Evidence of the role of honey bees (Apis mellifera) as vectors of the bacterial plant pathogen Pseudomonas syringae

Honey bees (Apis mellifera) have been implicated in the spread of the fire blight pathogen (Erwinia amylovora), and may transmit other bacterial plant pathogens in the process of pollinating crops. Furthermore, the movement of hives from one orchard to another could spread plant diseases over large distances. We investigated whether honey bees might play a role in the transmission of different pathovars of Pseudomonas syringae. We detected live P. syringae pv. actinidiae (Psa), a pathogen of kiwifruit (Actinidia spp.), on caged bees in hives 6 days after the bees were inoculated with Psa, and recorded up to 1.8 x 10(4) colony forming units of Psa on honey bees foraging naturally on flowers of Psa-infected vines. P. syringae pv. syringae (PssSmr), a pathogen with a wide host range, was spread to untreated bees in a hive within 24 h following the introduction of foragers doused in PssSmr-contaminated pollen and was still detected on bees 9 days later. PssSmr was found on caged bees in hives 6 d after they were inoculated and PssSmr survived in hives for at least 14 days. These results demonstrate that P. syringae can survive in beehives and spread within a hive, which broadens the applicability of results from studies of E. amylovora and supports recommendations for a stand down period before moving beehives from a contaminated to a non-contaminated orchard.