David C. Young

Mechanisms of sound-production and muscle contraction kinetics in cicadas

Summary1.The mechanisms of sound-production are described in 7 species of Australian cicadas:Abricta curvicosta, Arunta perulata, Chlorocysta viridis, Psaltoda argentata, P. claripennis, P. harrisii andTamasa tristigma. In all these species, sound is produced by a pair of tymbals, each of which is buckled by a large muscle (Figs. 1–7). The tymbal muscles are all of the synchronous (= neurogenic) type.2.There are great differences between species in the range of sound frequencies generated by their tymbal mechanisms and in the extent to which their songs are divided into pulses and subpulses. The most extreme case is the calling song ofChlorocysta viridis, in which there are no pulses and the sound produced is a modulated pure-tone (Fig. 3).3.In most species the left and right tymbal muscles contract alternately and so the muscle contraction frequencies during singing are half the observed pulse repetition frequencies. InT. tristigma, the two tymbal muscles contract only a few percent out of phase in calling but in full antiphase in protest song (Fig. 7). InA. perulata, there is some evidence that the two tymbal muscles contract in synchrony during calling even though they clearly alternate in protest song.4.Muscle contraction frequencies during calling songs vary from 56 Hz inC. viridis to 224 Hz inPsaltoda claripennis. Contraction frequencies during protest songs are somewhat lower than in calling.5.The tymbal muscle behaves as a single motor unit in all species, giving all-or-nothing twitches with a single, sharp threshold. The durations of isometric twitches are strongly correlated with the inferred cycle period (= reciprocal of contraction frequency) in a total of eleven species with synchronous tymbal muscles (Fig. 8).

Bilateral symmetry of sound production in the mole cricket, Gryllotalpa australis

Summary1.Males of the mole cricket, Gryllotalpa austrails (Orthoptera, Gryllotalpidae), produce their calling song from a specially constructed burrow, which has four horn-shaped openings at the surface of the soil.2.Males will also call from an artificial burrow with dimensions similar to the natural burrow, making it possible to study their wing movements during singing in the laboratory (Fig. 3).3.The calling song of G. australis is a continuous train of sound pulses with a mean frequency of 2.5 kHz (Fig. 4). The mean pulse repetition rate at 23°C is 70 Hz. Calling songs produced in the artificial burrows are similar to those produced in natural burrows.4.More than half the males studied in the artificial burrows sang with forewings arranged both right-overleft and left-over-right. Usually, males kept to one or other arrangement for the duration of a given calling song, but some males showed a propensity for changing wing arrangement during the song (Fig. 6).5.There was no significant difference between calling songs produced with the wings arranged right-over-left and those with the wings left-over-right, with respect to all major parameters including intensity (Fig. 5).6.The file and scraper structures are equally well developed on both left and right forewings of male G. australis (Fig. 7). The forewings lack the conspicuous group of sensory hairs that function to prevent a change of wing arrangement in field crickets.7.We conclude that mole crickets normally use both right-over-left and left-over-right wing arrangements in singing and that both are equally efficient at producing sound.