FLICK, K.C.; TU, M.S.; DANIEL, T.L.: Flight control by steering muscles in Manduca sexta

Coupling between neural control, musculoskeletal mechanics, and aerodynamics remains a central issue in the study of insect flight. The large size and stereotyped flight behaviors of the hawkmoth, Manduca sexta, make it an attractive animal in which to investigate wing hinge mechanics. An antagonistic pair of large, synchronous muscles drives gross up and down motions of the wings. At least three groups of steering muscles in the wing hinge control pitch and sweep. These steering muscles, though relatively small in comparison to the muscles that power the wingstroke, are essential for maneuvering in flight. One of these, the subalar muscle, originates on the exoskeleton just above the mesothoracic legs and inserts the subalar tendon cap (STC), a sclerite that “floats” in a flexible membrane beneath the wing hinge. Previous studies have shown that the phase of subalar muscle activity relative to the wing depressors (Dl1s) changes during maneuvers. Here we investigated the mechanical effects of such phase changes on wing kinematics. We placed individual moths in front of a moving visual grating and monitored subalar and Dl1 activity with electromyography, and subalar length and STC position with high speed video imaging. The subalar muscle fired once during each wingstroke. On each downstroke, a small extension on the base of the wing touched the STC. Further, changes in the phase relationship between the subalar and Dl1 altered the pattern of STC motion. These data suggest that the subalar muscle alters wing kinematics by regulating the location of the contact point between the STC and the wing.