You are here



  • This field guide focuses on the most problematic weeds in northwestern North 
    America for which there are at least some biocontrol agents established. Multiple 
    photos and descriptions of each weed included in this guide emphasize key 
    identification traits and plant ecology. Comparison tables are included to further 
    aid in identification of related weed species, where applicable. For each weed 
    included in this guide, all biocontrol agents currently found in North America are 
    described individually.
  • This guide by Drs. Scott Nissen, Andrew Norton, Anna Sher, and Dan Bean offers key options and considerations for tamarisk treatment, including biocontrol, targeted guidance on how to develop management plans, implement various control strategies, and plan restoration for treated sites. Useful resource as an accompaniment to Sher et al. 2010. 
    Nissen et al. 2010.   
  • Tamarisk Coalition produced a pamphlet that provides information on tamarisk and the tamarsik beetle, the biological control that was introduced by the U.S. Department of Agriculture to help manage the plant.

  • The MIGCLIM R dispersal model is calibrated and used to project the timing of arrival of subtropical tamarisk beetles into flycatcher habitats over the next 10 years, and to derive least dispersal time cost paths into these habitats.
  • Amanda Stahlke, University of Idaho, and Ellyn Bitume, Colorado State University present "Using Genomics to Understand Hybridization and Selection in Biocontrol: the Tamarisk Leaf Beetle as Case Study" at TC's 2016 Conference.  
  • Presentation from Dr. Dan Bean at TC's 2016 Research and Management Conference about the research and potential for Russian olive biocontrol. 

    • Invasive species disturb ecosystems and threaten biodiversity. Invasive species management, such as biological control, can cause additional disturbances, so quantifying how native species respond to invasive control is important
    to inform best management practices
    • We quantifed southwestern bird communities in sites that varied in the amount of the non-native plant tamarisk (Tamarix spp.), before and after biological control efforts
    • Following biocontrol, we found significant differences in community composition and diversity, and several bird species declined by ≥30%
    • Bird declines were ameliorated in the presence of native vegetation, consistent with the hypothesis that tamarisk biocontrol decreases prey availability and alters microclimate
    • We recommend land managers monitor areas dominated by tamarisk after biocontrol, and if re-establishment of native vegetation is slow or lacking, consider the feasibility of active restoration
    Salinity-Herbivore-Plant Interactions: Effects of Plant Health, Beetle Defoliation, and Local Adaptation on Tamarix Growth
    Randall Long1*, Tom Dudley2, Adam Lambert3, Kevin Hultine4
    1Ecology, Evolution, and Marine Biology, University of California Santa Barbara, Santa Barbara, CA
    2Marine Science Institute, University of California, Santa Barbara, Santa Barbara, CA
    3Marine Science Institute, University of California, Santa Barbara, Santa Barbara, CA
    4Research, Conservation and Collections, Desert Botanical Garden, Phoenix
    Tamarix, a non-native tree, is abundant in riparian areas throughout the western US and is highly successful in adverse environments that combine high salinity and arid conditions, with genotypes being locally adapted to the site conditions. In addition, Tamarix is repeatedly defoliated over the growing season by the tamarisk leaf beetle (Diorhabda spp.). This defoliation has resulted in variation of dieback, with soil salinity being shown to be correlated with dieback. To investigate whether there are synergistic interactions between salinity and herbivory we conducted a greenhouse experiment using two genotypes of Tamarix from different salinities at the Cibola National Wildlife Refuge. The plants were grown under reciprocal salinities and then defoliated using Diorhabda carinulata. Beetle preference for plant-salinity interactions were measured using choice trials to test if beetles preferred healthier plants as local adaptation to site salinity exists in Tamarix. Biomass accumulation was measured to test our hypothesis that there would be a synergistic effect of salinity and herbivory, with a prediction that low salinity genotypes would be most affected in high salinity.
    A Pearson’s Chi-squared test was used to evaluate if beetle choice was influenced by salinity, and was found to be significant (2(2) =20.67, p << 0.001,  =0.05). With beetles preferring plants that were grown in the salinity in which they were collected from, supporting our hypothesis that beetles preferred healthier plants. With respect to the synergistic effect of salinity and herbivory we found that there was a significant interaction between beetle herbivory and salinity on biomass accumulation of both leaves (ANOVA: F1,56 =19.84, p<<0.001) and stems (ANOVA: F1,56 =2.88, p =0.095). Combined these results indicate that beetles preferentially feed on healthy plants, but that increased salinity leads to synergistic effects in reducing total biomass.
  • Henry et al. 2018

