Dorsal wing-flip timing in tethered flying locusts

Insects provide a unique opportunity to study unsteady aerodynamic mechanisms during flight. One of these mechanisms, rotational lift, has been shown to be important for Drosophila in flight and it is an open question as to whether rotational lift is important for other insects. In this study, we seek to determine whether tethered locusts (Locusta migratoria) actively control the timing of wing rotation relative to the stroke reversal (i.e. flip their wings) in order to augment lift and the produce of steering torques during intentional steering maneuvers. Dual highspeed digital cinematography sequences of tethered flying locusts were stimulated unilaterally with high-frequency sounds in a subsonic wind tunnel. These sequences were used to compute left and right forewing stroke kinematics in 3D. Our results show: 1) that locusts either rapidly pronate both forewings prior to the stroke reversal during an attempted turn (22 of 47 trials) or rapidly pronate one forewing in advance of the stroke reversal and one wing after the stroke reversal (12 of 47 trials), 2) during an attempted turn, locusts pronate the wing on the outside of the turn path earlier than the wing on the inside of the turn path, and 3) the wing-flip is rapid (44 800 ± 16 704°s"1) and is completed within 5.11 ± 4.33 % of the wing stroke duration. This study supports the hypothesis that locusts are generating steering torques by changing the timing of the establishment of angle of attack for the downstroke.