Trichomyrmex abyssinicus Forel 1894

Trichomyrmex abyssinicus (Forel, 1894)

Fig. 5 A–C

Holcomyrmex abyssinicus Forel, 1894a: 83 (workers). Ethiopia: Afrotropic. Syntype workers [examined]. (Lectotype here designated: Erythrea, Ghinda, III.06 (Dr. Escherich) (MHNG) (CASENT0249906)).

Monomorium abyssinicus – Forel 1910: 250. — Viehmeyer 1923: 91 (q).

Trichomyrmex abyssinicus – Ward, Brady, Fisher & Schultz 2015: 16. — Bolton 1987: 321 (redescription).

Material examined

SAUDI ARABIA: 11 w, Al Bahah Province, Shada Al A’la, 19.86˚ N, 41.30˚ E, alt. 1225 m, 15 Nov. 2015, Aldhafer et al. leg.; 3 workers, same data, 29 Jul. 2015, Aldhafer et al. leg. (all in KSMA).

Description

Workers of this species exhibit marked size variation in any nest series.

Large workers

With a broad size variation ( TL 2.60–6.70; HW 0.60–1.94).

MEASUREMENTS. TL 3.55–5.35; HL 1.06–1.53; HW 1.05–1.56; SL 0.78–0.92; EL 0.14–0.20; ML 1.05– 1.56; PW 0.52–0.70; PTL 0.28–0.40; PTW 0.17–0.24; PPL 0.23–0.30; PPW 0.21–0.31; CI 98–105; EI

12–14; SI 59–74 (n = 6). Worker TL 2.60–6.70; HL 0.68–2.04; HW 0.60–1.94; SL 0.50–1.06; PW 0.38– 0.90; ML 0.72–1.74; CI 86–100; SI 55–110 (Bolton 1987).

HEAD. In full-face view with emarginated posterior margin and nearly parallel sides; posterior corners strongly rounded; mandibles blunted; scapes when laid back from their insertions fail to reach posterior margin of head.

MESOSOMA. Metanotal groove broad and distinctly impressed in profile; promesonotum strongly convex in profile; propodeal spiracle a vertical ellipse or slit; propodeal dorsum about twice as long as propodeal declivity in profile.

PETIOLE. Petiolar peduncle with a distinct anteroventral process that consists of a triangular lamella followed by a broad flange; petiolar spiracle situated at midline of petiolar peduncle.

PILOSITY. Underside of head with short straight hairs not forming a distinct psammophore; cephalic pilosity sparse; mesosoma with abundant standing hairs, the longest on pronotum and mesonotum, propodeal pilosity shorter; petiole, postpetiole and gaster with abundant, sparse suberect hairs.

SCULPTURE. Cephalic surface smooth and shining except area in front of eyes, which is finely rugulose in profile; mandibles strongly longitudinally rugulose; promesonotal dorsum strongly longitudinally rugulose or with disorganized rugulae, to smooth; propodeal dorsum distinctly transversely rugulose; mesosomal sides strongly rugulose; petiole and postpetiole irregularly rugulose, gaster smooth and shining.

COLOUR. Head, mesosoma, petiole and postpetiole reddish brown or dark brown, gaster darker than head and mesosoma, blackish brown or black; head with a dark median longitudinal line in full-face view.

Small workers MEASUREMENTS. TL 2.43–3.37; HL 0.65–0.89; HW 0.60–0.88; SL 0.57–0.70; EL 0.14–0.16; ML 0.70– 0.99; PW 0.33–0.45; PTL 0.21–0.28; PTW 0.11–0.14; PPL 0.14–0.21; PPW 0.16–0.18; CI 90–98; EI

18–24; SI 80–95 (n = 8). With a broad size variation.

HEAD. In full-face view with emarginated posterior margin and sides diverging anteriorly; anterior clypeal margin distinctly concave medially between two well developed teeth that are situated anteriorly in front of the antennal insertions; mandibles armed with three teeth; eyes small, situated in front of midline of head sides (EL 0.14-0.24 × HW), with eight ommatidia in longest row; antennal scapes distinctly short, when laid back from their insertions they fail to reach posterior margin of head.

MESOSOMA. Promesonotum nearly flat in profile; propodeal spiracle a vertical ellipse or slit; propodeal dorsum about twice as long as propodeal declivity in profile.

PETIOLE. Petiolar peduncle with a distinct anteroventral process that consists of a triangular lamella followed by a broad flange; petiolar spiracle situated at midline of petiolar peduncle.

PILOSITY. Subcephalic pilosity short and sparse; cephalic pilosity sparse, short, decumbent to appressed pubescence, and directed inward to midline of head.

SCULPTURE. Cephalic surface smooth and shining except for area in front of eyes, which is finely rugulose in profile; mandibles strongly longitudinally rugulose; propodeal dorsum weakly, irregularly, transversely rugulose; mesosomal sides faintly rugulose; gaster smooth and shining.

COLOUR. Lighter than large workers, pale brown or yellowish brown, gaster dark brown.

Differential diagnosis

Trichomyrmex abyssinicus can be distinguished from other Arabian species except T. perplexus by the vertical ellipse or slit propodeal spiracle. This species is similar to T. perplexus but can be separated from it by the convex promesonotum outline, the distinctly longer propodeal dorsum, and the irregularly rugulose propodeum, petiole and postpetiole.

Ecological and biological notes

Shada Al A’la Mountain peak is an extension of the Hijaz Mountains to the west and is a natural protectorate in Al Bahah Province. The region has a substantial plant biodiversity and the most abundant plants are Olea europaea ssp. africana (Mill.) P. Green. (Oleaceae), Coffea arabica L. (Rubiaceae), Juniperus procera Hochst. ex Endlicher (Cupressaceae), and Acacia spp. (Fabaceae).

Distribution

This species was originally described from Ethiopia and has a broad distribution in the Afrotropical region, especially the Sahelian Zone. It has been recorded from Benin, Burkina Faso, Ghana, Nigeria, Sudan, Tanzania (Bolton 1987), Egypt (Gebel Elba) (Sharaf 2006), and United Arab Emirates (Collingwood et al. 2011).

The distribution of T. abyssinicus appears to be restricted to the southwestern mountains of Saudi Arabia, since several years of collecting efforts by the senior author did not retrieve material from any region in the country except the present record, the first record from Saudi Arabia.