A beetle's life: one year later

GRAND JUNCTION, Colo.—The Bureau of Land Management Grand Junction Field Office (GJFO) continues to collaborate with staff from the Palisade Insectary after releasing Diorhabda elongata deserticola Chen, the tamarisk leaf beetle, in early August 2005. Riparian sites, selected for release of the tiny beetle with a huge appetite for tamarisk leaves, have long since lost their native vegetation to decades-old growth tamarisk. Through the efforts of these two agencies, waterways and riparian areas within the GJFO may begin to look much as they did a century ago in just a few years.

Today, of the 8,000 tamarisk beetles released in 2005, an encouraging yet small number of their offspring can still be found at the original release site. This confirms their ability to survive and reproduce in western Colorado. The goal this summer is to establish the tamarisk beetle at several new sites in anticipation of next year’s field season, which should reveal a significant increase in the population of beetles and some visible damage to the tamarisk.

“By 2008, we expect to see large-scale defoliation of tamarisk at the release sites,” Insectary Director Dan Bean, who has been involved with leaf beetle research for many years, said. “With Diorhabda, we can be hopeful that waterways and riparian areas throughout the West will once again be prime habitat for native willows and cottonwoods.”

Last year’s release of the beetle only occurred after years of research and interagency cooperation. The Palisade Insectary, operated by the Plant Industry Division of the Colorado Department of Agriculture, plays an important role in the release and monitoring of the insect, which underwent more pre-release testing than any other biological control agent in U.S. history. Experiments with beetle pheromone, the chemical released by beetles when they mate, are being conducted by Insectary staff at some release sites. The release tree is tagged with vials of beetle pheromone and a compound the tamarisk plant releases when it is under attack. The intent is to attract beetles to these trees, keeping them from dispersing. So far, it seems to be working.

“The Insectary has taken on a huge workload for the GJFO, monitoring these sites and bringing invaluable, in-depth experience to the project,” GJFO Weed Manager Sparky Taber said. “It is a great relationship we have going—good for both the Palisade Insectary and the BLM.”

Looking beyond 2008, BLM staff is excited to begin planning for what happens next. Some successful release sites may be used as an Integrated Weed Management experiment. After the tamarisk beetles kill the tamarisk stands through constant defoliation, noxious weeds such as Russian knapweed, purple loosestrife and cheatgrass are sure to invade the area. After effective treatment, the native seed bank should rebound to revegetate the restored areas.

For more information on the GJFO tamarisk project, contact Sparky Taber at 970-244-3004. To learn more about the Palisade Insectary programs, contact Dan Bean at (970) 464-7916.

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