Importance of wild bees in apple pollination

Background/Question/Methods

Recent declines in honey bee health and increasing demand for pollination services highlight a need for enhancing wild pollinators in agriculture.  One case in point is apple, an economically important crop in the U.S. that requires cross pollination by bees to set fruit. Though commercial growers rent increasingly expensive honey bees to insure adequate pollination, apple in New York blooms at a time of peak wild bee activity.  Little is known about the community of wild bees that visits apple, even less about their pollination services.  In 2009 and 2010, New York apple orchards were net surveyed for bee diversity and abundance.  Effects of orchard size, honey bee rentals, spray regime and alternative floral resources on bee diversity and abundance were tested. To begin to quantify the importance of wild bees in apple pollination, in 2010, we compared pollinator effectiveness of the dominant wild bees, Andrena in the subgenus Melandrena, with that of honey bees (Apis mellifera).  We recorded number of pollen grains deposited in a single visit to a virgin, emasculated apple flower; visit duration; approach (front or side-working) and foraging type (land only, pollen or nectar foraging).  To determine relative pollinator importance of Melandrena at the orchard level, we used the product of per-visit effectiveness and bee relative abundance.

Results/Conclusions

Wild bees were abundant and diverse.  Wild bee abundance decreased with orchard size, but was not affected by differences in pesticide use, alternative floral resources or the presence of honey bee hives.  On a per-visit basis, Melandrena was a more effective pollinator than Apis, depositing three times as many pollen grains.  Bee, approach, and foraging types had significant main effects on pollen deposition. Side-working bees deposited fewer grains, regardless of taxon.  Apis per-visit effectiveness was limited by its greater tendency to side-work.  Given high per-visit effectiveness and abundance, Melandrena was a more important pollinator than Apis in 70% of surveyed orchards. Our results support the importance of wild bees in apple pollination in NY and the potential benefits of protecting-- even enhancing-- their services.