Onconotus servillei Fischer von Waldheim 1846

Onconotus servillei Fischer von Waldheim, 1846

syn. Onconotus crassicaudus Ivanov, 1888

Material examined. In two hours, a total of 72 singing males were detected hidden in Ononis spinosa on investigated area. As the species is very rare and endangered in this part of Europe (Hochkirch et al. 2016), only one male was collected for song analyses. The specimens were recorded in net cages, with Roland R 05 digital recorder (sampling rate 96 kHz, 24-bit amplitude resolution, microphone response frequency up to 40 kHz) (Serbia) and Roland/Edirol R-09HR digital recorder (sampling rate 96 kHz, 24-bit amplitude resolution, microphone response frequency up to 45 kHz) (Romania). Microphones were placed about 15–20 cm from specimens. The sound analysis was run with Audacity 2.3.2. Song terminology follows Ragge & Reynolds (1998).

Acoustic recordings: male, Vajuga (44.5587°N, 22.6337°E), Serbia, 18 VII 2019, air temperature 24°C. Comparative material: male, Pâclele muddy volcanoes (45.3442°N, 26.7112°E), Romania, 23 VI 2014, air temperature 25°C.

Diagnosis. Micropterous species (Fig. 2A) with denticulated posterior border of disc of pronotum (Fig. 2B). In lateral view, disc of pronotum is S-curved (Fig. 2C), one of the main differences between O. servillei and O. laxmanni (Pallas, 1771) (Harz 1969). Male 10 th tergite with diverging broadly triangular terminal lobes (Fig. 2D), cerci short, with two small apical teeth (Fig. 3A). Titillators with wide basal arms, narrowed apically, bearing numerous teeth distributed in a one row (Fig. 3B). Stridulatory file of the Serbian specimen with 68 teeth of decreasing size from base to internal margin of the wing (Fig. 3C).

Song. Typically, the males stridulate in the morning and in the evening. The song is a faint, prolonged buzz lasting for several minutes, consisting of rapidly repeated syllable groups (echemes?) at a rate of 13–15 / second (Figs 4 A–D). The studied males from Serbia (Fig. 4A) and Romania (Fig. 4B) produce groups of three or four syllables. As the stridulatory movements have not yet been studied in Onconotus, we’ll presume that these groups are actually tri- or tetrasyllabic echemes. Within each syllable there are clear amplitude and period differences between the quieter opening and louder closing hemisyllables (Figs 4 C–D). However, the last part (syllable?) of a group is very short (6–9 ms) and of low acoustic intensity, without clear delimitation between hemisyllables. Thus, this may just be a part of the last closing hemisyllable. Each of the following syllables last for 21–30 ms and the total echeme length is 88–102 ms. Successive echemes are separated by an 8–13 ms interval. The dominant sound frequencies vary between 7–45 kHz, peak at 12 kHz (Fig. 4E).

The total number of O. servillei specimens is probably much higher, as we didn’t succeed to find females or males by visual search, excepting the singing males. In the same area, we recorded other 16 Orthoptera species: Conocephalus hastatus (Charpentier, 1825), Ruspolia nitidula (Scopoli, 1786), Decticus verrucivorus (Linnaeus, 1758), Platycleis affinis Fieber, 1853, Bicolorana bicolor (Philippi, 1830), Pachytrachis gracilis (Brunner von Wattenwyl, 1861), Rhacocleis germanica (Herrich-Schäffer, 1840), Oecanthus pellucens (Scopoli, 1763), Odontopodisma decipiens Ramme, 1951, Calliptamus barbarus (Costa, 1836), Acrida ungarica (Herbst, 1786), Mecostethus parapleurus (Hagenbach, 1822), Stenobothrus lineatus (Panzer, 1796), Chorthippus brunneus (Thunberg, 1815), Pseudochorthippus parallelus (Zetterstedt, 1821) and Euchorthippus declivus (Brisout de Barneville, 1848).

Since it is widespread in European Russia, O. servillei is assessed as Least Concern in Europe, but the subpopulations at the western margin of its range are severely fragmented, thus it is assessed as EN B2ab (i,ii,iii,iv,v) in the 28 countries of the European Union EU28 (Hochkirch et al. 2016). The highest threats to its habitat are overgrazing, afforestation and the use of pesticides (Hochkirch et al. 2016).

No such threats for the population found in Vajuga were noticed during our investigations in the area, but this locality needs urgent protection, since, for now, this represents the only locality where this species is present in Serbia. Future studies will be more focused on species detection in Serbia, mainly by acoustic search.