Patagonomyrmex

Observations made by Kusnezov (1949, 1953, 1960) form the bulk of what is known about the biology of ants in this genus. Most of his observations were for Patagonomyrmex odoratus, but the biology of these three species appears similar, and thus all three species are discussed together. Nests are variable, ranging from an entrance lacking a tumulus to one that is 10–12 cm in diameter. Typically, nests are located in open areas or under stones or other objects. Workers of all three species are diurnal, slow-moving, solitary foragers that are timid and non-aggressive. Little information is available on food items collected, though Kusnezov (1960) indicated that they were granivores. Colonies of P. odoratus probably contain fewer than 300–400 workers (Kusnezov, 1949); colony size for Patagonomyrmex angustus and Patagonomyrmex laevigatus appears to be similar (Kusnezov, 1949; 1960; pers. obs.). All three species of Patagonomyrmex are restricted to cool, relatively humid, short growing-season climates in southern Argentina and southern to southcentral Chile, typically in habitats dominated by Nothofagus or Austrocedrus (=Libocedrus in Kusnezov, 1949).

Identification
Johnson and Moreau (2016) - Patagonomyrmex workers share several characters with species in the former subgenus Ephebomyrmex including small size, poorly-developed psammophore, antenna with 12 segments, and hind legs with finely pectinate tibial spurs. Our molecular phylogram confirms that Patagonomyrmex represents a distinct lineage of ants and that Patagonomyrmex is the sister group to all other pogonomyrmecines (see also Ward et al., 2015).

One morphological difference between Patagonomyrmex and Pogonomyrmex regards palp forumula: 4,3 for Pogonomyrmex and 5,4 for Patagonomyrmex.

Pogonomyrmex contains several species groups in which workers possess a poorly-developed psammophore and thus might be confused with Patagonomyrmex. The best characters to separate Patagonomyrmex from these species are: (1) clypeus strongly convex in profile, and (2) anterior margin of clypeus convex in full-face view. No species of Pogonomyrmex with a poorly-developed psammophore have a clypeus that is convex in profile, and only species in the Pogonomyrmex cunicularius-group have a clypeus with the anterior margin weakly convex in full-face view. The small, acuminate spine on the anteroventral margin of the peduncle of the petiole is also distinctive: only species in the Pogonomyrmex sylvestris-group and sometimes ''Po. cunicularius''-group possess this character. Species of Patagonomyrmex also are geographically restricted to southern Argentina and southern and southcentral Chile. No species of Pogonomyrmex with a poorly-developed psammophore occur in Chile and only species in the ''Po. naegelii-group, Po. brevibarbis-group, and Po. cunicularius''-group occur in Argentina (Johnson, 2015; R.A. Johnson, unpub. data). Of these species, only those in the ''Po. brevibarbis-group occur in provinces inhabited by Patagonomyrmex'' (Neuquén, Río Negro, Chubut). The most southern occurrence for species in the ''Po. naegelii-group (Pogonomyrmex abdominalis, Pogonomyrmex naegelii, Pogonomyrmex tenuipubens) is central Argentina (Mendoza, San Luis, La Pampa Provinces), about 600 km north of the nearest locale for Patagonomyrmex'' (see Johnson, 2015).

Nomenclature

 *  PATAGONOMYRMEX [Myrmicinae: Pogonomyrmecini]
 * Patagonomyrmex Johnson & Moreau, 2016: 10. Type-species: Pogonomyrmex angustus, by original designation.

Diagnosis of worker. Monomorphic, small (HW = 0.81–1.16 mm), soil-nesting, myrmicine ants with the following combination of characters:

(1) Head weakly elongate to elongate (CI = 78.86–95.50).

(2) Mandible with six teeth.

(3) Psammophore poorly-developed, consisting of short to medium-length hairs scattered over ventral surface of head.

(4) Superior propodeal spines long; inferior propodeal spines moderately long to long.

(5) Dorsal surface of promesonotum smooth and shiny, lacking rugae or if rugae present, then interrugae strongly granulate-punctate, dull.

(6) Anteroventral margin of peduncle of petiole with a small, acuminate spine.

(7) In full-face view, anterior margin of clypeus convex and entire.

(8) In profile, clypeus strongly convex.

(9) Petiolar node triangular in profile, anterior surface slightly shorter than posterior surface, node subangulate to rounded.

(10) Palp formula = 5,4.

Diagnosis of queen—as in worker except:

(1) Small (HW < 1.25 mm and ML < 2.00 mm).

(2) Mandible with 5–6 teeth.

(3) Mesosoma with full complement of sclerites associated with presence of wings; head with well-developed ocelli.

(4) Forewing lacking Rsf2–3, with submarginal cell 1+2.

Diagnosis of male.

(1) Small (HW < 1.15 mm and ML < 2.00 mm).

(2) Anteroventral margin of peduncle of petiole with a small, acuminate spine.

(3) Funicular segments with very dense, short, suberect to erect pubescence.

(4) Forewing lacking Rsf2–3, with submarginal cell 1+2.

(5) In full-face view, strongly produced anterior margin of clypeus, nearly angulate medially.

(6) In profile, clypeus strongly convex.

Etymology
The genus name, Patagonomyrmex, alludes to the distribution of these species, which are mostly restricted to the Patagonia region of Argentina and Chile.