Graduate Thesis Or Dissertation
 

Non-target Effects of Biological Control: Ecological Risk of Tyria jacobaeae (Lepidoptera: Erebidae) to Senecio triangularis (Asteraceae) in Western Oregon

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/b8515q81z

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  • Non-target effects are one of the greatest potential risks of weed biological control programs, and understanding non-target effects of biological control at the population level is crucial for predicting when they will occur and altering the perception of biological control as a whole. In this thesis, we assessed the ecological risk of Tyria jacobaeae L. (Lepidoptera: Erebidae), the cinnabar moth, to Senecio triangularis Hook. (Asteraceae) in Western Oregon using a standard risk model that defines risk as the product of the hazard and the exposure to the risk (risk = hazard × exposure). Experimental manipulation of the timing of herbivory by cinnabar moth larvae revealed S. triangularis was sensitive to a match in phenology in year t between late instar larvae and S. triangularis capitula (flower heads) in the primordium, bud, and flower developmental stages. However, S. triangularis survival, growth, and reproduction in year t+1 were relatively insensitive to different timings and intensities of herbivory by cinnabar moth larvae in year t. A decade of observational regional data of populations of S. triangularis in Western Oregon showed a balance between cinnabar moth colonization and extinction and that the intensity of cinnabar herbivory appears to be stable. Across all colonized sites and years sampled, about half of all sampled ramets (individuals of a clone, or genet) were attacked by cinnabar moth larvae and damage was generally moderate (if attacked, conditional mean = 49%, conditional median = 40% leaf area removed per ramet). Lastly, a six-year demographic study showed a fluctuating herbivore regime where marked S. triangularis genets experienced up to four years of herbivory greater than or equal to 75% leaf area removed. Together, this relatively low hazard of herbivory and a widespread but moderate exposure to herbivory support conclusions that T. jacobaeae poses a low to moderate risk to S. triangularis with the potential for this risk to change with changes in phenology and/or climate.
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  • 2017-08-04 to 2018-03-02

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