Pogonomyrmex carbonarius, Mayr, 1868

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 : 57-67

Pogonomyrmex carbonarius

( Figures 24–28 )

Distribution—22C

Pogonomyrmex carbonarius Mayr, 1868: 172 (worker). Holotype worker examined [NHMW, CASENT0173355 ]. ARGEN- TINA, Gran Pampa del Sur , between the dry streambed of the Agua Caliente and Río del Diamante (February 1866, Strobel leg.).

Pogonomyrmex rastratus Mayr : Mayr, 1887: 611, description of male, incorrect synonymy.

Pogonomyrmex rastratus var. carbonarius: Emery, 1906: 157 , revived status, as subspecies, but taxonomic change was based on a series of sanmartini that was misidentified as carbonarius . See also Gallardo, 1932: 136, fig. 23 (redescription).

Pogonomyrmex carbonarius: Kusnezov, 1951: 251 , raised to species, but taxonomic change was based on two series of sanmartini that were misidentified as carbonarius .

Pogonomyrmex vermiculatus var. variabilis Santschi, 1916: 511 (worker, male). Syntypes examined: 1 worker [MHNG], 1 worker [MZSP]. Syntype worker at NHMB not examined. ARGENTINA, Río Negro: Corral Chico (Dr. Lehmann, 6 March 1915). See also Gallardo, 1932: 142, figs. 28, 29. MZSP worker here designated LECTOTYPE [CASENT0217252]. NEW SYNONYMY

Pogonomyrmex variabilis Santschi : Kusnezov, 1951: 253, raised to species.

Pogonomyrmex weiseri var. neuquensis Santschi, 1922a: 243 (worker). Syntypes examined: 1 worker [MACN], 1 worker [MLPA]. ARGENTINA, Neuquén: Cerro Policía, #1529 (Dr. Schiller leg.). Kusnezov, 1951: 252, incorrect synonymy under rastratus . See also Gallardo, 1932: 148. MACN worker here designated LECTOTYPE [CASENT0217256]. NEW SYNONYMY

Pogonomyrmex kusnezovi Cuezzo & Claver, 2009: 105 , figs. 3, 4 (worker). Holotype and 3 paratype workers examined [IFML]. ARGENTINA, Río Negro : Conesa, #5712 (N. Kusnezov leg., 10 January 1950). NEW SYNONYMY

Worker diagnosis. Workers of this species are uniquely characterized by the following combination of features: (1) striae extend over more than anterior two-thirds of first gastral tergum, posterior margin with striae or moderately to strongly coriarious; posterolateral margins moderately to strongly coriarious, weakly shining to dull, (2) at least some workers in a series with superior propodeal spines that consist of tubercles, denticles, or short spines with a length <0.3× the distance between their bases, (3) several to most hairs on anterior half of first gastral tergum> 0.18 mm long, and (4) usually bicolored with head reddish-orange and gaster reddish-orange to dark blackish-orange to black, mesosoma black, or rarely concolorous black (concolorous black known only in Mendoza Province) ( Figures 24–26 ).

Measurements — lectotype (n = 12). HL 1.77 (1.70–2.06); HW 1.87 (1.84–2.25); MOD 0.39 (0.34–0.45); OMD 0.43 (0.39–0.50); SL 1.27 (1.30–1.63); PNW 1.23 (1.13–1.43); HFL 1.94 (1.70–2.15); ML 2.34 (1.88–2.42); PW 0.44 (0.42–0.63); PPW 0.63 (0.60–0.81). Indices: SI 67.91 (60.75–78.26); CI 105.65 (104.55–116.15); OI 20.86 (18.22–20.74); HFI 103.74 (80.57–105.50).

