VISUALLY INDUCED YAW MOVEMENTS IN THE FLYING LOCUST, SCHISTOCERCA-GREGARIA (FORSK)

Movement of a small object in the lateral visual field of a flying locust mounted on a balance induces a turning response expressed as a yaw towards the stimulus. Wing movements have been filmed (Figs. 2, 3, 4) and analysed in detail. During the response there are: 1. A transient shortening of wing beat period (Fig. 5), more marked and occurring earlier, in the forewings. 2. Fore and hindwing pairs move in phase at the start of the response. Contralateral wings tend to move out of phase, wing on side of turn follows that on other side initially but then changes can occur in either direction (Fig. 6). 3. Forewing twisting was recorded. The forewing on the side of the turn remains pronated during the upstroke portion of the damped initial stroke. 4. Wing stroke amplitude is reduced initially and then rapidly increases but, more importantly, the starting and finishing points of the contralateral wing strokes are different. Wings on the side of the turn start from a lower point and move down further than those on the opposite side (Figs. 7, 8). 5. The hindleg on the side of the turn may be extended and the abdomen bent to that side also. This response develops and declines more slowly than the observed changes in wing motion. It is postulated that these changes, in different combinations, can account for the observed behaviour and that in free flight the insect would perform a banked turn towards the stimulus. © 1979 Springer-Verlag.