    In this study, we employ multi-scale analysis (Moran’s Eigenvector Maps) to better understand the variation in tree canopy exposed to defoliation by a biocontrol beetle (Diorhabda spp.).

    Plant Recruitment Under Beetle-Defoliated Tamarisk in Grand County, Utah: 2009 to 2019
    Tim Graham1*, Wright Robinson2, Tim Higgs2
    11701 Murphy Lane, Moab, UT 84532, USA;
    2Grand County Weed Dept., 1000 Sand Flats Road, Moab, UT 84532, USA;,
    Diorhabda carinulata (tamarisk leaf beetles) were first introduced in Grand County in 2004.  Regular monitoring of beetle abundance and distribution around the county began in 2007.  In 2009 we began exploring responses of other plants to the defoliation of tamarisk.  Initially, we simply recorded the presence of plants seen under and adjacent to stands of tamarisk selected to monitor this response, compiling species lists for each site and in total each year; we recorded whether species were native or introduced, and their life history strategy (annual, biennial, or perennial).  The number of sites has fluctuated as we’ve dropped and added sites for a variety of reasons.  In 2011 we began running a 30 m point-intercept transect at each site; providing cover estimates along the transects as well as the general survey species lists.  Results from 2009-2019 will be presented; 111 species have been observed at least once in the general surveys; the number seen at a single site varied from one to 26 species in a single year.  There is a trend toward increasing perennial native species, declining perennial introduced species, and increases in non-native annuals across all sites over the years.  The total number of vascular plant species increased over time but individual sites behaved very differently, depending on a variety of factors.  Average proportional plant cover estimated from point-intercept transects also fluctuated between sites and overtime at individual sites.
  • Authors: Anna A. Shera, Hisham El Waera, Eduardo Gonzáleza,b, Robert Andersona, Annie L. Henrya, Robert Biedrona, PengPeng Yuea

    This report includes a comprehensive and detailed analysis of the vegetation response to a single watershed-scale restoration effort that includes 40 sites along the Dolores River from 2010-2014.

