Pogonomyrmex laticeps

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 : 80-87

Pogonomyrmex laticeps

( Figures 38–41)

Pogonomyrmex laticeps Santschi, 1922: 350 (worker). Syntypes examined: 2 workers [MACN], ARGENTINA, Catamarca: Masao, #1376 (Weiser leg., March 1921); Kusnezov, 1951: 274, figs. 10a, 10b (ergatoid queen, brachypterous queen). See also Gallardo, 1932: 161, fig. 42; Peeters, et al. 2012: figs. 2–4, 6–7. MACN worker here designated LECTOTYPE [CASENT0217255].

Worker. Diagnosis. Within the P. laticeps -group, the combination of: (1) head and mesosoma dark reddish-black, gaster black, (2) rugae on promesonotum transverse, oblique, or irregular, rarely longitudinal, and (3) medial rugae along posterior margin of head usually partly rugoreticulate uniquely characterize this species ( Figure 38).

Measurements —lectotype (n = 52). HL 2.04 (1.56–2.07); HW 2.20 (1.65–2.25); MOD 0.37 (0.30–0.40); OMD 0.53 (0.39–0.64); SL 1.39 (1.08–1.59); PNW 1.38 (1.04–1.39); HFL 2.08 (1.45–2.24); ML 2.67 (1.85–2.62); PW 0.55 (0.0.39–0.59); PPW 0.79 (0.59–0.83). Indices: SI 63.18 (60.34–81.52); CI 107.84 (101.12–115.20); OI 16.82 (16.28–23.20); HFI 94.55 (81.22–110.56). See also Peeters et al. (2012).

Redescription. Head subquadrate to wider than long (CI = 101.12–115.20), widest just posterior to eye; posterior margin flat in full-face view. Longitudinal rugae on cephalic dorsum prominent, weakly wavy to irregular, sometimes weakly rugoreticulate on medioposterior margin; in full-face view, medial rugae diverging weakly toward posterior corners of head. In profile, rugae posterior to eyes converging toward vertex. Cephalic interrugae weakly granulate, shining; vertex rugose. Anterior margin of clypeus flat to weakly concave; dorsal surface with numerous subparallel, longitudinal rugae. Mandible with six teeth; mandibular dorsum coarsely rugose. Numerous long, curved, bristle-like, yellowish hairs project from anterior margin of clypeus and basolateral margin of mandibles. MOD ranging from 0.18–0.23x HL. In profile, eyes situated near middle of head, OMD = 1.19–1.60x MOD. Antennal scapes relatively long (SI = 60.34–81.52), failing to reach vertex by up to length of basal funicular segment; scapes smooth and shining, distal portion often weakly striate. Basal flange of scape flattened, well-developed with carinate margin. Psammophore well-developed.

Mesosomal profile flat to weakly convex; all mesosomal surfaces with prominent rugae. In profile and dorsal views, humeral shoulders of pronotum sometimes angulate, weakly elevated above medial portion of pronotum. Dorsum of promesonotum and sides of pronotum with coarse, transverse, longitudinal or oblique, irregular rugae, rugoreticulate to vermiculate; promesonotal suture weakly impressed on occasional workers. Mesopleura with wavy to irregular rugae angling posterodorsally, rugae often more irregular to rugoreticulate near anterodorsal margin. Dorsum of propodeum with transverse to irregular rugae that traverse anteroventrally on sides. Propodeum with long, acuminate spines connected by well-defined keel; spine length similar to or slightly longer than distance between their bases. Inferior propodeal spines absent or reduced to indistinct rounded or triangular process. Propodeal spiracles narrowly ovate facing posterad. Interrugae on mesosoma smooth, strongly shining. Legs moderately coriarious, weakly shining.

Peduncle of petiole about 0.8x as long as petiolar node, anteroventral margin usually with rounded to triangular tooth-like process. In profile, petiolar node asymmetrical with anterior surface about one-half as long as posterior surface; apex weakly angulate to rounded. In dorsal view, petiolar node longer than wide, sides subparallel to slightly wider near spatulate anterior margin; posterior surface and sides with moderately strong, wavy to irregular, transverse to arcuate 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 to irregular transverse rugae that are finer, denser than on posterior surface of petiolar node. Interrugae on posterior surface of petiolar node smooth and strongly shining, weakly to moderately granulate, weakly shining on dorsum of postpetiole. First gastral tergum moderately coriarious, weakly shining to smooth, strongly shining.

