Pogonomyrmex micans

Robert A. Johnson, 2015, A taxonomic revision of South American species of the seed-harvester ant genus Pogonomyrmex (Hymenoptera: Formicidae). Part I, Zootaxa 4029 (1), pp. 1-142 : 37-43

Pogonomyrmex micans

( Figures 14–16)

Pogonomyrmex bruchi Forel r. micans Forel, 1914: 268 (worker, male). Syntypes examined: 26 workers, 2 males [MHNG], 2 workers [MLPA], ARGENTINA, San Luis: Alto Pencoso near La Plata, #224 (Bruch leg.). See also Gallardo, 1932: 158, fig. 40. MLPA worker here designated LECTOTYPE [CASENT0217254].

Pogonomyrmex micans Forel : Kusnezov, 1951: 254, raised to species.

Worker. Diagnosis. Within the P. coarctatus -group, the combination of: (1) fine, dense, longitudinal striae cover cephalic dorsum, (2) coarse rugae on posterior surface of petiolar node, rugae less coarse and more dense on dorsum of postpetiole, (3) in profile, lateral lobe of clypeus poorly-developed with broad gap between clypeal lobe and frontal lobe (gap as wide as to wider than antennal scape), and (4) bicolored—head reddish-brown; mesosoma, petiolar node, postpetiole reddish-brown to blackish-red; gaster reddish-black to nearly black uniquely characterize this species ( Figure 14).

Measurements —lectotype (n = 20). HL 2.09 (2.02–2.64); HW 2.25 (2.10–2.80); MOD 0.45 (0.42–0.56); OMD 0.41 (0.40–0.60); SL 1.48 (1.23–1.73); PNW 1.48 (1.31–1.79); HFL 1.67 (1.81–2.32); ML 2.10 (2.17–2.80); PW 0.51 (0.49–0.70); PPW 0.70 (0.63–0.91). Indices: SI 65.78 (52.50–63.84); CI 107.66 (102.65–112.44); OI 20.00 (15.88–22.03); HFI 74.22 (68.95–89.05).

Redescription. Monomorphic, head slightly wider to wider than long (CI = 102.65–112.44), posterior margin flat to weakly concave in full-face view. Fine, dense, longitudinal striae cover cephalic dorsum, width of striae and interstriae similar; medial striae not diverging toward posterior corners of head. Cephalic interstriae dull to weakly shining; vertex smooth and shining or with very fine, dense striae; interstriae smooth, weakly shining to shining; entire cephalic dorsum with silky appearance. Anterior margin of clypeus concave; dorsal surface with numerous moderately coarse subparallel, longitudinal to oblique rugae. Numerous long, curved, bristle-like, yellowish macrochaetae project from anterior margin of clypeus and ventral surface of mandibles. Mandible with six teeth, rarely with an additional denticle between 4th and 5th teeth; mandibular dorsum coarsely rugose. MOD ranging from 0.17–0.23x HL. In profile, eyes situated anterior to middle of head, OMD = 0.88–1.13x MOD. Antennal scapes short (SI = 52.50–63.84), extending less than one-third the distance from posterior margin of eye to posterior corner of head. Base of antennal scapes smooth and shining, distal portion weakly striated, weakly to strongly shining; basal flange well-developed with carinate margin. Psammophore well-developed.

Mesosomal profile weakly to moderately convex; all mesosomal surfaces with prominent coarse, subparallel, weakly irregular, widely-spaced rugae. In dorsal view, humeral shoulders of pronotum rounded to knoblike. Dorsum of promesonotum with longitudinal rugae that diverge anteriorly toward humeral shoulders of pronotum; transverse rugae on anterior surface of pronotum continue obliquely or longitudinally on pronotal sides; rugae on mesopleura angle posterodorsally. Superior propodeal spines long, acuminate, connected by well-defined keel; spine length about equal to width between their bases; regular to weakly wavy, transverse rugae on propodeal dorsum traverse ventrally or anteroventrally on sides. Inferior propodeal spines wider than long, apex rounded to angulate. Propodeal spiracles narrowly ovate facing posterad. Interrugae on mesosoma weakly to moderately granulate, weakly shining to shining. Legs weakly granulate, weakly shining.

