Red raspberry is one of the many fruit crops reliant on the European honey bee for pollination services. Recent declines among managed honey bee colonies coupled with expanding U.S. acreage have led to a marked increase in the cost of U.S. colony rentals for raspberry. The current stocking density recommendation for raspberry is 2 to 5 colonies/ha. This estimate is based on the assumption that a raspberry flower requires dozens of visits to achieve maximal drupelet set. Recent studies, however, suggest that far fewer visits are required for full drupelet set. Here, drupelet set resulting from bee visitation to a raspberry flower is assessed to determine if two prolonged visits will suffice to maximize drupelet set. For all three red raspberry cultivars examined there was no difference in drupelet set resulting from two visits when compared with openly pollinated flowers, the two visits being the first prolonged visit on each of two consecutive mornings. These findings should help refine honey bee stocking densities to better match the pollination needs of cultivated red raspberries.
This work was supported by the Integrated Crop Pollination project funded by the USDA National Institute of Food and Agriculture through award 2012-51181-20105 from the Specialty Crop Research Initiative.
We are grateful to Byron Love and Kristen Lambert for their assistance in data collection, and Diane Alston, Brent Black, and Chad Finn for reviewing earlier drafts of this manuscript.