The Bacterium Pantoea ananatis Modifies Behavioral Responses to Sugar Solutions in Honeybees.

1. Honeybees, which are among the most important pollinators globally, do not only collect pollen and nectar during foraging but may also disperse diverse microbes. Some of these can be deleterious to agricultural crops and forest trees, such as the bacterium , an emerging pathogen in some systems. infections can lead to leaf blotches, die-back, bulb rot, and fruit rot. 2. We isolated bacteria from flowers with the aim of determining whether honeybees can sense these bacteria and if the bacteria affect behavioral responses of the bees to sugar solutions. 3. Honeybees decreased their responsiveness to different sugar solutions when these contained high concentrations of but were not deterred by solutions from which bacteria had been removed. This suggests that their reduced responsiveness was due to the taste of bacteria and not to the depletion of sugar in the solution or bacteria metabolites. Intriguingly, the bees appeared not to taste ecologically relevant low concentrations of bacteria. 4. Our data suggest that honeybees may introduce bacteria into nectar in field-realistic densities during foraging trips and may thus affect nectar quality and plant fitness.