Search

Over two million commercial bumblebee colonies are used on an annual basis to pollinate around 20 crop types worldwide. Despite their use, especially with crops grown in greenhouses, there is mounting evidence that many individuals also forage outside of them. Hence, the use of commercial bumblebees poses a risk to wild pollinators, especially to those who share floral resources and pathogens. To date, however, there is little evidence about the impact of commercial bumblebees on pollinator communities in Europe. We surveyed the abundance of commercial Bombus terrestris and the prevalence of four of its parasites in natural areas at increasing distances from vegetable crops in Cabo de Gata-Níjar (Almería, SE Spain), the most extensive greenhouse cultivation area in the world. We also estimated resource niche overlap (i.e., shared plants used) between commercial bumblebees and the native pollinator community. Finally, we explored whether the abundance and diversity of pollinators in natural habitats were influenced by agricultural expansion (i.e., distance to greenhouses) and bumblebee abundance. We found a sharp reduction in commercial bumblebee densities at increasing distances from greenhouses, with most bumblebees (95%) foraging within a radius of less than 200 m from them. However, these commercial bumblebees had high parasite prevalence (41% of individuals infected) of trypanosomatids, microsporidians and neogregarines. Moreover, their diet particularly overlapped with honeybees and large wild bees. Yet, pollinator density and diversity were not related to the distance from greenhouses or to bumblebee abundance. Although our results suggest that commercial bumblebees do not significantly harm wild pollinators, actions like preventing their escape from greenhouses, monitoring their health and optimising their use should be considered so as to minimise future risks.

In recent decades, there has been a remarkable expansion of pollinator-dependent crops. An increase in the use of commercial pollinator colonies associated with these crops may promote the spillover of managed pollinators into nearby natural habitats. There, these managed pollinators can exploit floral resources similar to those of wild pollinators, and thus increase competition for local resources. Nonetheless, managed pollinator spillover has been poorly studied and research has focused on only one species, the western honeybee (Apis mellifera). In south-western Spain, we investigated the presence, density and exploitation of floral resources by managed (Bombus terrestris) and native bumblebees (B. t. lusitanicus) in 19 Mediterranean pinewood understories across a landscape gradient of strawberry polytunnel greenhouse cover. Sampling was performed over two consecutive years in two seasons: winter, when strawberries begin flowering and farmers frequently use colonies, and spring, when there is greater availability of floral resources and wild pollinators thrive. In winter, the density of managed bumblebees in pinewoods was higher than that of native bumblebees. The presence of managed and native bumblebees in pinewoods showed contrasting patterns in relation to greenhouse cover in the landscape. The presence of managed bumblebees was positively associated with greenhouse cover, whereas that of native bumblebees was negatively associated with greenhouse cover. Overall, the presence and density of bumblebees did not differ between seasons. The two bumblebee subspecies showed similar wild flowering plant preferences, particularly in winter, when flowering plant species are scarce. We conclude that, although managed bumblebees are placed in greenhouse crops, their pollination role extends beyond these crops. Further studies are needed to assess the pollination function of managed pollinators in crops in order to reduce their spillover into natural habitats and thus, the risks posed to native pollinators., Funding was provided by the Spanish Ministry of Economy and Competitiveness project FLORMAS (‘Influence of mass flowering crops on pollinator biodiversity, project no CGL2012-33801’) and by the Biodiversa-FACCE project ECODEAL (‘Enhancing biodiversity-based ecosystem services to crops through optimised densities of green infrastructure in agricultural landscapes, project no PCIN-2014-048’). AT was supported by a Severo-Ochoa Predoctoral Fellowship (SVP-2013-067592). JPGV was funded by an Individual Fellowship from the Marie Sklodowska-Curie Actions (H2020-MSCA-IF-2014-656572).

Pollinator spill-over among habitats can arise in order to fulfill the pollination function and whenever differences in floral offering change over time or space. Flowering crops offer pulsed and abundant floral resources (i.e., mass flowering crops) that might promote pollinator spill-over between cultivated and adjacent natural areas. We explored pollinator patterns in the mass flowering legume crop Hedysarum coronarium and its influence on the bee pollinator communities of adjacent shrublands in a heterogeneous and patchy agricultural landscape. We studied the temporal (i.e., during vs. after mass flowering in adjacent shrublands) and spatial (i.e., inside crops, adjacent and distant shrublands during mass flowering) functional pollinator spill-over. The honeybee was highly attracted to Hedysarum crops, yet its abundance and that of other bee species visiting native plants in adjacent shrublands did not differ during and after Hedysarum mass flowering. However, at the landscape scale, the honeybee and the other bee species were less abundant in shrublands adjacent to Hedysarum crops compared to distant ones; their visitation rates showing a similar trend. These results show that some mass flowering crops can influence pollinator patterns in the surrounding landscape by competing for generalist pollinators with native plants. The characteristics of the crop species and the landscape can modulate and determine the role of mass flowering crops as competitors or supporters of wild pollinators for adjacent natural areas.

Entomophilous and obligate out-crossing non-native plants need to become well integrated in the resident plant–pollinator network to set seeds and become established. However, it is largely unknown how pollination patterns differ between native ranges and those where plants have been introduced. We compared the identity, abundance and visitation rates of pollinators, insect pollen loads, pollen deposition on stigmas, and fruit and seed sets of Hedysarum coronarium, an entomophilous short lived N-fixing perennial, in populations from native and introduced ranges in Spain (South of mainland Spain and Menorca Island, respectively). In both areas, Hedysarum was visited by a similar number of species, mainly hymenopterans; seven species were common between native and introduced areas. However, pollinator richness, abundance, and visits per flower were greater in the native than in the introduced range, as were fruit and seed sets. Hedysarum pollen loads on stigmas and on Apis mellifera, the most common pollinator, did not differ between areas. Lower abundance of pollinators might be causing lower visitation rates, and to some extent reducing Hedysarum fruit and seed sets in the introduced area. Our biogeographical approach shows that integration of a non-native plant in a resident pollinator network does not prevent pollen limitation in the introduced area. Therefore, despite being necessary, pollination mutualistic relationships might not be the key for non-native plant establishment success in the introduced area.