    Using Restriction Enzyme Digests as a New Method for Species Identification in Diorhabda Species
    Chris Schaaf1
    1Colorado Mesa University – Department of Biological Sciences, Grand Junction, CO, USA;
    Diorhabda species (tamarisk leaf beetles) were introduced into the United States as a biological control agent for the invasive tamarisk species, with some populations successfully controlling the spread of tamarisk and others failing. It has been proposed that this disparity in efficacy of different populations could be tied directly to the species of each population. The identification of Diorhabda spp. through traditional methods is taxing on researcher time, budgets, and laboratory materials. This research has developed a new method for performing species identification of Diorhabda spp. that can be performed cheaper, faster, entirely in-house, and with less of an environmental impact than the traditional protocol.
    Species identification is traditionally performed by Sanger sequencing of the mitochondrial gene, cytochrome c oxidase subunit 1 (COI), which costs $17.76 per sample and takes 10-14 days to accomplish. Through this research, a method for species identification of the Diorhabda genus has been developed that utilizes restriction fragment length polymorphism (RFLP) to target nucleotide sequences within the COI gene that are unique to each species. By performing two restriction enzyme digests that target these non-conserved sites, a significant difference in DNA fragment lengths can be observed through gel electrophoresis that allows for positive species identification. This method allows species identification to be performed in as little as two days, and at a 72% reduction in cost ($4.96 per sample) when compared to the traditional method. 
  • Author(s): Steven W. Carothers; R. Roy Johnson; Deborah M. Finch; Kenneth J. Kingsley; Robert H. Hamre
    In the Preface to volume 1, we discuss the development of riparian ecology as one of the newest of ecological fields that gained significant momentum in the 1950s and 1960s as part of the general “riparian movement” in the United States. The field expanded rapidly throughout the latter half of the 1900s. Volume 2 involves more than two dozen authors - most with decades of experience - who expand upon riparian and other topics introduced in volume 1. Two important recent developments are global climate change and impacts of introduced tamarisk leaf beetles (Diorhabda spp.) in the American West. Other chapters in volume 2 that provide current information evaluate the losses of riparian habitat, including “extirpation” of a large number of mesquite bosques (woodlands) in the Southwest; the restoration of riparian ecosystems damaged by anthropogenic activities; the importance of a watershed; and the importance of riparian ecosystems to recreation. The combination of volumes 1 and 2 examines the evolving understanding of scientific implications and anthropogenic threats to those ecosystems from Euro-American settlement of the region to present. >> Volume 1 is also available in Treesearch:
  • Authors:
    Kent R. Mosher, Heather L. Bateman
    Amphibians and reptiles (herpetofauna) have been linked to specific microhabitat characteristics, microclimates, and water resources in riparian forests. Our objective was to relate variation in herpetofauna abundance to changes in habitat caused by a beetle used for Tamarix biocontrol (Diorhabda carinulata; Coleoptera: Chrysomelidae) and riparian restoration. During 2013 and 2014, we measured vegetation and monitored herpetofauna via trapping and visual encounter surveys (VES) at locations affected by biocontrol along the Virgin River in the Mojave Desert of the southwestern United States. Twenty-one sites were divided into four riparian stand types based on density and percent cover of dominant trees (Tamarix, Prosopis, Populus, and Salix) and presence or absence of restoration. Restoration activities consisted of mechanically removing non-native trees, transplanting native trees, and restoring hydrologic flows. Restored sites had three times more total lizard and eight times more yellow-backed spiny lizard (Sceloporus uniformis) captures than other stand types. Woodhouse’s toad (Anaxyrus woodhousii) captures were greatest in unrestored and restored Tam-Pop/Sal sites. Results from VES indicated that herpetofauna abundance was greatest in the restored Tam-Pop/Sal site compared with the adjacent unrestored Tam-Pop/Sal site. Tam sites were characterized by having high Tamarix cover, percent canopy cover, and shade. Restored Tam-Pop/Sal sites were most similar in habitat to Tam-Pop/Sal sites. Two species of herpetofauna (spiny lizard and toad) were found to prefer habitat components characteristic of restored Tam-Pop/Sal sites. Restored sites likely supported higher abundances of these species because restoration activities reduced canopy cover, increased native tree density, and restored surface water.
