| The neural control of insect flight is characterized by massive convergence of multimodal sensory input onto patterned motor output. During flight, visual guidance cues are integrated with fast mechanosensory signals to control sophisticated flight maneuvers such as hovering and fast forward flight. One fundamental focus of the neurobiology of insect flight is to understand how the nervous system encodes patterns of optic flow and wing motions, as well as how these signals are used together to control the enigmatic mechanics and unsteady aerodynamics associated with flapping flight. My thesis addresses large-field visual control of lift and proprioceptive encoding of wing motions in the hawkmoth Manduca sexta. In the first chapter, I present a brief overview of the control of insect flight and how this thesis contributes to the substantial body of literature on the topic. In chapter 2, I specifically ask how the moth encodes patterns of optic flow across the retina during intact tethered flight. By independently varying image velocity and spatial frequency I show that Manduca encodes large-field visual flow based on the temporal frequency of the moving image and not its absolute velocity. In chapter 3, I show the effects of ablating a proprioceptor, the wing hinge stretch receptor, on the moth's ability to control lift during tethered flight. The bilateral ablation of a single pair of these mechanoreceptors results in a nearly 70% decrease in visually evoked lift. Finally, in chapter 4, I record the activity of the stretch receptor during intact tethered flight as well as in response to controlled deformation of the wing hinge in order to describe its encoding properties. During flight, the stretch receptor fires a burst of action potentials near the top of each wing stroke. The onset of the burst is tightly phase locked within the stroke cycle, and the number of action potentials contained in the burst encodes the degree of elevation during the stroke. In response to controlled mechanical deformation of its supporting tissue, the stretch receptor encodes both the extent of stretch and the total rate of stretch in a characteristic phasicotonic manner. |
