Abstract

Honeybees are well recognised for their key role in plant reproduction as pollinators. On the other hand, their activity may vector some pathogens, such as the bacterium Erwinia amylovora, the causative agent of fire blight disease in pomaceous plants. In this research, we evaluated whether honeybees are able to discriminate between healthy and E. amylovora-infected flowers, thus altering the dispersal of the pathogen. For this reason, honeybees were previously trained to forage either on inoculated or healthy (control) apple flower. After the training, the two honeybee groups were equally exposed to inoculated and control flowering apple plants. To assess their preference, three independent methods were used: (1) direct count of visiting bees per time frame; (2) incidence on apple flowers of a marker bacterium (Pantoea agglomerans, strain P10c) carried by foragers; (3) quantification of E. amylovora populations in the collected pollen loads, proportional to the number of visits to infected flowers. The results show that both honeybee groups preferred control flowers over inoculated ones. The characterisation of volatile compounds released by flowers revealed a different emission of several bioactive compounds, providing an explanation for honeybee preference. As an unexpected ecological consequence, the influence of infection on floral scent increasing the visit rate on healthy flowers may promote a secondary bacterial spread.

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Author contribution

AC, FS and SA conceived the study and designed the experiments; AC, ID and VG performed all the treatments, samplings and field experiments; MTRE, SS and VG performed the analyses of volatile compounds; BF performed the statistical analysis; FS supervised the whole work. AC and VG drafted the first version of the manuscript. All the authors elaborated the results, actively contributed to their discussion, revised the manuscript and approved the final version.

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Affiliations

  1. Department of Agricultural and Food Sciences, Alma Mater Studiorum - University of Bologna, viale G. Fanin 44, Bologna, 40127, Italy

    • Antonio Cellini
    • , Irene Donati
    • , Maria T. Rodriguez-Estrada
    • , Stefano Savioli
    •  & Francesco Spinelli
  2. Faculty of Science and Technology, Free University of Bozen-Bolzano, Piazza Università 5, Bolzano, 39100, Italy

    • Valentino Giacomuzzi
    •  & Sergio Angeli
  3. Department of Genomics and Biology of Fruit Crops, Research and Innovation Centre, Fondazione Edmund Mach, Via E. Mach 1, S. Michele all’Adige (TN), 38010, Italy

    • Brian Farneti

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The authors declare that they have no conflict of interest.

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Correspondence to Francesco Spinelli.

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https://doi.org/10.1038/s41396-018-0319-2