Pollinators of Astragalus monoensis Barneby (Fabaceae): new host records; potential impact of sheep grazing

Important bee species inhabiting the study area are listed, including those observed and collected foraging on Astragalus monoensis , a California rare plant. The significance of each species as a potential pollinator is assessed, based on frequency of occurrence in collecting, observed and published host plant records, and morphology. Three pollinator categories are proposed: observed and/or collected on the plant, probable visitors, and possible visitors. New host plant records for these species are listed. Current sheep grazing practices in the A. monoensis habitat endanger pollinators in four ways: (1) destruction of potential nest sites, (2) destruction of existing nests and contents, (3) direct trampling of adult bees, and (4) removal of food resources. Exposure of the major bee species to each of these factors is assessed utilizing experimental data and published information.