Tamarisk Beetle Monitoring: Spatial and Temporal Patterns of Diorhabda Carinulata Abundance and Tamarisk Defoliation in Grand County, Utah, 2007-2021


Tim B. Graham1*, Wright W. Robinson2, Tim Higgs2, Gery Wakefield3

1Dept. of Geography, University of Utah, Salt Lake City, UT 84532, and Grand County Weed Department; lasius17@gmail.com

2Grand County Weed Department, 125 E. Center St., Moab, Utah 84532; and 3Southeast Utah Group, National Park Service, 2282 S. Resource Blvd, Moab, Utah 84532


Diorhabda carinulata, the northern tamarisk beetle, was introduced at three locations in Grand County in 2004.  By August of 2006 it was obvious the beetle was well-established and already significantly affecting tamarisk at and beyond the release sites.  Quantitative monitoring began in 2007 and has continued through 2021, providing a record of abundance and distribution across Grand County.  Beetle numbers increased dramatically through 2012, but beetles were rare by the end of the 2012 activity period.  It appeared the population began to collapse in 2013, with extremely low numbers in 2014 and 2015.  In 2016, there was a large increase in both adults and larvae compared to 2014 and 2015.  Total counts of adults and larvae have slowly increased from 2016 to 2021 by which time numbers of adults and larvae had recovered to about 62% and 47 % of the high numbers recorded in 2012 just before the population collapse.  We present results of beetle monitoring and canopy foliage condition over the past 15 years looking for pattern(s) that might provide insights into mechanisms driving beetle population dynamics (e.g., food availability, distance between remaining tamarisk stands, weather) and guidance for how to management tamarisk as a relatively minor component of riparian plant communities now and into the future.