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In Battle Against Invasive Plant, Scientists Seek To Bring In The Ground Troops: Beetles

J. N. Stuart
The tamarisk beetle (Diorhabda carinulata) eats a scaly-leafed invasive shrub that has spread across the West.

The tamarisk plant, also called saltcedar, is infesting waterways across the West. The scaly-leafed shrub can grow taller than a person. It sucks up a lot of water and spits out salt, making the soil around it too salty for other plants to grow.

“It’s very bad, yes,” says Alex Gaffke, a graduate student in land resources and environmental science at Montana State University.

He says there are three ways to get rid of the plant. You can spray herbicides on it, but that’s expensive. You can gather a group of volunteers to tear it up with chainsaws and shovels, but that’s hard work and also expensive. Or, as he wrote in the journal Pest Science Management, you can commune with a special beetle and convince it to do all that work for you.

Tamarisk beetles eat tamarisk plants. They use a chemical called a pheromone to communicate with each other.

“That pheromone is basically a signal to everybody that, ‘Hey, this is where the party is. This is where there’s good food,’” he says.

The beetles want to be at the party, munching on tamarisk leaves and laying eggs that will hatch into larvae that will also munch on tamarisk.

The beetles, which are originally from places like Kazakhstan, were brought to the U.S. about 20 years ago to get rid of tamarisk, but their populations have struggled to bounce back as quickly as the plants they eat after events like floods. 

By carrying around a bit of the pheromone, Gaffke says, “You can basically be the Pied Piper of beetles.”

With funding from the USDA and Forest Service, he got hold of a putty containing the pheromone. Using a caulking gun, he squeezed the putty on tamarisk plants along Wyoming’s Bighorn River. Within hours of applying the mixture, beetles would cover the plants. It took two years of applying putty once a week, but Gaffke managed to attract enough beetles to crush 6-foot-tall shrubs into plants no bigger than seedlings.

Now, he’s working on a simpler process for use across the West – a way to get the same results with just three applications a year.

As High Country News has reported, some conservationists worry about the beetle’s impact on a bird called the southwestern willow flycatcher.

This story was produced by the Mountain West News Bureau, a collaboration between Wyoming Public Media, Boise State Public Radio in Idaho, Yellowstone Public Radio in Montana, KUER in Salt Lake City and KRCC and KUNC in Colorado. 

Rae Ellen Bichell was a reporter for KUNC and the Mountain West News Bureau from 2018 to 2020.