Pollinator effectiveness and importance between female and male mining bee (Andrena)

Bees are often considered to be effective pollinators in both agricultural and natural ecosystems but could be ineffective pollinators in that they collect large quantities of pollen for food provision but deliver little to stigmas. Male bees do not collect pollen to feed larvae, and their pollination role has been underappreciated. Here we compare pollination effectiveness, visit frequency and pollen foraging behaviour between female and male individuals of a mining bee, Andrena emeishanica, visiting a nectariferous spring flower (Epimedium pubescens). Female bees were observed to forage for both pollen and nectar, but male bees foraged only for nectar. Female bees had large hairy hind tibiae with conspicuous scopae, and nearly 90% of the pollen grains they collected went onto the hind legs. Male bees removed less pollen from anthers than female bees but deposited more pollen on stigmas per visit. The higher pollen transfer efficiency of male bees was due to 48.4% of pollen grains remaining ungroomed on the thorax and abdomen, available for stigma contact, but their visitation rate to flowers was much lower. Our results indicate that male solitary bees could transfer more pollen on the stigma per visit but were less important (transferred less pollen in total, because they made fewer visits per unit time) than females.