Musculoskeletal control of flight in the hawkmoth Manduca sexta

Insect flight arises from complex interactions of the nervous system, muscles, exoskeleton and aerodynamics. While detailed analysis of each subsystem can generate insight into aspects of flight behavior, understanding the performance of the integrated flight system requires comprehensive modeling of all these components. My thesis builds a new model of the flight apparatus for insects with synchronous, indirect power muscles. This model is used to explore the effect of variations in thorax morphology, muscle physiology and muscle activation timing on flight apparatus performance. In the first chapter, I present a brief overview of modeling insect flight and how this thesis contributes to the field. In chapter 2, I measure the passive elastic properties of the thorax which resist wing motion. I show that there is a constitutive relationship between wing angle and restoring moment in both sweep and stroke directions, which is best approximated by a cubic function. I also show how the non-linear character of the restoring force can passively control the wingstroke envelope. In chapter 3, I present a new model of the flight apparatus. The model predicts wing stroke trajectories and the resulting aerodynamic forces generated by active muscle forces. The model is based on a moment balance between internal and external (to the animal) forces, using measured parameters. Model results show that small variations in muscle timing and passive restoring forces can have large impacts on kinematics and resulting forces. Finally, in chapter 4, I present two finite element models of the dorsal aspect of the thoracic cuticle. Model results show that tensile contraction forces from the indirect dorso-longitudinal (DL) muscles are transmitted to the wing hinge along the lateral edges of the tergum. These results contradict previous flight mechanism models that specify vertical tergal displacement as the coupling mechanism between the DL muscles and the wing hinge.