Take-off mechanisms in parasitoid wasps.

High-speed video analyses of the natural behaviour of parasitoid wasps revealed three strategies used to launch the insects into the air. Which strategy is the most energy efficient? In , 92% of take-offs by were propelled entirely by movements of the middle and hind legs, which were depressed at their coxo-trochanteral and extended at their femoro-tibial joints. The front legs left the ground first, followed by the hind legs, so that the middle legs provided the final propulsion. Second, in other species of a similar mass, and , all take-offs were propelled by a mean of 2.8 and 3.8 wingbeats, respectively, with little or no contribution from the legs. The first strategy resulted in take-off times that were four times shorter (5 versus 22.8 ms) and take-off velocities that were four times faster (0.8 versus 0.2 m s). Calculations from the kinematics indicate that propulsion by the legs was the most energy-efficient strategy, because more energy is put into propulsion of the body, whereas in take-off propelled by repetitive wing movements energy is lost to generating these movements and moving the air. In heavier species such as and , take-off was propelled by the combined movements of the middle and hind legs and wingbeats. In , this resulted in the longest mean take-off time of 33.8 ms but an intermediate take-off velocity of 0.4 m s In all three strategies the performance could be explained without invoking energy storage and power amplification mechanisms.