Redescription. Head subquadrate to wider than long (CI = 104.55–116.15); posterior margin flat to weakly convex in full-face view. Longitudinal rugae on cephalic dorsum prominent, wavy; in full-face view, medial rugae continuing to posterior margin or weakly diverging toward posterior corners of head; interrugae moderately to strongly granulate, with a beaded appearance, dull to weakly shining. Posterior corners rugose, interrugae moderately granulate, weakly shining to smooth and shining. Anterior margin of clypeus moderately concave, dorsum with several subparallel longitudinal rugae. Numerous long, curved, bristle-like, yellowish macrochaetae project from anterior margin of clypeus and ventral side of mandibles. Mandibles with six to seven teeth; mandibular dorsum coarsely rugose. MOD ranging from 0.19–0.23× HL. In profile, eyes situated slightly anterior to middle of head, OMD = 1.05–1.28× MOD. In full-face view, eyes protruding slightly beyond lateral margins of head. Antennal scapes (SI = 60.75–78.26) failing to reach posterior corners by more than length of basal funicular segment. Antennal scapes with weak longitudinal striae, weakly to moderately granulate, weakly shining; basal flange well developed with carinate margin. Psammophore well developed.

Mesosomal profile weakly to moderately convex; all mesosomal surfaces with prominent parallel-subparallel wavy to irregular rugae. In dorsal view, humeral portion of pronotum enlarged, lateral margins weakly to distinctly angulate. Dorsum of promesonotum with very irregular longitudinal rugae, usually with numerous, short lateral branches to nearly rugoreticulate, rugae diverging toward pronotal shoulders or becoming rugoreticulate-vermiculate on pronotum; ventrally trending irregular rugae to rugoreticulate on pronotal sides; rugae on mesopleura angle posterodorsally. Superior propodeal spines range from short, triangular teeth to long spines, bases connected by well defined keel; wavy transverse rugae on dorsum of propodeum traverse anteroventrally on sides. Inferior propodeal spines well developed, slightly wider than high, apex subangulate to angulate. Propodeal spiracles narrowly ovate. Interrugae on mesosoma moderately to densely granulate, dull to weakly shining. Legs weakly shining to shining.

Peduncle of petiole about 0.8× as long as petiolar node, anteroventral margin flat with a very weakly to moderately well developed, broadly rounded process. In profile, posterior surface of petiolar node weakly convex; petiolar node asymmetrical with anterior surface longer than posterior surface, apex subangulate to angulate. In dorsal view, petiolar node longer than wide, widest near spatulate anterior margin, narrowing posterad. Sides and posterior surface of petiolar node with wavy to irregular transverse, oblique, or longitudinal rugae to rugoreticulate. Dorsum of postpetiole convex in profile; in dorsal view, widest near posterior margin, narrowing anterad, width and length similar. Wavy to irregular transverse rugae on dorsum of postpetiole are finer, denser than those on posterior surface of petiolar node; interrugae on posterior surface of petiolar node and dorsum of postpetiole weakly to moderately coriarious, weakly shining. First gastral tergum with striae over more than anterior two-thirds of segment, rest of segment with striae or moderately to strongly coriarious, weakly shining to dull; posterolateral margins moderately to strongly coriarious, weakly shining to dull.

Erect, mostly short, whitish pilosity moderately abundant on head. Moderately abundant suberect to semidecumbent 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 to long, whitish to yellowish setae; several to most hairs on anterior half of first gastral tergum> 0.18 mm long. Color highly variable, both within and across colonies. The most common color pattern is head and gaster reddish brown to orangish brown, mesosoma black. Other color patterns include: (1) head reddish brown to orangish brown, gaster dark reddish brown to blackish or black, and (2) concolorous black (concolorous black form know only from Mendoza Province) ( Figures 24–26 ).

