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October 30, 2014

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A beetle can save our water

But it would have to eat the thirsty tamarisk bush, home of the Southwest willow flycatcher, an endangered species

Image

Leila Navidi

Nicholas Rice, an environmental biologist with the Environmental Monitoring and Management Division of the Southern Nevada Water Authority stands among the invasive tamarisk plants that grow in abundance along the Las Vegas Wash. Rice has helped to remove 200 acres of tamarisk from around the wash and revegetate the area with native species.

Fighting an invader

Tamarisk plants cover the site of the lost town of St. Thomas near Lake Mead Thursday, February 28, 2008. Because of a fast-growing taproot, tamarisk draws down the water table, preventing other plants' roots from reaching the soil moisture. Launch slideshow »

Diorhabda elongata is a very picky eater — picky, but voracious.

Commonly called the tamarisk leaf beetle after the invasive tree it loves to eat, the tiny insect is the secret weapon against what some biologists have called the worst ecological disaster in the history of the western United States.

For the desert population of Southern Nevada, the tamarisk’s worst trait is its thirst. Up and down the Colorado River the tamarisk consumes as much as 325 billion gallons of water a year, according to estimates from the Bureau of Reclamation. That’s more water than the entire population of the Las Vegas Valley uses annually.

Across the West, there has been an ongoing battle to get rid of the invasive scrubby tree, but the tamarisk, also known as salt cedar, is formidable. It can survive floods, fires and drought and rebound after being attacked with machinery and chemicals.

In the end, it turned out that nature had the answer all along.

But in Southern Nevada — where the Water Authority and Lake Mead National Recreation Area officials are desperate to defeat the invader that is siphoning off so much of the region’s most precious resource — the beetle has been sidelined by a more mild-mannered opponent: the endangered Southwest willow flycatcher.

The flycatcher, which once lived in willow trees along stream banks throughout the Southwest, has adapted to nest in tamarisks since the foreign plant devastated the bird’s natural nesting grounds.

Although the beetle could be the answer to getting rid of the tamarisk — the first step toward restoring the flycatcher’s natural willow habitat — scientists fear killing the tamarisk would also kill the bird. Protected by the Endangered Species Act since 1995, the bird has prevented the tamarisk troops from using the beetles in parts of Southern Nevada, Arizona, New Mexico, Texas and Southern California where tamarisk is a scourge.

But the beetles are headed our way on their own.

A good idea gone bad

The tamarisk and the tamarisk leaf beetle are both native to Europe, Asia and parts of Northern Africa. The plant was brought here in the late 1800s as an ornamental shade tree — and subsequently spread like the worst kind of plague across the West, choking out native plants and animals.

As with many invasive species introduced by American settlers, the plant’s true character was unknown. Today its history is offered up offhand as a cautionary tale about the supremacy of nature or the folly of mankind.

Some critics argue that introducing the beetle on purpose isn’t much different from those first settlers’ planting tamarisk in the desert to shade their modest homes.

They say the concept of biological control, introducing a non-native insect not knowing the full effect, is troubling in itself. They fear the beetle could develop a devastating taste for native plants.

“There is no way to say they would never adapt to feed on any other plant. But there are a lot of barriers,” said Dan Bean, an entomologist with the Colorado Agriculture Department.

Tamarisk leaf beetles are specifically adapted to eat tamarisk, a difficult plant for most bugs to digest, and have a specially attuned sense of smell that helps them locate the plants.

Beetle proponents think the risks are worth it. Bean called the tamarisk infestation a disaster.

“The tamarisk is bad enough that we’re willing to take some risks with the solution,” he said.

After a decade of study, tamarisk leaf beetles were loosed in parts of the West to provide tamarisk with the one thing it lacks here: a “predator.” Scientists couldn’t have hoped for a happier result.

In 2001, 1,400 beetles got off to a slow start in Lovelock, about 100 miles from Reno near the California border. A year later the beetles had eaten the leaves off two acres of tamarisks and were still hungry. By 2004 they had defoliated 20,000 acres, Bean says.

Although it will take them years to devastate the tamarisks in Lovelock — previously blanketed with the nasty plants — Bean says they will prevail.

In Lovelock, “there were beetles everywhere. That’s what we had hoped for,” Bean said. “It’s a slow death, but eventually (tamarisks) suffer mortality. And that’s happening over some pretty vast stretches of Nevada.”

Since the success around Lovelock, the beetles have been set free in selected areas of Colorado, Northern California, Texas and Upper Colorado River Basin states.

Tamarisk water consumption declines 65 percent over the course of a season when beetles are present, according to Tom Dudley, an ecologist with UC Santa Barbara and UNR. After three years of coexisting with the beetle, the plant has a water use decline of 90 percent.

Those are the kinds of statistics that make ecologists big fans of the beetles. But even if the willow flycatcher had not been an obstacle, the initial batch of beetles probably wouldn’t have worked at Lake Mead.

