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The natural world. Looking pretty for 3.5b years.

Rescue Beetles

Author: Hugh Bollinger/Tuesday, July 15, 2014/Categories: sustainability, environment, Archive Pick of the Week

Anyone who has ever rafted the rivers of the American southwest knows the towering canyon walls and class 5 rapids that mark the route. What may not have been appreciated among all the redrock grandeur is an invader plague of major proportions the  tamarisk , or salt cedar.

 
Invasive Tamarisk (credit: Earlham College)      Salt Cedar Stands, Colorado (credit: CSU)

According to accounts, tamarisk was introduced to the US as an ornimental shrub, for windbreaks, and as a shade tree in the 19th Century. During the Depression, it was used to fight soil erosion and was planted by the millions. Two species escaped from cultivation to become a widespread invasive pest.

The biological characteristics of tamarisk make for a monster: it alters the structure of native plant communities; degrades native wildlife habitat (particularly for birds); draws salts from the subsoil resulting in salinization: draws down water resources and transpires it away; and increases the intensity fires and floods.

In the western canyonlands, dense stands of tamarisk have been shown to consume more water than similar groves of the native cottonwoods. One salt cedar tree has been measured to transpire 25% of its weight in water per day in a landscape water is essential for farms, cities, and recreation.
Managers at Departments of Interior and Agriculture and private land owners have tried control measures including burning, herbicides, and tree removal to little avail. One report determined that tamarisk clearing, combining herbicides, burning, and mechanical control has cost between $750-1300/ha or ~$1850-3200/acre and the trees just bounced back. What to do?

Enter the tamarisk leaf beetle, Diorhabda carinulata . Like the highly trained dogs that assist wildland firefighters and paramedics searching for victims or marines on patrol looking for lost comrades, the tiny beetle has come to the rescue. It was originally imported from China and was tested for twenty years to make certain it wouldn't become a pest itself. The beetle was found to only consume tamarisk leaves. The Grand Canyon Trust calls them astonishing. First released on ~2 acres of private land in Colorado, the beetles multiplied and by the 2nd year after establishment their populations had defoliated over 10 miles of tamarisk infestations on the Colorado River. Three years later a corridor from Moab, Utah near the Colorado state line had moved downstream 70 miles to the Green River leaving dead trees. The hope now is for the beetle larvae to keep munchingtamarisk all the way down the Grand Canyon to the Colorado River delta on the Gulf of California.

 
Tamarisk Leaf-beetle Larvae (credit: GCT)       Dead Tamarisk (Rocky Mt. Bird Observatory)

It is often said that "good things come in small packages". This has certainly been the case with these "rescue beetles".

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