Epiphytic bacteria on lettuce affect the feeding behavior of an invasive pest slug.
Plant-animal interactions are not isolated pairwise relationships but are always accompanied by diverse assemblages of microbes. Additional to direct effects of microorganisms on their hosts, recent investigations demonstrated that bacteria associated with plants can modify the behavior of organisms of higher trophic levels. However, in the context of herbivory, functions of non-phytopathogenic bacteria colonizing leaf surfaces remain understudied. This study showed that naturally occurring epiphytic bacteria affect the feeding behavior of a generalist herbivore. Epiphytic bacteria isolated from leaves of Lactuca sativa var. capitata were screened for their potential to influence feeding choices of the slug Arion vulgaris. Cultivated bacteria were inoculated in artificial food substrates or on sterile leaves of gnotobiotic lettuce plants and were offered to slugs in different behavioral bioassays. A large proportion of bacterial strains tested induced behavioral alterations in the feeding choices of slugs. Behavioral responses of slugs were further modified by antibiotic treatment of slugs prior to choice tests indicating that both bacteria associated with plants and animals affect plant-animal interactions. Our results emphasize the important role of bacteria in plant-animal interactions and suggest a prominent role of bacteria in herbivory in natural, horticultural, and agricultural systems.