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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
2013 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:
In the Rio Grande Valley, Arundo donax (giant reed) causes a security problem for Border Patrol, hides loose cattle that carry disease, and favors the larvae of cattle fever ticks. DHS provided ARS with significant funding to solve this problem through biological control. An introduced gall-forming wasp and an armored scale have thinned stands of the plant. EBCL is working with ARS at Mission, TX, to introduce a third agent (Lasioptera donacis, Cecidomyiidae, gall-forming flies). Swallow wort is an aggressive invasive weed in northern climates. A noctuid moth is a promising biological control agent, but attempts to collect and rear it in 2013 failed to produce enough material for specificity testing. It remains an important candidate for control of this weed and work will continue with ARS Ithaca. Medusa head rye is an invasive weed in the western United States. EBCL received BLM funding to look for both insect and microbial biological control agents. A chloropid grass fly, Dicraeus sabroskyi is being tested in central Turkey. A laboratory test in Thessaloniki showed that a smut (Ustilago phrygica) also attacked wheat, eliminating it from consideration. Microbial biological control agents against Canada thistle and Russian thistle are being developed in cooperation with the ARS laboratory at Fort Detrick. The agents are being tested against field populations of the plants in Greece, collaborating with Aristotle University. Results to date indicate that the pathogens will be specific and effective. EBCL is working with the French SupAgro Agricultural University to organize the 4th International Symposium on Weeds and Invasive Plants, to be held in Montpellier 18-23 May, 2014. This conference will be an occasion to compare many aspects of weed science from all over the world, as well as a chance to showcase ARS weed science. One of the scientists from EBCL is funded by OECD to perform a research project in New Zealand on food web interactions between biological control agents of Vincetoxicum (swallow wort), their parasitoids, and the plant itself. The hypothesis is that such complicated interactions might be manipulated to improve the effectiveness of biological control. `The EBCL is host to a Ph.D. candidate from SupAgro studying integrated management of leafy spurge in France. His research has shown that a mixture of methods can effectively suppress this weed. This project represents some significant achievements for the laboratory: its first French-funded Ph.D. student and a project that benefits the laboratory’s host country. The Biotechnology and Biological Control Agency (BBCA) is a private foundation based in Rome, whose funding comes from EBCL, BLM, and special projects. BBCA collaborates with other entities concerned with biological control of weeds, including CABI (Delémont, Switzerland), Plovdiv (Bulgaria) University, and the National Institute for Food and Agriculture (the W-3185 regional project). During 2013, BBCA did significant work on biological control of yellow star thistle, Scotch thistle, perennial pepperweed, Russian olive, giant reed, and Russian knapweed. Tests were conducted in Bulgaria, Turkey, and Serbia.


4.Accomplishments
1. Additional test on Larinus filiformis and L. latus, as new potential candidate agents for the biological control of yellow star thistle and Scotch thistle. Yellow star thistle is a significant weed in crops and also crowds out native plants in the United States, as does Scotch thistle. Finding biological control agents against these species has been a challenge because closely related plants are valued parts of the native flora. Open field tests carried out by cooperators in Rome, Italy and Plovdiv, Bulgaria clearly showed a narrow host range for the seed feeder weevils Larinus filiformis and L. latus, respectively on yellow star thistle and Scotch thistle. These are the most promising potential biological control agents found to date. Their successful development will decrease the use of herbicides on crops and restore important habitats to their original condition in the United States.

2. Discovery of the association of Arthrinium fungus with a natural enemy of giant reed. Giant reed is an invasive weed that grows twenty feet high in dense stands when it is in a riparian area. It was introduced from Europe into North America by the early colonists because of its utility for construction. This weed causes many problems in the Rio Grande Valley of Texas, creating a security risk for the Customs and Border Patrol, enhancing the likelihood of introduction of the cattle fever tick, and using precious water resources. The Department of Homeland Security has funded ARS to develop biological control agents that will eventually restore a natural balance between giant reed and its natural enemies. Two biological control agents have already been successfully introduced from Europe to Texas. The third is proving to be more difficult to rear and study in the laboratory. This year scientists at the European Biological Control Laboratory, Montpellier, France discovered that the female fly has specialized organ on its ovipositor that holds spores of a particular kind of fungus called Arthrinium. The fungus was identified using molecular techniques, taking spores directly from the fly’s ovipositor. An experiment showed that flies reared on plants inoculated with the fungus completed development successfully; whereas, uninfected plants failed to produce any flies. The fungus seems to be important for larval survival in the plant and may also be involved in damage to the plant. This basic knowledge about the fly and the fungus will allow scientists to perform host-range testing necessary to get permission to release it in Texas. It may also lead to artificial diets for the fly that would make rearing for release much more economical.

3. First international symposium on silver-leaf nightshade. Silver-leaf nightshade, Solanum elaeaginofolium, is native to the Western Hemisphere, but has become a devastating invasive weed in parts of the Mediterranean basin, including Greece. Earlier work by the European Biological Control Laboratory showed that populations of the weed in Greece probably originated from the southern United States. Biological control projects in the past have identified promising natural enemies, some of which have been used in South Africa. The European Biological Control Laboratory’s location in Thessaloniki, Greece conducted the first international symposium on this weed in cooperation with the American Farm School’s Perrotis College. The work shop was attended by 15 participants from 11 countries (France, Italy, Albania, Bulgaria, Greece, Turkey, Iraq, Jordan, Lebanon, Morocco, and the US). Participants reported that herbicides could be used to control the weed, but that the environmental risk and cost were prohibitive. A resolution was reached to cooperate in a larger biological control project. The project attracted positive media attention and will lead to action against this weed. Biological control may provide a permanent, cheap, and environmentally acceptable solution to the problem.


Last Modified: 9/10/2014
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