Las Vegas Sun

August 19, 2019

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Tamarisk-eating beetle could help here

A hungry imported beetle that is shaping up as a solution for the pesky tamarisk tree in Northern Nevada has the potential to help Clark County, too, but it will be years before scientists can unleash it here.

Researchers say the Chinese beetle has been phenomenally effective elsewhere in the state over the last three years at gobbling the leaves off tamarisk, or saltcedar, trees -- bushy invaders that suck up the water table and poison their gentler plant neighbors.

In three Northern Nevada locations, the bug has chewed the trees to the point that the scientists now predict the trees will soon start to die, a major feat for a plant that is nearly invincible.

The scientists, from federal agencies and the University of Nevada, Reno, would like to put the beetle to work on the fragile ecosystem of Southern Nevada's Virgin River.

But the U.S. Fish and Wildlife Service has blocked its efforts, saying the beetle's leaf-munching might evict an endangered bird that makes its home in the tamarisk tree.

"The southwestern willow flycatcher, which is listed as endangered, nests in certain places along the Virgin River," Cynthia Martinez, an assistant field officer for the wildlife service, said. And it often nests in tamarisk trees.

UNR's Tom Dudley and his fellow researchers on Monday submitted a request for $800,000 of Clark County funding for monitoring of tamarisk removal efforts over two years. The Bureau of Land Management on Monday was requesting additional funds for the removal itself.

The money would come from a county environmental fund made up of fees paid by developers. The county has six months to decide whether to accept the proposal, Dudley said.

Under the proposals, the BLM would remove tamarisks mechanically -- by bulldozing them -- and then would spray the stumps with herbicide to prevent the extremely hardy plants from growing back. BLM personnel would then try to bring back the willows, cottonwoods and mesquite that were the riverbanks' original denizens before the tamarisk elbowed them out.

"The thought is that if they actively try to restore the native plants, you have a better chance to keep the tamarisk from reinvading," said Matt Brooks, a research botanist with the U.S. Geological Survey in Henderson who is Dudley's co-principal investigator on the Virgin River project.

The scientists would then monitor the effects of the trees' removal on the native plants, the animals, and the water system.

But because of the wildlife service's concerns, the proposal stops short of suggesting introducing the Chinese beetle that has worked so well elsewhere.

Instead, the researchers will themselves strip the leaves off tamarisks in a very small area to compare it to the tree removal effort.

"Because of the willow flycatcher, which is actually nesting in the tamarisk in some places, Fish and Wildlife doesn't want any biocontrol (beetles) used there," Dudley said. "They want to know that there won't be any loss of habitat for that listed bird."

Instead, he continued, "What we want to do is simulate the use of the beetle with a low dose of herbicide, to defoliate the trees without killing them."

By seeing how the ecosystem responds to leafless tamarisk trees -- which are weaker and less thirsty -- the researchers will get an idea of the effect the beetles might have. If the rare birds continue to nest in the bare trees, it could be evidence that the beetles would not destroy their habitat.

For now, "We're not even proposing the beetles in the Virgin River system because it's too politically sensitive," Dudley said. But he said he hopes over the next three years to convince the wildlife service that the beetles are safe to introduce.

Scientists across the West have high hopes for the little bug, which is being hailed as "one of the most dramatic cases of biocontrol in history," according to Dudley.

The zebra-striped black beetle, whose scientific name is Diorhabda elongata, grows to about a one-third of an inch long, about the size of a large ladybug or an average adult pinky fingernail.

After years of testing the beetles in quarantined cages, the scientists set them loose in 2001 in the Stillwater National Wildlife Refuge, near Fallon; along the Walker River, near Schurz; and on a ranch in Lovelock near the Humboldt Sink.

The beetles took almost immediately to the latter two locales. And just last month, the scientists got word that the beetles were starting to establish themselves at Stillwater as well.

