The Mechanism of Flight Preparation in Some Insects*

IN 1928 Dotterweich published under the title " Beitrage zur Nervenphysiologie der Insekten" some very interesting and important observations and measurements mainly on Sphingidae, showing that the rapid vibration of the wings regularly observed in large moths before they take flight produces an increase in temperature of the wing muscles which is necessary to enable them to fly at all. The temperature reached was nearly the same in all cases, 32-34° C, and the time taken to reach it varied with the initial temperature deficit, up to 6 min. with a deficit of 23°. Moths kept at 34° or above would fly off at once, without any preparation, when stimulated. It had been assumed by v. Buddenbrock that this preparation was mainly required to attain the high frequency of the wing movements necessary for actual flight, but a number of observations made by Dotterweich on butterflies (Vanessa), in which the normal frequency is much lower, made it very probable that in these also preparatory wing movements were responsible for a rise in temperature necessary for actual flight. The general interest of these observations became greatly enhanced when it was shown by Marius Nielsen (1938) in this laboratory that, in man, muscular work is closely correlated with a rise in body temperature which is regulated to very sharply defined higher levels corresponding closely to the rate of work. The present paper contains a confirmation and extension of Dotterweich's results. Temperature measurements have been made throughout by means of thermojunctions made of o-i mm. constantan and 0-2 cm. copper wires inserted through the integument of. the insect in question. In most cases the wires ending in the thermojunction had a vertical free length of 30-40 cm. allowing the insect a considerable amount of freedom to move, while flight could be induced, in certain conditions, by lifting the insect from the support (Fraenkel, 1932).