FORAGING BUMBLEBEES AVOID FLOWERS ALREADY VISITED BY CONSPECIFICS OR BY OTHER BUMBLEBEE SPECIES

Honey bees, Apis mellifera, use short-lived repellent scent marks to d istinguish and reject flowers that have recently been visited by thems elves or by siblings, and so save time that would otherwise be spent i n probing empty flowers. Conversely, both honey bees and bumblebees, B ombus spp., can mark rewarding flowers with scent marks that promote p robing by conspecifics. We examined detection of recently visited flow ers in a mixed community of bumblebees foraging on comfrey, Symphytum officinale, in southern England. When foraging among inflorescences on a plant, three abundant species of Bombus probed fewer inflorescences more than once than would be expected from random foraging. Bees freq uently encountered inflorescences but departed without probing them fo r nectar. Examination of the incidence of such rejections in the two m ost common species, B. terrestris and B. pascuorum, revealed that the low incidence of multiple probing visits was due to two factors: bees both foraged systematically and selectively rejected inflorescences th at they had previously visited. When presented with inflorescences of known history, bees selectively rejected those that had been recently visited by themselves or by conspecifics compared with randomly select ed inflorescences. They were also able to distinguish inflorescences t hat had been visited by other Bombus species. Bees were unable to dist inguish and reject inflorescences from which the nectar had been remov ed artificially. We conclude that these Bombus species are probably us ing scent marks left by previous visitors. The significance of deposit ion and detection of interspecific scent marks for competitive interac tions between species is discussed. (C) 1998 The Association for the S tudy of Animal Behaviour.