RiversEdge West is monitoring the possible resumption of a battle between an exotic biological control agent, the tamarisk leaf beetle, and non-native tamarisk.
Both are Eurasian species. The U.S. Department of Agriculture unleashed the beetles in 13 states between 2001 and 2010 to battle quickly spreading tamarisk, which was introduced in the 1800s to prevent erosion in southwestern states.
According to RiversEdge West biologists, cooperating groups and community members are reporting new and returning populations of tamarisk beetles from the Amargosa River Basin in California to the Gila River in southern Arizona to northern Texas. Western Oklahoma may soon join that list.
“I am always searching for people in Oklahoma to keep watch for tamarisk beetles because they are likely to recolonize someday, likely moving north from Texas,” RiversEdge tamarisk beetle specialist Amanda Stahlke said via email.
“It’s a big mystery as to why beetles died out in that area and why they haven’t recolonized. That said, populations seem to be growing in northern Texas, so I’m actually expecting they may recolonize sooner than later, and it would be great to have folks looking,” she said.
Salt cedar is a problem in watersheds because it crowds out native vegetation to create a monoculture in limited riparian habitat along streams of the arid west. The deep-rooted trees are water hogs compared to native species and deposit salt on top of the ground with their deciduous needle-like leaves.
The USDA Animal and Plant Health Inspection Service tested the beetles as a control measure and found they left native vegetation alone. The beetles were more mobile than expected and spread to the home ranges of the endangered southwestern willow flycatcher.
The birds had turned to tamarisk for nesting habitat as river impoundments and diversion for irrigation reduced native willow and cottonwood habitat in New Mexico, Arizona, and eastern California.
It became a case of introducing one artificially introduced species to destroy another but potentially wiping out a native endangered species in the process.
However, The beetles continue to assist with much-needed tamarisk control across the western U.S. The beetles defoliate and can eventually kill tamarisk, which allows land managers to restore the diverse mix of native vegetation best for soil health and native wildlife.
The beetles also spread to parts of Oklahoma, where tamarisk encroaches on western rivers. Oklahoma is home to a different sub-species of willow flycatcher that has healthy populations. In 2013 the beetles were recorded as far east as Stillwater, on the Cimarron River,according to a RiversEdge ArcGIS map. Most residents were happy to see them.
The beetles died out in many areas years ago, including Oklahoma, but now they seem to be returning, and biologists are turning to citizens to help track that recovery.
RiversEdge reports it has worked with 70 partners since 2007 to document the insects, which now range from Chihuahua, Mexico, north to California and Oregon, and east to Idaho, Wyoming, and Kansas.
The larvae, mostly black with a yellow line down each side, are less than a half-inch long but do the most feeding and tree damage. Two to four generations cycle through each summer before adult beetles go into diapause (like hibernation) beneath the trees in winter.
Populations ebb and flow with available tamarisk. Adults will fly to a new patch or die after eating all of the tamarisks in an area.
People who want to help track the beetles can send observations (present or not present) with a unique GPS point and date to tamariskbeetledate@riversedgewest.org. RiversEdge also accepts shape files or Google Earth kmz/kml files, offers anExcel spreadsheet, and, new this year, will curate iNaturalist app observations under theTamarisk beetles (biocontrol agents) Project.
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