Beetle Warfare

What happens when an exotic bug is brought in to fight an exotic weed?


  • Dan Bean releases tamarisk beetle larvae along the Gunnison River in Western Colorado

  • Tamarisk at a bend in the Gunnison River in western Colorado. The reddish-brown foliage indicates the beetles are beginning to have an impact. Opposite: A tamarisk leaf beetle larva, perched on the "sand case" it makes before pupating.

  • Dan Bean looks for beetles among dying tamarisk along the Dolores River in southwestern Colorado. Beetles have spread about 20 miles upriver since they were introduced in 2005, killing tamarisk along the way. Above opposite: beetle on dying tamarisk foliage in the Palisade Insectary


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In a sunshine-filled laboratory at the Palisade Insectary, Jiana ten Brinke, a recent college graduate from California, is loading clear plastic containers of Diorhabda onto a rolling cart. Dan Bean, at a nearby lab bench, is inspecting a carton of weevils. 

"Those aren't quite as cute as these," she tells him. 

"Oh, come on," Bean says mildly. "They've got these little snouts ..." 

"These are cuter," ten Brinke says, opening one of her containers, showing a crowd of sunflower-seed-sized beetles clambering over a tiny bouquet of tamarisk. "They're round and stripey, like little watermelons." 

The beetles - which are, to an outside observer, not cute, but not as ugly as you might expect - are part of a veritable United Nations of beetles at the insectary. Populations from Crete, Kazakhstan, mainland Greece, Uzbekistan, and several areas of China are kept supplied with green tamarisk, all too easy to find here in the summer. In the winter, insectary workers turn to a few dozen scraggly-looking, nutrient-starved plants in their greenhouse. ("As soon as you try to grow a weed, you have all kinds of problems," says Bean.) When this emergency supply runs out, collaborators send buckets of green tamarisk from warmer climes and other greenhouses. 

For more than a half-century, the insectary has supplied "beneficial" insects to local orchardists, and now, in cooperation with the U.S. Department of Agriculture, it's added the tamarisk beetle to its list of charges. Insectary workers have raised up and shipped out some 400,000 beetles from northwestern China to nine states, including various sites within Colorado. "We have a really big FedEx bill here," says Bean. 

Bean and his colleagues are also studying how the beetles respond to new conditions. Diorhabda, as Bean observed when he first joined the project, is extremely sensitive to day length, and even small changes can cripple a population. But over time, the beetles do appear to adapt to different light regimes, and generation by generation, the captive beetles here at the lab are adjusting to the artificial light schedules they're placed in. That suggests that at some point - likely within a decade, Bean says - the beetles from China will be able to thrive farther south, beyond the limits of the 38th parallel. Regulatory quirks have also allowed researchers in Texas and New Mexico to release beetles from Crete, a population already well equipped for life in the Southwest. One way or another, the southwestern willow flycatcher will eventually contend with Diorhabda.

"People don't appreciate that biological systems aren't static," says Bean. "Anyone who thinks that the beetles are going to stop at the 38th parallel, and sit there for the rest of biological history, is going to be surprised." 

So far, Diorhabda is behaving very well. The beetles are eating plenty of what they're supposed to, and, as watchful researchers report, nothing that's forbidden. They've survived and spread beyond expectations. But not even the most fervent biocontrol advocate calls their introduction a success - not yet. For no one is sure what will follow in their path. 

"Killing tamarisk is a wonderful activity, but that's not the goal," says Tim Carlson, the executive director of the nonprofit Tamarisk Coalition, a group that works to connect tamarisk-control projects throughout the West. "We want to get rivers back to a healthy state, and we don't have a plan for doing that." 

On the Dolores, and in other places where cottonwoods and willows still stand shoulder-to-shoulder with tamarisk, the beetle's work may be enough to encourage a boom in native species. But in other places, where natives are sparse or nonexistent, Diorhabda could easily hand the advantage not to natives but to other exotics, such as Russian knapweed and the fast-colonizing perennial whitetop. 