Queen diagnosis. Queens of this species are diagnosed by the following combination of features: (1) striae extend over more than anterior two-thirds of first gastral tergum; areas lacking striae (including posterolateral margins) moderately to strongly coriarious, weakly dull to dull; in profile, striae visible over extensive parts of more medial portions of segment, (2) relatively large (HW = 1.87–2.49 mm; PNW = 1.34–1.80 mm; ML = 2.34–3.17 mm), (3) superior propodeal spines consist of short acuminate teeth to moderately long spines, (3) head dark ferruginous orange or orangish-brown to reddish-brown, gaster dark orangish-brown to reddish-brown or blackish, (4) mesoscutum, mesoscutellum concolorous orangish or dark reddish to reddish-brown; pronotum, anepisternum blackish to black, (5) most hairs on first gastral sternite approximately 0.7–0.8× MOD or longer, those near posterior margin often exceeding MOD ( Figure 27 ).

Measurements —(n = 12). HL 1.55–2.47; HW 1.87–2.49; MOD 0.38–0.52; OMD 0.43–0.58; SL 1.28–1.65; PNW 1.34–1.76; HFL 1.93–2.46; ML 2.52–3.17; PW 0.54–0.69; PPW 0.72–0.97. Indices: SI 58.80–72.63; CI 100.81–127.32; OI 18.06–21.93; HFI 87.10–106.42.

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 much wider than long (CI = 100.81–127.32), broadest just posterior to eyes, posterior margin flat to weakly convex. Longitudinal rugae on cephalic dorsum prominent; in full-face view, medial rugae diverging toward posterior corners of head; posterior corners rugose, interrugae on cephalic dorsum and posterior corners moderately to strongly granulate-punctate, dull to weakly shining. Mandibles with six teeth, dorsal surface coarsely rugose. Psammophore well developed.

All mesosomal surfaces except pronotal sides with subparallel-parallel, regular to wavy rugae, rugae irregular to rugoreticulate on pronotal sides; interrugae weakly to moderately granulate-punctate, weakly shining to weakly dull; superior propodeal spines consist of short acuminate teeth to moderately long spines. Inferior propodeal spines wider than tall, weakly rounded to angulate. Peduncle of petiole long, anteroventral margin angles downward then continues posterad parallel to dorsal surface. In profile, petiolar node asymmetrical with anterior surface shorter than posterior surface, apex subangulate to angulate. Posterior surface of petiolar node with wavy to irregular, transverse rugae. In dorsal view, postpetiole wider than long; dorsum with wavy to irregular, transverse rugae that are finer, denser than those on posterior surface of petiolar node, interrugae on both surfaces weakly granulate-punctate, weakly shining. Striae extend over more than anterior two-thirds of first gastral tergum; areas lacking striae (including posterolateral margins) moderately to strongly coriarious, weakly dull to dull. Most body surfaces with moderately abundant suberect to erect, short to medium length, whitish to cream colored setae; most hairs on first gastral sternite approximately 0.7–0.8× MOD or longer, those near posterior margin often exceeding MOD. Head dark ferruginous orange or orangish-brown to reddish-brown; gaster dark orangish-brown to blackish; ferruginous orange to orangish-brown, posterior margins of gastral terga with blackish bands; mesoscutum, mesoscutellum concolorous orangish or dark reddish to reddish-brown; pronotum, anepisternum, propodeum, legs, antennae blackish to black ( Figure 27 ).

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) in dorsal view, rugae on cephalic dorsum posterior to eyes longitudinal, subparallel-parallel, continuing to posterior margin, (3) anterior one-half or more of anepisternum and usually katepisternum smooth and shining; subparallel-parallel, longitudinal rugae present posterad, (4) bicolored: head and mesosoma black, gaster ferruginous orange to reddish-orange, (5) larger: HW = 1.34–1.61 mm, PW = 0.49–0.64 mm, PPW = 0.71–0.81 mm, (6) rugae on posterior surface of petiolar node and dorsum of postpetiole usually irregular to rugoreticulate or granulate, and (7) interrugae on mesoscutum, mesoscutellum, posterior surface of petiolar node, and dorsum of postpetiole usually moderately to strongly coriarious, dull ( Figure 28 ). Note that males are unknown for the closely related P. mapuche .

