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Project description

Ecological basis for biological control of giant reed, Arundo donax, in California. (06XN028)
Program Exotic Pests and Diseases Research Program
Principal
investigator
T. Dudley, Marine Science Institute, UC Santa Barbara
Host/habitat Riparian Area
Pest Giant Reed Arundo donax
Discipline Weed Science
Review
panel
Natural Systems
Start year (duration)  2006 (Two Years)
Objectives Conduct extensive surveys and collate information on Arundo distribution in California for future monitoring of agent dispersal and establishment.

Establish intensive baseline vegetation information to document impacts to target plants and ecosystem responses following eventual release of biocontrol agents.

Characterize invertebrate assemblages on Arundo, locally and in the Western states, in part to determine if existing herbivores cause significant impacts to this weed and may be suited for development of augmentative biocontrol.

Develop scientific and public information to facilitate public acceptance of, and participation in, the biocontrol and other habitat restoration actions.

Project
Summary
Giant reed (Arundo donax) may be the most destructive invader of California riparian areas. Classical biological control is a cost-effective and environmentally benign alternative to traditional control methods. Candidate agents have been identified, but their eventual release is predicated upon evidence that damage is substantial, and greater than that potentially caused by herbivores already present in North America. It is also important to establish monitoring programs so that efficacy can be evaluated when and if releases take place.

We will characterize vegetation for the Santa Clara River riparian ecosystem as a baseline for future evaluation of field effectiveness of Arundo biocontrol, and anticipated recovery of desired vegetation. Associated woody and understory plants will be surveyed, and plant growth parameters will be compared with those in the European range of origin. We will also characterize the herbivore complex already present on giant reed in North America, in particular a recently discovered stem-boring wasp in Ventura County, to evaluate the potential for augmentation biocontrol as an alternative to introduction of non-native natural enemies. We will create an internet-based outreach program for the dissemination of information critical for the control and management of Arundo populations, regionally and nationally.

Second-year
progress
We have sampled Arundo and associated vegetation intensively in the Santa Clara and Ventura rivers and extensively throughout southern California. At a subset of study areas, we documented Arundo growth parameters including stem densities, diameters, and percent cover.

In experimental plots in the Santa Clara River, we evaluated plant diversity, decomposition rates, soil moisture, and light availability in Arundo-infested and uninfested areas. Preliminary analysis shows that Arundo has significant negative impacts on all of the parameters measured.

We have sampled insects in Arundo populations in 10 riparian systems in Santa Barbara, Ventura, Los Angeles, Orange, and San Diego counties. These surveys have yielded three insect species that are characteristically associated with Arundo, all exotic in origin. One insect, Tetramesa romana, is an herbivorous wasp currently under evaluation by the USDA (Weslaco, Texas) for possible release. We have collected T. romana adults from these systems for genetic analysis to evaluate their relatedness to populations from the Mediterranean region, the origin of this species.

During summer 2007, we conducted host-range studies with T. romana, which we postulated was the most appropriate herbivore to consider for redistribution as an augmentative biocontrol tool to Arundo-infested sites in California. It was shown to be highly specific to the genus Arundo, and neither oviposited in nor was found in association with nontarget grasses, including numerous native and/or economic species, as well as non-native, large-stature grasses.

Following this test to ensure specificity, we conducted a trial redistribution exercise to release T. romana in two uninfested sites within Santa Barbara County, and that trial continues in 2008. In March 2008, we initiated an experiment to determine efficacy of T. romana,manipulating nitrogen level and a systemic insecticide to quantify herbivore impact, and how nutrient augmentation influences herbivore impact; that study also continues in summer 2008.

First-year
progress
We have been sampling Arundo and associated vegetation intensively in the Santa Clara and Ventura rivers and extensively throughout southern California. As our sampling progresses, we are documenting Arundo growth parameters, including stem densities and percent cover. In experimental plots in the Santa Clara River, we are evaluating plant diversity, decomposition rates, soil moisture, and light availability in Arundo infested and uninfested areas. Preliminary analysis shows that Arundo has significant negative impacts on all of the parameters measured.

We have sampled insects in Arundo populations in 10 riparian systems in Santa Barbara, Ventura, Los Angeles, Orange, and San Diego counties. These surveys have yielded three insect species that are characteristically associated with Arundo, all exotic in origin. One insect, Tetramesa romana, is an herbivorous wasp currently under evaluation by the USDA (Weslaco, Texas) for possible release. We have collected T. romana adults from these systems for genetic analysis to evaluate their relatedness to populations from its origin in the Mediterranean region.

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