Peduncle of petiole about 0.8x as long as petiolar node, anteroventral margin with broadly rounded process. In profile, posterior surface of petiolar node weakly convex; node asymmetrical with anterior surface notably shorter than posterior surface, apex rounded. In dorsal view, petiolar node longer than wide, widest near middle, narrowing to spatulate to weakly acute anterior margin. Sides and posterior surface of petiolar node with coarse, wavy to irregular, transverse rugae. Dorsum of postpetiole convex in profile; in dorsal view, widest near posterior margin, narrowing to anterior margin, maximum width about equal to length. Regular to wavy, fine, dense, transverse rugae on dorsum of postpetiole, sometimes lacking on anterior margin; interrugae on posterior surface of petiolar node and dorsum of postpetiole weakly to moderately granulate, dull to weakly shining. First gastral tergum moderately coriarious, weakly shining to smooth and shining.

Erect white to yellowish pilosity moderately abundant on head, variable in length and arising from foveae; longest hairs not exceeding MOD, few>0.5x MOD. Moderately abundant suberect pilosity on scape; abundant decumbent hairs on funicular segments. Legs with moderately abundant suberect to decumbent setae. Mesosoma, petiolar node, postpetiole, first gastral tergum with moderately dense erect setae that are similar in length, longest hairs shorter than MOD; length of hairs on margins of posterior gastral terga occasionally>MOD. Head reddishbrown; mesosoma, petiolar node, postpetiole reddish-brown to blackish-red; antennae, legs, gaster reddish-brown to nearly black ( Figure 14).

Queen. Diagnosis. This caste is diagnosed by: (1) caste-specific morphology of the mesosoma related to wingbearing and presence of ocelli on head, (2) large size (HW = 2.94–3.09 mm), (3) striae cover cephalic dorsum, (4) in profile, lateral lobe of clypeus not enlarged with broad gap (similar to the width of antennal scape) between clypeal lobe and frontal lobe, and (5) bicolored—head reddish-orange; gaster reddish-brown to nearly black ( Figure 15).

Measurements —(n = 7). HL 2.50–2.84; HW 2.94–3.09; MOD 0.55–0.64; OMD 0.59–0.64; SL 1.52–1.68; PNW 2.01–2.23; HFL 2.20–2.47; ML 3.46–3.62; PW 0.77–0.91; PPW 1.04–1.19. Indices: SI 49.19–55.08; CI 108.10–122.13; OI 18.71–20.85; HFI 71.66–80.98.

Description. Large species (HW = 3.94–3.09 mm) with caste-specific morphology of the mesosoma related to wing-bearing and presence of ocelli on head. In full-face view, head wider than long (CI = 108.1–122.1), posterior margin weakly concave medially. Fine, dense, longitudinal striae cover cephalic dorsum; striae on vertex often less abundant or absent. Interstriae weakly shining to shining. Mandible with six teeth, dorsal surface coarsely rugose. Psammophore well-developed.

All mesosomal surfaces with subparallel, weakly irregular rugae. Superior propodeal spines short. Peduncle of petiole slightly shorter than petiolar node, anteroventral margin with blunt to angulate process. In profile, petiolar node asymmetrical with anterior surface notably shorter than posterior surface, apex rounded. Postpetiole slightly wider than long. Posterior surface of petiolar node and dorsum of postpetiole with wavy to irregular transverse rugae, rugae coarser on petiolar node than postpetiole; interrugae weakly punctate, weakly shining. Gastral terga smooth, weakly shining to shining. Most body surfaces with moderately abundant suberect to erect, short white to yellowish setae. Head reddish-orange; mesosoma, petiolar node, postpetiole reddish-brown to blackish-red; gaster reddish-brown to nearly black ( Figure 15).

Male. Diagnosis. This caste is diagnosed by: (1) first gastral tergum lacking striae, (2) large (HW> 1.80 mm; HL> 1.65 mm; ML> 2.75 mm), (3) hairs on head (especially posterior to eyes) and dorsum of mesosoma dense, long and flexuous, length of numerous hairs approach to exceed MOD, (4) mandibles with four teeth, and (5) interrugae on katepisternum dull ( Figure 16).

