The horned mason bee, Osmia cornuta, as a managed orchard pollinator: current status and future perspectives.

Osmia cornuta is a cavity-nesting solitary bee that occurs across most of continental Europe. Because of its early activity period, its strong affinity for Rosaceae fruit tree pollen and its high pollinating effectiveness, methods have been developed to manage this species as a crop pollinator. In this review, we identify the main challenges associated with O. cornuta management: synchronisation of population emergence with the blooming period of the focal orchard, female establishment at the nesting sites and pesticide exposure. We discuss how to address these challenges and suggest research avenues and management practices to increase population returns in orchard environments. As with other managed pollinators, the deployment of O. cornuta populations may have negative effects on wild pollinators, including competition for floral resources, parasite and pathogen spillover and genetic introgression. We argue that, because of the low densities used, these threats are relatively small when managing O. cornuta. In addition, we emphasise the advantages of working with local populations and the need to establish a legal framework to regulate Osmia trade. Due to the low densities used, and because the orchard management measures proposed to enhance O. cornuta populations are also beneficial to other pollinators, the management of O. cornuta is compatible with the promotion of wild pollinator communities within an integrative and diversified crop pollination approach.