Influence of rough handling and environmental factors on blue orchard bee (Osmia lignaria) nest establishment

The manner in which orchard managers handle blue orchard bees, Osmia lignaria, prior to release may affect their nesting behavior, resulting in decreased nesting of females at commercial nest sites. Decrease in nesting may be on account of increased dispersal, increased mortality, or other unknown reasons. We addressed the hypothesis that excessive rough handling of bees prior to emergence results in poor nest establishment at commercial shelters in an orchard. In 2007 and 2008, two groups of bees, one shaken and one unshaken, were distributed across 10 shelters and allowed to emerge from cocoons inside their nests. Ten days prior to placement in the orchard, the shaken group was placed on a shaker table at 250 rpm for 2 min. Shaking was repeated three days prior to release. Nests were monitored twice daily so that as female bees emerged from their cocoons, they were paint-marked according to treatment and shelter of emergence. The proportions of bees from each group that nested in the same nesting shelter and in the common orchard were evaluated. Also, the influence of precipitation, maximum temperatures, and minimum temperatures on nest establishment was evaluated. The number of nests initiated by shaken bees and unshaken bee nests was not significantly different in either year, but there was a difference in nest establishment by both treatment groups across years. This difference could not be satisfactorily explained by examining environmental factors. The results of this study indicate that rough handling does not contribute to decreased nesting in commercial orchards.