Vibratory Communication in Stingless Bees (Meliponini): The Challenge of Interpreting the Signals

Abstract

Foragers of several species of stingless bees (Apidae; Meliponini), a group of eusocial bees comprising more than 400 mainly tropical species, produce pulsed thoracic vibrations inside the nest when returning from a successful foraging trip. These vibrations do not provide navigational information on the direction and distance of a food source. Instead, both their occurrence and their temporal pattern correlate with the net gain during a foraging trip. The vibrations are therefore considered important information for potential foragers about the profitability of a food patch. Their repeated presentation lowers the foraging threshold of potential food collectors. The vibrations are considered as an alerting signal, which increases the colony’s foraging activity. So far, nothing is known about how foragers of stingless bees perceive the pulsed thoracic vibrations of the recruiters. Yet, consideration of the corresponding receptors and their thresholds in honeybees suggests three possible pathways for their transmission to the nestmates: (1) the substrate (vibrations), (2) the air (air particle movements), and (3) direct physical contact (tactile stimuli). The corresponding differ significantly. Whereas substrate vibrations will reach receivers up to ten bee lengths away (medium-range transmission), air particle oscillations and direct vibrations can be detected only by bees very close to, or in contact with, the forager (short-range transmission). Thus, depending on the transmission pathway and the recipient’s sensory capacity, the signal generated by thoracic vibrations will have different meanings. Indeed, substrate vibrations attract both food processors and potential foragers to the vibrating bee, whereas air particle oscillations and direct contact vibrations, in addition to important olfactory and gustatory information, may well be used by prospective recruits to evaluate the profitability of the advertised food source. In contrast to the honeybee waggle dance vibrations, there is no indication in stingless bees of an air jet potentially providing directional information.