Eumodicogryllus chivensis ( Tarbinsky, 1930 )

Eumodicogryllus chivensis ( Tarbinsky, 1930)

Figs 144 View Figure 144 , 145 View Figure 145 , 146 View Figure 146 , 147 View Figure 147

Diagnostic notes.

With less than 1 cm, E. chivensis is a relatively small member of the true crickets on Socotra. It is characterised by a light brown, sandy colour, six faint longitudinal stripes on the occiput and a strongly curved epistomal suture between the antennae, forming an almost right angle with a sharp apex (Fig. 144 View Figure 144 ). The latter character is diagnostic for the genus Eumodicogryllus , compared to Modicogryllus . The tegmina have two harp veins.

The pseudepiphallus forms a curved plate with a distinct wedge-shaped notch in its posterior margin, giving it a bifurcated appearance. In the middle, it has a characteristic transverse fold. Its main lateral lobes are pointed apically (Fig. 145 View Figure 145 ).

We identified our specimens from Socotra as E. chivensis , based on its phallic structure (Fig. 145 View Figure 145 ) and head pattern by comparing the illustrations in Gorochov (1978). We also used the key in Gorochov (1978) and the species description in Tarbinsky (1930). Our specimens seem relatively small compared to the holotype, based on the morphometrics mentioned by Tarbinsky (1930) (Table 5 View Table 5 ).

Taxonomic notes.

Tarbinsky (1930) described Gryllus chivensis as follows: “ Lower part of face distinctly rounded in profile; lower frontal margin forms a strongly angularly inflexed line; frons under the middle ocellus with transverse brown spot separated from the other, upper, brownish part of the head, by a yellow stripe, very narrow in the middle. Occiput with indistinct narrow longitudinal yellow stripes. Lateral lobes of the pronotum with a short brown stripe reaching neither the hind nor the anterior margins. Tegmina of males and females are unicolourous; in females, they are one and a half times longer than the pronotum with a roundly prominent apex. The apex is somewhat tapering in males, with a broad apical field. Ovipositor longer than hind femora ”.

Chopard (1961) moved Gryllus chivensis Tarbinsky, 1930 , amongst many other taxa, to his newly-erected genus Modicogryllus Chopard, 1961 . Gorochov (1978) distinguished three groups within this genus, based on the shape of the male genitalia and the curvation of the epistomal suture. One group was formed by M. bordigalensis and M. chivensis , for which Gorochov (1986) later erected the subgenus Eumodicogryllus , designating M. bordigalensis as the type species. In 1993, Gorochov elevated Eumodicogryllus to the genus level without further explanation, which was noted and subsequently accepted by Coray and Lehmann (1998).

The genus Eumodicogryllus contains five species ( Cigliano et al. 2024 a): E. bordigalensis (Latreille, 1804) , E. chinensis (Weber, 1801) , E. chivensis , E. theryi ( Chopard, 1943) and E. vicinus (Chopard, 1968) .

Recently, Ma et al. (2021) erroneously synonymised E. chivensis and E. bordigalensis with E. chinensis . They stated that Chopard (1967) made a mistake when synonymising E. chinensis with E. bordigalensis and claimed that, based on the principle of priority, the senior synonym should be E. chinensis instead of E. bordigalensis .

Chopard (1967), however, did not synonymise E. chinensis with E. bordigalensis . He only considered the specimens formerly identified as chinensis by several authors as belonging to E. bordigalensis . He kept E. chinensis as a valid species by mentioning “ chinensis (nec Weber) ”. Harz (1969) agreed on this.

Ma et al. (2021) synonymised E. chivensis with E. bordigalensis mainly because they found “ E. bordigalensis and E. chivensis to be very similar ”. They referred to the illustrations of the phallic structure of both species in Gorochov (1978). They stated they “ could find those two types of male genitalia in specimens collected in China ”. These arguments are too weak for synonymising two species widely accepted for decennia and OSF does not accept this proposed synonymy ( Cigliano et al. 2024 a).

We compared the male genitalia of a specimen from Socotra with a specimen of E. bordigalensis from Italy and found several differences. The phallic structure of E. chivensis from Socotra is much smaller than the one from E. bordigalensis , with a width of the pseudepiphallus of 0.6 mm and 1.0 mm, respectively. There is also a difference in the shape of the pseudepiphallus. In E. chivensis , the wedge-shaped notch in the posterior margin of the pseudepiphallus is more profound and broader than in E. bordigalensis ; as a result, the mean (lateral) lobes of the pseudepiphallus are more slender, corresponding to the illustration in Gorochov (1978). Finally, the songs of both species differ.

Distribution and occurrence.

E. chivensis was described from Ak-Mechet, near Khiva, in modern Uzbekistan (not Khazachstan as indicated by OSF). It is known from Oman and Saudi Arabia ( Gorochov 1993), the United Arab Emirates ( Gorochov 2017) and China ( Ma et al. 2021). It is new for Socotra and is only known from three specimens at Neet (Fig. 146 View Figure 146 ).

Habitat and biology.

In Central Asia, E. chivensis occurs in semi-deserts near salt lakes ( Gorochov 2017). On Socotra, it was found in a sandy habitat with salt marsh vegetation behind the first row of dunes at 2 m a. s. l. (Fig. 2 View Figure 2 ). The crickets were calling from the entrances of small holes in the ground.

Bioacoustics.

The calling song of Eumodicogryllus chivensis is an echeme, repeated at the rate of about 3–4 per second, lasting 70–120 ms, produced in continuous series or broken up in groups of 2–15 (Fig. 147 A View Figure 147 ). Echemes consist of 9–11 syllables of more or less equal duration, repeated at 110–120 per second (Fig. 147 B View Figure 147 ). Usually, the first one or two syllables are quieter and are repeated at a lower rate. The carrier frequency of the song is around 7.7–8.0 kHz and the song has few harmonics at higher frequencies (https://www.xeno-canto.org/877946).

The song is markedly different from E. bordigalensis , as the song of that species has echemes with 14–20 syllables repeated at about 40–60 per second. Additionally, the carrier frequency in E. bordigalensis is much lower ( Ragge and Reynolds 1998).