What is the Tamarisk Beetle?

The tamarisk beetle (Diorhabda spp.) is the biological control strategy for managing tamarisk
 
Biological control is the introduction of an insect or other “natural enemy” that predates the invasive plant of concern. The tamarisk beetle was tested by the US Department of Agriculture for over 10 years to ensure that it would be effective, and not feed on native plants or crops here in the western United States.  In 2001, the US Department of Agriculture approved it for release and the tamarisk beetle has since become an important component of tamarisk control.
 
RiversEdge West does not release tamarisk beetles; rather, we provide critical information concerning the tamarisk beetle to land managers to help them with decision making as part of our Tamarisk Beetle Monitoring Program
 
How Does the Tamarisk Beetle Help to Control Tamarisk?
Mechanical and chemical control methods are commonly used to manage tamarisk but may have limited success due to landowner goals, site accessibility, size of the tamarisk stands, expense, and other factors.
 
The tamarisk beetle is another management tool to control tamarisk; the tamarisk beetle and its larvae feed on the leaves of tamarisk, leaving them dry and brown and, in doing so, significantly weakens the plant so that mechanical and chemical controls are more effective. This is referred to as “defoliation” or “browning”.  This browning may happen several times during a growing season and does not signify that the tamarisk plant is dead. Depending on location and specific micro-environmental factors, recent research indicates that it may take 5-7 years of repeated beetle infestation and defoliation for a tamarisk tree to be killed.
 
The tamarisk beetle reduces the reproductive viability of tamarisk. The effectiveness of the beetle is apparent across portions of many western states and parts of northern Mexico, where large areas of tamarisk beetle affected tamarisk can be observed (see pictures below for example).  
 
Although the tamarisk beetle will not singlehandedly eliminate tamarisk, the goal is to help control the spread of tamarisk by reducing its reproductive viability, consequently giving native plants a chance to recover. 
 
   
Before Tamarisk Beetle After Tamarisk Beetle
Tamarisk lines the Colorado River. The tamarisk beetle defoliated the leaves of tamarisk, turning the tamarisk brown. 
 
What Will Take the Place of the Tamarisk?
Land managers and researchers estimate that the tamarisk beetle will probably contribute to the defoliation and eventual mortality of 70-85% of tamarisk in infested areas over the next several years. As tamarisk gradually dies back, space opens up, allowing native plants to re-grow if conditions are suitable. However, native vegetation is often out-competed by weedy species and consequently, land managers are encouraged to monitor their respective river corridors that have been impacted by the tamarisk leaf beetle to understand specific vegetative impacts in their area. 
 
What does the Tamarisk Beetle Look Like?
The adult beetle is yellow to straw colored with roughly four brown stripes running down the forewings covering its back. This beetle is roughly the same size as a ladybug, with a thinner body. Pinkish egg masses are laid near the ends of individual branches. The larvae are very small and appear completely black in the earliest stage; the second and third stages are typically characterized by a long yellow stripe running down either side of its abdomen.
 
Ecosystem Implications
Although biological control can play an important role in suppressing tamarisk and restoring native plant biodiversity, there is an inherent risk when releasing a foreign organism.
 
One unforeseen consequence of tamarisk beetle defoliation is the risk posed to the endangered southwestern willow flycatcher (Empidonax traillii extimus), where beetle populations and flycatcher critical habitat overlap. Tamarisk defoliation during the flycatcher breeding season can expose nests and eggs to the elements and predators. Reestablishment of native trees can provide good habitat in the future but takes a considerable amount of time.  Monitoring of beetle dispersal is needed to assess impacts to the flycatcher and to identify where restoration should be focused to minimize risks.  Fortunately, RiversEdge West has been leading the monitoring of the tamarisk beetle since 2007.  
 
Other potential issues from the beetle include: standing dead biomass mitigation, bank destabilization, restoration challenges, and repercussions implicit with a rapidly changing landscape. Biological control may assist in the long-term recovery and resiliency of riparian communities, but potential short-term consequences cannot be disregarded.
 
Tamarisk Beetle Monitoring Program
RiversEdge West coordinates a diversity of partners to track the tamarisk beetles' distribution (via presence/absence monitoring) to create an annual map that displays the beetle presence across the West. We also educate the public about its potential ecosystem impacts and compile data from applied research so that land managers can effectively employ new approaches for restoration in areas affected by the beetle. 
 
Our tamarisk beetle monitoring program has grown tremendously with over 70 partners (spanning 2007 to 2018).  With documented populations now ranging from Chihuahua, Mexico to California, and up into Oregon, Idaho, Wyoming, and Kansas, the tamarisk beetle (Diorhabda spp.) has quickly become a part of many riparian ecosystems in the West. We work with land managers in all of these places to create the annual map.
 
Workshops and Training
REW hosts workshops to train land managers on how to collect and submit monitoring data and conducts outreach presentations to raise awareness of the tamarisk beetle issues and potential impacts. Each year more people are contributing to the data set that indicates where the beetle is located. The impacts of this program are paying off as an increasing number of land managers are incorporating the beetle into their riparian management plans.
 
To learn about upcoming workshops and training visit our event board.
 
For more information, view these helpful links:
For more information contact Ben Bloodworth at bbloodworth@RiversEdgeWest.org.
 

 

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