Activity of asynchronous flight muscle from two bee families during sonication (buzzing)

The indirect flight muscles of bees are used to produce a variety of actions in addition to flight, including sonication, which has a higher frequency than flight. We observed the dynamic movement of the scutum during sonication and the transition from tethered flight to sonication. During sonication, the scutum oscillated above its rest position, indicating that the conformation of the structural components of the thorax had been altered. Sonication vibrations of the thorax occurred by deformation of the scutum rather than by opening of the scutal fissure and are smaller than vibrations associated with flight. During tethered flight, the ratio of muscle activity (recorded via electromyograms) between the dorsal longitudinal muscles and the dorsoventral muscles approached 1, but during sonication the ratio was significantly higher (up to 4.0). This increase may cause the dorsal longitudinal muscles to contract further than the dorsoventral muscles and close the scutal fissure during sonication, so limiting the displacement of the wings and 'decoupling' them from the indirect flight muscles.