Measurements —(n = 12). HL 1.18–1.59; HW 1.34–1.61; MOD 0.48–0.62; OMD 0.15–0.25; SL 0.33–0.53; HFL 1.42–2.08; ML 2.06–2.72; PW 0.49–0.64; PPW 0.71–0.81. Indices: SI 24.63–33.97; CI 101.26–120.66; OI 32.05–38.51; HFI 97.26–139.13.

Additional material examined. ARGENTINA: Chubut: Rt 2 at 6.5 km E Jct Rt 3, 300’, Feb 16, 2014 ( RAJC) ; Rt 3 at 16.4 km S Jct Rt 4, 130’, Feb 18, 2014 ( RAJC) ; Rt 3 at 11.9 km S Río Negro-Chubut border, 550’, Feb 17, 2014 ( RAJC) ; 19.9 km N Malaspina , 550 m, Dec 13, 1966 ( CASC; LACM) ; 3 km N Puerto Lobos , 20 m, Dec 14, 1966 ( CASC; LACM) . La Pampa: Rt 151 at 2.3 km N Puelén , 1520’, Feb 14, 2014 ( RAJC) ; Río Colorado , no date ( MLPA) ; no loc, no date (MACN). Mendoza: Rt 220 at 15.3 km NW El Sosneado , 5570’, Jan 24, 2008 ( RAJC) ; Rt 220 at 30.6 km NW El Sosneado , 6150’ ( RAJC) ; Rt 220 at 34.4 km NW El Sosneado , 6300’ ( RAJC) ; Rt 40 at 20.5 km ENE El Sosneado , 4490’ ( RAJC) ; Rt 40 at 23.7 km S El Sosneado , 4980’ ( IFML; LACM; MACN; RAJC; USNM) ; Rt 40 at 15.9 km N Dique Agua de Toro , 5300’, Feb 12, 2104 ( RAJC) ; Rt 101 at 2.9 km S Río Diamante , 5220’, Feb 12, 2014 ( IFML; LACM; MACN; RAJC; UCDC; USNM) ; Rt 101 at 4.2 km S Río Diamante , 5300’, Feb 12, 2014 ( RAJC) ; Rt 101 at 34.2 km S Río Diamante , 5770’, Feb 12, 2014 ( RAJC) ; Rt 222 to Las Leñas, Jan 30, 1999 ( IFML) ; Cochico, no date (MLPA); Rt 188 at 11.8 km W Canalejas , 1260’, Jan 27, 2008 ( RAJC) ; 5.69 km SE Cachueta , 1796 m, Jan 8, 2008 ( RAJC; WPMC) ; 6.01 km SW Cachueta , 1567 m, Jan 8, 2008 ( RAJC; WPMC) ; Portrerillos, Nov 21, 2009, ( RGPC) ; no loc, no date (MZSP). Neuquén: Covunco, Jan 10, 1950 ( IFML) ; P. Huincul (= Plaza Huincul), Apr 5, 1920 ( IFML) . Río Negro: Rt 3 at 71.5 km S Jct Rt 23, 500’, Feb 17, 2014 ( RAJC) ; Rt 151 at 5.6 km S Río Negro-La Pampa border, 1170’, Feb 14, 2014 ( RAJC) ; Rt 151 at 47.8 km S Río Negro-La Pampa border, 1090’, Feb 14, 2014 ( RAJC) ; Rt 151 at 87.2 km S Río Negro-La Pampa border, 1480’, Feb 14, 2014 ( RAJC) ; Rt 23 at 13.1 km E Valcheta , 620’, Feb 17, 2014 ( RAJC) ; Rt 23 at 29.4 km W Valcheta , 730’, Feb 16, 2014 ( RAJC) ; Rt 23 at 45.7 km E Valcheta , 590’, Feb 17, 2014 ( RAJC) ; Rt 3 at 18.3 km S Jct Rt 23, 630’, Feb 17, 2014 ( RAJC) ; Rt 6 at 29.7 km SW Jct Rt 22, 1180’, Feb 15, 2014 ( RAJC) ; Rt 6 at 62.1 km SW Jct Rt 22, 1470’, Feb 15, 2014 ( IFML; LACM; MACN; RAJC; UCDC; USNM) ; Rt 6 at 145.7 km SW Jct Rt 22, 2870’, Feb 15, 2014 ( RAJC) ; 1.7 km S General Conesa , 260’, Jan 21, 2011 ( RAJC) ; Rt 251 at 76.0 km S General Conesa, 200’, Jan 21, 2011 ( RAJC) ; Conesa, Oct 1, 1950, ( IFML) ; 11.7 km S Jct Rts 251 & 2, 100’, Jan 21, 2011 ( RAJC) ; 35.6 km NW Jct Rts 251 & 2, 360’, Jan 22, 2011 ( RAJC) ; 71.8 km S Jct Rts 251 & 2, 560’, Jan 22, 2011 ( RAJC) ; Rt 22 at 15 km E Choele Choel , 400’, Jan 2003 ( RAJC) ; Rt 250 at 34.0 km SE Choele Choel, 380’, Jan 22, 2011 ( RAJC) ; Rt 22 at 25.3 km W Chimpay , 520’, Jan 23, 2011 ( RAJC) ; Villa Regina, Dec 20, 1946 ( IFML) ; Corral Chico, no date (IFML); 6 km W Pelligrini Lake , Nov 21, 1995 ( CRSC) ; San Antonio Oeste, Dec 12, 1966 ( LACM) ; Cerro Catriel, 30 Jan, 2010 (RGPC); Roca (= General Roca), no date ( MACN) ( Figure 22C ).

