Horatosphaga leggei ( Kirby, 1909 )

Heller, Klaus-Gerhard, Hemp, Claudia, Liu, Chunxiang & Volleth, Marianne, 2014, Taxonomic, bioacoustic and faunistic data on a collection of Tettigonioidea from Eastern Congo (Insecta: Orthoptera), Zootaxa 3785 (3), pp. 343-376 : 347

Horatosphaga leggei ( Kirby, 1909)

[B] CH 4946–50 3 ♂, 2 ♀; [C] CH 4976–7 2 ♂; [D] CH 4940–42, 78–81 7 ♂

H. leggei ( Fig. 1 A) can be easily identified by the broad tegmina and the characteristic venation ( Ragge 1960). Its calling song has been already presented as oscillogram by Ragge (1968; male from Uganda, recorded by W.J. Bailey).

Song. The characteristic calling song was recorded in the field and in the laboratory. In Fig. 2 a registration of the stridulatory movement is shown. As in the two other available recordings, the animal very slowly changed its position during singing, and this displacement is reflected as a continuous upward change of the baseline (until about the 6th second and continued at the end). It is not connected with the stridulatory movement. Between the 9th and 11th second the amplifier settings were slightly changed manually.

The male starts its song ( Fig. 2 , 3 ) by slowly opening the wings and beginning with fast, oscillating movements of small amplitude. During opening and closing, sound impulses of similar amplitude are produced (microsyllables A). After a few hundred milliseconds, the oscillating movement stops and the wings are nearly completely closed. During this movement a series of soft impulses are also produced. Then a series of distinct movements follows, again with small amplitude. The series of impulses is less dense than in the first phase, but the impulses produced during the closing movement have larger amplitudes (microsyllables B). During this period (or its end) the wings are more or less gradually opened again. The duration of both parts, but especially of the second, varied greatly between recordings. This alternation is repeated several times (again variable in number), but the impulses produced during the large closing movement become increasingly louder. After some time, at first a second large closing movement is added immediately after the first (at 6–7 s in Fig. 2 ; Fig. 3 ), and the period of fast movements becomes shorter, then typically a series of large movements with loud impulses follows (macrosyllables), until after a final short series of fast movements only large closing movements can be observed. During this period, the impulses produced during the opening movements are much softer than that during closing. After some seconds the wing movements become more slowly in rhythm and the sound softer, until the song dies away.

Surprisingly the spectral composition of the song is not the same in all parts. During the fast oscillating movements, in the spectrum low frequency components are visible, which are not found in any other part of the song (see Fig. 3 , 4 ) except at the beginning of the large closing movement. Possibly some parts of the tegmina are put into vibration only if the wings are very wide open and the scarper touches the outermost parts of the file. Since nothing is known about the behaviour of the species, it is too early to speculate about a biological significance of the frequency differences. The main sound energy was found in a band at about 10 to 15 kHz. W.J Bailey mentioned (pers. comm.) that puncturing the tegmina would diminish the intensity of the song strongly, but judging from the shape of the spectrum there does not seem to be one single sharply tuned resonator. In the right tegmen, there is no obvious mirror ( Fig. 5 B; compare the situation in Zeuneria biramosa Fig. 5 C).

The stridulatory file does not show any irregularities ( Fig. 5 A). Starting from the outer edge of the tegmen, the teeth (n = 88; one specimen) become broader towards the middle and more narrow again near the articulation.

Figures

FIGURE 1. Habitus. A— Horatosphaga leggei, B— Pardalota asymmetrica, C— Pardalota asymmetrica, ♀ nymph, D— Arantia congensis ♂ CH 4991, E— Arantia congensis ♀ CH 4943, F— Arantia congensis ♀ nymph, G— Zeuneria biramosa, H—? Tetraconcha sp. ♀ (A, F photos Alois Liegl).

FIGURE 2. Oscillograms of stridulatory movements and song [synchronous registration of left tegmen movement (upward deflection represents opening, downward closing) and sound; 15 s sequence]. In the first half of the recording of H. leggei, the stridulatory movement is superimposed by a slight body movement, mimicking a continously increasing opening of the tegmina.

FIGURE 3. Detail of calling song of Horatosphaga leggei. Oscillograms of stridulatory movements and song [synchronous registration of left tegmen movement (upward deflection represents opening, downward closing) and sound; 1.5 s sequence], combined with a sonographic evaluation (2 kHz high pass; T> 25.5 ºC).

FIGURE 4. Frequency spectra of calling songs. In Horatosphaga leggei, the black line respresents the evaluation of a 50 ms part of the song during the production of microsyllables A, the solid part that of a 50 ms part during the production of macrosyllables (same scale).

FIGURE 5. A—Stridulatory file of Horatosphaga leggei (articulation below), B—Base of right tegmen of Horatosphaga leggei, C—Base of right tegmen of Zeuneria biramosa, D—Stridulatory file of Zeuneria biramosa (articulation below). Scales 0.5 mm.