Investigation of Apis mellifera L. foraging behaviour to promote pollinator-friendly urban cities in Japan

Urbanization is a primary cause of pollinator biodiversity loss because it depletes floral and nesting resources. Since green areas are limited in urban zones, it is crucial to promote urban greening to provide pollen and nectar sources for pollinators. To investigate the floral resources of the urban environment, we used an efficient floral bio-sampler, Apis mellifera L., to identify the contribution of the urban road network to plant diversity. Pollen samples were collected every month at four study sites (Kiba, Kashiwanoha, Yaesu, and Nishichiba) during 2017 and 2018. DNA metabarcoding of pollen samples was used to identify the taxonomic composition of the floral resources. The results showed that 168 species belonging to 57 taxonomic families were acting as pollen sources, with a large number of honey-plant species in the Fabaceae (15 spp.), Asteraceae (14 spp.), or Rosaceae(8 spp.) families. Fifty-two per cent of the floral resources were alien species, 20% were cultivar species, 25% were native to Japan, and the remaining 3% were not identified. We observed that spontaneously colonizing plant species and street plantings were important sources for urban honeybees. We then located the spatial occurrences of the most foraged species by honeybees around hives. Sixty floral species on urban roads were targeted, and after 60 transects in May 2019, 24 of them were identified. Our results suggested that the urban road network could be not only the refuge of a majority of exotic pollinator species (63%) but also of a large proportion of cultivar species (25%) and a minority of indigenous species (13%). Urban greening programmes based on our findings could enhance biodiversity by creating green spaces suitable for all pollinators, whether generalists or specialists.