Etymology. The specific epithet, carbonarius (from Latin, carbon = relating to coal, and - arius = suffix added to noun stems to form adjectives denoting belonging to), derives from the black coloration of this species. In his description, Mayr noted that the worker was similar to P. rastratus , but black.

Discussion. Pogonomyrmex carbonarius is highly variable within and across colonies with respect to color, length of the superior propodeal spines, and patterning of rugae on the mesosoma. In regard to color, nests can contain workers with a black head and mesosoma and a ferruginous orange to blackish-orange gaster, while other colonies contain workers with multiple color patterns. Concolorous black workers are known from only Mendoza Province.

Pogonomyrmex carbonarius is separated from most congeners by: (1) striae extend over anterior one-half or more of first gastral tergum, posterior margin with striae or moderately to strongly coriarious, and posterolateral margins moderately to strongly coriarious, weakly shining to dull. These characters separate P. carbonarius from all but three congeners: P. mapuche , P. propinqua , and P. weiseri .

Pogonomyrmex carbonarius is most likely to be confused with P. propinqua . For P. carbonarius : (1) color variable: concolorous black or with head and gaster reddish-orange to dark blackish-orange to black with a weak orangish infusion, gaster often notably darker than head, (2) at least some workers in a series with superior propodeal spines that consist of tubercles, denticles, or short spines with a length <0.3× the distance between their bases, and (3) several to most hairs on anterior half of first gastral tergum> 0.18 mm long. In P. propinqua : (1) head and gaster concolorous light to dark ferruginous orange, (2) superior propodeal spines long, length usually> 0.6× the distance between their bases, and (3) most hairs on anterior half of first gastral tergum <0.16 mm long. These two species are easily separated with queens or males when these castes are available (see keys). Pogonomyrmex carbonarius and P. propinqua have mostly non-overlapping distributions, but they occur in close proximity or in sympatry from Potrerillos to San Rafael, Mendoza Province.

