Managed honeybees affect the foraging behaviour of bumblebees in Geranium sylvaticum

Due to shared evolutionary history, native pollinator diversity and coexistence is promoted by niche partitioning and behavioural differences between species. Introduced insect species, however, have potential to compete with wild pollinators and negatively affect native insect populations. Honeybee (Apis mellifera) is an introduced pollinator species in northern Europe and may affect native pollinator populations negatively. Diversity in plant communities also promotes variation in the associated pollinator communities. Diversity of a community encompasses not only species diversity but includes within species variation as well. Within species, genetic diversity could promote insect coexistence and affect competitive interactions between pollinator insects. In this study, we measured floral visitation rates in female and hermaphrodite Geranium sylvaticum genotypes in the presence and absence of a beehive (Apis mellifera) in an experimental field located in Central Finland. We show that competition with honeybees reduced visitation rates by bumblebees, but not by other native pollinator groups. Furthermore, bumblebees preferred some plant genotypes in the absence of the honeybees, but not in the presence of honeybees. Overall, bumblebees preferred females over hermaphrodite plants, but honeybees showed no such preference. Our study links the native pollinators and genetically diverse plant populations, and sheds light on the competition between pollinator insects.