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In arid West, a foreign legion of beetles takes on a thirsty invader

Scientists say the beetles released on Southwest riverbanks could tame the water-sucking tamarisk trees.

By Staff writer of The Christian Science Monitor / September 23, 2008

Defoliated tamarisk bushes line the Virgin River in the northwestern corner of Arizona. Just three weeks earlier, beetles known as Diorhabda elongata passed through the area, feeding on the green leaves of the tamarisks and leaving behind these browning bushes. The result pleased scientists who helped introduce the foreign beetles to parts of the American West as tamarisk-control measure.

Tony Avelar/ Special to the Christian Sceince Monitor

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Virgin Gorge, Ariz.

Armies of foreign beetles are on the march along the river systems of the desert Southwest, and ecologist Tom Dudley greets them as little green liberators.

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He is among a group of scientists and land managers who are bringing the beetles to America to wage war on tamarisk, an invasive plant that now dominates the Southwest riverbanks. The program holds out the promise – and potential peril – of shifting the environment in the west for trees, birds, and humans alike.

The tamarisk has become a pariah in these parts for crowding out native willow and cottonwood trees, and worsening wildfires. But it’s the plant’s thirst that earns it the most ire. By some estimates, the slender-branched shrub uses up more of the Colorado River than the residents of Las Vegas and southern Nevada.

“We wanted to improve the habitat for native vegetation,” which has the added benefit of using much less water, “maybe half as much,” says Mr. Dudley, a professor at the University of California, Santa Barbara.

That puts ecologists like Dudley, who are interested in repairing stressed habitats, in league with government agencies that want steady and sustainable water sources. Lake Powell and Lake Mead, the water tanks of the Southwest, are below 50 percent capacity after years of drought.

“We’re not talking about getting extra water that everyone divvies up, we are talking about getting those [lake levels] up” to avoid rationing, says J.C. Davis, spokesperson for the Southern Nevada Water Authority. “To the extent you keep the water in the reservoir rather than in the roots of the tamarisk, then everyone on the river benefits – including us.”

When picky eating is a good thing

In a gorge carved by the Virgin River, a tributary of the Colorado, Dudley swings a net over some tamarisk and peers into his catch: dozens of green, tic-tac-sized beetles. The beetle, Diorhabda elongata, eats one thing only – the tiny, scaly green leaves of the tamarisk.

It’s a point researchers spent years confirming before anyone was allowed to release the bugs, brought over from places like Kazakhstan and Crete into the US. It’s not unusual for insects to be such picky eaters – that’s what makes them valuable for so-called biocontrol efforts such as this, says Dudley.

The first permitted releases of beetles began on Western rivers in 2001, and these early sites are just beginning to yield information about the long-term impacts of the more than 1 billion beetles now in the US.

Their burgeoning numbers speak to some concerns about the idea. “Biocontrol is not a very fine-edged tool,” notes Mark Sogge of the US Geological Survey. “It’s something that once you release it, you don’t have control over where it goes, how fast it acts....”

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