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United States Department of Agriculture

Agricultural Research Service

Research Project: Discovery and Evaluation of Classical Biological Control Agents for Invasive Eurasian Weeds Affecting Agricultural and Natural Areas
2011 Annual Report


1a.Objectives (from AD-416)
Objective 1: Characterize the basic biology of target weeds, such as hoary cress, swallow-worts, medusahead, and guineagrass, and their natural enemies. Sub-objective 1.A. Characterize the genetic diversity and basic biology of target weeds and determine their regions of origin. Sub-objective 1.B. Conduct foreign exploration in Europe, Asia, and Africa for natural enemies of U.S. target weeds. Objective 2: Elucidate plant-natural enemy interactions and identify potential candidates for U.S. introduction. Sub-objective 2.A. Conduct preliminary host-specificity and effectiveness testing and facilitate U.S. introduction through prioritization and rearing of agents for target weeds, including, but not limited to giant reed, and swallow-worts. Sub-objective 2.B. Evaluate plant-insect interactions in evolutionary and ecological contexts – the role of visual ecology in host plant finding, selection and acceptance by candidate agents; evolution of differential host specificity in a biological control agent; efficacy of multiple vs. single weed biological control agents.


1b.Approach (from AD-416)
We have adopted a “weed management pipeline” approach to our research that answers essential questions for successful classical biological control. A significant focus of this research is aimed at understanding the basic biology of target weeds, especially characterization of the genetic diversity of targets in their native and adventive ranges. This work will help identify the target’s region of origin, as well as the region(s) from which populations of the target have been introduced into the U.S. Foreign exploration for natural enemies will be conducted concurrently with these studies on target biology; this exploration will provide candidate biological control agents for the following studies. These investigations address target weed-natural enemy interactions, which will include host-specificity and effectiveness testing to facilitate introduction to the U.S., as well as experiments aimed at developing a mechanistic understanding of the evolutionary, ecological, and physiological factors of plant-insect interactions relevant to weed biological control. Successful control of a target weed usually requires decades of research effort, and the research proposed here will be an important step towards ecologically-rational management of some of the most important invasive weeds in the U.S.


3.Progress Report
We began research on leafy spurge invasion biology in France and preliminary host range testing of a psyllid natural enemy of French broom. Exploration for medusahead rye in Asia found seed feeding flies and pathogens. Field experiments are evaluating the host range of the flies and target impact. Seed predation is under study. Genetic diversity in native and invasive medusahead races identified source regions, narrowing the search for biocontrol agents. Results show that multiple introductions came from different parts of Europe; agents from each part of the range may be needed to attain specificity to each population. Projects 0212-22000-023-10R and 023-13R (BLM) support our rangeland weed research. Medusahead pathogen studies are planned by our Greek substation and cooperators. Swallowwort biocontrol studies characterized the biology and behavior of a phytophagous European moth. Host range tests show the moth is restricted to this target. Climatic comparisons indicate it is better adapted to the US range than other agents. Enemies of giant reed were collected in Europe and sent to Texas. A scale insect was the second agent released in the US. Recoveries indicate it is establishing. Collections will continue until mass rearing is achieved. A leaf mining cecidomyiid fly was associated with inoculation of pathogens of giant reed, themselves potential biocontrol agents. We will study the fly’s biology and association with the pathogens. Herbivorous insects feeding on African guinea grass were identified. We analyzed gene sequences of African and Texan samples and found that the grass is a species complex. Molecular analyses revealed that the invasive grass in the US came from E and not W Africa as once thought. New exploration for adapted natural enemies is planned. SCA 0212-22000-023-14S (BBCA) funds biocontrol exploration and evaluation research on five weed targets. Impact evaluations were conducted with Turkish weevils feeding on yellow starthistle, Sicilian stemborer weevils feeding on Russian thistle, and stem and crown boring weevils feeding on Scotch thistle. Host range tests were made with populations of stemborer flea beetle feeding on Scotch thistle. Host range tests of a Turkish fruit boring moth on Russian thistle will begin next season. The host ranges of a root borer weevil and a mite on perennial pepperweed were evaluated. Exploration in Eurasia collected biocontrol agents of French broom, including a psyllid and seed feeding weevil. American Farm School MOU 0212-22000-023-11M gives our Greek substation lab and office space, facilitating exploration and field work in the Balkans. Agents of silverleaf nightshade found include five insect herbivores and several pathogens; pathogens will be studied with Greek cooperators. The origin of nightshade in Greece was identified as distinct introductions from Texas and Mexico; results will define a search for effective biocontrol agents. Research on the impact of Canada thistle rust disease is ongoing. We also characterized isolates of rhizobacterium agents of weed targets and samples of other targets and agents. Plans were made to study the visual ecology of agents of invasive weeds.


4.Accomplishments
1. Field releases and establishment of a new giant reed natural enemy in Texas. Giant reed, ARUNDO DONAX, is an invasive weedy grass species from the Mediterranean region that clogs waterways in southern border states, wasting precious water and hindering effective border patrol activities. It became a problem in the U.S. because it lacks effective natural enemies in North America. Exploration for its natural enemies conducted by ARS EBCL in southern Europe has thus far resulted in a number of species being evaluated in the U.S. for safety and efficacy against the grass. A scale insect, RHIZASPIDIOTUS DONACIS, was the second biocontrol agent to receive an APHIS release permit, and has been released in Texas by ARS and cooperators. Overwintering recoveries this year indicate its successful establishment there. As it spreads it will help to suppress the grass and restore original riparian habitats.

2. Significant genetic variability identified in introduced medusahead rye. The invasive grass medusahead rye currently infests parts of CA, ID, NV, OR, UT, and WA states, where it is an important rangeland weed. Allozyme diversity was compared in samples from native and introduced invasive populations of medusahead rye in an attempt to identify the source populations and narrow the search for targeted biological control agents. Initial results support the idea that multiple introductions have occurred from different regions of Europe. This suggests that multiple agents from different parts of the native range may be needed in order to address the specificity that might be required for each population of grass.


Review Publications
Maguire, D., Sforza, R., Smith, S.M. 2011. Impact of herbivory on performance of Vincetoxicum spp., invasive weeds in North America. Biological Invasions. DOI 10.1007/s10530-011-9955-4.

Gaskin, J.F., Bon, M.C., Cock, M.J.W., Cristofaro, M., De Biase, A., De Clerck-Floate, R., Ellison, C.A., Hinz, H., Hufbauer, R., Julien, M., and Sforza, R. 2011. Applying molecular-based approaches to classical biological control of weeds. Biological Control. 58:1–21.

Last Modified: 12/20/2014
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