UC Riverside

California contains numerous horticultural nurseries: large lots encompassing patches of healthy containerized flowering plants year-round. While some ornamental plants attract pollinators, the ecological relationships between nurseries and wild bees remain uncharacterized. Management regimes such as systemic insecticide use may pose hazards to bees, while others, such as irrigation, may improve floral resources. My dissertation explored bee assemblages in nurseries, how individual bees forage on ornamental plants, and how plant management impacts bee reproduction.In Chapters I and II, I documented bee assemblages in 13 nurseries during spring, summer, and autumn over two years and detected over 150 species visiting over 90 plant varieties. Greater cultivation of native plants influenced the abundance, richness, and composition of wild bee assemblages. A wide variety of bee species use plants inside nurseries across seasons, and nursery characteristics can influence the abundance and types of bees present. In Chapter III, I used mark-recapture techniques to determine the fidelity of individual bees to nursery plants across days. I marked foraging sweat bees in nurseries and returned after 24 hours. I consistently rediscovered half of individuals across nurseries and seasons, with higher recapture rates on native plants. Nearly all recaptured individuals were found on the same plant species as the previous day, suggesting a high degree of plant fidelity. Wild bees thus regularly use nursery plants as resources over time. In Chapter IV, I explored how ornamental plant management—irrigation level and insecticide application—affect bee foraging and reproduction. In flight cages, irrigation level influenced floral resources and pesticide concentrations in nectar, but did not affect reproduction of solitary bees. Neonicotinoid treatment below the label rate almost entirely halted bee nest initiation and brood cell construction. These results underscore dangers posed by irresponsible use of nursery insecticides. This dissertation addressed the need for an understanding of bee community ecology in horticultural systems, foraging preferences between native and non-native ornamental plants, and impacts of nursery management practices on bee reproduction. This knowledge can be applied to inform practical management strategies that minimize exposure of wild bees to potential stressors, while simultaneously reflecting positively on environmentally minded nursery patrons.