Amoimyrmex bruchi

Always found in dry and open habitats and co‐occurring sympatrically, in part, with the Amoimyrmex silvestrii. It can be assumed that the conditions for the occurrence of these two species are similar, spreading across Argentinian regions of the Chaco and Pampa (Kempf 1972; Brandão 1991)

Identification
Cristiano, Cardoso and Sandoval (2020) - Workers of this species can be distinguished from its congeners by combination of the following features: body reddish‐brown, dark brown to almost black; pronotum with a pair of small median pronotal spines, best seen in frontal view; shiny integument covered by rough irregular striae and dense yellowish non‐decumbent setae, varying in length; posterior cephalic corner acute to rectangular; anterior portion of the first gastral tergite covered with long and dense irregular striae, discernible in medium magnification (~50×).

Amoimyrmex bruchi workers are smaller and slightly less shiny than those of its congeners and less variable in worker size. Workers may vary in the size and angular projections of the lateral pronotal and propodeal spines and the colouration of some specimens. Likewise, compared to the other Amoimyrmex species, the alates of ''Am. bruchi'' are rare and must be restricted to a specific period of the year. Always found in dry and open habitats and were similar in external appearances to one another and co‐occurring sympatrically, in part, with the Amoimyrmex silvestrii. It can be assumed that the conditions for the occurrence of these two species are similar, spreading across Argentinian regions of the Chaco and Pampa (Kempf 1972; Brandão 1991).

Distribution based on Regional Taxon Lists
Neotropical Region: Argentina, Bolivia.

Habitat
Always found in dry and open habitats across Argentinian regions of the Chaco and Pampa (Kempf 1972; Brandão 1991)

Nomenclature

 * . Atta (Moellerius) silvestrii r. bruchi Forel, 1912e: 180 (w.) ARGENTINA (Buenos Aires).
 * Forel, 1913l: 236 (q.m.).
 * Combination in Acromyrmex (Moellerius): Forel, 1913l: 236.
 * combination in Amoimyrmex: Cristiano, Cardoso & Sandoval, 2020: 657.
 * Subspecies of silvestrii: Forel, 1913l: 236; Bruch, 1914: 217; Bruch, 1915: 529; Santschi, 1916b: 512; Santschi, 1916e: 389; Emery, 1924d: 351; Santschi, 1925a: 389 (in key); Kempf, 1972a: 16; Bolton, 1995b: 54.
 * Status as species: Gallardo, 1916d: 335; Bruch, 1917d: 431; Gallardo, 1919b: 245; Cristiano, Cardoso & Sandoval, 2020: 657.

Worker
Cristiano, Cardoso and Sandoval (2020) - Range (specimen used for redescription): TL 3.75–7.88 (6.48), HL 0.82–1.79 (1.48), HW 0.84–2.09 (1.62), ML 0.29–0.68 (0.60), SL 0.75–1.74 (1.43), EL 0.16– 0.32 (0.26), WL 1.16–2.59 (2.00), PL 0.24–0.57 (0.45), PW 0.22–0.60 (0.38), PPL 0.24–0.50 (0.38), PPW 0.40–0.93 (0.81), GL 0.92–1.82 (1.57), CI 102.22–130.23 (109.68), MI 29.03–46.67 (40.32), OI 14.29–20.00 (16.18), SI 81.54– 113.95 (96.77) [N = 97].

Head. In full‐face view, posterior cephalic margin medially emarginate. Posterior cephalic corner acute to rectangular, with a small spine directed upwards, rising on dorsum of head in lateral view and a small tubercle laterad. Integument covered by dense rough irregular striae and yellowish non‐decumbent setae, varying in length. Frontal carina, which may be confused with striae, extending to the vertex but not reaching the posterior cephalic corner. Mandible with 8–11 teeth, dorsally glossy, strongly striated and covered by light‐coloured hairs, with larger and thicker ones at the apical margin. Eye convex, 17–24 ommatidia across largest diameter. Frontal lobe partially covering antennal insertions, with a hook shape. Antennal scrobe absent. Antennal scape slightly surpassing posterior cephalic margin, less than 1/3 of its length (SI = 81.54– 113.95). Colour reddish‐brown, dark brown to almost black. Some specimens with darker vertex, occipital and frontal lobes and reddish‐brown mandibles, clypeus, antennae and gena. Mesosoma. Pronotum armed with two large lateral pronotal spines and a pair of small median pronotal spines, best seen in frontal view, but can be vestigial in larger workers. Mesonotum with two lateral mesonotal spines and two posterior mesonotalspines, with similarsize and approximately half of the size of the lateral pronotal spines. Propodeum bearing two very large sharp spines, almost double the length of the lateral pronotalspines. Integument covered by rough irregular striae and dense non‐decumbent pilosity, extending up the spines. Legs with conspicuous reticulation, in some cases with coxa and femur darker than the rest of the body. Metasoma. Petiolar node with four spine‐like projections directed upwards and backwards and two lateral longitudinal carinae. Postpetiolar node with two small teeth on the lateral margins, located in the medial portion, projecting to the sides and slightly backwards, best seen in dorsal view, and two lateral longitudinal carinae. Dorso‐posterior region of node with up to eight small tubercles. Postpetiole with eight small tuberculiform projections in the dorso‐posterior region of node. Integument of petiole and postpetiole covered by irregular striae and non‐decumbent pilosity. Gaster with smooth and shiny integument and dense yellowish non‐decumbentsetae of two sizes, with the longest ones twice the length of shorter ones. Anterior portion of first gastral tergite covered with long and dense irregular striae, discernible in medium magnification (~50×).

Queen
Cristiano, Cardoso and Sandoval (2020) - TL 9.85–10.69, HL 1.84–1.89, HW 2.19–2.23, ML 0.75–0.80, SL 1.54–1.64, EL 0.31–0.34, WL 2.75–3.05, PL 0.70–0.72, PW 0.67–0.68, PPL 0.75–0.77, PPW 1.01–1.12, GL 3.06–3.08, CI 117.99–119.02, MI 40.76– 42.33, OI 16.85–17.99, SI 83.69–86.77 [N = 4].

Head. In full‐face view, posterior cephalic margin medially emarginate but less accentuated than worker. Posterior cephalic corner angular, with a small spine directed upwards and a small tubercle laterad. Integument covered by rough irregular striae, denser than in worker. Frontal carina present (may be confused with striae), shorter than in worker. Eye larger and less convex than in worker. Number of ommatidia across largest eye diameter 20–26. Mandibles with apical tooth larger and more prominent than in worker. Mesosoma. Integument with well‐defined longitudinal and parallel striae and non‐decumbent pilosity. Scutellum strongly convex in lateral view, narrowing posteriorly with a trapezoidal outline in dorsal view, bearing two tuberculiform denticles in the posterior margin. Propodeum with a pair of protruding long spines, directed upwards. Metasoma. First gastral tergite with two yellowish spots located anterolaterally in dorsal view, contrasting with the black gaster. First gastral tergite with semicircular striae, mainly at the base, and with dense non‐decumbent setae.

Type Material
Cristiano, Cardoso and Sandoval (2020) - Lectotype: we designate the following syntype (worker) as the lectotype ☿ '' ‘A. (Moellerius) silvestri'' Em. R. Bruchi ☿ type For. Buenos Ayres (Bruch)/Coll. A. Forel/Typus/ANTWEB CASENT0909437’ [specimen examined].