The bumblebee Bombus ardens ardens (Hymenoptera: Apidae) is the most important pollinator of Oriental persimmon, Diospyros kaki (Ericales: Ebenaceae), in Hiroshima, Japan

Oriental persimmon, Diospyros kaki Thunb. (Ericales: Ebenaceae), is a generally diclinous tree. Because the representative cultivar, ‘Fuyu’, sets nearly exclusively female flowers and has low parthenocarpic ability, it requires pollen from other cultivars for pollination. Here, we identified the most important pollinator of D. kaki in hilly orchards surrounded by secondary forest in Hiroshima, southwestern Japan. To estimate the contribution of each flower visitor to pollination, we used an index of potential pollen transport, namely the rate of visitation per female flower multiplied by the estimated number of pollen grains on the body surface. Among nine functional groups, the value of this index was greatest for bumblebees followed by small bees, whereas that for honeybees was low because of the relatively few Diospyros pollen grains on the body surface. Bombus ardens ardens Smith (Hymenoptera: Apidae) was the predominant bumblebee species in terms of both monitored frequency of visits by insects and number collected for identification. We also counted the fruit set and seed number of ‘Fuyu’ fruit in various pollination treatments using exclusion mesh to assess the effectiveness of insects of different sizes. Bombus ardens ardens was the most important pollinator and small bees were the second most important.