The beetle appears to be doing its job -- diligently munching leaves as a way to eventually kill the nonnative trees -- but there's no comprehensive program to keep an eye on the bug's spread and make sure it's not unleashing unintended, large-scale environmental consequences, according to University of Utah researchers.
The scientists say they think satellite technology can be harnessed for that job, especially for tracking progress in many of the West's remote waterways where tamarisk, or salt cedar, has taken hold.
"It's a cheap way to do it over large areas," said Philip Dennison, an assistant professor of geography and a lead author of a study looking at ways to track the battle between the beetles and the tamarisk.
Tamarisk arrived in North America in the late 1800s and was used for windbreaks, erosion control and as landscape decoration, according to the U.S. Animal and Plant Health Inspection Service.
But since then, it has flourished out of control in some places, especially along rivers and streams where it sucks water and out-competes many native species.
In 2001, scientists began experimental releases of the tamarisk leaf beetle, a quarter-inch bug that evolved in Eurasia and only feeds on tamarisk.
The idea? Release the beetles into areas infested with tamarisk, let them feast on the leaves and, over time, hopefully the trees would die.
It's been tried in at least 14 states with federal approval in recent years, and has been most successful in parts of Nevada, Utah, Colorado and Wyoming, said Dan Bean, an entomologist with the Colorado Department of Agriculture.
"The beetles are doing what they're supposed to," Bean said.
Beetles were released in Grand County, Utah, in the state's southeast corner in 2004 where tamarisk has taken root along the Colorado, Green and other waterways. Already, many trees have been stripped of their leaves and some appear ready to finally keel over.
"I think were going to start seeing some good success," said Tim Higgs, the county's weed supervisor.
It can take several years for the beetles to weaken trees before they die. When the beetles run out of food, they fly somewhere else or, more likely, drop dead. They don't have a taste for anything but tamarisk.
But Dennison and others on the study say the experiment needs to be watched more closely on a large scale to make sure it doesn't backfire.
"We don't have any idea of the long-term impacts of using the beetles," he said. "Their release may have unexpected repercussions."
That includes the possibility of degrading wildlife habitat, having the beetle switch to an unexpected food source and opening the door for other invasive species to move in.
In parts of southwestern Utah and northwestern Arizona, the beetle is threatening tamarisk nesting areas of the endangered southwestern willow flycatcher, according to the Center for Biological Diversity, an environmental group. The group said in December it plans to sue the U.S. Department of Agriculture.
Dennison and others on the study say they'd be able to track widespread changes in tamarisk defoliation by using satellite images from red or infrared light that reflects plant pigments. They tried the technique along parts of the Colorado River. The results are scheduled to be published later this month in the scientific journal Remote Sensing of Environment.
They also found that, by analyzing data collected on the ground and with satellite images, tamarisk may have an undeserved reputation as a water hog.
Rather than guzzling 200 gallons of water day, a typical tamarisk is probably drinking about 20 gallons a day, Dennison said.
"So even though the beetle releases have the good intention of saving water, we're probably not going to see big savings," he said.