Prevalence of Nosema microsporidians in commercial bumblebees (Bombus terrestris) is not related to the intensity of their use at the landscape scale
The use of commercial bumblebees to aid crop pollination may result in overcrowding of agricultural landscapes by pollinators. Consequently, transmission of parasites between pollinators via shared flowers may be substantial. In SW Spain, we assessed the initial infection status of commercial Bombus terrestris colonies and then explored spatial and seasonal influences on changes in parasite prevalence across a landscape where bumblebee colonies are intensively used to pollinate berry crops. Colonies were placed inside strawberry greenhouse crops and in woodlands adjacent and distant to crops, in winter and in spring, as representative periods of high and low use of colonies, respectively. Worker bumblebees were collected from colonies upon arrival from a producer and 30 days after being placed in the field. The abdomen of each bumblebee was morphologically inspected for a range of internal parasites. Upon arrival, 71% of the colonies were infected by spores of Nosema. Three bumblebees from two colonies harboured Apicystis bombi spores at the end of their placement in woodlands adjacent to the crops. Nosema colony prevalence did not change significantly either among sites or between seasons. We found no evidence for the density of commercial B. terrestris impacting Nosema prevalence in those commercial colonies, but our results highlight the potential risk for parasites to be transmitted from commercial bumblebees to native pollinators.
Keywordsagricultural landscape Apicystis bombi Fragaria × ananassa parasite
We thank J. Angelidou, C. Apostolidou, A. Montero-Castaño, D. Ragel and E. Tsiripli for the field assistance and the farmers for letting us work on their lands. We thank J. Bagi and E.J. Bailes for the lab support. We would also like to thank the editor and the anonymous reviewers for their comments that significantly improved the manuscript.
AT and MV conceived this research and designed the experiments; MJFB participated in the design and interpretation of the data; AT performed the experiments, analyses and wrote the first draft of the manuscript; MJFB and MV edited and contributed to the writing of the manuscript. All authors read and approved the final manuscript.
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) and by a Short Term Scientific Mission from the COST Action (FA1307:35075) for international mobility.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
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