    Tamarisk Leaf Beetle Species and Habitat Analysis with Management Implications for the Middle Rio Grande, NM
    Ondrea Hummel1*, Matthew Johnson2*, Chris Sanderson1
    1 Tetra Tech, Albuquerque, NM, USA;, 505-235-6470;   
    2 Northern Arizona University, Flagstaff, AZ, USA;
    The introduction and proliferation of tamarisk leaf beetle (Diorhabda spp.) [TLB] for the biological control of tamarisk (Tamarix spp.) since 2001 has initiated landscape-scale compositional shifts in riparian vegetation communities and altered habitat conditions. TLB populations in the Middle Rio Grande have increased from 2015 through 2018 with overall effects on tamarisk dominated habitat.  This increase is mainly due the presence of the Northern TLB (Diorhabda carinulata) that arrived in 2012 and the Subtropical TLB (Diorhabda sublineata) that expanded range into New Mexico from Texas in 2015.
    The biocontrol of tamarisk may result in a reduction of habitat and population decline for the Southwestern Willow Flycatcher (Empidonax traillii extimus) [flycatcher] and/or Yellow-billed Cuckoo (Coccyzus americanus) [cuckoo]. Moreover, reductions in tamarisk vegetative cover may result in  increased Russian olive (Elaeagnus angustifolia) abundance and additional management problems.
    In 2017, the study was initiated to analyze TLB related changes to tamarisk-dominated habitat, examine specific locations the study area over time using remote sensing (RS), and field monitoring of vegetative and avian communities. Vegetation data was collected at 30 selected locations in 2017; avian population data was collected in 2018; and TLB data was collected in both 2017 and 2018. Data was collected in order to understand baseline conditions, ongoing effects of TLB use, and provide a reference to post-treatment patterns and dynamics related to vegetation composition and structure, and associated habitat conditions. The study documents system responses related to riparian habitat structure and plant community alterations (based upon TLB use over time), as well as resulting possible changes to avian species richness and density. The ongoing monitoring of riparian systems altered by TLB is critical to understand management implications to vegetation and the avian community, especially the flycatcher.
    Impact of Tamarix Biocontrol on Understory Plant Community Traits
    Annie Henry1*, Eduardo González2, Anna Sher3
    1 University of Denver, Department of Biological Sciences, Denver, CO, USA;
    2 Colorado State University, Department of Biology, Fort Collins, CO USA;
    3 University of Denver, Department of Biological Sciences, Denver, CO, USA;
    The biological control agent Diorhabda spp. has spread farther and faster than originally anticipated, leading to the pressing question of what plant communities will replace Tamarix as its dominance is reduced. While previous research has examined plant community response to Tamarix defoliation in terms of species composition, this research uses a trait-based approach for a more mechanistic understanding of the environment-plant community relationship. A functional trait approach focuses on the morpho-physiological characteristics of organisms rather than species identity, to directly relate plant community response (response traits) to environmental filters such as light and water availability and effects (effect traits) on environmental processes, such as resistance to floods through variations in surface roughness. Using a cluster analysis of plant traits, we found five distinct guilds present in Tamarix dominated biocontrol and non-Tamarix dominated reference sites. These guilds were primarily defined by the plants ability to reproduce asexually and to resprout after damage. Secondarily, guilds were defined by drought or anaerobic tolerance, height, seed weight and specific leaf area. Higher cover of guilds that are able to reproduce asexually was associated with higher precipitation and permanent water sources. Guilds that only reproduced sexually were associated with higher temperatures and greater distance to water. Disturbance tolerant understory plants were associated with biocontrol sites with little live Tamarix. This approach will provide managers with a tool to anticipate the effects of Tamarix biological control and more successfully revegetate after removal, based on knowledge of what trait combinations will thrive given specific site characteristics. Ultimately, this approach will also allow us to anticipate ecosystem effects of altered plant communities.
  • Sher et al. 2018