The recipe for a healthy river is an elusive one, and differs for each site. But tamarisk adversaries agree that in most cases, the beetle is only the beginning, and that rivers will need more meddling, not less. In some places, rivers may need to be seeded or planted with native species. Beetle-killed dead tamarisk may need to be taken out with chainsaws or prescribed fire. 

On dammed rivers, where flood timing can favor tamarisk and other exotic species, tamarisk may be only a symptom of a deeper malaise. Lasting success may mean changing water management - never an easy task in the West. "There's a belief that all you have to do is get rid of tamarisk, and the native vegetation will come back," says U.S. Fish and Wildlife Service biologist Greg Beatty. "But in many instances, our management choices are the reason why tamarisk is flourishing." 

Like the long-running efforts to defeat tamarisk with hacksaws, bulldozers and poison, river restoration projects following tamarisk removal are small, underfunded and diffuse. There's no one agency in charge of river health, and most rivers flow through a patchwork of landowners and regulations. The Tamarisk Coalition is organizing local partnerships and encouraging state agencies to provide matching funds to groups and communities interested in river restoration. They're also negotiating with oil and gas companies to fund weed eradication and restoration projects, and pressing Congress to fund a 2006 law supporting tamarisk control and research. But for now, there's much more talk than action surrounding post-beetle restoration. "It's a giant experiment," Carlson acknowledges. 

The experiment will almost certainly involve the southwestern willow flycatcher. Since the species was listed as endangered in the mid-1990s, flycatcher numbers have risen significantly, likely due to a combination of genuine habitat expansion and more intense study. But the promise of a Diorhabda debut in the Southwest within the next decade still worries wildlife researchers. "I doubt that saltcedar control would drive the flycatcher to extinction," says U.S. Geological Survey biologist Mark Sogge. "But without proactive restoration, recovery might be a lot harder." 

On the Utah-Colorado border, in the river canyons of Dinosaur National Monument, botanist Tamara Naumann is pioneering one strategy for the future. Years before Diorhabda received its federal approval, Naumann focused her volunteer tamarisk-removal campaign on campsites and other highly visible areas - places where beetle-killed tamarisk, she knew, would be unpopular and dangerous. When she began releasing the beetles in the park in 2006, she chose remote places rarely reached by volunteers or visitors. "I consider them my newest volunteer corps," she says of the beetles. "Their job is to eat and have lots of sex." 

Naumann, who has recruited well over 5,000 human volunteers over the 11 years of her tamarisk control program, fully expects her crews to keep boating the Yampa and Green rivers each summer. Their job may shift from tamarisk extraction to debris removal and native-plant restoration, or even to control of other weed species, but it won't end. "The beetle is never going to replace those volunteers," she says, looking horrified at the prospect. "I'd be an idiot to get rid of them." 

On another fall day, in another redrock canyon near the Utah-Colorado border, Dan Bean extracts a small Coleman cooler from his truck. Inside are cardboard pint containers filled with thousands of Kazakh Diorhabda, recently captured in Utah and bustling toward freedom. 

Bean and his two colleagues march into a crescent-shaped tamarisk thicket, a place as green and humid and buggy as any Eastern forest. They select a tree near the center of the stand, take a GPS reading, and, as if salting a steak, start emptying the containers onto the tamarisk's limbs. 

If all goes as planned, the entomologists will see larvae here next spring, and the tamarisk will start to brown. Within a few years, these beetles will likely cross paths with those making their way up the Dolores, some 40 miles away. Bean surveys the tamarisk, some of which reach 25 feet overhead. "I think these will provide some pretty good food," he says. But here, there are few cottonwoods and willows: The pink flowers of Russian knapweed carpet the ground, interrupted only occasionally by native species like the skunkbush sumac, a shrub with leaves pungent as a beauty salon. 

In the wake of Diorhabda, these species will begin a struggle for new territory, but for now at least, the tamarisk towers solidly over them all. The beetles drop from their containers, light as air, and vanish into the greenery, intent on surviving the winter. 

Michelle Nijhuis is a High Country News contributing editor.


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