Multiple introduction of honeybee colonies increases cross- pollination, fruit-set and yield of 'Black Diamond' Japanese plum (Prunus salicina Lindl.)

Japanese plum (Primus salicina Lindl.) belongs to the Rosaceae family, which carries the S-RNase-mediated gametophytic self-incompatibility system, which prevents self-fertilisation, and thus promotes out-crossing. The plum cultivar 'Black Diamond'® has become, one of the most important cultivars in Israel in the last decade, yet its yield is low in comparison with its known potential. Honeybees (Apis mellifera) are the most important pollinators for plums and several studies have demonstrated an apparent relationship between the number of honeybees and the size of the fruit crop. Therefore, in this study, we focussed on improving bee management in a 'Black Diamond' orchard. In four consecutive years of experiments, we examined the effects of increasing the density of bee colonies, and of making multiple introductions of colonies, on honeybee activity and on their effectiveness as pollinators of 'Black Diamond'. We showed that four separate introductions, each of 0.625 colonies ha ^-1, every 2 - 3 d from 10% full bloom to 3 d after full bloom, with a total density of only 2.5 colonies ha^-1, resulted in the greatest level of fruit set.