    Abstract: Removal of invasive species is often an important, if not central, component of many riparian restoration projects, however little is known about the response of plant communities following this practice. In particular, active control of the exotic, dominant tree Tamarix spp is often a focus of riparian restoration, much of which occurring against a backdrop of biological control by a folivore  beetle. Our research employed controls in both time and space to investigate the impact of active Tamarix removal methods in sites subjected to biological control in 40 sites sampled three times over a period of five years. We found that reduction in Tamarix cover was much greater over time with active means of removal, however the native understory increased both with and without active removal. Importantly, change in the relative cover of understory native species was significantly negatively correlated with change in Tamarix cover, with those sites that received a combination of low-disturbance-mechanical, chemical and bio-control showing greater increases in native understory dominance than those sites with biological control alone or high-disturbance mechanical control. Sites with only biocontrol still contained 10% live Tamarix cover>7 yr since the beetle was released there. Taken together, these results suggest that the reduction of this exotic tree, even by biological control that leaves some canopy intact, can
    facilitate recovery of the native plant community. As such, this study supports the Field of Dreams hypothesis that states that once niches are restored, native plants should be able to recolonize.

    The Biology of Biocontrol: Enhancing the Biological Control of Tamarisk to Better Serve Riparian Restoration and Recovery
    Dan Bean1*, Alex Gaffke2, Tom Dudley3, Levi Jamison4, Amanda Stahlke5 and Zeynep Ӧzsoy6
    1Colorado Department of Agriculture, Palisade Insectary, Palisade, CO, USA;
    2USDA ARS, Gainesville, FL, USA;
    3Marine Science Institute, University of California, Santa Barbara, CA, USA;
    5University of Idaho, Moscow, ID USA;
    6Colorado Mesa University, Grand Junction, CO, USA;
    Beetles in the genus Diorhabda were first released in North American in 2001 for the control of shrubs in the genus Tamarix.  Since then they have spread to many river systems in the western US and have more recently entered Mexico. They have been successful in reducing Tamarix densities in some areas and yet have been difficult to establish in other areas.  They have also moved into areas where Tamarix is utilized by the endangered southwestern willow flycatcher, Empidonax traillii extimus, raising concerns that episodic defoliations could negatively impact this and other wildlife species.  Resource managers are searching for methods to better predict and increase the likelihood of defoliation events as well as to prevent defoliation in areas in which Tamarix serves as nesting substrate for the endangered flycatcher. Our knowledge of the behavior and phenology of Diorhabda has steadily increased since beetles were first released. In addition, through the use of new techniques in genomics we are developing an ever richer array of molecular tools for tracking population genetics as well as the potential identification of genes involved in biological processes critical to biocontrol efficacy such as host plant interactions, behavior, and phenology.  We will present recent work on manipulation of beetle populations using the male-produced aggregation pheromone (beetle herding), prediction of phenological events using a newly developed model as well as progress and potential in Diorhabda genomics.  These will be presented in the context of using science to better manage riparian ecosystems.
  • A look at current and near-future biocontrol agents in Colorado.

    Tamarisk Beetle Colonization of The Rio Grande in New Mexico: A Long-Term, Multi-Faceted Study Using Genetic Analysis and Field Surveys
    Levi Jamison1*, Zeynep Ozsoy-Bean2, Amanda Sthalke3, Matthew Johnson4
    2Colorado Mesa University, Grand Junction, CO, USA;
    3University of Idaho, Moscow, ID, USA;
    4EcoPlateau Research, Flagstaff, AZ, USA;
    This poster summarizes the results of a long-term study on the colonization of the Rio Grande by tamarisk beetles (Diorhabda spp.), a group of biocontrol agents introduced to manage invasive/non-native tamarisk (Tamarix spp.). Using a combination of genetic analysis and field surveying, we documented the rapid spread of tamarisk beetles and their impacts to tamarisk along the Rio Grande between Albuquerque, NM, and El Paso, NM. During the study, we monitored two different populations of tamarisk beetles as they spread across the watershed from opposite directions, eventually overlapping. We studied this unique field occurrence using two kinds of genetic analyses to understand the degree of hybridization between the species within the field and the outcomes of this overlap. In addition, we used field survey data to look at changes in tamarisk beetle demographics and changes in tamarisk canopy health over a five-year period. The results of this multi-year study are useful for understanding the long-term composition and behavior of tamarisk beetles and will help guide the management of tamarisk invaded riverways in the West.
    Author(s): R. Roy Johnson; Steven W. Carothers; Deborah M. Finch; Kenneth J. Kingsley; John T. Stanley
    Fifty years ago, riparian habitats were not recognized for their extensive and critical contributions to wildlife and the ecosystem function of watersheds. This changed as riparian values were identified and documented, and the science of riparian ecology developed steadily. Papers in this volume range from the more mesic northwestern United States to the arid Southwest and Mexico. More than two dozen authors - most with decades of experience - review the origins of riparian science in the western United States, document what is currently known about riparian ecosystems, and project future needs. Topics are widespread and include: interactions with fire, climate change, and declining water; impacts from exotic species; unintended consequences of biological control; the role of small mammals; watershed response to beavers; watershed and riparian changes; changes below large dams; water birds of the Colorado River Delta; and terrestrial vertebrates of mesquite bosques. Appendices and references chronicle the field’s literature, authors, "riparian pioneers," and conferences. >> Volume 2 is also available on Treesearch:
  • Using high-resolution  multitemporal, multispectral data, the authors classified tamarisk defoliation in the Glen Canyon area in Arizona. The high spatial resolution classification provides key information to effectively inform restoration treatments regarding where and how much mechanical removal or controlled burning could be performed. Furthermore, the defoliated tamarisk classification can help understand the site-specific and spatially-variable relationship between tamarisk and the tamarisk beetle at this critical state when their interactions are still developing and currently unknown. 

