Effects of stretch receptor ablation on the optomotor control of lift in the hawkmoth Manduca sexta

In insects, fast sensory feedback from specialized mechanoreceptors is inte grated with guidance cues descending from the visual system to control flig ht behavior. A proprioceptive sensory organ found in both locusts and moths , the wing hinge stretch receptor, has been extensively studied in locusts for its powerful influence on the activity of flight muscle motoneurons and interneurons. The stretch receptor fires a high-frequency burst of action potentials near the top of each wingstroke and encodes kinematic variables such as amplitude and timing. Here, I describe the effects of stretch recep tor ablation on the visual control of lift during flight in the hawkmoth Ma nduca sexta. Using a combination of extracellular muscle recordings, force and position measurements and high-speed video recording, I tracked power m uscle activity, net vertical flight force (lift), abdomen deflection and wi ng kinematics in response to image motions of varying velocity during tethe red flight in a wind tunnel. As a result of bilateral ablation of the wing hinge stretch receptors, visually evoked lift decreased to nearly one-third of that exhibited by intact animals. The phase and frequency of indirect p ower muscle action potentials and the patterns of abdominal deflection were unaffected; however, wingstroke amplitude was clearly reduced after ablati on. Collectively, these results suggest that stretch receptor feedback is i ntegrated with descending visual cues to control wing kinematics and the re sultant aerodynamic force production during flight.