Stenohippus socotranus ( Popov, 1957 )

Stenohippus socotranus ( Popov, 1957) View in CoL

Figs 54 View Figure 54 , 55 View Figure 55 , 56 View Figure 56 , 57 View Figure 57

References for Socotra.

Popov (in Uvarov and Popov (1957)): 382–383, fig. 36 [as Leva socotrana ]; Jago 1996: 114–116, 120, figs 153–155, 182; Wranik 2003: 325, plate 158 [as Leva socotrana ].

Diagnostic notes.

The Socotran material can be recognised as Stenohippus , based on the main characteristics according to the key in Jago (1996): frontal ridge flat to slightly convex above the median ocellus, while lightly concave below it; long-winged; temporal foveolae rhomboid; well-developed lateral carinae in prozona and metazona of the pronotum.

S. socotranus can be distinguished from other members of the genus by a longer fastigium of the vertex (narrow, elongated and with an equal width at the level of the transverse groove to the length in front of this groove), relatively short antennae (slightly longer than head and pronotum together) and a prozona of the pronotum that is somewhat shorter than the metazona; see key in Jago (1996) — considered to be closely related to S. xanthus (Karny, 1907) occurring in Africa, Asia and Arabia ( Oman, Yemen and Saudi Arabia).

Stenohippus socotranus is the only grasshopper on Socotra resembling European Gomphocerinae of the genus Chorthippus : a subconical head, sloping frons and subcylindrical pronotum, which is slightly constricted in the prozona and with angularly incurved lateral carinae (Figs 54 View Figure 54 , 55 View Figure 55 ). Tegmina and hind wings are fully developed and the male subgenital plate is conical.

The genus Stenohippus is characterised by a high degree of polychromatism and polymorphism. There is a significant variation in colour patterns and some well-defined variations are separated. On Socotra, the variation S. socotranus var. marginellus is very common, at least amongst females. This variation is characterised by a large triangular dark brown mark on the pronotal side lobe. This character is accompanied by much less curved lateral carinae in the prozona of the pronotum. Jago (1996) stated that, despite the high degree of polymorphism in Stenohippus , the shape and dimensions of the fastigium of the vertex are considered stable to separate species reliably.

Taxonomic notes.

Popov (in Uvarov and Popov (1957)) temporarily described Stenohippus socotranus ( Popov, 1957) as a member of Leva Bolívar, 1909 , despite the fact that he already recognised more similarities with Stenohippus Uvarov, 1926 (Fig. 55 View Figure 55 ). Jago (1971) synonymised Stenohippus with Leva , based on his statement that the sulcation of the upper part of the frontal ridge (above the ocellus) is the only real difference between the two genera. Jago (1996) thoroughly revised Leva and Stenohippus , restored the latter genus and moved Popov’s socotranus from Leva to Stenohippus .

Distribution and occurrence.

It is an endemic species to Socotra and widely distributed and common, especially on the plains (Fig. 56 View Figure 56 ). In 2009, it was abundant at Taaqs, Ba’a and Qeysoh.

Habitat and biology.

The typical habitat of S. socotranus is open, grassy patches with sparse and low vegetation on plains and hillsides in all lower vegetation types (Fig. 4 View Figure 4 ). It seems absent in typical montane vegetation. It occurs year-round, from 5–1000 m a. s. l.

Bioacoustics.

The calling song consists of an echeme lasting 2–4.5s with about 40–100 syllables repeated at 18–23 per second (Fig. 57 A View Figure 57 ). Syllables last about 10 ms with a weak first part (hardly visible in the oscillograms) and a loud second part (Fig. 57 B View Figure 57 ) ( XC 877924, accessible at https://www.xeno-canto.org/877924). During rivalry, males produce shorter echemes, sometimes down to a few syllables. The song resembles the song of Stenohippus mundus (Walker, 1871) , known from the UAE ( Buzzetti et al. 2014), but with shorter echemes.