Meeting Abstract

55.4  Tuesday, Jan. 5  Phase modulation and control of flight power muscles during visually-induced turning responses in the hawkmoth, Manduca sexta SPONBERG, S.*; DANIEL, T.L.; Univ. of Washington; Univ. of Washington bergs@u.washington.edu

The established perspective of flight control in insects holds that their remarkable maneuverability arises from neural modulation of relatively small steering muscles acting in concert with the regular, clock-like activation of larger power muscles. While in asynchronous fliers, phase modulation of the main power muscles is unlikely, synchronous fliers, like the hawkmoth, Manduca sexta, could have control capability in these muscles. To test the capacity for such control, we hypothesized that the main power muscles of M. sexta flight are bilaterally phase locked, with modulation of wing motions and aerodynamic forces arising from the action of the steering muscles. We recorded from the bilateral pair of dorso-ventral muscles (DVMs) in adults using bipolar tungsten electrodes. We used an oscillating vertical grating pattern to visually stimulate tethered moths, which induced strong, sustained yaw maneuvers. We found significantly larger variance in the phase of the two muscles during induced turning responses than during steady flight with a static visual stimulus. During maneuvers, changes in relative timing ranged over more than 20% of wing beat period; a very significant effect since even subtle phase shifts in these muscles can lead to large changes in muscle work output. Moreover, in some trials the phase of activation between the bilateral DVM pair closely tracked the phase of a 1 Hz sinusoidal visual stimulus. We reject the hypothesis that power muscles necessarily operate in phase, demonstrating that the DVMs can be asymmetrically modulated via a visual sensorimotor feedback loop. Our results support the emerging view that phase modulation of neuromuscular activity encodes significant information for locomotor control of insects.