Beetles from Central Asia are sweeping down the Colorado River and into Southern Nevada, making pests of themselves even as they munch on a pesky plant along the Southwest’s most crucial watershed.
Just don’t blame the bugs. We’re the ones who invited them.
The tamarisk leaf beetle was introduced across the West in 2001 to prey on the tamarisk plant, an unrelenting menace introduced roughly 100 years earlier. So far, the bugs have done just what they were brought here to do: Eat tamarisk to death in one place and move on to another to eat more tamarisk, all without bothering other plants.
But along the Colorado and its tributaries in Nevada and southern Utah, the beetle is complicating efforts to save the endangered Southwest willow flycatcher.
This poor, put-upon bird lost much of its nesting habitat when dams went up on the river and the banks were cleared for agriculture, forcing the flycatcher to start building nests in the less welcoming tamarisk trees that quickly replaced native willow and cottonwood.
Then along came the beetles to defoliate the tamarisk, leaving flycatcher nests exposed and prone to failure.
It’s just the sort of unintended consequence that can happen when researchers deploy what are known, sometimes laughably, as biological controls.
Even the name smacks of hubris. It turns out humans are great at altering and manipulating the natural world, but not always good at controlling it.
AN INVITATION TO INVASION
It was people, after all, who brought the Central Asian tamarisk, or salt cedar, to North America to decorate gardens in the 1800s. The hearty, fast-growing plants were later placed along railroad tracks and elsewhere to blunt the wind and hold sand in place.
From there, the plant escaped into the wild.
Tamarisk exploded across the Colorado River basin during the mid-20th century, as the temperamental river was dammed into submission. That weakened the flood-adapted native plants and opened the door to an invasion.
Curt Deuser has been at war with the tamarisk for 25 years.
Now the supervisory restoration ecologist for Lake Mead National Recreation Area, he was hired by the National Park Service in 1988 to design and implement a tamarisk control program for the 1.5 million-acre park.
The plant has proven to be a formidable foe.
“Its seeds will blow for miles over mountain ranges, find a wet spot in the desert and take hold,” Deuser says. “It’s a wildfire threat. It consumes water. It impacts native species. We don’t have enough money or chain saws to control it.”
Enter a greenish brown bug smaller than a Tic Tac.
To some, the tamarisk beetle seemed like the perfect way to fight back against the advancing salt cedar army.
Longtime state entomologist Jeff Knight helped release the imported insects and monitor their progress along several watersheds in Northern Nevada. He remains a believer in the biological control program.
“We have areas in Northern Nevada where the native plants are coming back because there’s less competition from the tamarisk,” Knight says. “Personally, I think if you’re going to control this stuff, the beetle is far better than spraying lots and lots of herbicide.”
BEETLES ON THE MOVE
Already, though, the bugs have spread faster and farther than expected — and into areas the federal government didn’t want them to go.
Guidelines for the program prohibited the release of beetles within 200 miles of habitat and 300 miles of nesting areas used by the Southwest willow flycatcher. But those rules failed to stop some state and local officials from conducting their own releases wherever they pleased.
A few private landowners also got in on the act by swiping bugs from approved locations and taking them home to eat salt cedars not far from the Colorado River watershed.
Once the beetles got loose, they went where the food was. As one federal biologist puts it: “Bugs don’t listen to the U.S. Fish & Wildlife Service.”
The beetle’s range now extends from northern Mexico to Oklahoma, across the Colorado River basin, and into California.
Their discovery here was less a surprise than an inevitability. For several years, researchers have been watching the insects make their way down the Virgin River and into the main stem of the Colorado by way of Lake Mead.
ADAPT AND ADVANCE
Tom Dudley is a researcher from the University of California, Santa Barbara who has been working with tamarisk and tamarisk beetles for 15 years. For the past six years or so, most of his time has been spent on the Virgin and lower Colorado, tracking the movement and impact of beetles and planning for the restoration of native plants where tamarisk is now in decline.
