Pogonomyrmex pronotalis, Santschi, 1922

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 : 136-143

Pogonomyrmex pronotalis

( Figures 65–67 )

Distribution—68A

Pogonomyrmex pronotalis Santschi, 1922b: 350 (worker). Syntypes examined: 2 workers [MACN], 3 workers [NHMB]. AR- GENTINA, Mendoza: Cordillera de Mendoza, Cajón de Guanaco, #1395 (Dr. Carette). See also Gallardo, 1932: 149. MACN worker here designated LECTOTYPE [CASENT0235277].

Worker diagnosis. Workers of this species are uniquely characterized by the following combination of features: (1) head and mesosoma blackish to black, gaster light to dark ferruginous orange, (2) first gastral tergum lacking striae, weakly to moderately coriarious, weakly shining to smooth and shining, (3) longitudinal rugae on cephalic dorsum irregular, widely spaced, not deeply incised, (4) pronotal rugae coarse, (5) medial rugae on mesonotum diverging or becoming transverse to rugoreticulate on pronotum but not continuing to anterior margin of pronotum, and (6) in dorsal view, promesonotal suture usually absent ( Figure 65 ).

Measurements — lectotype (n = 12). HL 1.76 (1.58–1.82); HW 1.81 (1.61–1.81); MOD 0.38 (0.34–0.40); OMD 0.42 (0.41–0.49); SL 1.36 (1.16–1.44); PNW 1.21 (1.10–1.22); HFL 1.75 (1.64–1.87); ML 2.10 (1.93–2.38); PW 0.40 (0.43–0.51); PPW 0.60 (0.56–0.65). Indices: SI 75.14 (69.14–79.63); CI 102.84 (95.27–106.10); OI 20.99 (20.99–24.39); HFI 96.69 (97.73–106.90).

Redescription. Head subquadrate to quadrate (CI = 95.27–106.10), widest just posterior to eyes; posterior margin flat in full-face view. Longitudinal rugae on cephalic dorsum prominent, widely spaced, wavy to irregular. In full-face view, medial rugae diverging toward posterior corners of head; medial posterior margin with transverse to oblique rugae. In profile, rugae posterior to eyes converging at or near posterior corners. Interrugae on cephalic dorsum strongly granulate, dull; posterior corners rugose, interrugae smooth to moderately granulate, weakly to strongly shining. Anterior margin of clypeus concave; dorsal surface with numerous subparallel, longitudinal rugae. Numerous long, curved, bristle-like, cream to light yellowish ammochaetae project from anterior margin of clypeus and basolateral margin of mandibles. Mandibles with six to seven teeth (20% with six teeth, 46% with seven teeth) or number differing on each mandible (31% with six/seven teeth, 3% with seven/eight teeth; n = 35); mandibular dorsum coarsely rugose. MOD ranging from 0.21–0.26× HL. In profile, eyes situated slightly anterior to middle of head, OMD = 1.07–1.35× MOD. Antennal scapes relatively long (SI = 69.14–79.63), ranging from failing to reach posterior corners by up to length of basal funicular segment to reaching posterior corners, scape weakly striate, moderately shining to smooth and shining. Basal flange of scape moderately well developed with carinate margin. Psammophore well developed.

Mesosomal profile weakly convex; all mesosomal surfaces with prominent rugae. In profile and dorsal views, humeral shoulders of pronotum enlarged, dorsolateral margin angulate. Dorsum of promesonotum with coarse, irregular, longitudinal rugae that diverge anterad toward humeral shoulders of pronotum, anterior pronotal margin with transverse to oblique rugae or rugoreticulate, pronotal sides rugoreticulate to vermiculate. Promesonotal suture usually absent. Mesopleura with irregular rugae that angle posterodorsally. Dorsum of propodeum with irregular transverse rugae that traverse anteroventrally on sides. Superior propodeal spines long, length usually> 0.6× the distance between their bases, spines connected by well defined keel; tips blunt to acuminate. Inferior propodeal spines triangular, wider than tall, tips rounded to subacuminate. Propodeal spiracles narrowly ovate facing posterad. Interrugae on mesosoma moderately to strongly granulate, dull to weakly shining. Legs weakly coriarious, weakly shining to smooth and shining.

