Pogonomyrmex pulchellus (Santschi, 1925) Johnson, 2021

Johnson, Robert A., 2021, A taxonomic revision of South American species of the seed-harvester ant genus Pogonomyrmex (Hymenoptera: Formicidae). Part II, Zootaxa 5033 (1), pp. 1-230 : 149-155

Pogonomyrmex pulchellus NEW STATUS

( Figures 72–74 )

Distribution—68C

Pogonomyrmex rastratus var. pulchellus Santschi, 1925: 223 (worker). Syntypes examined: 1 worker [MACN], 1 worker [NHMB]. ARGENTINA, Catamarca: Corral Quemado, (Weiser leg.). See also Gallardo, 1932; 137. NHMB worker here designated LECTOTYPE [CASENT0281097].

Worker diagnosis. Workers of P. pulchellus can be variable, and thus are characterized twice. This species is uniquely characterized by the following combination of features: (1) striae extend over anterior two-thirds or more of medial portion of first gastral tergum, posterolateral margins mostly smooth and shining, (2) rugae on dorsum of promesonotum strongly irregular, often continuing to anterodorsal margin of pronotum, sometimes becoming rugoreticulate on pronotum, (3) dorsum of pronotum notably darker than adjoining mesonotum, (4) head orangish-brown, rest of body mostly blackish to black except for an orangish infusion on dorsum of mesonotum and sometimes anterior portion of mesopleura, and (5) regular to irregular rugae on mesopleura longitudinal or angle posterodorsally, rarely with short lateral branches.

Alternatively, (1) for most to all workers in a series, rugae on dorsum of promesonotum well defined, very regular and continuous, lacking short lateral branches; longitudinal rugae on mesonotum diverging toward humeral shoulders of pronotum; anterodorsal margin of pronotum with one to several straight, strong, continuous, transverse rugae, (2) superior propodeal spines consist of short, acuminate triangular teeth to short spines; height of inferior propodeal spines usually similar to or greater than superior spines, (4) rugae between frontal lobes subparallel-parallel, medial rugae usually continuing onto frontal triangle, (5) head and mesosoma mostly concolorous ferruginous orange to light orangish-black, mesosoma sometimes slightly darker than head ( Figure 72 ).

Measurements — lectotype (n = 13 + 1 paralectotype). HL 1.59 (1.44–1.83); HW 1.59 (1.51–1.89); MOD 0.36 (0.35–0.46); OMD 0.39 (0.38–0.48); SL 1.15 (1.15–1.43); PNW 1.05 (1.00–1.23); HFL 1.58 (1.51–1.82); ML 1.87 (1.74–2.16); PW 0.37 (0.34–0.48); PPW 0.53 (0.52–0.64). Indices: SI 72.33 (68.57–77.84); CI 108.16 (96.69–105.85); OI 22.64 (22.99–25.71); HFI 99.37 (90.42–103.31).

Redescription. Head subquadrate to quadrate (CI = 96.69–108.16); posterior margin flat. Longitudinal rugae on cephalic dorsum prominent, weakly irregular to regular; rugae between frontal lobes subparallel-parallel, medial rugae continuing onto frontal triangle. In full-face view, medial rugae diverging to posterior corners; in posterodorsal view, posterior margin with one to few irregular, arcuate rugae, usually with strongly irregular, discontinuous rugae with short lateral branches medially. Interrugae on cephalic dorsum moderately to strongly granulate, with a beaded appearance, dull to weakly shining; posterior corners rugose, interrugae smooth and shining, occasionally moderately granulate-punctate, dull to weakly shining. Anterior margin of clypeus moderately concave, dorsum with numerous subparallel, longitudinal rugae. Numerous long, curved, bristle-like, cream to light yellowish hairs project from anterior margin of clypeus and basolateral margin of mandibles. Mandibles with six or seven teeth; mandibular dorsum coarsely rugose. MOD ranging from 0.23–0.26× HL. In profile, eyes situated slightly anterior to middle of head, OMD = 0.90–1.11× MOD. In full-face view, eyes protruding slightly beyond lateral margins of head. Antennal scapes (SI = 68.57–77.84) failing to reaching posterior corners of head by width of basal funicular segment. Antennal scapes usually weakly to moderately striate, interstriae weakly to moderately granulate-punctate, weakly shining to smooth and shining; basal flange well developed with carinate margin. Psammophore well developed.

