Wild bumble bees reduce pollination deficits in a crop mostly visited by managed honey bees

We assessed the pollinator community of two cultivars of highbush blueberry (Vaccinium corymbosum, Duke and Bluecrop), and determined the importance of different pollinators to overall crop yield by measuring pollination deficits. The importance of distance to putative wild pollinator habitat (natural field edges) for pollinator abundance within fields and crop yield was also considered. Managed honey bees made 70% of flower visits (85% to Duke, 49% to Bluecrop). Wild bumble bees made half of the visits to Bluecrop. Though bumble bees were observed less frequently as distance from the natural edge increased, there was no effect of distance on levels of crop pollination. Pollination deficits were less pronounced in Duke than Bluecrop, with maximum (hand) pollination leading to a 12% (Duke) to 23% (Bluecrop) increase in yield. Exclusion of pollinators reduced yield by 50-80% compared to ambient pollination. For both cultivars, pollination deficits declined most strongly with either increasing bumble bee visits or increasing total visits (honey bees and bumble bees combined), and in no case were deficit levels significantly reduced by honey bees alone. This study supports a growing body of literature that suggests managed honey bees alone cannot reduce deficits, and that wild pollinators are needed to maximize yields in pollinator-dependent agricultural systems. (C) 2014 Elsevier B.V. All rights reserved.