Dependence of Asian honeybee on deciduous woody plants for pollen resource during spring to mid-summer in northern Japan

Apis cerana japonica Radoszkowski, endemic to Japan, is known to be one of the most important pollinators for wild plants and crops, such as buckwheat, in cool to warm temperate Japan. To determine the degree of dependence of A. cerana japonica on forest resources, we analyzed pollen brought back to nests in a typical Satoyama landscape with relatively high deciduous forest coverage in northern Japan. We divided the landscape elements of the study area into three types: deciduous forest, conifer plantation and open land according to landcover digital data, and each pollen taxon was assigned to one of these three types of landscape elements. We collected total pollen loads of 15.75 g (total of colonies A and B) in May (spring), 1.57g ( total of colonies A and C) in June (early summer), 19.03 g (total of colonies A, B and C) in July (mid-summer) and 45.61 g (total of colonies A, B and D) in September (autumn). Deciduous forests are the most important foraging habitats for A. cerana japonica in the Satoyama landscape especially from spring to mid-summer when mass flowering of tall trees and shrubs species provides rich floral resources for developing bee colonies. On the other hand, the bees frequently foraged from herbaceous plant species in autumn when flowering of tree species reduces and herbaceous plant species have flowering peaks. In turn, the bees provide pollination services to a number of wild flowers blooming in various forest layers ranging from the canopy to the understory layer.