Foraging habitats and foraging distances of bumblebees, Bombus spp. (Hym.,apidae), in an agricultural landscape

In selected foraging habitats of an agricultural landscape flower visits of bumblebees and community structure of foraging bumblebees were studied, wi th special regard to the role of crops as super-abundant resources. Most cr ops represent temporal foraging habitats with high abundance of bumblebees but mainly with low diversity in the bumblebee forage community, in contras t to permanent foraging habitats such as, for example, a hedgerow. The high numbers of bumblebees in the monoculture of crop plantations consisted mai nly of short-tongued bumblebee species. The role of foraging distances for the visitation rate of foraging habitats was studied by performing capture- recapture experiments with natural nests of Bombus terrestris, Bombus lapid arius and Bombus muscorum. Differences were found on the species as well as the individual level. The foraging distances of B. muscorum were more rest ricted to the neighbourhood of the nesting habitat than the foraging activi ty of B. terrestris and B. lapidarius. High percentages of B. terrestris wo rkers were recaptured while foraging on super-abundant resources in distanc es up to 1750 m from the nest. Isolated patches of highly rewarding forage crops, in agricultural landscapes, are probably only accessed by bumblebee species with large mean foraging distances, such as the short-tongued B. te rrestris. Species like the rare, long-tongued B. muscorum depend on a close connection between nesting and foraging habitat. A restricted foraging rad ius might be one important factor of bumblebee species loss and potential p ollinator limitation in modern agricultural landscapes. Furthermore, long-d istance flights of bumblebee pollinators have to be considered in the prese nt discussion on gene flow from transgenic plant species on a landscape sca le.