Pogonomyrmex rastratus, , G. 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 : 155-163

Pogonomyrmex rastratus

( Figures 75–77 )

Distribution—78A

Pogonomyrmex rastratus Mayr, 1868: 171 (worker). Syntypes examined: 2 workers [NHMW]. ARGENTINA, Mendoza: Pampa de Canota, in the mountains near Mendoza (Strobel leg., January 1866). See also Gallardo, 1932: 134, fig. 20. NHMW worker here designated LECTOTYPE [CASENT0173352].

Worker diagnosis. Workers of this species are uniquely characterized by the following combination of features: (1) longitudinal striae on first gastral tergum usually extending to posterior margin or posterior margin moderately to strongly coriarious, dull to weakly shining; posterolateral margins smooth and shining to weakly coriarious, weakly shining, (2) for most to all workers in a series, rugae on dorsum of promesonotum well defined, regular to very regular and continuous, lacking short lateral branches; longitudinal rugae on mesonotum diverging toward humeral shoulders of pronotum, (3) anterior margin of pronotum with one to several straight, strong, continuous, transverse rugae, (4) superior propodeal spines consist of short triangular teeth to long spines, length> 0.5–0.6× the distance between their bases for some to all workers in a series, (5) height of inferior propodeal spines less than to rarely similar to length of superior spines, and (6) head, mesosoma, gaster mostly to completely ferruginous orange; mesopleura, petiole, postpetiole often with a blackish infusion to blackish ( Figure 75 ).

Measurements — lectotype (n = 12). HL 1.81 (1.39–1.89); HW 1.84 (1.43–1.98); MOD 0.44 (0.34–0.46); OMD 0.44 (0.36–0.47); SL 1.31 (1.11–1.39); PNW 1.33 (0.97–1.27); HFL 1.86 (1.42–1.93); ML 2.45 (1.69–2.23); PW 0.46 (0.35–0.46); PPW 0.63 (0.50–0.63). Indices: SI 71.20 (68.18–78.57); CI 101.66 (98.72–104.91); OI 23.91 (22.08–24.48); HFI 101.09 (87.20–100.00).

Redescription. Head subquadrate to quadrate (CI = 98.72–104.91); posterior margin flat in full-face view. Longitudinal rugae on cephalic dorsum prominent, regular to weakly wavy. In full-face view, medial rugae diverging toward posterior corners of head. Interrugae on cephalic dorsum moderately to strongly granulate-punctate, weakly shining to dull, usually with a beaded appearance. Posterior corners rugose, interrugae weakly to moderately granulate, weakly shining to smooth and shining. Anterior margin of clypeus moderately concave, dorsum with numerous subparallel, longitudinal rugae. Numerous long, curved, bristle-like, yellowish macrochaetae project from anterior margin of clypeus and basolateral margin of mandibles. Mandibles with six teeth; mandibular dorsum coarsely rugose. MOD ranging from 0.21–0.26× HL. In profile, eyes situated slightly anterior to middle of head, OMD = 0.92–1.18× MOD. In full-face view, eyes protruding slightly beyond lateral margins of head. Antennal scapes (SI = 68.18–78.57) failing to reach posterior corners of head by less than to about the length of basal funicular segment. Antennal scapes moderately to strongly striate, interstriae weakly to moderately granulate, weakly shining to smooth and shining; basal flange with a well developed carinate margin. Psammophore well developed.

Mesosomal profile flat to weakly convex; all mesosomal surfaces with prominent regular, subparallel-parallel rugae. For most to all workers in a series, rugae on dorsum of promesonotum well defined, regular to very regular and continuous, lacking short lateral branches; longitudinal rugae on mesonotum diverging toward humeral shoulders of pronotum and continue onto pronotal sides; anterior margin of pronotum with one to several straight, strong, continuous, transverse rugae, rarely only one transverse rugae restricted to medial portion of anterior margin. Occasional workers with irregular rugae on promesonotum. In dorsal view, humeral shoulders of pronotum enlarged, dorsolateral margin strongly angulate. Promesonotal suture present or absent. Regular to weakly irregular rugae on mesopleura angle posterodorsally; regular transverse rugae on dorsum of propodeum traverse anteroventrally on sides, rugae on dorsum of propodeum rarely longitudinal. Superior propodeal spines consist of triangular teeth to long spines, length> 0.5–0.6× the distance between their bases for some to all workers in a series, spines connected by well defined keel. Inferior propodeal spines wider than high, apex broadly rounded to acuminate; height less than to rarely similar to length of superior spines. Propodeal spiracles narrowly ovate facing posterad. Interrugae on mesosoma moderately to densely granulate, dull to weakly shining. Legs moderately coriarious, weakly shining to smooth and shining.

