The tymbal muscles of the cicada Cyclochila australasiae Donovan are synchronous, those of Platypleura capitata (Oliv.) asynchronous. The tymbal structure and the individual sound pulses are similar in the two species. The sound pulse frequency during calling song is higher in P. capitata (389 Hz) than in C. australasiae (234 Hz).
Muscle action potentials during protest songs are simultaneous in the two tymbal muscles of P. capitata, alternating in C. australasiae. Each action potential, or direct electrical stimulus to the muscle, is followed by a single, sometimes bimodal, sound pulse in C. australasiae, and by a burst of sound pulses in P. capitata.
The isometric twitch duration (30 °C) is much longer in P. capitata (107 ms) than in C. australasiae (18 ms) and the tetanic fusion frequency correspondingly lower.
Myofibrils are slightly wider and sarcoplasmic reticulum much sparser in tymbal muscles of P. capitata than in those of C. australasiae; otherwise the muscles are structurally similar.
Flight muscles in both species are synchronous with an action potential for each contraction.
Tymbal muscles of the two species are used to illustrate the diagnostic features of synchronous and asynchronous muscles.