Erect whitish pilosity moderately abundant on head, variable in length, longest hairs not exceeding 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, and gastral terga with moderately dense, erect setae, variable in length, only those on posterior gastral terga approaching MOD. Head, mesosoma dark orangish-black to reddish-black; petiolar node, postpetiole slightly darker; legs, gaster dark brown to black ( Figure 38).

Ergatoid queen. Diagnosis. This caste is diagnosed by: (1) ergatoid, with small ocelli on head and mesosoma lacking morphological structures related to wings, (2) larger species (HW> 1.40 mm), (3) first gastral tergum smooth and shining to moderately coriarious, (4) interrugae on cephalic dorsum smooth and shiny, and (5) head, mesosoma, petiolar node, postpetiole dark reddish-black; gaster blackish ( Figure 39).

Measurements —(n = 25). HL 1.85–2.18; HW 1.99–2.32; MOD 0.35–0.44; OMD 0.5–0.67; SL 1.25–1.65; PNW 1.28–1.45; HFL 1.83–2.24; ML 2.26–2.75; PW 0.49–0.64; PPW 0.78–0.96. Indices: SI 53.88–76.39; CI 104.19–113.00; OI 16.09–20.39; HFI 83.04–100.00. See also Peeters et al. (2012).

Brachypterous queen. Diagnosis. This caste is diagnosed by: (1) brachypterous with very small wings and small ocelli on head, (2) in dorsal view, mesoscutum poorly-developed, anterior margin barely surpassing humeral shoulders of pronotum, (3) pronotum well-developed, (4) in profile, the pronotum rises at an approximately 45o angle to meet the mesoscutum, and (5) head and mesosoma dark reddish-black, gaster black ( Figure 40).

Measurements —(n = 30). HL 1.90–2.36; HW 2.09–2.49; MOD 0.40–0.46; OMD 0.55–0.69; SL 1.35–1.66; PNW 1.29–1.59; HFL 2.01–2.44; ML 2.26–2.87; PW 0.53–0.63; PPW 0.83–1.02. Indices: SI 57.26–70.09; CI 104.66–119.29; OI 16.46–19.66; HFI 84.10–102.14. See also Peeters et al. (2012).

Male. Diagnosis. The combination of: (1) first gastral tergum lacking striae, (2) rugae on dorsum of postpetiole usually longitudinal, interrugae weakly shining to shining, (3) dorsum of mesoscutum and mesoscutellum with prominent wavy to weakly irregular longitudinal rugae, interrugae weakly shining to shining, (4) in dorsal view, dorsum of propodeum depressed, lacking rugae, weakly shining to shining; prominent rugae traverse posteroventrally lateral to depression, and (5) notauli present ( Figure 41).

Measurements —(n = 12). HL 1.20–1.43; HW 1.32–1.52; MOD 0.43–0.55; OMD 0.22–0.32; SL 0.34–0.42; HFL 1.50–1.96; ML 2.13–2.62; PW 0.44–0.58; PPW 0.65–0.81. Indices: SI 23.68–31.82; CI 103.50–122.58; OI 30.94–36.18; HFI 107.91–146.27.

