Honey bee (Apis mellifera L.) and wild bee resource competition: how big is this problem?

The Western honey bee (Apis mellifera L.) has been managed by humans for centuries for honey, wax, and most recently, crop pollination. The deep history of human association with this species has enabled agricultural practices that reduce biodiversity of pollinating wild bees, largely through habitat modification. However, there is also interest in determining if Apis mellifera presence itself contributes significantly to wild bee population declines. Herein we review the evidence of Apis mellifera competitive impacts on wild bees, with a particular emphasis on the scope of effects associated with resource competition. Despite accelerated research in this area, only ~13% of resource competition studies evaluated fitness effects of Apis mellifera on wild bees, a research gap that has persisted for over 20 years. About three times as many studies have evaluated effects of Apis mellifera on wild bee community parameters, including wild bee abundance, which provides a measure of a landscape’s “bee carrying capacity”. Just over 20% of these studies show a negative correlation with Apis mellifera abundance. In a novel additional analysis of 68 studies measuring bee communities for other reasons found negative correlations between Apis mellifera abundance and any measure of the wild bee community for only 10; conversely, 10 studies show positive relationships between Apis mellifera and wild bee abundance, and most show no relationship at all. We found no pattern to explain which habitat types are more vulnerable to Apis mellifera competition, nor is the literature clear on impactful densities of managed hives in particular environment types. Overall, the data do not support a generalized and widespread negative relationship between Apis mellifera abundance and wild bee fitness and community health. Rather, conservation measures that reliably improve wild bee health (habitat preservation and restoration) will likely have positive effects on Apis mellifera, and vice versa.