Peduncle of petiole about as long as petiolar node, anteroventral margin usually with a rounded triangular process. In profile, posterior surface of petiolar node weakly convex; node asymmetrical with anterior surface notably shorter than posterior surface, apex weakly rounded to angulate. In dorsal view, petiolar node longer than wide, narrowest at posterior margin, gradually widening to spatulate anterior margin; posterior surface and sides with moderately coarse, wavy, transverse rugae. Dorsum of postpetiole convex in profile; in dorsal view, widest near posterior margin, narrowing to anterior margin; maximal width about equal to length; dorsum and sides with wavy, transverse rugae that are finer, denser than those on posterior surface of petiolar node. Interrugae on both surfaces weakly granulate, weakly shining to smooth and shining. First gastral tergum moderately coriarious, weakly shining to smooth and strongly shining.

Erect whitish pilosity moderately abundant on head, variable in length, usually with 1–2 long hairs near vertex and on frontal lobes that approach to exceed MOD. Moderately abundant suberect to semidecumbent pilosity on scape, abundant decumbent hairs on funicular segments. Legs with moderately abundant semidecumbent white setae. Mesosoma, petiolar node, postpetiole, gastral terga with moderately dense, erect setae, mostly similar in length, longest about 0.7× MOD. Head, mesosoma, funicular segments, legs, petiolar node black, often with an orangish infusion on mandibles and legs; postpetiole blackish-orange; gaster ferruginous orange, often with darker transverse band on posterior margin of terga ( Figure 65 ).

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) first gastral tergum smooth and strongly shining, (3) head, mesosoma, petiolar node, postpetiole black; gaster dark ferruginous orange, and (4) superior propodeal spines moderately well developed ( Figure 66 ).

Measurements —(n = 12). HL 1.58–1.79; HW 1.77–1.88; MOD 0.39–0.44; OMD 0.37–0.46; SL 1.33–1.44; PNW 1.40–1.73; HFL 1.72–1.93; ML 2.41–2.73; PW 0.49–0.58; PPW 0.77–0.83. Indices: SI 71.12–77.97; CI 102.79–116.05; OI 21.20–23.89; HFI 96.22–106.21.

Description. With caste-specific morphology of the mesosoma related to wing-bearing and presence of ocelli on head. In full-face view, head subquadrate to wider than long (CI = 102.79–112.66), widest just posterior to eyes, posterior margin flat. Longitudinal rugae on cephalic dorsum prominent, wavy to weakly irregular; in full-face view at least one to two medial rugae not diverging toward posterior corners of head, interrugae moderately to strongly granulate-punctate, dull to weakly shining; posterior corners rugose, interrugae weakly granulate-punctate, weakly shining to smooth and shining. Mandibles with six teeth, dorsal surface coarsely rugose. Psammophore well developed.

All mesosomal surfaces with regular, subparallel, wavy or irregular rugae, except for irregular rugae to rugoreticulate on pronotal sides; interrugae on mesoscutum and mesoscutellum weakly to moderately coriarious, weakly shining; interrugae on propodeum moderately granulate-punctate, dull. Propodeum with moderately long superior spines; inferior propodeal spines poorly developed, wider than tall, apex subangulate to rounded. Peduncle of petiole long, anteroventral margin lacking a process or with a weakly developed, broadly rounded process that continues posterad more or less parallel to dorsal margin of peduncle. In profile, petiolar node asymmetrical with anterior surface shorter than posterior surface, apex subangulate to angulate. Posterior surface of petiolar node with irregular transverse, oblique, or longitudinal rugae; rugae on dorsum of postpetiole transverse, arcuate, or oblique, and finer, denser than those on posterior surface of petiolar node; interrugae on posterior surface of petiolar node and dorsum of postpetiole weakly to moderately granulate-punctate, weakly shining. First gastral tergum smooth, strongly shining. Most body surfaces with moderately abundant suberect to erect, medium-length, white setae; moderately abundant suberect to erect hairs on first gastral tergum, those on second and third terga restricted to posterior margins. Gaster dark ferruginous orange, mandibles orangish-black to blackish-orange, rest of body black ( Figure 66 ).

Male diagnosis. Males of this species are diagnosed by the following combination of features: (1) first gastral tergum lacking striae, (2) bicolored: head and mesosoma black, gaster ferruginous orange, (3) erect hairs lacking on first gastral tergum, (4) mesopleura with longitudinal rugae, (5) in profile, lateral hairs along posterior margin of first gastral tergum <0.2–0.3× the length of longest hairs on first gastral sternum, (6) strong, irregular to regular transverse rugae on posterior surface of petiolar node, and (7) notauli absent ( Figure 67 ).

