Masters Theses

Date of Award


Degree Type


Degree Name

Master of Science


Entomology and Plant Pathology

Major Professor

John A. Skinner

Committee Members

Phillip Wadl, William Klingeman III


Pityopsis ruthii (Small) Small, also known as Ruth’s golden aster, is a federally endangered herbaceous perennial, endemic to two river systems, the Hiwassee and the Ocoee, within the Cherokee National Forest, Polk County, Tennessee. There are approximately 13,000 individuals that may be at high risk of short-term extirpation (Thompson and Schwartz, 2006). Little is known of the basic reproduction and life history of P. ruthii. Clebesh and Sloan (1993), Cruzan (2001), Park (1998), and Wadl et al. (2014) found evidence that seed production and seed viability are highly variable. Clebesh and Sloan (1993) indicated that pollinator visitation was highly temporal variable, while limited genetic diversity may also be preventing cross-compatibility (Sloan, 1994) in this self-incompatible species (Bowers, 1972). This research project identified the pollinators to P. ruthii and characterized the impacts of genetic diversity and pollinator abundance to seed set. The objectives were to: 1) collect and identify insect floral visitors to P. ruthii, 2) assay pollen carried by insects for qualitative estimates of pollination service, and 3) compare the pollinator communities across the endemic landscape and to an experimental ex situ plot to contribute evidence of pollinator dynamics and gene flow to the variability in seed production. Based on this study, the primary pollinators of P. ruthii include Bombus impatiens Cresson, which is the most important pollinator due to abundance, large pollen load, confirmed P. ruthii pollen presence, and behavior and Apis mellifera L. that is less widespread, and may be more temporally variable. Toxomerus geminatus Say (hover fly) is prevalent, yet its pollen load and behavior is less significant for performing pollination services. Differences in mean seed production by population indicate that floral visitor abundance significantly affects P. ruthii seed production (R2 [R squared] =0.91, P=0.046), while flower density impacts the frequency of Apoidea visitation (R2 [R squared] =0.219, P=0.007). Genetic deficiencies like in-breeding depression and poor diversity are likely contributing to limited sexual reproductive output, based on seed viability and germination tests. Understanding the vectors of gene flow and variability in vector abundance is essential to facilitating preservation of P. ruthii in its endemic habitat

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