Males produce prolonged loud echeme-sequence (Fig. 2) from 11 to 25 s. in length. It is completely consistent with data of other authors who registered signals of 10 s. up to 30 s. (Vedenina & Bukhvalova, 2001; Tishechkin & Bukhvalova, 2009). A male usually produces the discrete loud echeme-sequence right after landing. Sitting for a long time, prior to the loud echeme- sequence, a male can protractedly stridulate dis- crete echemes of syllables with unstable intervals (up to 1.5–2.0 min.), emitting the so-called «introduction» (Ragge & Reynolds, 1998). According to these characteristics, no differences among all the males studied were revealed.
The echeme repetition period in loud echeme- sequence is the most important for acoustic identifi- cation of a sexual partner in grasshoppers as well as the number of syllables per echeme (Table 1). Loud echeme-sequence of the calling signal of Staurode- rus scalaris consists of numerous echemes. Each of them consists of two parts, formed by long and short syllables. However, at large sweep speed, it is clear that there is one more transition phase between these parts where syllables follow with shorter (in contrast to the second part) intervals and occasionally they are poorly distinguishable (Fig. 2, shown by arrows). Also, this phase can not be referred to longer sylla- bles, because at the same sweep speed their internal structure is completely indistinguishable, unlike the transition phase. This phase is the result of a change of the algorithm of leg movement during stridulation (Elsner & Popov, 1978) from low to high amplitudes. It should be noted that during the calculation of num- ber of long and short syllables, the transition phase can not always be accounted.
The obtained results (Table 1) show that main characteristics of acoustic signals of the males from Samarskaya Luka and the Republic of Tuva fit into their variation range from different locations. Note- worthy, that repetition period of echemes and number of syllables in them vary, decreasing from the beginning to the end of a loud echeme-sequence (Table 2). Hence, a male begins to stridulate faster with shorter echemes. This feature is observed for calling signals of S. scalaris from all the locations studied.
Although populations of S. scalaris have a discrete distribution within its area (Sergeev, 2014), calling signals of males are more or less similar and overlap by the characteristics studied according to literature. Thus, we can talk about quite high acoustic conservatism of the species throughout the whole area. However, in our opin- ion, it is worth to pay attention to the differences between intermediate phases in echemes. The problem is that most publications are based on studies of calling signals of 1–2 males from each location. It does not allow us to draw any conclusions in regard to this characteristic at the present stage. It is also possible that this is just some individual variability.
Since acoustic calling signals in grasshopper communities differ by amplitude-time character- istics (Bukhvalova & Zhantiev, 1993), little atten- tion is paid to studies of the frequency spectrum. It is known that the frequency spectrum is broad- band and occupies most part of the audio range, including ultrasound area. In all studied males of S. scalaris the main frequency maximum lied in the range 6–14 kHz. [1]