predictable.”
Three years ago, tamarisk beetles were released upstream of Gateway and near Bedrock in a program that partnered the insectary with the BLM.
“It was a big success,” Bean said. “They’ve pretty much defoliated all the tamarisk on the Dolores River. It was impressive.”
Officials also released the beetles downstream of Loma.
Those bugs are “taking off, moving upstream and downstream,” Bean said. “Coming in from Utah is another big wave of beetles.”
The beetles were studied for 10 years before they were released in the United States, Bean said. They were imported from Asia, where the tamarisk originated.
“This insect has had more research on it than any other insect in biocontrol,” Carlson said.
When tamarisk was introduced into the United States, it was done so without the beetle, its natural enemy. As a result, tamarisk has taken off throughout the West.
The beetles’ only food is tamarisk.
“We’re just reintroducing these guys to their hosts,” Bean said. “They don’t leave an area until they pretty well destroy all the tamarisks.”
Once they decimate a tamarisk plant, the bugs smell out new sources of food and they fly off in search of it.
“They are very sensitive to the smell of tamarisk,” Bean said. “They can also smell each other and are drawn to each other.”
It takes multiple defoliations to kill the tamarisk plant. Even so, biologists and entomologists expect nature to reach a balance between beetle and plant.
One of the first releases of the tamarisk beetle was in western Nevada in 2001. Now, mortality of the tamarisk is at 80 percent, Bean said.
“It will never wipe it out entirely. After they start knocking back the plant population, there will be some balance eventually,” Bean said. “They do it by brute force numbers.”
He’s heard the complaint that introducing the beetles will change the ecosystem. His response:
“We hope it does. It’s difficult to have a plant that has no natural enemies,” Bean said. “If we knew there was a downside, we wouldn’t have gone through with it. That’s part of the 10 years in researching it.”
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