Master of Science, The Ohio State University, 2023, Entomology

Bumble bees (Bombus) are essential pollinators for wildflowers and crops worldwide, but many species are currently in decline. Habitat loss and fragmentation are leading factors in these declines. Urbanization is a source of habitat loss and fragmentation; however, robust and abundant bumble bee populations are often found in metropolitan areas. Though prior research has broadly examined bumble bee abundance and diversity in urban areas, little work has focused on individual abundances of different species, which may differ in their relationships with urban land. Furthermore, the potential impacts of urban land on gene flow and other genetic health factors in bumble bees remain largely unknown. The first goal of this research was to evaluate and compare the abundances of three target species—Bombus impatiens Cresson, 1863, B. griseocollis De Geer, 1773, and B. bimaculatus Cresson, 1863—along an agricultural-to-urban gradient in Madison, WI, USA. Bumble bees were collected from 16 sites during the summer of 2019 and 19 sites during the summer of 2020. The second goal was to evaluate genetic differentiation, heterozygosity, allelic richness and colony numbers among populations of these species along the same gradient. Percentage of impervious surface cover was used as a metric for urbanization, and this percentage was measured within both 500 m and 1500 m buffers around each study site to account for both local-scale and landscape-scale effects. Impervious surface cover showed no relationship with abundances of B. impatiens or B. griseocollis, but showed a positive relationship with abundance of B. bimaculatus. Impervious surface cover also showed no relationship with genetic differentiation, allelic richness or colony number for all three species in both years, and no relationship with heterozygosity for any species in 2019. In 2020, heterozygosity was negatively correlated with impervious surface cover for B. impatiens at the 500 m buffer but not the 1500 m buffer. (open full item for complete abstract)

Committee: Jamie Strange (Advisor); Andy Michel (Committee Member); Mary Gardiner (Committee Member) Subjects: Entomology