Sensory and Neuromuscular Aspects of Insect Flight Control

Arguably the most significant contributor to the evolutionary success of insects lies in their capacity for flight, facilitating their diversification and the occupation of otherwise inaccessible niches. The extensive array of insect flight behaviours only arises from the intricate nature of their flight motor system, which enables precise and rapid control of wing motion, and remains adaptable to modifications triggered by multi-modal sensory input. This thesis presents novel research relating to aspects of flight control; the temporal rate at which flying insects can visually process their environment, the adaptations within the neuromuscular system that enable flight initiation, and the potential confoundment of mechanosensory information during tethered flight. When optic flow stimuli were projected at various refresh rates, insects only performed optomotor responses when refresh rates matched or exceeded particular thresholds. Such thresholds were species-specific, and partially dependent on stimulus characteristics, but consistently lower than each species’ previously reported flicker fusion frequencies, indicating reduced temporal acuity compared to previous assumptions. Simultaneous electromyography and high-speed imaging of blowflies at the onset of flight showed that the indirect power muscles, which drive thoracic contractions, were activated before wing engagement. This was consistently preceded by activation of the mesothoracic leg extensor. The subsequent activity of several steering muscles stabilised kinematics over the first wingbeats, though none were active before flight began. The movement of the haltere’s base, a potential artefact of dorsally-tethered flight, was found here to be considerably reduced when blowflies were instead ventrally-tethered. Mathematical simulations implicated base movement in amplifying fictitious forces imposed on the haltere’s beating plane, though these did not influence kinematics in the manner hypothesised, validating the continued use of dorsal-tethering in future studies. These insights enhance our fundamental understanding of how flexible flight control is achieved in miniature systems, and how this can be applied to biomimetic design.