Urban flower-power for wild bee and hoverfly conservation

Wild bees and hoverflies are some of the most important pollinator groups across the globe, including in urban areas. Urban areas are increasingly recognized as potential pollinator refugia, mostly due to the lower pressure from agrochemicals in comparison to rural areas and often high floral diversity in human-maintained landscapes. Because many factors influence the suitability of urban green spaces for pollinators local studies considering different taxa are needed to best inform the pollinator-friendly management. We studied bee and hoverfly communities across urban green spaces of Zagreb, a city in an understudied region of Europe. We tested how temperature, urbanization, and availability of floral resources impact pollinator species richness. We report 123 species of wild bees and 50 species of hoverflies for Zagreb, including 7 species of conservation interest at the European level. Increased average site temperature, due to urban heat island effect, negatively impacts hoverfly species richness, but not that of the bees. Sites with higher floral abundance had higher species richness of both pollinator groups. Our results show that a simple intervention such as reducing the intense mowing regime in urban green areas to increase abundance of floral resources, can have significant positive impact on urban pollinator diversity and contribute to conservation of threatened species.