“It’s been an amazingly effective program,” he says, “with complications.”
To chart the spread of the beetles, he hangs traps baited with a synthetic version of the pheromone males put out to attract females.
Tamarisk beetles were spotted in the Las Vegas Wash for the first time last year. Today they can easily be found munching away on salt cedar along the northern edge of Old Silver Bowl Park near Sam Boyd Stadium.
On a recent visit to the area, Dudley smacks the branches of a tree with a wooden staff and catches what falls out on a square of white canvas called a “beating sheet.” Mixed in with the leaf litter are about a dozen beetles and a handful of tiny, caterpillar-like larvae.
There was some thought early on that the beetles would be hemmed in by geography. Research suggested they would not be able to survive below a certain latitude for complicated reasons involving day length and dormancy.
So far, they are defying expectations as they continue to spread south along the Colorado River. This suggests something that excites researchers like Dudley: The bugs are evolving.
SPURRED INTO ACTION
Concerns over the beetle and the flycatcher came to a head in 2009, when a pair of environmental groups sued the federal government for failing to protect the endangered bird from its own biological control program.
The U.S. Department of Agriculture responded in 2010 by shutting the whole thing down. Permits for bug releases were rescinded. Beetle importation was halted. Funding was slashed, even for monitoring the insects already out there.
By then, it was already too late.
The beetles now in Southern Nevada and making their way south along Lake Mohave likely descended from a batch set free near St. George, Utah, in 2006 or 2007, years before the lawsuit and the moratorium on releases.
The expansion of the beetle is forcing land managers to speed up work to re-establish native trees and shrubs pushed out by the invading tamarisk and changes to the river system.
What was a more methodical effort is now a race to replace growing swaths of dead and dying tamarisk. The problem for the agencies involved is finding the resources and money they need to finish the work the beetles have started.
“It’s part of our mission to go in and restore those areas,” says Alice Newton, vegetation manager for Lake Mead National Recreation Area. “I view the beetle as a facilitator, both the carrot and the stick. It’s raising the urgency level of what we’re doing.”
WORKING OUT THE BUGS
More than 8,100 acres of native habitat is scheduled to be restored or built from scratch along the lower Colorado over the next 45 years as part of a sweeping, multiagency conservation program along a 400-mile swath of the river from Lake Mead to the Mexican border.
That restoration work eventually will include almost 6,000 acres of new willow and cottonwood stands for endangered flycatchers to call home.
Dudley insists there was nothing haphazard about the introduction of the tamarisk beetle in the United States. Decades of planning and research went into the program.
Then in 1995, just as the first releases were set to take place, the flycatcher was added to the endangered species list, forcing several more years of study, discussion and delay.
“We had to feed tomato plants to these beetles just to be able to say, ‘OK, these things don’t eat tomatoes either.’ The effort that goes into making sure these things are specialists is huge,” Dudley says.
But even those who have seen biological controls work in other situations worry about possible future impacts from the tamarisk beetle program that no one can predict.
Says Lake Mead’s Newton: “A professor once told me you never say never and you never say always when it comes to biology. It’s sort of like the whole Jurassic Park thing all over again: Life finds a way.”
Dudley thinks the spread of the beetles could wind up being a good thing for the Southwest willow flycatcher. After all, the bug and its voracious appetite are injecting a sense of urgency into habitat restoration work that hasn’t always been a top priority along the Colorado River.
“It’s like with a lot of things,” he says. “If you don’t have a crisis, it’s hard to get someone to come out of their office and decide to do something.”
With that, Dudley holds out his beating sheet and smacks another branch down by Old Silver Bowl Park.
This time he gets about 10 tamarisk beetles. They linger on the canvas for a few seconds and then take flight one by one. They’re off to find their next meal.
Contact reporter Henry Brean at firstname.lastname@example.org or 702-383-0350.