Mesosomal profile weakly convex; all mesosomal surfaces with prominent widely spaced, subparallel-parallel irregular to regular rugae. For most to all workers in a series, rugae on dorsum of promesonotum well defined, very regular and continuous, short lateral branches mostly lacking; medial longitudinal rugae on mesonotum diverging toward humeral shoulders of pronotum, anterodorsal margin of pronotum with one to several transverse rugae or longitudinal rugae on promesonotum with or without several to numerous short lateral branches, medial rugae on mesonotum continue to anterior margin of pronotum. In dorsal view, humeral shoulders of pronotum enlarged, strongly angulate. Promesonotal suture usually weakly impressed, occasionally absent. Regular to irregular rugae on mesopleura longitudinal or angle posterodorsally, rarely with short lateral branches; transverse regular to irregular rugae on dorsum of propodeum traverse ventrally or anteroventrally on sides. Superior propodeal spines consist of short, acuminate triangular denticles or short teeth, width at base usually greater than height; keel connecting superior propodeal spines moderately well developed. Inferior propodeal spines wider than high, triangular, tips broadly rounded to subacuminate, height usually similar to or greater than length of superior spines. Propodeal spiracles narrowly ovate facing posterad. Interrugae on mesosoma moderately to strongly granulate-punctate, often with a beaded appearance, dull to weakly shining. Legs weakly to moderately coriarious, weakly shining to smooth and shining.

Peduncle of petiole approximately 0.8× as long as petiolar node, anteroventral margin with a poorly to moderately developed broadly rounded process with broadly rounded apex. In profile, posterior surface of petiolar node weakly convex; petiolar node asymmetrical with anterior surface shorter than posterior surface, apex angulate to weakly rounded. In dorsal view, petiolar node longer than wide, widest immediately posterior to spatulate anterior margin. Posterior surface of petiolar node with transverse rugae, sometimes irregular and discontinuous arcuate rugae anterad, or with oblique to nearly longitudinal rugae anterad, rarely oblique to nearly longitudinal over entire surface. Dorsum of postpetiole convex in profile; in dorsal view, widest near posterior margin, narrowing to anterior margin, width and length similar; transverse to weakly arcuate rugae posterad, anterad rugae transverse or traversing medially from lateral margin then curving anterad to become longitudinal; anterolateral rugae concentric, curving from lateral to anterior margin. Rugae on dorsum of postpetiole finer, denser than those on posterior surface of petiolar node, interrugae on both surfaces weakly to moderately coriarious, weakly shining to shining. Striae extend over anterior one-half to two-thirds or more of first gastral tergum, posterior and posterolateral margins smooth and shining.

Erect, mostly short, whitish pilosity moderately abundant on head, most hairs <0.2× MOD. Moderately abundant semidecumbent to decumbent pilosity on scape; abundant decumbent hairs on funicular segments. Legs with moderately abundant, suberect to decumbent whitish setae. Rest of body with moderately dense, erect, medium length, whitish setae; longest hairs on mesosoma, petiolar node, and postpetiole approximately 0.5× MOD. Head orangish-brown with blackish to black mandibles, malar area, antennae, and anterior margin of clypeus; mesosoma mostly blackish to black except for dark orangish to orangish-brown mesonotum, sides and/or dorsum of pronotum notably darker than adjoining mesonotum and mesopleura; legs, petiolar node, postpetiole blackish to black; gaster blackish-orange to black, occasionally with a dark orangish infusion ( Figure 72 ).

