Ecological Effects of the Biocontrol Insects, Larinus Planus and Rhinocyllus Conicus, on Native Thistles

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dc.contributor.advisorInouye, David Wen_US
dc.contributor.authorDodge, Gary Jonathanen_US
dc.contributor.departmentBiologyen_US
dc.contributor.publisherDigital Repository at the University of Marylanden_US
dc.contributor.publisherUniversity of Maryland (College Park, Md.)en_US
dc.date.accessioned2005-08-03T13:57:17Z
dc.date.available2005-08-03T13:57:17Z
dc.date.issued2005-05-11en_US
dc.description.abstractBiological control of invasive weeds is, by nature, a delicate balance between introducing effective biological control agents and not introducing another invasive species. A disconcertingly similar suite of traits is used to describe invasive insect species and to identify appropriate biological control agents (or candidates): good control agents and invasive exotic species are good dispersers, they are good colonizers, they have high reproduction rates, and they are suited for broad distribution. It shouldn't come as a surprise that two previously released weed biological control agents can now be characterized as invasive species. The purpose of this dissertation is twofold: first, it is to explore the ecological relationship between predispersal seed predation and plant population dynamics, and second, it is to elucidate the risks to native plants involved with introduction and redistribution of exotic species. Rhinocyllus conicus and Larinus planus are Eurasian seed-head weevils, introduced and redistributed broadly across the western U.S. to control exotic thistles. Exclusion experiments on native thistles, including one that is rare and imperiled, at sites in Colorado present strong evidence that a decrease in seed production due to herbivory by both R. conicus and L. planus has lead to a reduction in recruitment of the thistles. The density of seedlings in both cases, even in the excluded units, was far below where density dependent effects may play a role in the dynamics of the thistle. Further, a survey of eight western states demonstrates established populations of L. planus and effects on seed production in multiple native species in four states. It also documents the near ubiquity and broad diet breadth of R. conicus. The process for approval of phytophagous biocontrol agents has become more cautious and more efforts are made to prevent nontarget herbivory. Nevertheless, land managers still routinely redistribute previously approved, non-regulated agent insects that appear to pose a higher risk to the native flora. The results of this research will benefit resource managers who wish to consider use of phytophagous insects as biological control agents as well as help ecologists and environmental managers understand the risk probabilities of biological control applications.en_US
dc.format.extent887099 bytes
dc.format.mimetypeapplication/pdf
dc.identifier.urihttp://hdl.handle.net/1903/2413
dc.language.isoen_US
dc.subject.pqcontrolledBiology, Ecologyen_US
dc.subject.pqcontrolledBiology, Botanyen_US
dc.subject.pqcontrolledBiology, Entomologyen_US
dc.subject.pquncontrolledCirsiumen_US
dc.subject.pquncontrolledbiological controlen_US
dc.subject.pquncontrolledinvasive speciesen_US
dc.subject.pquncontrollednontarget effectsen_US
dc.subject.pquncontrolledherbivoryen_US
dc.subject.pquncontrolledRocky Mountain Biological Laboratoryen_US
dc.titleEcological Effects of the Biocontrol Insects, Larinus Planus and Rhinocyllus Conicus, on Native Thistlesen_US
dc.typeDissertationen_US

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