Global invasions of the western honeybee (Apis mellifera) and the consequences for biodiversity

The western honeybee, Apis mellifera, has been globally transported for honey production and pollination for hundreds of years and is often kept in large numbers in beekeeping operations. Concern has been expressed that it might act as an invasive species with large impact on biodiversity. However, although the honeybee has spread into the wild and has established feral populations in Australia and the Americas, the extent to which introduced honeybees alter biodiversity remains controversial. Here we focus on the best documented cases of A. mellifera invasions and discuss the effects on biodiversity under three different conditions: 1) regions where other subspecies of A. mellifera are endemic (Europe, Africa, and western Asia), 2) regions where A. mellifera is not endemic, but other species of Apis naturally occur (central and eastern Asia), 3) regions where Apis species are not endemic (America, Australia). Although some studies show an impact on native bee survival, fecundity, or population density in response to large A. mellifera aggregations (e.g., on apiaries), there are no reports that feral honeybees caused the extinction of native bee pollinators, which are the most likely competing group of organisms. Honeybee introductions have had or still may have negative effects only within the genus Apis, primarily interfering with beekeeping activities. Although honeybee invasions seem to have had little if any effect on biodiversity of native pollinators so far, we nevertheless caution against transporting honeybees around the globe, and we particularly advise against importing foreign Apis species into tropical ecosystems.