Courtship song mechanism of Cotesia congregata (Hymenoptera: Braconidae)

Courtship songs have been characterized for several parasitic wasp species, yet beyond attributing the sounds to wing movement, the mechanisms of sound production have not been examined. We describe the male courtship song of Cotesia congregata (Hymenoptera: Braconidae) and examine the biomechanics of sound production using high-speed videography (2,000 fps) and synchronized audio recordings. The two part song consists of “wing fanning” followed by a series of pulsatile higher amplitude “boings.” Each boing consists of a series of wing strokes at 229 ± 3 Hz lasting 121.2 ± 2.8 ms at a greater down stroke displacement than wing fanning. Boings are preceded by a 22.8 ± 0.7 ms gap in which no sound is produced, and followed by a 203.6 ± 6.4 ms buzz similar to wing fanning. Boings are not produced by inter-wing contact or contact with the substrate or abdomen; also, maximal sound amplitude does not occur during maximal velocity of wing motion, thereby ruling out a typical mechanism of sound generation. Instead, sound is generated at the termination of the wing down stroke when displacement and acceleration are maximal but wing velocity is zero. Calculations rule out a whip-like action caused by rapid acceleration of the wing tip to supersonic speeds. The sudden change in wing direction at the bottom of the stroke likely generates a mechanical sound as the dominant dipole contribution and also could promote the generation of vortices that act as an aerodynamic source.