Pogonomyrmex carbonarius is distinguished from P. mapuche by: (1) head and/or gaster usually orangish to orangish-black, (2) for at least some workers in a series, superior propodeal spines long, length> 0.4–0.6× the distance between their bases, and (3) height of inferior propodeal spines usually less than length of superior propodeal spines. In P. mapuche : (1) head dark red to reddish-black; rest of body black or with blackish-red gaster, (2) for all workers in a series, superior propodeal spines consist of tubercles or denticles, rarely short, acuminate teeth, and (3) height of inferior propodeal spines usually similar to or greater than length of superior propodeal spines.

Pogonomyrmex carbonarius is distinguished from P. weiseri by: (1) head and/or gaster reddish-orange to black, (2) mandibles with six to seven teeth, and (3) longitudinal rugae on dorsum of promesonotum irregular to rugoreticulate with short lateral branches that usually contact one another. In P. weiseri : (1) head and gaster ferruginous orange, (2) mandibles with six teeth, and (3) the longitudinal rugae on dorsum of promesonotum more regular, usually do not contact one another and lack short lateral branches. These two species are also separated geographically as P. carbonarius occurs in more southern provinces of Argentina (Mendoza to Chubut) than P. weiseri (La Rioja to Salta).

Pogonomyrmex varicolor is sometimes very similar to P. carbonarius . However, in P. varicolor one or more workers in a series has a black head and mesosoma and a ferruginous orange gaster. This color pattern is lacking in P. carbonarius . Additionally, in P. carbonarius , rugae on the posterior surface of the petiolar node and dorsum of postpetiole are often irregular to very irregular and the interrugae are dull to weakly shining, whereas these rugae are regular to wavy and the interrugae are usually smooth and shining in P. varicolor .

Gustav Mayr described six South American species of Pogonomyrmex , including P. carbonarius , and his collection is at NHMW. Syntypes for all of these species except P. carbonarius were at NHMW, and no specimens labeled as types of P. carbonarius were found at other museums. However, one NHMW worker was labeled P. rastratus, G. Mayr type, and the label reads “Pampa del Sur”, Strobel (collector). Pampa del Sur was the type locality from which Mayr briefly described P. carbonarius based on a collection by Strobel. This specimen also fits the vague description given by Mayr (1868): “worker: length 6.5 mm, quite similar to P. rastratus , differs in its black color, and with tarsi (except metatarsi) more or less fulvous-ringed, and metanotum with two triangular teeth. There are numerous nests of this species in the vast plain called Gran Pampa del Sur, the worker was collected between the dry streambed of the subterranean stream Agua Caliente and the flowing river named Río Diamante in the month of February, 1866”. The Pampa del Sur worker is black, and the sculpturing is similar to that of P. rastratus , which Mayr described in the same paper ( Mayr, 1868). Moreover, Mayr apparently labeled this specimen as a type of P. rastratus after he placed P. carbonarius as a junior synonym of P. rastratus ( Mayr, 1887) , but curiously he never placed a label with the name P. carbonarius on the pin. The description by Mayr (1868) gives only one length measurement for P. carbonarius , suggesting that there was only one syntype, and it was the only syntype located during this study. Thus, this worker with the label “Pampa del Sur” must be a syntype of P. carbonarius , and it is considered to be the holotype, and it was labelled as such.

The holotype worker of P. carbonarius matches specimens collected by the author near the type locality in the western foothills of the Andes along Río Diamante, Mendoza Province, Argentina. These collections demonstrate that morphology of P. carbonarius is highly variable in terms of coloration, patterning of rugae, and length of the superior propodeal spines. These collections also show that coloration of the holotype worker is atypical because the vast majority of workers are bicolored. Colonies near the type locality contained concolorous black workers, but this color morph was uncommon compared to bicolored workers (head and gaster ferruginous orange to reddishorange; mesosoma black). I have also collected concolorous black workers from south of El Sosneado, Mendoza, but workers collected from the rest of the geographic range invariably were bicolored.

