2009 Annual Report
1a.Objectives (from AD-416)
1: Investigate ecological mechanisms important for the development of bio-rational strategies for suppression of exotic and invasive weeds on western watersheds.
Sub-objective 1.A. Conduct foreign exploration for natural enemies of saltcedar and cruciferous weeds, and evaluate candidate species for risk to non-target organisms.
Sub-objective 1.B. Conduct organismal, population, and community-level ecological studies of weed natural enemies and their interactions with the environment.
Sub-objective 1.C. Develop remote-sensing technologies useful in evaluating and characterizing weed biological control strategies.
2: Define ecosystem responses to integrated weed management and identify and test appropriate restoration technologies.
Sub-objective 2.A. Determine the interactive effects of Diorhabda elongata herbivory and saltcedar defoliation on the ecohydrology of riparian ecosystems.
Sub-objective 2.B. Monitor native plant and animal taxa as potential indicators of impacts of saltcedar control at successive trophic levels.
Sub-objective 2.C. Investigate restoration and rehabilitation strategies following integrative control of invasive weeds in riparian ecosystems.
1b.Approach (from AD-416)
New biological control agents of saltcedar will be identified, characterized, and evaluated for both efficacy and safety in conjunction with on-going projects on saltcedar biological control and management. This work will be accomplished with other projects within the Research Unit and with cooperators at other ARS locations. Additional linkages with overseas cooperators in areas native to saltcedar will also be developed to aid in the assessment of potential biological control agents prior to regulatory approval. New risk analysis techniques will be developed and applied to assess both pre- and post-release impacts of approved biological control agents on target and non-target organisms. Detailed studies will be conducted to assess natural enemy impact on the target plant along with similar impacts caused by other methods of integrated vegetation management strategies. Studies will be conducted in both agricultural and natural areas for vegetation characterization and change. New methods of revegetation of affected habitats will be conducted using ecological methods guiding plant succession toward desired beneficial species. Species complexes are expected to be different depending upon the specific habitats of concern, environmental conditions at affected sites, and the goals of the local land managers. Research procedures will strive to produced effective and economically viable methods of revegetation that are practical for both public and private land management agencies.
We continued foreign exploration and initiated field trials for natural enemies of saltcedar, perennial pepperweed, and Russian olive in Eurasia. Several potential natural enemies were collected; specimens from these collection trips are now awaiting taxonomic determination and subsequent biological studies. In its adventive range of the western U.S., the biology of perennial pepperweed (faunistic arthropod surveys, geographic range assessment, genetic characterization of diversity and modes of dispersal, and pest status surveys) was studied. Field and laboratory studies were conducted to develop immunological labeling methods for weed biocontrol agents, which will facilitate identification of important natural enemies of biocontrol agents. We continued monitoring lizard and bird populations in areas where the saltcedar leaf beetle was released for biocontrol of saltcedar. This provides an index of predation intensity on newly released biocontrol agents, as these animals are the primary vertebrate insectivores occurring in saltcedar habitats. We continued monitoring small mammal populations in native riparian habitats and in saltcedar habitats as indicators of effects of saltcedar invasion on wildlife. The beetle established its first populations at one of our sampling sites (Stillwater National Wildlife Refuge) during 2008 and became abundant there in 2009, so current efforts are focused there. Although some rare riparian obligate species have only been found to occur in native habitats, there are few differences to date in the species composition of small mammal communities in these areas as compared with saltcedar. Aerial and satellite imagery and ground collection of beetles was conducted in California, Nevada, and Utah to quantify beetle dispersal and biological control success. Beetles dispersed in a near exponential manner, documenting continued defoliation and spread across wide areas adjacent to the test sites. A simulation model of beetle development and population growth rates is now fully operational, and is currently being spatialized. Saltcedar was repeatedly sampled to determine water source use and the amount of water used per unit sapwood area. Additionally, measurements of leaf area index and beetle density were collected in a spatio-temporal sampling scheme. Gas exchange was measured to determine the effects of herbivory on carbon uptake and water loss. One site was continuously sampled for eddy covariance data including carbon and water fluxes. Isotopic sampling of water vapor was delayed in favor of completing several studies to determine the effect of beetle herbivory on litter decomposition and nutrient cycling. A study was initiated on the water relations of perennial pepperweed. Additionally, due to stakeholder concerns, monitoring of understory plant species composition was initiated. In implementing across-site responsibilities for subordinate projects, the ADODR conducted several personal visits with the UNR College of Agriculture, and had discussions with the Principal Investigators (BBCA, Univ. of Idaho, and Univ. of Nevada) & others via telephone & at scientific meetings.
Effects of a biological control agent, saltcedar leaf beetle, on weed physiology. The effects of beetle herbivory on plant physiology and leaf litter quality are important to gain a better understanding of beetle biocontrol on saltcedar-invaded riparian systems. ARS scientists at Albany, CA conducted a greenhouse experiment to understand the effects of beetles on saltcedar physiology, particularly the proximate cause of early leaf fall that results from beetle herbivory, and a year-long field study to understand the effects of early leaf fall on litter quality and decomposition rates. The greenhouse experiment demonstrated that early leaf fall results from localized response to herbivory that renders saltcedar unable to control water loss during both the day and night, and leaf fall is a result of increased water stress, while the field study demonstrated that early leaf fall produces litter of higher quality because plants were unable to retranslocate both nitrogen and phosphorus and this litter decomposed more rapidly. Physiological responses to herbivory were shown to have potential impacts on carbon, water and nutrient cycling, and contribute to understanding the restoration potential of these highly valued riparian ecosystems.
Immunological marking of biological control agents for ecological studies. Interactions between biocontrol agents and their natural enemies are important because natural enemies may disrupt the agent’s population development, thereby hindering its impact on the weed. ARS scientists in Albany, CA, conducted lab and field studies to assess the utility of using immunolabels to study predation of weed biocontrol agents. They demonstrated that.
1)retention of two labels (i.e., chicken and rabbit proteins) was greater than 2 weeks, and.
2)protein labels can be transferred directly from eggs to larvae. These results indicate that protein labeling can be used in field studies of predation on different life stages of biocontrol agents. Improved knowledge of predator-prey interactions will benefit weed biocontrol programs during the critical phase of agent establishment, and in the later stages of weed biocontrol when the control agent and the target weed have achieved low density equilibrium.
Beltran-Przekurat, A., Peilke, R.A., Peters, D.C., Snyder, K.A., Rango, A. 2008. Modeling the effects of historical vegetation change on near-surface atmosphere in the northern Chihuahuan Desert. Journal of Arid Environments. 72:1897-1910.
Allred, B.W., Snyder, K.A. 2008. Ecophysiological responses of Chihuahuan desert grasses to fire. Journal of Arid Environments.72:1989-1996.