The effects of human management on spatial distribution of two bumble bee species in a traditional agro-forestry Satoyama landscape

We examined the relationship between flower preference and the spatial distribution of two Bombus species in a traditional agroforestry Satoyama landscape where human activities maintain a mosaic of landscape units, including old-growth and secondary forests, conifer plantations, cutover lands (stands 5-7 years after clear-cutting of secondary forests), and paddy fields. Bombus ardens prefers shallow woody flowers, whereas B. diversus tends to forage on herb flowers with long corolla tubes. Bumble bees were collected by window traps at seven types of landscape units. Most B. ordens individuals (77%) were caught at upper forest strata of old-growth stands. B. diversus queens displayed a similar preference for old-growth stands, whereas approximately half of the workers were captured in open land, such as cut-over land and paddy fields. These findings suggest that B. ardens mainly uses old-growth forests, where woody species diversity and woody flower abundance is high, whereas B. diversus visits forest herbs and shrubs until early summer and then spreads into open land to seek autumn-blooming herbs.