Wild bee populations have undergone declines in recent years across much of the Western world, and these declines have the potential to limit yield in pollination-dependent crops. Highbush blueberry, Vaccinium corymbosum, and tart cherry, Prunus cerasus, are spring-blooming crops that rely on the movement of pollen by bees and other insects for pollination. Wild bee populations can be increased on farmland by providing floral resources, but whether the addition of these plants translates into increased pollinator density on crop flowers has not been documented in most cropping systems. To determine the importance of providing additional floral resources for wild bee pollinator communities, we selected blueberry fields and tart cherry orchards with and without herbaceous floral enhancements in western Michigan, USA. The bee communities visiting crop flowers, enhancements and control grassy field margins were sampled over a 5-yr period. In addition, the pollen diets of the most abundant wild bee crop pollinators were quantified across Michigan to better understand their foraging niches and to identify potentially important alternative host plants. The presence of floral enhancements did not increase the abundance of wild bees on either blueberry or cherry flowers during bloom. The bee community visiting blueberry was evenly composed of short-season bees that fly only during the spring and long-season bees that fly in both spring and summer. In contrast, the bee community visiting cherry was dominated by short-season spring bees. The majority of pollen collected by the wild bee communities visiting blueberry and cherry was from spring-flowering woody plants, with limited use of the herbaceous enhancements. Enhancements attracted greater abundance and species richness of bees compared to control areas, including twice as many floral specialists. Conserving summer-flying, grassland-associated bees is an appropriate goal for pollinator conservation programs. However, herbaceous enhancements may not provide adequate resources for the wild bees that pollinate spring-flowering crops. This study demonstrates that an examination of the pollen collected by wild bees across their flight periods can identify plant species to help them persist in intensively managed landscapes.
Bibliographical noteFunding Information:
This research was funded by USDA-NIFA Specialty Crop Research Initiative award 2012-51181-20105 (Developing Sustainable Pollination Strategies for U.S. Specialty Crops) and by Operation Pollinator. We thank Keith Mason, Karen Powers, Mike Haas, Knute Gundersen, Erin Treanore, Clara Stuligross, Shaana Way, Shiala Naranjo, Erin Forester, Elisabeth Anderson, Lauren Gedlinske, Katherine Odanaka, Cecily Kowitz, Jacquelyn Albert, Hannah Rice, Gabriela Quinlan, Olivia Horton, and Holly Hooper for their technical assistance. We are very grateful to the Fritz, Hartmann, Leduc, Bodtke, Reenders, Carini, Riley, Send-Emeott, and Cherry Bay Orchards family farms and their staff for their generous assistance with this research. We would also like to thank Alison Brody and two anonymous reviewers whose comments greatly improved the manuscript. Authors’ contributions: R. Isaacs, J. K. Wood, L. Gibbs, and N. Rothwell conceived the project; all authors designed the methodology and collected data; T. J. Wood analyzed the data and led the writing of the manuscript; all authors contributed critically to the drafts and gave final approval for publication.
© 2018 by the Ecological Society of America
Copyright 2018 Elsevier B.V., All rights reserved.
- bee conservation
- habitat quality
- pollen diet
- wild bees