In the seven other states where the beetles were introduced, their effect was disappointing or nonexistent. But they have taken enthusiastically to Northern Nevada.

Speaking from the Lovelock site on Monday, Dudley said, "We're amazed -- the beetles have moved about 20 miles further than we expected." He added, "I've been talking to the Pershing County Water Authority, and they're just tickled pink."

But anytime an organism is introduced to a new environment there are dangers. Often, the alien has no natural predators in its new home.

The tamarisk itself is an example of this peril. Native to central Asia and southern Europe, the tree was introduced to the American Southwest in the 19th century to serve as a windbreak along railroad lines and to stabilize riverbanks against erosion.

With roots that can seek groundwater as deep as 100 feet underground and the ability to drink water too salty for other plants, the tamarisk leaves other southwestern plants unable to compete. It spreads rapidly and can survive almost anything, from being submerged in water for more than a year to being consumed by wildfire.

Like a horror-movie alien, the tamarisk regenerates. If you chop it down and do not treat it with herbicide within half an hour, it will have sealed over the cut and begun to grow anew.

Once, the Virgin River -- which enters Nevada from the east at Mesquite and meanders southwest to Lake Mead -- occupied a mostly empty flood plain punctuated with stands of willows. Today, the riverbanks -- some 10,000 acres -- are 95 percent covered with tamarisk, said Dale Devitt, a UNR professor of soil and water based in Las Vegas.

Among the thriving tamarisk, Devitt said, are "remnant galleries of willow" -- the ghostly remains of the area's original inhabitants.

If, through removal or defoliation of tamarisk, the trees' water consumption could be reduced by half -- a big if -- an extra 50,000 acre-feet of water per year could make its way to Lake Mead, Devitt said. That's enough water to supply 125,000 people.

Tamarisk are not the West's only troublesome plant. Another notorious invader is cheatgrass, which came to the mountain West as a stowaway in grain lots, spread rapidly to scrublands and has been responsible for many of the area's fires over the past century.

And there are plenty of examples of pest animals overrunning foreign environments, from the nutria, a beaver-like rodent that was brought to Louisiana from South America by fur farmers, to the poisonous cane toad, exported to Australia from Hawaii to eat bugs off sugar cane.

Could the tamarisk-eating beetle be another dangerous alien? "That has been a question for us," the wildlife service's Martinez said. "Is it going to interact with any other species? Would it jump species to some other native tree or plant?"

Dudley said the scientists are certain there is no way for the beetle to harm anything but the tamarisk because that is all it eats. And none of the plants native to the area is even distantly related to tamarisk, he said.

"Since they're (the beetles) so specialized, there's really no chance" of their becoming a pest, he said.

Instead, when the beetles run out of tamarisk leaves to eat, they simply die, Dudley said, with sadness in his voice. "You'll see thousands of beetles in lines, running away looking for something to eat, literally going off to their doom," he said.

In addition, the beetles are very sensitive to latitude. Because their life cycles are based on the lengths of days, they cannot live very far north or south of their native area.

The beetle subspecies that is thriving in Lovelock is not adaptable to southern Nevada, Dudley said; if the beetles are to be introduced to the Virgin River, another subspecies will have to be found that is more suited to the area.

Using the beetles has obvious advantages over bulldozing the tamarisks. It is less disruptive and can easily treat a large area. Except for the cost of the research, it is basically free, whereas mechanical clearing costs $1,000 to $5,000 per acre.

However, defoliation by beetle does not reduce the fire hazard tamarisk poses, which is the main reason BLM is clearing the trees from the Virgin River, especially near Mesquite. A combination of approaches is probably the answer, Brooks said.

But in the battle of tamarisk vs. beetle -- or even tamarisk vs. human -- the tamarisk will never be defeated, Dudley said.

"Unfortunately, the plant is good at growing back," he said. "A few weeks after the beetles have done their defoliation, it's starting to regenerate. It's more about reducing the weed down to a level where it's more tolerable."