The role of honeybees in spreading Erwinia amylovora.

The purpose of the studies carried out in the spring of 2000 and 2001 under greenhouse conditions, was to evaluate the role of honeybees in the dispersal of Erwinia amylovora in pear blossoms and successive fire blight development. It was demonstrated that honeybees, while visiting for 24 h pear flowers experimentally inoculated with E. amylovora (10⁶ cfu/ml), became contaminated with the pathogen and were able to disperse the bacteria to healthy pear trees in full bloom; 48 h after initial contact of honeybees with inoculated flowers no viable bacteria were detected on honeybee bodies and in honeybee intestines. In other trials, it was demonstrated that honeybees were able to disseminate E. amylovora from experimentally contaminated beehives (10⁸ cfu/ml) to healthy pear flowers for less than 48 h after initial contamination of the beehives. No viable bacteria were re-isolated from analysed honeybee body and honeybee intestine samples 48 h after initial contamination of beehives. E. amylovora detection was based on quantitative re-isolations on CCT medium. The identity of the representative colonies was determined by Bio-PCR (Schaad et al., 1995) using the primers of Bereswill et al. (1992).