Scientists discovered those beetles had a weakness. The ones released south of a certain line of latitude disappeared. Scientists say that’s because the bugs are sensitive to the length of the day and hibernate early when days are shorter than 14 hours and 45 minutes. They have fewer offspring, go to sleep in early July and eventually starve to death over the winter.

So researchers working on the project returned to Europe to look for a better beetle, one that could thrive in Southern Nevada and the other parts of the Southwest that needed the bug’s help. They found what they were looking for in Crete: beetles already adapted to sunnier climes with shorter summer days. The Cretan beetles are now widely used in parts of Texas, such as Big Spring, where they’ve defoliated 45 acres of tamarisk.

“These beetles have the potential to be preadapted to someplace like Southern Nevada,” Bean said.

The problem here is “if the beetles do well, we don’t necessarily have alternative habitat, native vegetation, for (willow flycatchers) to move into,” said Debra Hill, a biologist with the U.S. Fish and Wildlife Service. “No one thinks that (tamarisk) is good, but we do have an endangered species that is nesting in it.”

Jack DeLoach, an entomologist with the U.S. Agriculture Department and a longtime beetle researcher, said the bug’s supporters are cautious about its effect on the flycatcher, too.

“It’s difficult to test this kind of thing, and you can’t be testing an endangered species,” he said.

Hill said she knows the beetles are effective at taking out tamarisks — an admirable goal.

“When these beetles do take off ... they can take out a large swath of salt cedar for a hundred miles,” she said.

But until there’s a plan to revegetate with native plants in which flycatchers can nest, it’s Fish and Wildlife’s duty to protect the delicate bird, Hill said. And replacing those plants could cost millions of dollars, experts say.

Tim Carlson, executive director of Colorado’s Tamarisk Coalition, said it can cost anywhere from $250 to revegetate a lightly infested acre to $5,000 for a devastated acre.

Curt Deuser, an ecologist with the National Park Service tasked with controlling tamarisk on parklands, says the traditional boots-on-the-ground methods of using bulldozers, root rakes and chemical sprays to control tamarisk can’t match the efficiency of the beetles.

Deuser, who has been directing crews on parkland in eradication efforts since 1995, said he thinks the insects are “the best long-term management for tamarisk in North America.”

There simply isn’t enough time, money or manpower to kill the trees manually or with chemicals.

“Hand crews aren’t the way to go. It’s way too expensive. You need larger-scale methods,” he said.

Another advantage the beetles hold over traditional methods is their constancy. Vacillating interest in tamarisk doesn’t bother them. “They work through the funding cycles,” Deuser said.

They’re on their way

Whether or not flycatcher advocates like it, descendants of the beetles already released in the United States will soon be moving into the birds’ trees, experts say.

Already the Lovelock beetles are slowly spreading south, adapting to the climate as they go, Bean said. And with 2 million acres of their favorite food spread out before them, they have plenty of incentive to continue their march.

“I believe they’re probably going to be coming here whether we like it or not,” Deuser said.

Dudley said the beetles are adapting quickly to southern climates in part because of their short life cycles. Three or four generations of beetles can live and die in a single summer. Beetles released in St. George, Utah, might soon make their way into Southern Nevada, he said.

Hill said beetle researchers revealed at a recent meeting in El Paso, Texas, that the beetle and the flycatcher are likely to meet for the first time along the Virgin River in Southern Utah or Northern Arizona.

“Soon we will have a chance to see what will happen when we do have flycatchers and beetles in the same place,” Hill said.

The original release of the beetle in eight Western locations went through years of study and a rigorous review process by the federal Agriculture Department’s animal and plant health inspection service, which regulates release of all “biocontrol” agents, or natural weed managers such as the beetle.

There are those who think the flycatcher will adapt to the lack of tamarisk as it did to the plant’s original appearance.

“I am supportive of the flycatcher and want it to survive,” Deuser said. “But I believe it will adapt. It’s adapted already to the widespread reduction of willow. I’m confident it will survive through beetle infestation as well and adapt (back) to native plants in the future.”

DeLoach said the beetles don’t work so quickly that the flycatcher’s habitat will disappear all at once, either. As tamarisks are defoliated, they must be replaced slowly, over years, by native plants, he said.

And Dudley said in many cases native vegetation will do the work on its own, spreading and flourishing as tamarisks decline. But he said it is important to make sure that native plants, not invasive weeds, fill the void left behind.

Dudley said a team of a dozen scientists will study the effects of the beetles in Nevada. They will simulate defoliation of tamarisks by beetles using herbicides and monitor animal and native plant reactions to eradication.

Even if the tamarisk leaf beetle were released in Southern Nevada and the rest of the Southwest tomorrow, experts say they know tamarisk will never be gone for good.

“You’re not going to get complete control anywhere,” DeLoach said. “Biological control won’t ever do that. You never eradicate the plant.”

Once the beetles truly beat the tamarisk back, their own populations start to decline. Then the cycle begins again.

“Even if you had enough money and tried to eradicate (tamarisk), it’s not going to happen,” Bean said. “It’s all a matter of balance.”

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