Habitat quality of field margins in a Finnish farmland area for bumblebees (Hymenoptera: Bombus and Psithyrus)

Abstract

Of all non-arable habitats, field margins are the most important ones for bumblebees in agricultural environment, especially as they are wide-spread and offer food resources, but they are also places for reproduction and overwintering. This study was made to investigate bumblebee abundance in the agricultural environment and to obtain information on the use of southern Finnish field margins by bumblebees. Bumblebees and cuckoo bumblebees were studied in a farmland area in Lammi, southern Finland, in 1996. Line-transect counts in field margins were made to compare habitat availability of patches of farmland and qualities of field margins within the patches. Landscape variables, dicotyledonous flower abundances and ecological and morphological characteristics of flowers were used as factors to explain variation in bumblebee assemblages and their frequencies of visits to the field margins. Bumblebee species richness and total density were higher in patches of farmland where field margins had more dicotyledonous flowers rather than being grassy. Abundance and flowering phenology of a limited number of flower species during the bumblebee breeding season were the most important factors explaining bumblebee visits in field margins. The most important flower species was zigzag clover ( Trifolium medium). The width of field margins was significantly related to the total density of bumblebees and cuckoo bumblebees, but not species number or diversity.