It appears that neither Kusnezov nor Emery examined the holotype worker of P. carbonarius because both authors confused P. carbonarius with what Kusnezov was later to describe as P. carbonarius sanmartini . Emery (1906) elevated P. carbonarius to a subspecies of P. rastratus using material from near Río Santa Cruz in southern Santa Cruz Province, Argentina. This location is far south of the geographic range of P. carbonarius (see Figure 22C ). Emery also said that the posterior margin of the first gastral tergum was sometimes smooth and shining, which also indicates that his specimens were not P. carbonarius . Moreover, Emery (1906) elevated P. carbonarius to a subspecies of P. rastratus using misidentified specimens. To his credit, Emery (1906) indicated that there were problems with the identity and his specimens may comprise two species, but he did not have sufficient material to make this judgement. Pogonomyrmex carbonarius remained as a subspecies of P. rastratus until the revision by Kusnezov (1951).

Kusnezov (1951) based his concept of P. carbonarius on two series of workers in the collection of Dr. Bruch that were labeled P. rastratus var. carbonarius (Santa Cruz #586: 2 workers [MACN] & Bariloche #1528: 7w, 1aq, 1dq [MACN; MLPA]). It is unclear who identified these specimens. From these specimens, Kusnezov (1951) indicated that P. carbonarius was characterized by very regular longitudinal rugae on the dorsum of the mesonotum and mesopleura and that these rugae were more regular than those on P. rastratus and all other P. rastratus -group species. Based on this difference, Kusnezov (1951) re-elevated P. carbonarius to species rank. Unfortunately, workers that Kusnezov (1951) used to establish his concept of P. carbonarius were those of an undescribed species that he later described as P. carbonarius sanmartini . Thus, all taxonomic changes for P. carbonarius used specimens of P. sanmartini (see discussion under P. sanmartini ). Moreover, Kusnezov (1951) used concolorous black with striae on the first gastral tergum as the diagnostic characters to identify P. carbonarius , and he considered P. carbonarius to include all specimens from southern Argentina that displayed these two characters. These two diagnostic characters also were used in keys by Taber (1998) and Cuezzo and Claver (2009).

Santschi (1916) described P. vermiculatus var. variabilis , naming it for its variation in color, patterning of rugae, and variable superior propodeal spines. He also indicated that fine striae completely covered the first gastral tergum. The two syntype workers that I examined displayed this variability, which was also noted by Kusnezov (1951), who elevated P. variabilis to species rank with much reserve because the species was highly variable in all respects. The type locality for P. variabilis is Corral Chico (Laguna), Río Negro Province (now Ministro Ramos Mexía). The author did not find specimens at Ministro Ramos Mexía, but nest series were collected both east and west of this locale. Workers from both locales matched syntype workers of P. variabilis , as well as bicolored workers of P. carbonarius collected near the type locality. Thus, P. variabilis is placed as a junior synonym of P. carbonarius .

Santschi (1922a) also described P. weiseri var. neuquensis , saying that it differed from the type in that the thorax was more densely punctate and that the superior propodeal spines consisted of no more than two small, rounded teeth that were smaller than the inferior propodeal spines. The two syntypes that I examined varied in color and patterning of rugae on the promesonotum, and as noted by Santschi (1922a), the superior propodeal spines consisted of teeth that were shorter than both the width at their base and the height of the inferior propodeal spines. The type locality for P. weiseri var. neuquensis was Cerro Policía, Neuquén Province (Cerro Policía is actually in Río Negro Province near the border with Neuquén Province), which is approximately midway between the type localities for P. carbonarius and P. variabilis . The two syntypes of P. weiseri var. neuquensis , as well as workers collected near the type locality all matched bicolored workers of P. carbonarius collected near the type locality along the Río Diamante. Thus, P. weiseri var. neuquensis is placed as a junior synonym of P. carbonarius .

