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More than 200,000 yellow-striped Diorhabda beetles, Diorhabda elongate, are coming to the rescue in Colorado.  In order to take a great big bite out of tamarisk, 100,000 leaf-eating Chinese beetles have already been released along the banks of the Arkansas River. 

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Tamarisk

Native to Asia, African and Europe, tamarisk, or salt cedar, has taken over 80,000 acres along several rivers in Colorado.  With roots as deep as 100 feet, it is estimated that one single tamarisk can soak up more than 200 gallons of water every day, drying up streams and springs and lowering water levels, impacting wildlife.  Tamarisk produces around 500,000 tiny wind-dispersed seeds a year while the dead branches and leaves create fuel for wildfires.  Wildlife, insects and livestock apparently do not like the leaves.  And with no natural enemies in the United States, tamarisk is difficult and expensive to destroy.

Yellow-striped Diorhabda

When released in Nevada in 2001, adult beetles defoliated thousands of acres of tamarisk, killing about 70 percent of the weeds in just five years.  The beetles gang up on the tamarisk and move from weed to weed, returning later to eat any remaining shoots.  The beetles, just over a quarter inch in length, only eat tamarisk and will starve to death if the weed is not available. 

Delicate Balancing Act

But the project is not without controversy.  Although the release of the yellow-striped Diorhabda may help control the highly invasive weed, the release of the insects may also threaten the Southwestern Willow flycatcher, Empidonax traillii extimus, an endangered bird known to nest on tamarisk. It is estimated only 900 to 1,300 pair remain.

Two groups, the Center for Biological Diversity and the Maricopa Audubon Society, filed a lawsuit earlier this year against the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service (APHIS) and the U.S. Fish and Wildlife Service.   The suit was filed due to granting permits for “indiscriminate introduction” of the beetle in areas inhabited by the Southwestern Willow flycatcher, threatening the habitat of the endangered bird.

Chris Diogini, acting executive director of the National Invasive Species Council, said the challenge “is making sure you don’t get rid of one invasive species only to see it replaced by another.”
 
It is expected that another 100,000 beetles will be placed on the weed sometime this week.   If successful, the beetle may be used on other invasives.

For more information, visit the Colorado Weed Management Association (CWMA) and the Tamarisk Leaf Beetle Monitoring Protocol 2009.   Read Biocontrol of Tamarisk Using the Tamarisk Leaf Beetle, by Dr. Dan Bean, Director of Biological Pest Control at Palisade Insectary for the Colorado Department of Agriculture (CDA).

Photographs courtesy of Steven Damron via Flickr.
 

 

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