February 1992
February 1992

Colorado Basin Riparian Restoration Program

The Tamarisk Biocontrol Project  is one of the most intensively studied invasive plant control programs ever undertaken. With over 10 years of testing to ensure Diorhabda  was not only effective, but also would not feed on native plants nor crops, the U.S. Department of Agriculture authorized its release, with input from a technical advisory group that included the U.S. Fish and Wildlife Service. While long-term benefits of tamarisk control are anticipated, there is always some risk when releasing a foreign organism.

2000 - The cost of water lost to tamarisk is estimated at $133 to 285 million annually

2006 - D. carinulata transferred from central Utah to Virgin River near St. George (37.1*N)

2008 - D. carinulata is considered established in the Virgin River area and has dispersed downstream to the Virgin Gorge.

2009 - D. carinulata dispersal and defoliation marked at the Arizona-Nevada border (36.8*N)

2010 - The beetle has defoliated throught the Virgin Valley (36.6*N)

2010 - APHIS decides to halt biological control program

2010 - In December, a flood event occurred - shifting the active channel path and wiping out many restoration sites.  

2008-2010 – goal of assessing whether or not active revegetation will lead to an improvement in SWFL colonization using rapid response and sustainable methods

2011 - 20 meter transects were established to assess biocontrol affects in 2011, focusing on aspects such as plant richness ad solar radiation.

2011 - The beetles is found around Lake Mead and the former town of St. Thomas (36.4*N) Both the larvae and the adults feed on and scrape the leaves, leading to defoliation.

2011 – Upper Gila River designated as Critical Habitat for Southwestern Willow Flycatcher (SFWL) by U.S. Fish and Wildlife Service.

2012 - D. carinulata becomes established below Hoover Dam, marking the arrival into the Colorado River Basin

  • The tamarisk leaf beetle in the region (D. carinulata) does not choose all species of tamarisk as suitable hosts. Though there are other, more suitable species or ecotypes of the Diorhabda beetle for the different tamarisk species, it is unlikely that that they would be approved for release - as such, not all of the tamarisk may be removed with this particular biocontrol method.

2013 – Strategy proposed to clear a mosaic of tamarisk and allow for planting of native plants with the intent of having native understory species compete with other invasive species. This would allow the remaining tamarisk to provide vertical and structural diversity for habitat and native species to thrive in the connected communities without tamarisk.

2014 – D. sublineata moving westward through New Mexico

2009 – 2014 - surveys were done along the Virgin River to assess biodiversity prior to and after the tamarisk beetle’s arrival to the area, to assess the impacts of bio-control of the area. For example, the SWFL were monitored at 60 point count station sites for two years in order to establish nesting success for comparison.  (Desert Southern Rockies Final LCC Proposal - Bateman, Johnson, Dobbs, Dudley, Kuehn)

  • Ground arthropods were initially measured in 2009 and 2010, with post-biocontrol effects measured from 2011 to 2012.
  • In order to assess the effect of biocontrol on wildlife diet composition, fecal matter was looked at under microscope to measure whether beetles were being chosen in lieu of other food types or in addition to.
  • From 2009 to 2010, a variety of birds were measured initially, with the post-biocontrol effects measured from 2011 to 2012, in order to assess the effects of the beetle on nesting factors such as temperature and relative humidity related to defoliation.