Measurements —(n = 2). HL 1.36–1.44; HW 1.34–1.44; MOD 0.51–0.51; OMD 0.18–0.20; SL 0.42–0.44; HFL 1.80–2.03; ML 2.44–2.62; PW 0.56–0.58; PPW 0.75–0.76. Indices: SI 30.56–31.34; CI 98.53–100.00; OI 35.42–38.06; HFI 134.33–140.97.

Additional material examined. ARGENTINA: Mendoza: Valle Hermosas , 7430’, Dec 6, 2003 ( CASC; IFML; RAJC); Rt 145 at 42.2 km W Bardas Blancas, 5380’, Jan 26, 2008 ( IFML; RAJC); 3.9 km W entrance Reserva Provincial Laguna Diamante, 8450’, Feb 11, 2014 ( IFML; LACM; MACN; MCZC; RAJC; UCDC; USNM) ( Figure 68A ) .

Etymology. The specific epithet, pronotalis (Latin, from pronoto - for pronotum, plus – alis = suffix added to noun stems, meaning pertaining to), was derived from the wide pronotum, which Santschi described as: “middle of pronotum wider than mesonotum …”.

Discussion. The color combination (black head and mesosoma, gaster ferruginous orange) and lack of striae on the first gastral tergum separate P. pronotalis from all congeners except for P. mendozanus and P. meridionalis . Pogonomyrmex pronotalis has been confused with P. mendozanus , with the latter having been misidentified as the former in several publications (see discussion under P. mendozanus in Johnson, 2015). Pogonomyrmex pronotalis is separated from P. mendozanus by the widely spaced, irregular rugae on the cephalic dorsum and mesosoma, whereas these rugae are closely spaced, regular, subparallel-parallel, and deeply incised in P. mendozanus . Pogonomyrmex pronotalis is separated from P. meridionalis by its: (1) smaller size (HW = 1.61–1.81 mm), (2) anterior portion of the first gastral tergum weakly coriarious, weakly shining to smooth and shining, (3) coarse rugae on pronotum, and (4) medial rugae on mesonotum diverging or becoming transverse to rugoreticulate on pronotum but not continuing to pronotal collar. Pogonomyrmex meridionalis is: (1) usually larger (HW = 1.76–2.06 mm), (2) first gastral tergum moderately to strongly coriarious, dull to weakly shining anterad, (3) rugae on pronotum weak to moderately coarse, and (4) medial rugae on the mesonotum usually continue to anterior margin of the pronotum.

Biology. Pogonomyrmex pronotalis workers are solitary foragers. Nests consist of a tumulus up to 15 cm in diameter that is placed in clumps of Stipa sp. (Poaceae) or under rocks in sandy soil. Partial nest excavations indicated that colonies of P. pronotalis probably contain 400– 700 workers. Sexuals have been collected on 11 February, which suggests that mating flights occur during the austral summer.

Several papers have used the name P. pronotalis ( Claver & Fowler, 1993; Nobua-Behrmann, Lopez de Casenave, Milesi, & Pavan, 2013; Nobua Behrmann et al., 2010; Pirk & Lopez de Casenave, 2006; Pirk et al., 2007; Pirk et al., 2004; Pirk et al., 2009; Pol & Lopez de Casenave, 2004; Pol, Lopez de Casenave, Feldhaar, Milesi, & Gadau, 2008), but this name was based on a misidentification, and all of these papers should be referred to P. mendozanus (see Johnson, 2015).

Pogonomyrmex pronotalis inhabits elevations from 1630–2560 m. This species occurs in the Southern Andean steppe ecoregion, as defined by Olson et al. (2001) ( Figure 68A ).

Figures

FIGURE 65. Photographs of Pogonomyrmex pronotalis worker: (A) frontal view of head, (B) lateral view of body, and (C) dorsal view of body (CASENT0102688). Photographs by April Nobile from www.AntWeb.org.

FIGURE 66. Photographs of Pogonomyrmex pronotalis alate queen: (A) frontal view of head, (B) lateral view of body, and (C) dorsal view of body (CASENT0914370). Photographs by Michele Esposito from www.AntWeb.org.

FIGURE 67. Photographs of Pogonomyrmex pronotalis male: (A) frontal view of head, (B) lateral view of body, and (C) dorsal view of body (CASENT0914369). Photographs by Michele Esposito from www.AntWeb.org.

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.