Neuro-muscular control of dipteran flight.

Since the discovery of the myogenic nature of the main flight-muscle rhythm in flies and some other insects (Pringle, 1949; Roeder, 1951) there has been wide agreement that the nervous command to individual motor units must be one in which the significant aspect of the temporal code is the average frequency of nerve impulses and not detail of sequential pattern or the phase of each impulse (Wilson & Wyman, 1963; Burton, 1964; Barber & Pringle, 1966). There are interesting impulse-sequence patterns among the motorneurons in the flight control systems of flies (Wyman, 1966); but as far as we can tell these have no significance for the muscle performance although they must indicate something of the co-ordinating mechanisms within the thoracic ganglion. Although some isolated studies support the argument that the code must be a pulse-frequency modulation, one in which pulse phase is irrelevant (Wilson & Wyman, 1963), there has yet been no careful study of the correlation between nervous events and aerodynamic output in myogenic insects. It has also been assumed that there is a spatial coding, or a differently varying command to different muscles, for the control of such behaviour as turning. This seems necessarily true, but there has been little study of this aspect of control. Such a study is presently needed, for example, as background for attempts at correlating optomotor reaction behaviour with underlying nervous phenomena. We have tried to obtain a broad picture of muscle function and nervous command of the whole flight musculature in normal flight and during strong turning in flies. The results have been correlated as far as possible with the known features of wing kinematics (Nachtigall, 1966).