Innate recognition of flowers by bumble bees: orientation of antennae to visual stamen signals

Abstract

The innate behaviour of flower-naive bumble bees (Bombus terrestris, Bombus lucorum) was observed at artificial flowers that consisted of a corolla and a guide area. A set of key stimuli was found to release a sequence of reactions, including the bee's approach, antennal reaction, and landing. For each reaction a binary choice between visual and olfactory signals was presented at the artificial flowers. Approach from a distance was released by the spectral purity of the corolla colour. The antennal reaction, which is the first antennal contact at an artificial flower, and occurs while the bumble bee is in flight, was oriented toward those areas with colours of the highest spectral purity. The landing reaction was released by visual and olfactory signals from the areas contacted during the antennal reaction. The combined presentation of visual signals from the anthers and olfactory signals from the pollen most effectively promoted landing. The antennal reaction allows precise alignment for landing and the antennal tips contact the visually conspicuous guide areas. This leads to effective perception of visual and olfactory stimuli from the guide area. The pollen and anthers, as well as the floral guides, which act as landing signals, of entomophilous flowers (Linaria vulgaris, Melampyrumpratense) possess olfactory qualities. In contrast, the pollen of one anemophilous plant (Pinus cedrus) exhibits no such qualities.