Distribution and habitat preferences of Osmia lignaria (Hymenoptera: Megachilidae) and associated cavity-nesting insects in California’s Sierra Nevada foothills adjacent to the Sacramento Valley

Trap nests were used to assay species richness, abundance and distribution of cavitynesting insects in California’s Sierra Nevada foothills bordering the Sacramento Valley. Particular focus was placed on the agriculturally significant native bee Osmia lignaria Say, 1836 because of its potential use as a pollinator of local orchard crops. Osmia lignaria and four other species were obtained from half of the eight study sites. Unidentified nests were constructed at the remaining sites. The strength of correlation between three habitat variables and species abundance was determined. Floral resource availability yielded the strongest correlation, followed by habitat type, then proximity to water. These findings document the presence of cavity-nesting native bees and their associates, highlighting their potential in pollinating important agricultural crops.