The presence of a larval honey bee parasite, Ascosphaera apis, on flowers reduces pollinator visitation to several plant species

Abstract

Many floral traits have evolved through pollinator-mediated selection. In selecting flowers for forage, pollinators rely on multi-modal flower signals and innate preferences. However, pollinators are known for their flexible foraging behavior which varies with experience and numerous cues, such as the presence of competitors and floral resource availability. The shared use of flowers by many pollinators leads to high rate of parasite transmission among pollinators, and flowers can be seen as hot-spots of parasite dispersal. Throughout the animal kingdom, behavioral adaptations enable avoidance of parasite exposure. Bumblebees are known to avoid contaminated flowers, however nothing is known regarding the impact of parasite presence on overall pollinator visitation. In this study, we measured the effect of a larval honey bee parasite, the fungus Ascosphaera apis causing chalkbrood disease, on hymenopteran pollinator visitation of several plant species in a natural setting. Several contaminated flowering plant species suffered not only the subsequent reduction of visitation by honey bees but also the subsequent reduction of their overall pollinator visitation. Two plant species with similar flower architecture were the least impacted by the presence of the spores. This study highlights the negative impact of the presence of pollinator parasites for plants and its possible consequences for floral evolution.