FLIGHT INITIATIONS IN DROSOPHILA-MELANOGASTER ARE MEDIATED BY SEVERALDISTINCT MOTOR PATTERNS

We have monitored the patterns of activation of five muscles during fl ight initiation of Drosophila melanogaster: the tergotrochanteral musc le (a mesothoracic leg extensor), dorsal longitudinal muscles # 3, # 4 and # 6 (wing depressors), and dorsal ventral muscle # Ic (a wing ele vator). Stimulation of a pair of large descending interneurons, the gi ant fibers, activates these muscles in a stereotypic pattern and is th ought to evoke escape flight initiation. To investigate the role of th e giant fibers in coordinating flight initiation, we have compared the patterns of muscle activation evoked by giant fiber stimulation with those during flight initiations executed Voluntarily and evoked by vis ual and olfactory stimuli. Visually elicited flight initiations exhibi t patterns of muscle activation indistinguishable from those evoked by giant fiber stimulation. Olfactory-induced flight initiations exhibit patterns of muscle activation similar to those during voluntary fligh t initiations. Yet only some benzaldehyde-induced and voluntary flight initiations exhibit patterns of muscle activation similar to those ev oked by giant fiber stimulation. These results indicate that visually elicited flight initiations are coordinated by the giant fiber circuit . By contrast, the giant fiber circuit alone cannot account for the pa tterns of muscle activation observed during the majority of olfactory- induced and voluntary flight initiations.