Comparative Physiology of Insect Flight Muscle

Abstract

Insect flight is powered by muscles that attach more-or-less directly to the wings (direct flight muscles) and muscles that bring about wing movement by distorting the insect’s thorax (indirect flight muscles). Flight stability and steering are achieved by differential activation of power muscles and by the activity of control muscles that alter wing stroke amplitude and angle of attack. One evolutionary trend seen when comparing more advanced with less advanced fliers is a reduction in the number of power muscles and an increase in the number of control muscles. On the basis of the neural control of contraction, insect muscles may be divided into synchronous muscles and asynchronous muscles. In synchronous muscles there is neural input and evoked muscle action potentials associated with each contraction. Asynchronous muscles are turned on by neural input, but, when activated, they can contract in an oscillatory manner if attached to an appropriate, mechanically resonant load. The features of asynchronous muscles that allow oscillatory contraction are delayed stretch activation and delayed shortening deactivation. Because asynchronous muscles do not have to be turned on and off by neural input for each contraction, they are expected to be more efficient and more powerful than are synchronous muscles for high frequency operation.