The birds and the bee(tle)s

The end of a controversial tamarisk biocontrol program may be good news for habitat

  • Tamarisk trees along the Colorado River downstream of Moab, Utah, turn brown as tamarisk beetles gain a foothold. The native willows, bright green in the distant background, have been increasing here as the tamarisk continues to decline.

    Tom Dudley UCSB
  • Tamarisk beetle

    USDA Agricultural Research Service
  • Introduced tamarisk leaf beetles are now well-established on the Colorado Plateau, and spreading on their own. In June, the feds put the kibosh on a region-wide effort to use the beetles to kill invasive tamarisk, because the insects have spread into the Virgin River watershed (in the vicinity of St. George) where they could threaten nesting endangered southwestern willow flycatchers.

    the Tamarisk Coalition
 

The beetles are dead and gone, shriveled in the heat or eaten by ants, but otherwise the Owens Valley, Calif., research site looks the same as the last time scientist Tom Dudley saw it. Tinemaha Reservoir glimmers beyond a wall of brush. The sharp peaks of the Sierra Nevada decorate the skyline. Invasive Eurasian tamarisk, or saltcedar, trees still freckle the valley floor, their feathery branches casting long shadows across the native sagebrush in the early morning light. And Dudley's beige beetle cage, the last of a set, still envelops a single tamarisk, as if the five-foot cube of fabric could contain the plant and everything it stands for. Unzipping the mesh, Dudley steps inside with his screwdriver.

It's time to let go.

Dudley, a wild-haired, gray-bearded riparian ecologist from the University of California at Santa Barbara, is dismantling part of a more-than-decade-long research project on whether an Asian leaf beetle, Diorhabda elongata, can help rid the West of tamarisk. In June, partly in response to a lawsuit by the Center for Biological Diversity and the Maricopa Audubon Society, the U.S. Department of Agriculture's Animal and Plant Health Inspection Service (APHIS) indefinitely suspended its Diorhabda biocontrol program, including Dudley's research permits. It turns out that the insects -- a group of related species each about the size of a grain of rice -- may be threatening the endangered southwestern willow flycatcher, which nests in tamarisk in areas where the plant has displaced its preferred willow habitat.

The stakes holding down the cage are stuck in the ground, so with a rip and a clang Dudley uses a metal pole to pry the mesh away. He is frustrated with what he sees as putting the good of individual birds over the health of an ecosystem. "I'd prefer a system that was dominated by native species," he says. Finally the cage comes off, and he sets the plant free. "OK, bush, grow grow grow!" he says wryly.

Most Westerners have heard that tamarisks guzzle water, mess with soil salinity, push out native species, and destroy habitat. Land managers often crusade for its eradication. In the Owens Valley, the Inyo County Water Department spends around $300,000 a year fighting tamarisk with chainsaws and herbicides. The beetle, on the other hand, costs little to release. Under the right conditions, a few hundred insects can multiply across tens of thousands of acres in just three or four years. The larvae and adults strip tamarisk leaves summer after summer, gradually wearing groves into submission. Eventually, many trees die; the rest grow more modestly, their vigor and dominance reduced by the beetle's constant attacks.

Over the past decade, APHIS has permitted beetle releases in 18 states across the West and Midwest, and worked to establish nurseries of the insects in 10 of those. At many sites, the beetles failed to thrive, but at some they spread faster and farther than scientists had anticipated. Today, the insects swarm across the upper Colorado Plateau, and though no one tracks exact numbers, adding up local reports suggests they've defoliated tamarisk on a total of at least 11 million acres. By that measure, certainly, the beetle program has been a success.

But APHIS' recent decision makes it illegal to transport beetles across state lines. That means no new releases in states where the beetles aren't already established, such as Idaho and Washington –– much to the dismay of biocontrol supporters like Dudley. APHIS intended its moratorium to "raise awareness" and "encourage thought about intrastate movement" of the insects, and it has; in Montana and in the Owens Valley, for example, land managers have abandoned plans to use the beetles. Meanwhile, the insects are spreading deeper into flycatcher territory, and frustrated endangered species activists worry that APHIS' caution may have come too late to help the birds.

Yet despite all the furor, the agency's decisions –– both to approve the program in the first place and to suspend it now –– could well prove to be a net positive. The suspension may not close off all possibility for future biocontrol. And the march of the beetles is inspiring a new emphasis on proactive habitat restoration in flycatcher territory.

The current heart of the beetle saga is the Virgin River, a tamarisk-tinged Colorado River tributary that flows through Utah and Arizona before emptying into Nevada's Lake Mead. The Virgin hosts about 50 of the 1,300 willow-flycatcher nesting sites remaining in the Southwest, and connects, via the Colorado, to hundreds more. When APHIS began actively distributing leaf beetles in 2005, it agreed not to release any insects within 200 miles of the bird's known critical habitat. But insects have a way of ignoring boundaries.

According to the Center for Biological Diversity, APHIS employees allowed local officials in southern Utah to help themselves to some beetles from an approved nursery farther north in 2006. The Utah officials released the insects in the Virgin River watershed. Originally, the beetles couldn't survive so far south -- the  short  summer  days cued them to hibernate too early -- but they quickly adapted and began to thrive. Though scientists knew that might happen, they'd predicted it would take at least a decade. Instead, in 2008, the beetles crossed the invisible line into active flycatcher nesting territory, just a couple miles from the release area, and an unplanned, high-stakes experiment began.

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