Printed in Great Britain MUSCULAR ACTIVITY DURING PREPARATION FOR FLIGHT IN A BEETLE

In many insects flight is preceded by a period of muscular activity, during which the temperature of the thorax is raised (Dotterweich, 1928; Krogh & Zeuthen, 1941). The temperature changes accompanying this phenomenon in hawk-moths have recently been reinvestigated by Dorsett (1962) and the influence of temperature on the performance of flight muscles from various species has been considered by Neville & Weis-Fogh (1963), Machin, Pringle & Tamasige (1962) and Miller (1964), but little attention appears to have been paid to the mechanisms by which mechanical activity is generated. In the case of those insects (Orthoptera, Lepidoptera, Odonata) where the flight muscles are of the synchronous type with the rhythm of muscular activity determined by the pattern of motor nerve impulses there is little difficulty in understanding how movements of small amplitude can be produced by twitches of the flight muscles. But in insects with asynchronous, fibrillar flight muscles (Diptera, Hymenoptera, Coleoptera) it is known that rhythmic muscular activity depends on the form of the mechanical loading and it is not immediately apparent how vibration and heating can be produced when the wings are folded. No movement of the wings o