Queen diagnosis. Queens of this species are diagnosed by the following combination of features: (1) caste-specific morphology of the mesosoma related to wing-bearing and presence of ocelli on head, (2) striae on first gastral tergum extend over anterior one-half or more of segment, medioposterior one-quarter to one-third or more of first gastral tergum (including posterolateral margins) smooth and shining, (3) mesoscutum, mesoscutellum, axillae, and anepisternum light to dark ferruginous orange, and (4) in posterodorsal view, medial rugae diverge to posterior corners of head; posterior portion of head with moderately irregular, longitudinal rugae and one or more irregular transverse rugae that usually continue laterally to posterior corners of head ( Figure 73 ).

Measurements —(n = 12). HL 1.79–1.99; HW 1.88–2.04; MOD 0.44–0.48; OMD 0.43–0.52; SL 1.21–1.47; PNW 1.38–1.50; HFL 1.53–1.97; ML 2.39–2.73; PW 0.49–0.58; PPW 0.71–0.83. Indices: SI 64.36–73.74; CI 96.98–106.70; OI 22.06–24.61; HFI 79.69–98.94.

Description. With caste-specific morphology of the mesosoma related to wing-bearing and presence of ocelli on head. In full-face view, head quadrate to slightly wider than long (CI = 96.98–106.70), broadest just posterior to eyes, posterior margin flat. Longitudinal rugae on cephalic dorsum prominent, weakly irregular to regular, interrugae moderately to strongly granulate, dull to weakly shining, with a beaded appearance; in posterodorsal view, longitudinal rugae along posterior margin irregular, diverging to posterior corners of head; posteromedial margin with a triangular area with one to few irregular, transverse rugae that sometimes continue to posterior margins; interrugae on posteromedial margin moderately to strongly granulate, dull. Mandible with six teeth, dorsal surface rugose. Psammophore well developed.

All mesosomal surfaces with regular to wavy, subparallel rugae, interrugae weakly to moderately granulatepunctate, weakly shining; superior propodeal spines consist of short, triangular denticles to short teeth, tips bluntly acuminate to acuminate, inferior propodeal spines wider than tall, apex broadly rounded to subacuminate. Peduncle of petiole long, ventral surface with a weakly to moderately well developed, broadly rounded process. In profile, petiolar node asymmetrical with anterior surface shorter than posterior surface, apex of node subangulate to angulate. Posterior surface of petiolar node with transverse or longitudinal rugae, interrugae weakly granulate-punctate, weakly shining to smooth and shining. In dorsal view, postpetiole slightly wider than long; dorsum with wavy, transverse rugae that are finer, denser than those on posterior surface of petiolar node, interrugae weakly granulate-punctate, weakly shining to smooth and shining. Striae cover anterior one-half or more of first gastral tergum, posterolateral margins smooth and shining. Most body surfaces with moderately abundant suberect to erect, medium-length, whitish to cream-colored setae. Head, mesoscutum, mesoscutellum, anepisternum ferruginous orange to reddish-orange; pronotal sides concolorous blackish-orange to black; first gastral tergum ferruginous orange to reddish or reddish-brown with a black posterior margin, rest of gaster blackish to black ( Figure 73 ).

Male diagnosis. Males of this species are diagnosed by the following combination of features: (1) striae extend over more than anterior one-half of first gastral tergum, (2) smaller: HW = 1.26–1.35 mm, PW = 0.44–0.48 mm, PPW = 0.60–0.67 mm, (3) in profile, apex of petiolar node angulate or node shaped irregularly, (4) in profile, anepisternum and katepisternum mostly smooth and shining to strongly shining, if rugae present posterad then interrugae smooth and shining, and (5) in profile, posterior surface of petiolar node irregular ( Figure 74 ).

