Commercial bumble bees on soft fruit farms collect pollen mainly from wildflowers rather than the target crops

Abstract

SummaryCommercially-reared nests of bumble bees are widely used for pollination of glasshouse crops such as tomatoes, and in recent years they have begun to be increasingly used outdoors for soft fruit crops which are either uncovered or in open-sided polytunnels. In the UK, approximately 15,000 Bombus terrestris nests per year are imported for use in this way. Here we examine pollen loads on commercial bumble bees returning to their nests, stationed next to soft fruit crops at three farms in Scotland, UK, to determine whether pollen-collecting bees are visiting the target crop. Only 12% of pollen was of Rubus type (most likely raspberry) and 15% was of Potentilla type (probably strawberry). The remaining 73% of pollen was from a range of non-target wildflowers, in declining importance: Brassicaceae (22%), Filipendula type (18%), Violaceae (11%), Trifolium type (6%) and Apiaceae (6%). It is unclear how this relates to the pollination service provided, since the bees may make nectar-collecting visits to the fruit crops. Nonetheless a substantial proportion of foraging by commercial bees is clearly not on the target crops. Means for improving the efficiency of fruit pollination, and possible ecological implications of use of wild flowers by commercial bumble bees are discussed.