Increased bumblebee abundance along the margins of a mass flowering crop: evidence for pollinator spill-over
Although the practice of cultivating mass flowering crops (MFCs) is seen as a means of counteracting the widespread decline of insect pollinators, no study to-date has evaluated whether the increased pollinator abundance associated with MFCs influences pollinator visits to assemblages of adjacent native, non-crop plant species (pollinator 'spill-over'). In this study we quantified bumblebee abundance along hedgerow transects in MFC (field bean) vs non-MFC (wheat) margins. Surveys were conducted on east and west-facing margins twice daily (morning and afternoon) for three or four days during the main MFC flowering period (June) over four years involving paired bean and wheat fields in Devon and Cornwall, southwest England. Although no single bumblebee species showed any consistent change in relative frequency, when taken across all years and bumblebee species combined, we observed twice as many bumblebees visiting flowers adjacent to the MFC. However, when we compared bumblebee activity along hedgerow transects two weeks after bean flowering, there was no difference between crops. We thus conclude that although there is evidence for pollinator spillover from the bean MFC to nearby semi-natural habitat, the effect is comparatively short lived and not specific to any single bumblebee species. We also suggest that while pollinator services to native plant species might be briefly enhanced by MFC cultivation, the possible repercussions of bumblebee spill-over from MFCs to semi-natural habitats and the other pollinator groups they support should be evaluated before MFC cultivation is considered as a means of conserving declining bumblebee populations.
Author(s): Hanley, ME; Franco, M; Dean, CE; Franklin, EL; Harris, HR; Haynes, AG; Rapson, SR; Rowse, G; Thomas, KC; Waterhouse, BR; Knight, ME