Turning manoeuvres in free-flying locusts: high-speed video-monitoring.

High-speed video-monitoring (500 f/s) was employed to analyse the flight path of free-flying locusts. A 3-D reconstruction enabled the simultaneous documentation of the motion of the body and all four wings. Particular attention was paid to turning manoeuvres. It is shown that angular changes during yawing and rolling are closely related; both are coupled, enabling natural banking of a free-flying animal. Rolling depends on bilateral inequalities in stroking of both wing pairs, whereby the differences are more conspicuous for the forewings. A relatively shorter downstroke occurs for the "inner" side of a turn. The determination of the phase ratio allows a reliable description of the instantaneous rolling manoeuvre. There is no change in cycle duration correlated with turning. The downstroke shortening results from a slight delay of downstroke initiation and an advance of the upstroke reversal. In parallel, the stroke amplitude is reduced on the "inner" side. The effects of bilateral asymmetries are immediate; they influence the instantaneous wing-beat cycle, but not the subsequent cycle. These correlations are consistent, though variable, in their magnitude, as is to be expected for a complex system in which several parameters have to be combined for the behaviourally relevant output.