Measurements —(n = 12). HL 1.67–1.95; HW 1.82–2.11; MOD 0.59–0.68; OMD 0.20–0.38; SL 0.44–0.56; PNW 1.64–1.99; HFL 1.81–2.20; ML 2.99–3.49; PW 0.68–0.83; PPW 0.82–1.02. Indices: SI 22.34–29.26; CI 100.00–126.35; OI 30.41–35.29; HFI 95.90–115.51.

Additional material examined. ARGENTINA: Catamarca: Rt 157 at 25.2 km NNW Jct Rt 60, 750’, Mar 21, 2015 (RAJC); Rt 20 at 0.7 km NE Esquiú, 800’, Mar 21, 2015 (RAJC). Córdoba: Rt 34 at Minas Clavero, 3005’, Dec 18, 2006 (RAJC); 2.6 km N Nono, Dec 19, 2006 (CSC); 5 mi N Deán Funes, Feb 8, 1951 (CASC); Rt 16 at 6.1 km NE Jct Rt 38, 1630’, Mar 20, 2015 (RAJC); Rt 16 at 15.2 km N Chuña, 1670’, Mar 20, 2015 (RAJC); Rt 60 at 27.7 km NW Quilino, 700’, Mar 21, 2015 (RAJC). Jujuy: Valle Grande, Feb 11, 1951 (FML). La Rioja: 4.2 km S Jct Rts 79 & 73, 1620’, Jan 22, 2006 (RAJC); Rt 38 at 8.1 km W of Córdoba-La Rioja border, 710’, Jan 14, 2010 (RAJC); Rt 38 at 9.2 km E Chamical, 1500’, Jan 14, 2010 (RAJC); Rt 38 at 15.4 km SE Chamical, 1400’, Mar 19, 2015 (RAJC); Rt 38 at 1.6 km W Chamical, 1490’, Mar 20, 2015 (RAJC); Rt 79 at 1.5 km S Catuna, 1610’, Jan 22, 2010 (RAJC); Rt 79 at 14.2 km S Catuna, 1810’, Mar 19, 2015 (RAJC); Rt 79 at 34.6 km S Catuna, 2050’, Jan 22, 2006 (RAJC); Rt 79 at 6.9 km SE Ulapes, 1250’, Jan 22, 2006 (RAJC); Rt 79 at 26.8 km SE Ulapes, 960’, Mar 19, 2015 (RAJC); Rt 79 at 2.6 km N Ulapes, 1360’, Mar 18, 2015 (RAJC); Rt 141 at 1.7 km E Chepes, 2150’, Mar 17, 2015 (RAJC); Rt 141 at 30.8 km E Chepes, 1880’, Mar 18, 2015 (RAJC), Rt 79 at 4.2 km S Jct Rt 141, 1750’, Mar 19, 2015 (RAJC); Rt 79 at 55.1 km NE Jct Rt 38, 1240’, Mar 22, 2015 (RAJC); Rt 60 at 15.4 km NE Jct Rt 20, 660’, Mar 23, 2015 (RAJC). Mendoza: Rt 7 at 5.8 km W Desaguadero, 1530’, Dec 28, 2005 (RAJC); no loc, no date (MACN). Salta: Piedras Lumbrera, May 24, 1949 (FML); Lumbreras, no date (LACM); Rt 9 at 1.2 km N turnoff to Lumbrera, 2390’, Apr 4, 2015 (RAJC); Piedras, no date (USNM). San Luis: La Tranca, Feb 10, 2009 (RGPC); La Punta, 2790’, Mar 6, 2005 & Dec 27, 2005 (RAJC); Rt 20 at 1 km NE Luján, 1940’, Dec 26, 2005 (CASC; RAJC); Rt 20 at 38.8 km W Luján, 2030’, Dec 27, 2005 (RAJC); Rt 20 at 75.6 km W Luján, 1570’, Dec 27, 2005 (CASC; MCZ; RAJC); Rt 20 at 1 km SW Quines, 1670’, Dec 26, 2005 (RAJC); 3.7 km SE Jct Rts 20 & 147, 2380’, Dec 27, 2005 (RAJC); Rt 7 at Alto Pencoso, 2330’, Dec 27, 2005 & Dec 20, 2006 (RAJC); Rt 7 at 3.5 km W Alto Pencoso, Dec 19, 2006 (CSC); 38.8 km N Jct Rts 20 & 79, 1240’, Jan 22, 2006 (RAJC); no loc, no date (MACN; MLPA; USNM); Rt 147 at 1.3 km NW turnoff to Parque Nacional Las Quijadas, 2300’, Mar 16, 2015 (RAJC). Santa Fe: Ruta 34 at 3 km W Santa Ana, 145 m, Dec 20, 2004 (RAJC). Santiago del Estero: Rt 130 at 11.5 km NW Jct Rt 34, 870’, Apr 7, 2015 (RAJC); Rt 64 at 3.7 km W Jct Rt 157, 870’, Apr 9, 2015 (RAJC). Tucumán: Ticucho, Dpto Trancas, Nov 6, 1965 (MZUSP); Uruena, Dec 5, 1959 (FML). PARAGUAY: Boquerón: Ruta Trans-Chaco, 180 m, Dec 4, 2002 (ALWC) ( Figure 17).