    Northern Tamarisk Beetle Impact to Tamarisk and Phenology in Western Colorado on a Ten-Year Scale
    Nina Louden1 and Dan Bean2
    1Colorado Department of Agriculture, Biological Pest Control, 750 37.8 Rd., Palisade, CO 81526, USA;
    2Colorado Department of Agriculture, Biological Pest Control, 750 37.8 Rd., Palisade, CO 81526, USA;
    Northern tamarisk beetles (Diorhabda carinulata) and their impact to tamarisk continue to be monitored at sites throughout Colorado by the CDA, Palisade Insectary as initiated in 2008. Currently, twelve sites are located in western CO and eight sites in eastern CO for a total of 20 monitoring sites. To date, all 12 sites in western CO have undergone at least two to eight defoliation events. Despite lower beetle abundances measured across sites in 2011 and 2014 through 2016, beetle numbers have steadily increased across all sites in western CO from 2017 to 2019. In 2018 and 2019 beetles were observed moving up the Gunnison River into the town of Delta which has never been observed despite multiple years of beetle releases at the Rattlesnake Gulch Site. Increases in tamarisk dieback have occurred across defoliated sites with sites undergoing multiple defoliations ranging in dieback from 40%-70%.  Tree mortality has shown more variable (0-52%) at an average of 21%. Finally decreasing tamarisk flowers resulting from beetle herbivory have reduced the mean number of trees to flower by 57% with defoliated sites never reaching more than 40% flowers per canopy as had initially been observed and continuously measured at Rattlesnake Gulch previous to beetle arrival. To date, beetle establishment has resulted in long term and cost-effective control over tamarisk invasion in the west. Here we examine their impacts in western CO over a ten year period along with emerging patterns of beetle population dynamics.
    Adaptation of Diapause Induction Cue Enables Range Expansion of the Tamarisk Leaf Beetle Across Latitude
    Eliza Clark1*, Ellyn Bitume2, Dan Bean3, Amanda Stahlke4, Paul Hohenlohe5, Ruth Hufbauer6
    1Graduate Degree Program in Ecology, Colorado State University, Fort Collins, CO, USA;
    2US Forest Service, Hilo, HI, USA;
    3Colorado Department of Agriculture, Palisade, CO, USA;
    4University of Idaho, Moscow, ID, USA;
    5University of Idaho, Moscow, ID, USA;
    6Graduate Degree Program in Ecology, Colorado State University, Fort Collins, CO, USA;
    Biological control agents encounter novel environments as they expand from initial release points.  For hibernating and diapausing species, adapting to environmental cues that indicate seasonal change is crucial.  The northern tamarisk leaf beetle (Diorhabda carinulata), biological control agent of the invasive plant tamarisk, has rapidly adapted to different daylengths across latitudes that signal to the beetle to prepare for winter.  Understanding evolution of these cues will help us study the impacts of local adaptation during range expansions across heterogeneous environments. 
    We define a new trait, days until diapause at one day length, to study adaptation to daylength at an individual level. We measured the genetic variation in days until diapause in one northern population in both home and away environments and the responses of eight populations from varying latitudes to both northern and southern environments.
    We found that days until diapause was highly variable for the population in its home environment and not significantly variable in a novel environment. When comparing populations across the range, we found significant differences in the diapause behaviors of northern core beetles and southern edge beetles in each environment.
    The variation in the trait days until diapause indicates that adaptive evolution is possible, but only when populations are near their home environment.  Days until diapause across the range indicated that populations have become locally adapted.  These results can be used to predict the rate of range expansion and control of the target weed and inform research on ecological factors important to range expansions.

RiversEdge West's

mission is to advance the restoration of riparian lands through collaboration, education, and technical assistance.