Pollination efficiency of Apis mellifera (Hymenoptera: Apidae), solitary bees (Hymenoptera), and flies (Diptera) in an insect-pollinated Japanese pear orchard

Previously we suggested the significance of some of the hymenopteran (Andrenidae, Apidae, and Halictidae) and dipteran (Syrphidae) families in Japanese pear pollination. However, they might contribute differentially to the pollination reflecting their pollination efficiencies. For this study, we investigated the pollination efficiency of three insect pollinator groups at an insect-pollinated Japanese pear orchard: Apis mellifera (Hymenoptera: Apidae), solitary bees (Hymenoptera), and flies (Diptera). First, we examined the contribution of the insect pollinator groups to the fruit-set ratio of inflorescences. Results indicated that the floral visits of A. mellifera had a positive effect on the fruit-set ratio. Then, for two consecutive years, the numbers of Rosaceae pollen grains deposited on the stigma after a single floral visit by insects were examined. The obtained results were not consistent, but data in one year showed that A. mellifera and Andrena spp. (Hymenoptera: Andrenidae) deposited more pollen grains than Panurginus crawfordi (Hymenoptera: Andrenidae) did. Third, we examined the presence of pollen grains derived from the pollinizer variety among those removed from the body surfaces of the flower-visiting insects. Results indicated the involvement of the three pollinator groups in pollen grain transfer of the pollinizer variety. Finally, we recorded the abundance of flower-visiting insects by walking around the study site. Results demonstrated that flies were observed stably irrespective of temperatures during the survey period, unlike A. mellifera and solitary bees, which exhibited little flower-visiting activity under low temperatures. Results also demonstrated that solitary bees were abundant at the study site in the late flowering period. These results suggest that hymenopterans and dipterans contribute differentially but mutually complementarily to open insect pollination in the Japanese pear orchard.