Acromyrmex charruanus

An inquiline social parasite species that usurps colonies of the thatch-mound-building, leaf-cutting ant A. heyeri from Uruguay.

Distribution based on Regional Taxon Lists
Neotropical Region: Uruguay.

Nomenclature

 *  charruanus. Acromyrmex charruanus Rabeling, Schultz, Bacci & Bollazzi, 2015, figs. 1a, c, e, 2a, c, e, 3a, 4a, c (w.) URUAGUAY.

Description
Holotype: alate gyne, URUGUAY, Florida Department, 6 km SW of Cerro Colorado, Eucalyptus globulus plantation ‘‘Plantacio´n Cruz Roja’’, GPS coordinates: S33.9042, W055.59418, elevation 224 m above sea level, collection date: 25 February 2013, col. Bollazzi & Rabeling; collection code: CR130225-03, ex Acromyrmex heyeri nest. The holotype is deposited at the MZSP and carries the unique specimen identifier No. USNMENT00758784. Paratypes: same data as holotype, 73 alate gynes and 119 males, USNMENT00758785-00758977. Same data as holotype, but ‘‘27 February 2013, collection code: CR130227-31’’, 7 alate gynes and 6 males, USNMENT00758778-00758990. Description, holotype gyne: TL 6.92, WL 2.08, HL 1.21, HW 1.33, IOD 1.54, ML 0.92, FLD 0.74, SL 1.28, EL 0.31, EW 0.26, PrW 1.1, FL 2.03, PL 0.51, PW 0.41, PPL 0.41, PPW 0.74, GL 1.79, CI 111, MI 77, SI 96. One of the smallest Acromyrmex leaf-cutting ant species known (WL 2.08; TL 6.92), with long mandibles (MI 77) and appendages (FL 2.03; SI 96) relative to body size. Integument with microscopic honey-comb pattern, which becomes visible at 409 magnification and higher; sculpturing of head, meso-, and metasoma coarsely granulate with distinct rugae and tubercles; integument with oily or waxy sheen. Body surface covered with long, appressed, and distinctly coarse setae. Color: shades of brown, variable from yellowish to reddish to dark brown; mandibles distinctly lighter in color, dark orange; ridges of rugae and tips of tubercles black; dorsum of mesosoma dark brown, with black markings. Head: head shape trapezoidal, slightly wider than long (CI 111); sides moderately tapering anteriorly between the eyes and mandibular insertion; head size small relative to mesosoma. Mandible broadly triangular with a distinct apical and preapical tooth, followed by seven smaller teeth, some of which are interspersed by even smaller denticles; mandible surface smooth and distinctly shiny. Palp formula 4:2, the plesiomorphic condition of fungus-growing ants. Posterior margin of clypeus trapezoidal, broadly inserted between frontal lobes; anterior margin of clypeus shiny and median portion concave. Unpaired median clypeal seta thin and short (0.15), only projecting over the anterior clypeal margin by half its length. Frontal lobe broadly rounded, fully covering the condylar bulb in full-face view; lateral margin of frontal lobe serrate with two distinct tooth-like projections. Frontal carina extending towards the posterolateral corner of the head. Preocular carina forming a straight line in lateral view and traversing the area of the antennal scrobe by one third of the scrobe’s width. Eyes large (EL 0.31, EW 0.26) and strongly convex. In contrast, the three ocelli are small and embedded in the integument. Antennae with 11 segments. Antennal scape long (SL 1.28) with abundant, appressed setae, surpassing the posterior margin of the head by one third of its length. Mesosoma: Mesosoma slender with caste-specific modifications related to wing bearing. Dorsolateral pronotal spine long, slender, and sharply pointed in dorsal view. Ventrolateral pronotal spine narrowly triangular and sharply pointed, not curved. Dorsum of mesosoma covered with longitudinal and reticulate rugulae. Posterior margin of scutellum concave and bidentate in dorsal view; teeth wide at base, forming a broad, almost 90 angle. Bulla and meatus of metapleural gland not notably modified from the condition in the host species. Propodeal spines straight, long, slender, and sharply pointed, projecting away from the propodeum at a 90 angle in lateral view. Metasoma: anterior peduncle of petiole short, about one fourth the length of the petiolar node. Dorsum of petiolar node with a pair of short teeth, almost as wide at their bases as they are high. Postpetiole wider than long in dorsal view (PPW 0.74; PPL 0.41), posterior margin straight. Gaster short (GL 1.79). First gastric tergite notably tuberculate, covered with abundant recurved setae. Except for the smaller size, forewing and hindwing resembling the wings of A. heyeri. Measurements; paratype gynes (n = 10): TL 6.64–7.23, WL 2.03–2.15, HL 1.15–1.28, HW 1.28–1.36, IOD 1.46–1.59, ML 0.9–0.95, FLD 0.74–0.77, SL 1.26–1.31, EL 0.28–0.31, EW 0.23–0.28, PrW 1.1–1.21, FL 1.92–2.08, PL 0.46–0.54, PW 0.41–0.46, PPL 0.38–0.46, PPW 0.72–0.77, GL 1.67–1.97, CI 106–113, MI 72–80, SI 94–100.