Etymology. The specific epithet, micans (from Latin, micans = shining, gleaming, or sparkling), apparently refers to the head, which Forel described as subopaque with a silky aspect.

Discussion. Pogonomyrmex micans co-occurs with P. coarctatus , and it likely co-occurs with P. lobatus . Pogonomyrmex micans is distinguished from P. coarctatus using the following characters: (1) in P. micans , fine, dense, longitudinal striae cover the cephalic dorsum, (2) dorsum of postpetiole has prominent moderately coarse rugae, and (3) workers are bicolored (dark red and blackish). In P. coarctatus : (1) the very fine, dense, longitudinal striae are often indistinct and cover only part to most of head, (2) dorsum of postpetiole is weakly to moderately granulate-punctate, occasionally with weak rugae near posterior margin, and (3) the body is mostly concolorous reddish-orange to reddish-brown. Pogonomyrmex micans is distinguished from P. lobatus by the following characters: (1) the lateral lobe of clypeus not enlarged, (2) the dorsum of the postpetiole has prominent moderately coarse rugae, and (3) workers are bicolored (dark red and blackish). In P. lobatus : (1) the lateral lobe of clypeus is massively enlarged, nearly contacting the frontal lobe, (2) dorsum of postpetiole weakly to moderately granulate, rarely with weak transverse rugae posteriorly, and (3) workers are concolorous reddish-orange to reddish-brown. Pogonomyrmex marcusi is only known from mid- to higher elevations in central Bolivia and thus is geographically isolated from P. micans ; these two species can be separated using characters in the key.

Biology. Pogonomyrmex micans is a solitary forager that harvests the seeds of various grass and nongrass species, but very loose columns of scattered foragers also have been observed. Nests are variable, ranging from entrances lacking a tumulus to ones with a tumulus up to 15 cm in diameter. Colonies of P. micans are probably similar in size to those of P. coarctatus suggesting that they contain up to about 2000 workers.

Collection dates for sexuals range from 26 December to 22 January, suggesting that mating flights occur during the austral summer (January–February). Queens of P. m i c an s contained an average of 12.5 ovarioles (n = 2); queen dry mass averaged (± SE) 20.7 ± 0.4 mg (n = 5) (R.A. Johnson, unpub. data).

Pogonomyrmex micans is a lowland species that inhabits elevations from 145–910 m. This species is most common in the Dry Chaco, but it also ranges into the Humid Chaco and the eastern edge of the Low Monte Desert ecoregion as defined by Olson et al. (2001). The Jujuy record appears to be an outlier at the edge of the Central Andean Puna/Southern Andean Yungas ecoregions; these specimen were probably collected in a valley at lower elevations ( Figure 17).