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United States Department of Agriculture

Agricultural Research Service

Research Project: Achieving Uniform Pollination by Osmia Lignaria, the Blue Orchard Bee, by Improved Bee Distribution and Retention

Location: Pollinating Insects-- Biology, Management and Systematics Research

2011 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

To determine factors that influence the distribution and retention of blue orchard bees in almond orchards, we conducted a large trial in a commercial almond orchard (~80 acre) near Bakersfield, California and also a smaller trial (~8 acres) outside of Modesto, CA. In these trial orchards, cavities inside nesting boxes for use as blue orchard bee nest sites were deployed in two arrangements, with each arrangement having the same number of cavities overall. One arrangement had many cavities per nesting box, and the other had ¼ as many cavities per nesting box. Blue orchard bee males and females were released according to local management practices. The number of bees roosting in the cavities at night and the number of plugged nests were counted throughout the nesting season. In late summer 2011, the exact number of cells made and progeny sex ratio will be determined. Data concerning the use of cavities of the two arrangements and the reproduction in those cavities will reveal any influence of the arrangements on the distribution, retention, and reproductive success of the bees in the orchards. Also, at almond harvest, the number of nuts produced will be assessed at various distances from nesting boxes representing the two arrangements to show any effect of bee nesting distribution on nut yield. The intended impact of this project is to gain better management strategies for sustaining populations of blue orchard bees in almond orchards and enhancing nut yield.

ADODR monitoring is done via e-mail, phone conversations, site visits, and meetings.


Last Modified: 4/24/2014
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