Measurements —(n = 6). HL 1.28–1.46; HW 1.26–1.35; MOD 0.44–0.48; OMD 0.16–0.23; SL 0.39–0.45; HFL 1.52–1.81; ML 2.12–2.42; PW 0.44–0.48; PPW 0.60–0.67. Indices: SI 29.77–34.35; CI 91.97–101.56; OI 34.35–37.30; HFI 118.75–134.07.

Additional material examined. ARGENTINA: Catamarca: Rt 43 at 133.1 km SE Antofagasta de la Sierra, 10,450’, Jan 18, 2006 ( RAJC) ; Rt 43 at 101.5 km SE Antofagasta de la Sierra, 12.630’, Jan 18, 2006 ( MCZC; RAJC; UCDC; USNM) ; Rt 43 at 4.4 km W turnoff to Laguna Blanca , 11,050’, Jan 27, 2019 ( RAJC) ; Rt 43 at 15.2 km W turnoff to Laguna Blanca , 12,320’, Jan 27, 2019 ( RAJC) ; Rt 43 at 25.3 km W turnoff to Laguna Blanca , 12.880’, Jan 27, 2019 ( RAJC) ; Rt 43 at 42.0 km W turnoff to Laguna Blanca , 13,090’, Jan 27, 2019 ( RAJC) ; Laguna Blanca , no date ( MACN) ( Figure 68C ).

Etymology. Santschi did not discuss naming this species pulchellus (from Latin, pulchellus = beautiful), but he apparently thought that this was a beautiful ant.

Discussion. Pogonomyrmex pulchellus likely co-occurs with P. longibarbis and possibly other P. rastratus - group species that are restricted to high elevation habitats in the Andes. Pogonomyrmex pulchellus is separated from most congeners by: (1) striae on the first gastral tergum extend over more than anterior one-half of segment, posterior and posterolateral margins smooth and shining, (2) for most to all workers in a series, rugae on dorsum of promesonotum well defined, very regular and continuous, lacking short lateral branches; lateral longitudinal rugae on mesonotum diverging toward humeral shoulders of pronotum; anterodorsal margin of pronotum with one to several straight, strong, continuous, transverse rugae, and (3) superior propodeal spines consist of acuminate denticles, short triangular teeth, or short spines. These characters separate P. pulchellus from all species except P. apterogenos , P. lagunabravensis , and P. longibarbis . Pogonomyrmex pulchellus can be distinguished from P. apterogenos based on the following characters: (1) rugae on cephalic dorsum between frontal lobes subparallel-parallel, medial rugae usually continuing onto frontal triangle, and (2) head and mesosoma mostly concolorous ferruginous orange to light orangish-black or reddish-brownish, mesosoma sometimes darker than head. In P. apterogenos : (1) rugae on cephalic dorsum between frontal lobes weakly converge, 1-2 pairs of medial rugae usually converging together near posterior margin of frontal triangle, and (2) head ferruginous orange, dorsum of pronotum and mesonotum concolorous orangish-black, rest of mesosoma blackish-orange to blackish. Pogonomyrmex pulchellus is distinguished from P. lagunabravensis based on: (1) superior propodeal spines consist of minute teeth, short triangular teeth, or short spines (all acuminate), (2) inferior propodeal spines shorter than to as tall as superior spines, (3) keel connecting superior propodeal spines well developed, and (4) dorsum and sides of pronotum concolorous with adjoining mesonotum. For P. lagunabravensis : (1) superior propodeal spines consist of tubercles, denticles, or minute teeth (all rounded to blunt tipped), (2) inferior propodeal spines longer than superior spines, (3) keel connecting superior propodeal spines absent, and (4) dorsum and sides of pronotum concolorous with adjoining mesonotum. For P. pulchellus : (1) superior propodeal spines consist of minute teeth, short triangular teeth, or short spines (all acuminate), (2) inferior propodeal spines shorter than to as tall as superior spines, (3) keel connecting superior propodeal spines well developed, and (4) dorsum and sides of pronotum concolorous with adjoining mesonotum. Pogonomyrmex pulchellus is distinguished from P. longibarbis based on: dorsum and sides of pronotum concolorous with adjoining mesonotum. For P. pulchellus : dorsum and sides of pronotum orangish-black to blackish, darker than adjoining mesonotum.