Additional material examined. ARGENTINA: Catamarca: Punta de Balasto, no date (MACN); Rt 40 at 3.8 km S Punta de Balasto, 7040’, Jan 27, 2010 (MCZ; RAJC); Catamarca airport, Feb 4, 1967 (MCZ); Santa María, no date (FML; LACM; MCZ); Valle de Santa María, no date (MCZ); Rt 39 at 0.4 km N Santa María, 5930’, Mar 25, 2015 (RAJC); Rt 39 at 15.1 km S Santa María, 6480’, Mar 25, 2015 (RAJC); Valle Masan, no date (MCZ); Rt 60 at Casa de Piedra, 790’, Mar 21, 2015 (RAJC); Rt 38 at 0.6 km S entrance to Catamarca, 1630’, Mar 22, 2015 (RAJC). La Rioja: El Portezuelo, Apr 16, 2009 (RGPC); Rt 29 at 38.7 km S El Portezuelo, 2250’, Apr 9, 2015 (RAJC); 96.8 km N Jct Rts 9 & 38, 1750’, Jan 7, 2006 (RAJC); Rt 38 at 20.8 km ESE Patquia, 1210’, Mar 19, 2015 (RAJC); Rt 38 at 20.8 km ESE Patquia, 1210’, Mar 22, 2015 (RAJC); Rt 38 at 30.8 km SE Patquía, 1330’, Jan 15, 2010 (RAJC); Rt 38 at 44.2 km SE Patquia, 1270’, Mar 22, 2015 (RAJC); 18.0 km NW Patquía, 1970’, Jan 20, 2006 (RAJC); Rt 27 at 22.5 km S Patquia, 1590’, Apr 9, 2015 (RAJC); Rt 27 at 69.4 km S Patquia, 1900’, Apr 9, 2015 (RAJC); Rt 38 at 35.7 km N Jct Rt 74 (Patquia exit), 1410’, Mar 22, 2015 (RAJC); 30.8 km E Jct Rts 5 & 38, 1160’, Jan 21, 2006 (RAJC); Rt 40 at 6.0 km N Chilecito, 3200’, Jan 3, 2006 (RAJC); Rt 40 at 11.3 km N Chilecito, 3230’, Feb 6, 2010 (RAJC); Rt 40 at 14.0 km N Chilecito, 3410’, Feb 4, 2006 (RAJC); Rt 40 at 25.4 km W Shaqui, 4070’, Jan 5, 2006 (RAJC); Rt 40 at 49.1 km S Pituil, 4270’, Jan 20, 2006 (RAJC); Rt 73 at 60.7 km NE Chamical, 1430’, Jan 21, 2006 (RAJC); Rt 38 at 19.2 km NW Chamical, 1290’, Mar 20, 2015 (RAJC); Nonogasta, no date (MACN); Rt 141 at 17.2 km E border with San Juan, 1560’, Mar 17, 2015 (RAJC); Rt 141 at 2.7 km E Chepes, 2130’, Mar 18, 2015 (RAJC); Rt 79 at 66.5 km NE Jct Rt 38, 1270’, Mar 23, 2015 (RAJC). Salta: Cafayate, Feb 20–26, 1948 (FML; LACM; MCZ); Cafayate, no date (LACM; MZUSP; USNM); Rt 40 at 5.6 km N Cafayate, 5480’, Jan 11, 2006 (RAJC); Rt 40 at 28.4 km N Cafayate, 5400’, Jan 11, 2006 (RAJC); Cafayate-Santa María- Frontera Salta-Tucuman, Jan 28, 1942 (FML); Rt 40 at 0.2 km N Tucumán border, 5560’, Mar 24, 2015 (RAJC); Rt 40 at 13.4 km N Tucumán border, 5710’, Mar 24, 2015 (RAJC); Rt 40 at 8.2 km N Jct Rt 68, 5510’, Mar 26, 2015 (RAJC); Rt 40 at 2.6 km N San Carlos, 5470’, Mar 26, 2015 (RAJC). San Juan: Rt 141 at 14.6 km E turnoff to Marayes, 1550’, Mar 17, 2015 (RAJC). San Luis: 3.7 km SE Jct Rts 20 & 147, 2380’, Dec 27, 2005 (RAJC); Parque Nacional Sierra las Quijadas, 2610’, Mar 6, 2005 (RAJC); Rt 147 at 1.3 km NW turnoff to Parque Nacional Las Quijadas, 2300’, Mar 16, 2015 (RAJC); Rt 20 at 75.6 km W Luján, 1570’, Dec 27, 2005 (RAJC); La Tranca, Feb 10, 2009 (RGPC). Tucumán: Rt 307 at 6.8 km NW Amaicha de Valle, 6080’, Jan 27, 2010 (RAJC); Rt 40 at 9.8 km NW Amaiche del Valle, 5930’, Mar 24, 2015 (RAJC); Rt 40 at 10.0 km NW Amaicha del Valle, 5940’, Jan 10, 2006 (CASC; RAJC); SW Amaicha de Valle, 2100 m, Feb 3, 1995 (MCZ); Bañado de Quilmes, no date (MACN) ( Figure 42 A).

