Wolfgang H. Kirchner

HOW HONEYBEES PERCEIVE COMMUNICATION DANCES, STUDIED BY MEANS OF A MECHANICAL MODEL

SummaryA mechanical model of a dancing honeybee was used to investigate the role of various components of the wagging dance in the transfer of information to follower bees. The model simulates the dance, carries a scent, and has an acoustic near-field similar to that of live dancers. The movements of the model are controlled by a computer, and selected components of the dance can be manipulated independently of others. The number of bees approaching scented baits at various distances and directions from the hive was observed, both during simulated “normal” dances and dances in which different components provided potentially conflicting information about the location of the food. The results indicate that the wagging run is the “master component” of the dance. The figure-of-eight dance path does not seem to convey information. Both sound and wagging must be present in the dance, but no specific roles were found for these components. Both sound and wagging convey information about distance and direction, and they appear to be largely redundant.

Sound and vibrational signals in the dance language of the honeybee, Apis mellifera

SummarySound and vibrational signals exchanged by honeybees during the performance of wagging dances were simultaneously recorded by means of a microphone and a laser vibrometer. Previous descriptions of the 280-Hz sounds emitted by the dancing bee were confirmed, and no vibrational (substrate-borne) component could be detected. In contrast, the 320-Hz “begging signals” (emitted by bees following a dancer and used as a request for food samples from the dancer) do vibrate the comb with peak-peak displacement amplitudes up to 1.5 μm. Artificially-generated comb vibrations of sufficient amplitude cause bees standing on the comb to “freeze”. The threshold for obtaining a detectable freezing response was measured for frequencies between 100 Hz and 3 kHz. At 320 Hz it is just below the amplitude of the natural begging signals. Thus it seems likely that these signals are received by the bees as vibrations of the comb. The propagation velocity of waves, damping, and mechanical input impedance of honeybee combs were studied. These results, combined with the observed amplitudes of the begging signals, support the assumption that the begging signals are generated with the flight muscles. The begging signal propagates as a bending wave. The attenuation of the begging signal with distance is relatively small, so the amplitude of the signal probably needs to be carefully adjusted in order to restrict the range of the communication.

The acoustic near field of a dancing honeybee

SummaryThe acoustic near field close to honeybees performing the wagging dance was investigated with pairs of small, matched microphones placed in various positions around the dancing bees. The dance ‘sounds’ are produced by the wings, which act as an asymmetrical dipole emitter. Close to the abdomen, the ‘sound’ pressures in the air spaces above and below the plane of the wings are totally out of phase. A zone of very intense acoustical short-circuiting exists close to the edges of the wings, where pressure gradients of about 1 Pa/mm are observed in the dorso-ventral direction (perpendicular to the plane of the wings). The pressure gradients drive air movements with velocity amplitudes up to about 1 m/s. The pressure gradients are much smaller in directions radially away from the bee and decrease rapidly with increasing distance from the wings. The ‘sound’ pressure detected by a stationary probe at one side of the bee is strongly modulated at 12–13 Hz as a result of the bees side-to-side wagging. Surprisingly little ‘sound’ is found near the dancers head. The positions of the follower bees reflect the properties of the acoustic field: The follower bees place their antennae in the zone of maximum acoustical short-circuiting where the air particle movements are most intense. These observations suggest 1) how follower bees can avoid mixing up the messages carried by the dance ‘sounds’ when two or more bees are dancing only a few cm apart and 2) how the followers might extract information about a dancers spatial orientation from the acoustic near field she produces. The observations also provide clues regarding the nature of the putative ‘sound’ receivers.

Vibrational signals in the tremble dance of the honeybee, Apis mellifera

SummaryThe tremble dance is a behavior sometimes performed by honeybee foragers returning to the hive. The biological significance of this behavior was unclear until Seeley (1992) demonstrated that tremble dances occur mainly when a colonys nectar influx is so high that the foragers must undertake lenghty searches in order to find food storers to unload their nectar. He suggested that tremble dancing has the effect of stimulating additional bees to function as food-storers, thereby raising the colonys capacity for processing nectar. Here I describe vibrational signals emitted by the tremble dancers. Simulation experiments with artificial tremble dance sounds revealed that these sounds inhibited dancing and reduced recruitment to feeding sites. The results suggest that the tremble dance is a negative feedback system counterbalancing the positive feedback of recruitment by waggle dances. Thus, the tremble dance seems to affect not only the colonys nectar processing rate, but also its nectar intake rate.

The causes of the tremble dance of the honeybee, Apis mellifera

Tremble dances are sometimes performed by returning forager bees instead of waggle dances. Recent studies by Seeley (1992) and Kirchner (1993) have revealed that this behaviour is part of the recruitment communication system of bees. The ultimate cause of tremble dances is, according to Seeley (1992), an imbalance between the nectar intake rate and the nectar processing capacity of the colony. This imbalance is correlated with a long initial search time of returning foragers to find bees to unload them. However, it remained unclear whether a long search time is the direct proximate cause of tremble dancing. Here we report that a variety of experimental conditions can elicit tremble dances. All of them have in common that the total search time that foragers spend searching for unloaders, until they are fully unloaded, is prolonged. This finding supports and extends the hypothesis that a long search time is the proximate cause of tremble dancing. The results also confirm the previous reports of Lindauer (1948) and others about factors eliciting tremble dancing.

Acoustical signals in the dance language of the giant honeybee, Apis dorsata

SummaryAcoustical signals emitted by dancing bees have recently been shown to transmit information about the location of food sources in the western honeybee, Apis mellifera. Towne (1985) reported that in the Asian honeybee species Apis dorsata, which builds a single comb in the open under overhanging rocks or tree branches, sound signals were not emitted by the dancers. This led to the conclusion that acoustical communication is restricted to bees that nest in the dark, like A. mellifera. Here we show that in fact A. dorsata produces dance sounds similar to those emitted by A. mellifera, and that these acoustical signals contain information about distance, direction and profitability of food sources. The acoustical transfer of information has thus evolved independently of nesting in dark cavities. The significance of nocturnal activity in Apis dorsata for the evolution of sound communication is discussed.

Transfer of Information during Honeybee Dances, Studied by Means of a Mechanical Model

The transfer of information about distance and direction from a dancing honeybee to follower bees can be studied by means of a mechanical model of a dancing bee. The model simulates the oscillating air flows around a dancing bee. The bees are recruited by the model and follow its instructions on where to fly. The model is used for investigating the role of individual dance parameters in the transfer of information.