INITIATION OF FLIGHT IN THE UNRESTRAINED FLY, DROSOPHILA-MELANOGASTER

Using high speed cinematography and videography, we determined that un restrained Drosophila melanagaster can initiate flight in two differen t ways, which we have designated Type 1 and Type 2 flight initiation. Type 1 behaviour is executed when the fly initiates flight 'voluntaril y'. Type 2 behaviour is executed in response to a visual stimulus and is presumably an escape response. During both types of flight initiati on, the fly pushes off from the substratum using only the mesothoracic legs. The mesothoracic legs extend at the coxo-trochanteric, femoro-t ibial and tibio-metatarsal joints. Although the movements of the legs are similar during both Type 1 and Type 2 flight initiation, the movem ents of the wings are different. Prior to the onset of leg extension, during Type 1 flight initiation, the wings are raised and rotated from their resting position to a preflight position dorsal to the thorax. The wings are held in this upright position for several milliseconds a nd then rapidly depressed during leg extension. Prior to Type 2 flight initiation, by contrast, the wings are not raised and rotated, nor ar e the wings depressed during leg extension. Thus Type 1 flight initiat ion involves simultaneous leg extension and wing depression, whereas T ype 2 flight initiation involves only leg extension.