Some series of P. pulchellus contain workers with wavy to irregular rugae on the mesosoma that continue to anterodorsal margin of pronotum, sometimes becoming rugoreticulate on pronotum. Series containing such workers are most similar to P. tafi as workers of both species usually have a pronotum darker than the adjoining mesonotum. For P. pulchellus : rugae on mesopleura usually regular to wavy, lacking lateral branches; posterior margin of first gastral tergum smooth and shining. For P. tafi : rugae on mesopleura wavy to irregular, usually with numerous lateral branches that often connect with adjacent rugae; posterior margin of first gastral tergum usually with striae or moderately to strongly coriarious, rarely smooth and shining.

The brief description of P. rastratus var. pulchellus by Santschi (1925) separated it from P. rastratus as follows: “different from the type by the black gaster, the mesonotum a little more narrow and red like the head. The rest of the thorax, clypeus, frontal carina, mandibles, and legs black. Sides of the pronotum horizontally striate-rugoreticulate”. The description also compared P. rastratus var. pulchellus to P. rastratus var. caracola Santschi , but the latter form was never described. Other differences between P. pulchellus and P. rastratus include: (1) superior propodeal spines of P. pulchellus consist of short triangular teeth to short spines, whereas in P. rastratus they are usually long, with a length> 0.5× the distance between their bases, and (2) pronotum usually notably darker than adjoining mesonotum and mesopleura in P. pulchellus , whereas the pronotum and mesosoma are concolorous in P. rastratus . Thus, I raise P. rastratus var. pulchellus from synonymy to rank as a valid species.

Pogonomyrmex pulchellus appears to be restricted to higher elevations (> 3100 m) in the Andes. Consequently, it seems doubtful that Corral Quemado, Catamarca Province, Argentina, is the type locality. Corral Quemado is at the western base of the Andes at an elevation of approximately 2050 m, while all series collected by the author have been at> 3150 m. The author also searched in the area of Corral Quemado and nearby foothill areas of the Andes without finding P. pulchellus . Most likely, the syntypes were collected higher in the Andes and Corral Quemado was the closest reference point to that locale.

Biology. Pogonomyrmex pulchellus workers are solitary foragers. Nests are placed in open, exposed sites, at the edge of grass clumps, or under shrubs in deep sand to gravelly-rocky soil, with the entrance consisting of a tumulus that ranges up to 15 cm in diameter. Partial nest excavations indicated that colonies consist of 500–1000 workers. Sexuals have been collected on January 18, indicating that mating flights occur during the austral summer.

Pogonomyrmex pulchellus inhabits elevations from 3165–3965 m. This species occurs in the High Monte, Central Andean puna, and Southern Andean steppe ecoregions, as defined by Olson et al. (2001) ( Figure 68C ).

Figures

FIGURE 68. Geographic distribution of: (A) Pogonomyrmex pronotalis, (B) P. propinqua, (C) P. pulchellus. The large black circle in each panel denotes the type locality. See text regarding the type locality for P. pulchellus.

FIGURE 72. Photographs of Pogonomyrmex pulchellus worker: (A) frontal view of head, (B) lateral view of body, and (C) dorsal view of body (CASENT0172692). Photographs by Ryan Perry from www.AntWeb.org.

FIGURE 73. Photographs of Pogonomyrmex pulchellus alate queen: (A) frontal view of head, (B) lateral view of body, and (C) dorsal view of body (CASENT0249053). Photographs by Will Ericson from www.AntWeb.org.

FIGURE 74. Photographs of Pogonomyrmex pulchellus male: (A) frontal view of head, (B) lateral view of body, and (C) dorsal view of body (CASENT0172691). Photographs by April Nobile from www.AntWeb.org.