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Corvallis, OR, United States

Ferrarese E.,Earth Design Consultants Inc. | Garono R.J.,Earth Design Consultants Inc.
Biological Control | Year: 2010

Dispersal of biological control agents and their subsequent population growth can be a major determinant of the success of landscape-scale weed control programs. Biocontrol agents must be able to disperse across the distances between patches of host plants in order to colonize and control their targets. The presence of three species of biocontrol agents for purple loosestrife (Lythrum salicaria L.): Galerucella calmariensis L. (Coleoptera: Chrysomelidae), Galerucella pusilla Duftschmid (Coleoptera: Chrysomelidae), and Nanophyes marmoratus Goeze (Coleoptera: Brentidae), on relatively remote islands in the Columbia River Estuary (CRE) indicate that these organisms have the ability to disperse across large expanses of open flowing water to colonize remote sites. Previous studies suggest that colonization of these islands by active flight is highly unlikely; therefore, some other dispersal mechanism must be responsible for colonization. A spatial database of all known biocontrol agent release sites for purple loosestrife within 68 river kilometers of our CRE study area was developed and field surveys for biocontrol agents were conducted. A GIS was used to model dispersal distances between biocontrol agent recovery sites and the nearest conspecific release site. Tidal water flow within the CRE was assessed as a potential dispersal mechanism across the modeled distances. The ability of the biocontrol agents to withstand submersion was evaluated in field tests. Our results indicate that it is highly likely that passive water transport has been responsible for some of the long-distance open-water dispersal that would have been necessary for colonization of the remote islands where biocontrol agents were recovered. © 2009 Elsevier Inc.

Ferrarese E.R.,Earth Design Consultants Inc. | Garono R.J.,Earth Design Consultants Inc.
Wetlands | Year: 2011

Previous studies have concluded that biological control of Lythrum salicaria may not be possible in tidal environments because the biological control agents are easily removed from their host plants by tidal action. In this study, we examined the spatial relationships between L. salicaria, its biocontrol agents, and the agents' feeding damage in relation to elevation using Spatial Analysis by Distance IndicEs (SADIE) at three sites within the Columbia River Estuary (CRE), USA. We then compared the abundances of overwintering Galerucella pusilla adults recovered along an elevational gradient at two sites within the CRE. Galerucella pusilla aggregated most frequently at elevations above mean high water; however, clusters of feeding damage tended to be evenly spread across all elevations. We found significantly more overwintering beetles at high elevations than low elevations, despite similarities in the availability of overwintering habitat (number of dead stems). Our results indicate that although biological control of L. salicaria may be possible at higher elevations in tidal estuaries such as the CRE, it will not likely be an effective means of controlling infestations at low elevation areas. An approach that integrates multiple management strategies to control L. salicaria is therefore recommended for tidal ecosystems. © 2011 Society of Wetland Scientists.

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