2012 Annual Report 1a.Objectives (from AD-416): Determine factors that influence the distribution and retention of Osmia lignaria bees following release in almond orchards, including locations of bee release and locations and density of artificial nest sites; determine relationship between bee nest site use and nut yield according to location. 1b.Approach (from AD-416): Work will be performed during early spring in large (>100 acre) trial and commercial almond orchards in California over five years. In the first three years, research will be done in trial orchards, which will be pollinated with relatively small numbers of Osmia lignaria (8,000-20,000 per orchard) along with the standard number of honey bees (two hives per acre). In these orchards, cavities for use as O. lignaria nests will be deployed at various densities and patterns. Also, O. lignaria males and females will be released according to different management practices. Analyses of nest occupancy by bees will determine if placement of release location and availability of nests in different densities and locations influence the distribution and retention of bees in the orchards. Analyses of offspring size, number of offspring, and offspring sex ratio will be used to measure reproductive success under the various treatments. Data will be collected on the distribution of bees as indicated by occupied nests and also the yield of nuts in relationship to where bees nested throughout the orchards. Analyses will reveal effects of the distribution of nesting bees on nut yield. In years 4&5, trial orchards will be exclusively pollinated by O. lignaria and the nest distribution experiment replicated. In addition, techniques based on previous years’ observations will be applied to counteract the tendency of the bees to nest preferentially in some areas and the consequent irregularity in pollination and hence nut yield. 3.Progress Report: The objective this year was to determine factors that influence the distribution and retention of blue orchard bees in almond orchards. Two trials were performed in one large (160 ac) almond orchard near Bakersfield, California. The blue orchard bee will build its nests in cavities (such drilled holes or straws) in artificial nesting boxes. In one trial, the number of cavities in the nesting boxes was varied (100 vs. 400 cavities per box), and we deployed the same number of cavities per acre (as done in 2011). However, the number of bee release points was either one or 15 per testing area in the orchard, to determine the effect of bee release points on bee nest site choice. In the second trial, bee nest cavities were deployed in four arrangements (25, 50, 100, and 200 cavities per box) and in different colored boxes, as a follow-up to the 2011 study. Blue orchard bee males and females were released according to local orchard management practices and according to experimental design. The number of bees roosting in the cavities at night and the number of plugged (completed) nests were counted throughout the nesting season. In the late summer and fall of 2012, bee nesting activity will be quantified (the number of cells made and the progeny sex ratio) for each treatment. Data will reveal any influence of the nesting box and cavity arrangements, optimal number of bee release points, and nest box color preference on the distribution, retention, and reproductive success of the bees in almond orchards, and on almond yields. The number of almonds produced will be assessed by collecting, counting, and weighing nuts at various distances from nesting boxes. The intended impact of this project is to identify better management strategies for sustaining populations of blue orchard bees in almond orchards and enhancing pollination.