An Aerodynamic Sense Organ Stimulating and Regulating Flight in Locusts

Abstract

IT is a curious fact that nearly all insects, even the best flyers, lack static organs, which are so highly developed in other flying or swimming animals. Sensory systems sensitive to air currents have, however, been suggested¹ or found² in certain Diptera, and at the Eighth International Congress of Entomology at Stockholm (August, 1948) I gave a paper on an aerodynamic sense organ in the locusts Schistocerca gregaria Forskål and Locusta migratoria L.³. Since 1947, this knowledge has been used in the late Prof. August Krogh's laboratory, where studies on insect flight are going on. In short, the sensory organ consists of sensory hairs situated on the frons and the vertex of locusts. In suspended animals which have no contact with the ground, stimulation of these hairs by means of a jet of air induces flight movements. Flying stops when the air jet is removed, and starts again on fresh stimulation. In this way sustained 'stationary' flight is possible for at least one hour. The forelegs are retracted as in normal flight; but, under these conditions, the hind legs are never drawn up. It is impossible to induce sustained flight by means of a jet of air when the sense organ has been covered with cellulose paint; uncovering results in a return to normal sensitivity. By covering different parts of the surface of the animal, including the antennæ, it has been shown that only covering of the patches of hairs on the frons and the vertex prevents the flight responses; but if some of them are left uncovered, flight may be induced. Recently (March 1949) similar observations on other Acrididæ have been described by Boyd and Ewer⁴.