Cuezzo and Claver (2009) described P. kusnezovi based on four workers that Kusnezov collected from General Conesa, Río Negro, Argentina, on January 10, 1950 (#5712). In their discussion, Cuezzo and Claver (2009) indicated only that P. kusnezovi was closely related to P. andinus , which is curious given that these two species have little resemblance to one another. It is also unclear why they did not compare P. kusnezovi to the more geographically proximate and morphologically similar forms P. variabilis and P. weiseri var. neuquensis , or why their paper did not include the several additional IFML series that matched their types of P. kusnezovi (see specimens examined above), including another series collected at Conesa on the same date. The holotype and three paratype workers of P. kusnezovi all matched bicolored workers of P. carbonarius collected near the type locality. Thus, P. kusnezovi is placed as a junior synonym of P. carbonarius .

Biology. Pogonomyrmex carbonarius workers are solitary foragers. Nests of P. carbonarius are placed in open, exposed sites, or at the edge of rocks, or in a clump of Stipa sp. (Poaceae) or under shrubs. The nest entrance ranges from a hole in the ground to a tumulus up to 35 cm in diameter. Nests are most easily located by baiting workers with cookie crumbs, then following them back to the nest. Partial nest excavations indicated that colonies contain approximately 500–1000 workers. Sexuals have been collected from January 24–February 17, and one dealate queen was collected on December 12, indicating that mating flights occur during the austral summer. Several papers have examined foraging activity and natural history of P. carbonarius (Aput, Farji-Brener, & Pirk, 2019; Lescano, Elizalde, Werenkraut, Pirk, & Flores, 2017; Pirk, 2014; Pirk, Elizalde, Lescano, & Werenkraut, 2020; Pirk & Lopez de Casenave, 2017), but the species in all of these studies is now P. sanmartini (see above discussion and section on P. sanmartini ).

Pogonomyrmex carbonarius inhabits sites at elevations from 20–1865 m, and it occurs in the Lower Monte, Patagonian steppe, and Southern Andean steppe ecoregions with one record in the Espinal ecoregion, as defined by Olson et al. (2001) ( Figure 22C ).

Figures

FIGURE 22. Geographic distribution of: (A) Pogonomyrmex atratus, (B) P. bolivianus, and (C) P. carbonarius. The large black circle in each panel denotes the type locality. See text regarding the type locality for P. atratus.

FIGURE 24. Photographs of Pogonomyrmex carbonarius worker: (A) frontal view of head, (B) lateral view of body, and (C) dorsal view of body (CASENT0922103). Workers of P. carbonarius are highly variable: photographs show bicolored worker (head and gaster dark reddish-orange, mesosoma black) with long superior propodeal spines. Photographs by Michele Esposito from www.AntWeb.org.

FIGURE 25. Photographs of Pogonomyrmex carbonarius worker: (A) frontal view of head, (B) lateral view of body, and (C) dorsal view of body (CASENT0922157). Workers of P. carbonarius are highly variable: photographs show bicolored worker (head dark reddish-orange, mesosoma and gaster blackish to black) with medium length superior propodeal spines. Photographs by Michele Esposito from www.AntWeb.org.

FIGURE 26. Photographs of Pogonomyrmex carbonarius worker: (A) frontal view of head, (B) lateral view of body, and (C) dorsal view of body (CASENT0922102). Workers of P. carbonarius are highly variable: photographs show concolorous black worker with short, blunt superior propodeal spines. Photographs by Michele Esposito from www.AntWeb.org.

FIGURE 27. Photographs of Pogonomyrmex carbonarius alate queen: (A) frontal view of head, (B) lateral view of body, and (C) dorsal view of body (CASENT0922159). Photographs by Michele Esposito from www.AntWeb.org.

FIGURE 28. Photographs of Pogonomyrmex carbonarius male: (A) frontal view of head, (B) lateral view of body, and (C) dorsal view of body (CASENT0922158). Photographs by Michele Esposito from www.AntWeb.org.