Native solitary bee health in western Washington

Abstract

Bees are a vital part of the terrestrial ecosystem, providing pollination services to plants and contributing to biodiversity. Spring-emerging solitary native bees face numerous challenges to survival, including inclement weather in early spring, harmful bacteria and parasites, and the need to accumulate nutritious pollen from potentially highly variable and fragmented landscapes to feed developing offspring. I examined the relationship between climate variables, plant richness, nutritional content of pollen, and presence of bacteria and fungi and the developmental success of the solitary cavity-nesting bee, Osmia lignaria Say, across 22 sites in western Washington located along an urban-to-rural gradient. Studies were conducted over two to four years, and during two distinct bee foraging periods: one that was synchronized with the phenologically-typical O. lignaria foraging period, and one to simulate asynchrony between O. lignaria and its phenologically-typical host plants. I used novel Next-Generation Sequencing (NGS) technology to perform DNA metabarcoding of plant pollen, bacteria, and fungi to quantify species richness, and used metabolomic techniques to quantify protein and lipid concentrations in pollen. To collect weather data, I used community science data in the form of temperature, wind speed, and rainfall from Weather Underground stations across King County, Washington. The results showed that O. lignaria larval development success and adult emergence increases with increasing hours with zero precipitation. NGS revealed that bees visited between 2-32 plants, consistently visiting certain genera including Acer, Salix, and Rubus species, and that plant species richness did not predict bee development success in either foraging period. The nutritional quality of pollen did not change with increasing plant richness, and in both foraging periods high lipid concentrations were associated with higher rates of development and emergence. Certain specific lipid classes were found to increase larval development success, including cholesterol ester and hexosylceramide. I also report on novel associations between fungi and bacteria and solitary bees. Bacterial richness increased during the second foraging period when the weather is conducive to bacterial growth and more plants are in bloom. Fungal analysis revealed that richness decreased with increasing plant richness, urging further microbial analysis in O. lignaria foraging behavior and development. Potentially harmful fungi for bee health were detected in sequencing analysis, including Ascosphaera spp. This study informs native solitary bee conservation efforts, especially in heavily urbanized areas, provides a basis for exploring in-depth relationships between lipid and protein content of pollen and bee development, and presents novel information on bacterial and fungal associations with solitary bee foraging activity and their potential role in bee health.