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United States Department of Agriculture

Agricultural Research Service

Research Project: Biological Control of Invasive Terrestrial and Riparian Weeds in the Far Western U.S. Region, with Emphasis on Thistles, Brooms and Cape-Ivy

Location: Exotic and Invasive Weeds Research

2011 Annual Report


1a.Objectives (from AD-416)
1) Characterize the diversity and basic biology of target weeds, including yellow starthistle and other weeds such as Russian thistle and Cape-ivy, estimate their potential range and environmental/economic impacts, and determine their regions of origin..
2)Discover and evaluate the host-specificity and potential efficacy of arthropod biological control agents for target weeds such as Cape-ivy, yellow starthistle, Russian thistle, French broom, and Scotch and bull thistles..
3)Evaluate the population dynamics and efficacy of biological control agents, their impact on non-target species, and relevant interactions in associated biological communities and farming systems, for weeds such as Cape-ivy, French broom, yellow starthistle, and Russian, Scotch and bull thistles.


1b.Approach (from AD-416)
We will develop classical biological control programs to help control invasive alien plants such as Cape-ivy, yellow starthistle, Russian thistle, French broom, and Scotch thistle. Molecular genetic methods will be used to help characterize genetic diversity of the target weeds and determine their geographic origin, which are necessary to direct foreign exploration for prospective agents. Climatological analysis of the known geographic distribution of target weeds will predict potential geographic range for invasion in the USA. Field and laboratory experiments will be used to measure the environmental and economic impacts of these target weeds. With the assistance of foreign cooperators, we will discover prospective arthropod biological control agents for the above weed targets. We will evaluate the host-specificity and potential efficacy of these agents in experiments conducted in our quarantine laboratory and in the field where these agents are native. Host specificity bioassays and GC-MS analysis of volatile organic chemicals of target and nontarget plants will help determine the importance of plant secondary chemistry in determining specificity of prospective biological control agents. We will conduct field experiments to study the population dynamics and efficacy of biological control agents after they have been released for weeds such as Cape-ivy, French broom, yellow starthistle, and Russian, Scotch and bull thistles. This will include studies on impact on non-target species, and on possible interactions within targeted biological communities and farming systems. Replacing 5325-22000-020-00D 11/01/2010.


3.Progress Report
Progress was made on all three main objectives, protection of natural ecosystems from terrestrial, aquatic, and wetland weeds. For Objective 1 Biodiversity, specimens of Scotch thistle were collected in Turkey and Spain and sent to cooperators for DNA analysis as part of an on-going study of genetic variation of the species. For Objective 2 Host specificity, a colony of the psyllid, Arytainilla hakani, collected in France was established in our quarantine laboratory in preparation to further study its host specificity and potential efficacy. We completed host specificity evaluations on 7 of 13 additional species of nontarget plants for two prospective agents of Cape Ivy: a stem-boring moth, Digitivalva delaireae, and the gall-forming fly, Parafreutreta regalis. Exploration was conducted in the Mediterranean region for prospective biological control agents of Russian thistle and Scotch thistle. Three species of insects were sent to our quarantine laboratory for host specificity evaluation: Lixus cardui and Lixus rosenschoeldi, stem-boring weevils of Scotch thistle and Russian thistle, respectively, and Larinus fliformis, a weevil that destroys flower heads of yellow starthistle. Olfactometer studies were conducted in conjunction with chemical analysis of volatile plant compounds to help understand how a host-specific insect, Ceratapion basicorne, chooses its host plant. Studies were conducted to measure the potential impact of predatory mites on a prospective mite biological control agent of Russian thistle, Aceria salsolae. For Objective 3 Impact, flower heads of bull thistle were sampled at 24 sites to determine the distribution and abundance of the previously released fly, Urophora stylata. Populations of yellow starthistle and Russian thistle were monitored at long-term study sites in California.


Last Modified: 12/20/2014
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