Pollinators of Oriental persimmon in Japan

Japanese farmers who grow Oriental persimmon, Diospyros kaki Thunb. (Ericales: Ebenaceae), occasionally introduce Apis mellifera L. (Hymenoptera: Apidae) hives into their orchards during the flowering season, mainly because cultivars such as ‘Fuyu’ require pollination for stable fruit set. However, wild pollinators might serve this function. Thus, we aimed at identifying the most important pollinators of D. kaki in Japan by surveying visitation frequency across ten prefectures and pollination efficiency. The predominant flower visitors were Bombus ardens ​ardens Smith (Hymenoptera: Apidae) and A. mellifera, with similar pollination efficiencies. The estimated threshold number of pollen grains for fruit set of D. kaki ‘Fuyu’ was 27, which was comparable to the number deposited by a single visit of either species, meaning one visit of these dominant visitors probably induces fruit set. However, more pollen grains deposited by multiple visits further ensured fruit set. To achieve > 80% fruit set, more than about 70 pollen grains were needed. These results indicate that several visits by the bees would be sufficient for fruit set of D. kaki ‘Fuyu’.