Take-off mechanisms in parasitoid wasps

ABSTRACT 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 Pteromalus puparum, 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, Cotesia glomerata and Leptopilina boulardi, 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−1). 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 Netelia testacea and Amblyteles armatorius, take-off was propelled by the combined movements of the middle and hind legs and wingbeats. In A. armatorius, this resulted in the longest mean take-off time of 33.8 ms but an intermediate take-off velocity of 0.4 m s−1. In all three strategies the performance could be explained without invoking energy storage and power amplification mechanisms. Summary: Parasitoid wasps use three strategies to take off: propulsion by rapid leg movements, propulsion by flapping wing movements and a combination of the two. Leg movements provide the most energy-efficient mechanism.