Etymology. The specific epithet, laticeps (from Latin, latus = wide, and the suffix - ceps = head), is derived from the wide head of this species; in his description, Santschi noted that the head was clearly wider than long.

Discussion. Pogonomyrmex laticeps is not known to co-occur with P. mendozanus or P. tinogasta . Pogonomyrmex laticeps can be distinguished from P. mendozanus by the coarse, irregular rugae on the head and mesosoma, whereas cephalic and mesosomal rugae on P. mendozanus are fine, incised, and very regular. Pogonomyrmex laticeps can be distinguished from P. tinogasta based on the following characters: (1) head and mesosoma dark reddish-black, gaster black, (2) rugae on promesonotum transverse, oblique, or irregular, rarely longitudinal, and (3) medial rugae along posterior margin of head usually partly rugoreticulate. In P. tinogasta : (1) the body is concolorous black except for a dark reddish band encircling the eye, (2) the promesonotal rugae are longitudinal, usually regular, and (3) the medial rugae along the posterior margin of the head are longitudinal, rarely rugoreticulate.

Several authors have misinterpreted the type locality for P. laticeps . In describing the species, Santschi (1922) listed the type locality as Masao, Catamarca Province, Argentina (see also Baldini & Scattolin, 1993). Alternatively, Gallardo (1932) listed the type locality as Masas, and Kempf (1972) apparently questioned the locality by indicating it as <Masao> (=Mazán?). Additionally, the label on an MCZ specimen was interpreted as Valle Masan.

Biology. Pogonomyrmex laticeps is a solitary forager that harvests seeds. Nests usually have a tumulus that is up to 15 cm in diameter, sometimes with an external midden of seed chaff. Colonies of P. laticeps are relatively small: Kusnezov (1951) estimated colony size at 25–50 workers, but I have excavated colonies with up to 200 workers (Peeters et al., 2012), suggesting that colony size probably ranges up to 300–400 workers. Colonies in southern portions of the range sometimes contain up to 1000 workers, and very loose columns of scattered foragers have been observed.

This species is interesting morphologically because it has two non-flying queen phenotypes—ergatoid and brachypterous queens (Peeters et al., 2012). Only one queen phenotype is produced within a colony, and both queen phenotypes have similar reproductive potentials with a spermatheca and 12–15 ovarioles (Peeters et al., 2012). Colonies of both phenotypes can produce>50 queens, which Peeters et al. (2012) used to suggest that both queen phenotypes initiate nests using independent colony founding. Little is known about mating, but ergatoid queens have been collected from 6 February to 16 April. Brachypterous queens were larvae, pupae, or callows near the end of January and mature brachypterous queens have been collected from 20 February to 9 April. Mating has not been observed, but both ergatoid and brachypterous foundresses have been observed running on the ground (Mar 23 for ergatoid queens; Mar 24–25 for brachypterous queen), and both phenotypes exhibit independent colony founding; one haplometrotic ergatoid queen was excavated on March 22, and one haplometrotic brachypterous queen was excavated on March 24. Both ergatoid and brachypterous foundresses were observed to forage outside the nest (pers. obs.). Mating activities and colony founding appeared to have been triggered by late summer rains.

Data also indicate that the two queen phenotypes have a non-random geographic distribution; ergatoid queens are known to occur only in southern portions of their range (San Luis, La Rioja, eastern San Juan, and southeastern Catamarca Provinces), whereas brachypterous queens are only known to occur in northern portions of their range (northeastern Catamarca, southern Salta, and western Tucumán Provinces) ( Figure 42 A). These two populations may represent two closely-related species, but firm data to substantiate this hypothesis are lacking. Consequently, these two populations are retained within P. laticeps until additional data become available.

Pogonomyrmex laticeps inhabits sites at elevations from 240-2135 m. This species occurs from northwestern San Luis to southcentral Salta, and it is restricted to northern and central portions of the High Monte Desert and southwestern portions of the Dry Chaco ecoregions as defined by Olson et al. (2001) ( Figure 42 A).