Peduncle of petiole about 0.8× as long as petiolar node, anteroventral margin with a weakly to well developed, weakly angulate to broadly rounded process. In profile, posterior surface of petiolar node weakly convex; petiolar node asymmetrical with anterior surface shorter than posterior surface, apex subangulate to angulate. In dorsal view, petiolar node longer than wide, sides subparallel anterad, gradually narrowing posterad, anterior margin spatulate to broadly rounded. Sides and posterior surface of petiolar node with regular to moderately irregular transverse rugae that are sometimes weakly arcuate anterad. Dorsum of postpetiole convex in profile; in dorsal view, widest near posterior margin, narrowing anterad, maximum width and length about equal; regular to moderately irregular transverse rugae posterad, anterad rugae transverse to more commonly weakly arcuate or concentric rugae that curve 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 granulate, weakly shining to smooth and strongly shining. Longitudinal striae on first gastral tergum usually extending to posterior margin or posterior margin moderately to strongly coriarious, dull to weakly shining; posterolateral margins smooth and shining to weakly coriarious, weakly shining.

Erect, mostly short to medium length, whitish pilosity moderately abundant on head, most hairs <0.3× MOD. Moderately abundant suberect to semidecumbent pilosity on scapes; abundant decumbent hairs on funicular segments. Legs with moderately abundant suberect to decumbent, whitish setae. Rest of body with erect, moderately dense, medium-length, whitish setae, length of most> 0.4–0.5× MOD. Head, mesosoma, gaster mostly to completely ferruginous orange; mesopleura, petiole, postpetiole often with a blackish infusion to blackish; legs blackish ( Figure 75 ).

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 cover anterior two-thirds or more of medial portion of first gastral tergum, posterolateral margins smooth and shining, (3) head and first gastral tergum ferruginous orange, first gastral tergum often with a black, transverse band along posterior margin, (4) in profile, pronotum usually lighter than adjoining anepisternum and/or katepisternum, (5) longitudinal rugae on cephalic dorsum posterior to eyes regular, lacking short lateral branches, interrugae weakly to moderately granulate, weakly shining, (6) superior propodeal spines consist of triangular denticles to long acuminate spines, and (7) rugae cover posterior surface of petiolar node and dorsum of postpetiole ( Figure 76 ).

Measurements —(n = 12). HL 1.66–2.00; HW 1.70–2.13; MOD 0.42–0.50; OMD 0.40–0.54; SL 1.24–1.48; PNW 1.27–1.57; HF 1.66–1.96; ML 2.34–2.92; PW 0.43–0.60; PPW 0.67–0.84. Indices: SI 66.50–74.71; CI 101.74–109.57; OI 22.22–25.88; HFI 84.91–100.58.

Description. With caste-specific morphology of the mesosoma related to wing-bearing, presence of ocelli on head. In full face view, head subquadrate to wider than long (CI = 101.74–109.57), broadest just posterior to eyes, posterior margin flat. Longitudinal rugae on cephalic dorsum prominent, regular, rugae posterior to eyes lacking short, lateral branches. In full-face view, medial rugae weakly diverging to diverging toward posterior corners of head; posterior corners rugose, interrugae on cephalic dorsum and posterior corner weakly to moderately granulate, dull to weakly shining. Mandibles with six teeth, dorsal surface coarsely rugose. Psammophore well developed.

All mesosomal surfaces with subparallel, irregular to regular rugae; interrugae on mesoscutum, axilla, and mesoscutellum moderately to strongly granulate-coriarious, weakly shining to dull; superior propodeal spines consist of triangular denticles to long acuminate spines; inferior propodeal spines moderately well developed, wider than tall, apex weakly to broadly rounded, height usually less then length of superior spines. Peduncle of petiole long, anteroventral margin with a very broadly rounded process. In profile, petiolar node asymmetrical with anterior surface notably shorter than posterior surface, apex of node angulate. Posterior surface of petiolar node with irregular transverse to longitudinal rugae. In dorsal view, postpetiole wider than long; dorsum with wavy to irregular, transverse to arcuate rugae that are finer, denser than those on posterior surface of petiolar node; interrugae on both surfaces weakly to moderately granulate-coriarious, weakly shining. Striae cover anterior two-thirds or more of medial portion of first gastral tergum, posterolateral margins smooth and shining. Most body surfaces with moderately abundant suberect to erect, short to medium-long, whitish to cream-colored setae. Head and first through third gastral terga ferruginous orange, gastral terga often with a transverse black band along posterior margin; in profile, pronotum usually lighter than adjoining anepisternum and/or katepisternum ( Figure 76 ).

Male diagnosis. Males of this species are diagnosed by the following combination of features: (1) striae extend over anterior one-half or more of first gastral tergum or strongly coriarious, dull, (2) petiolar node and postpetiole ferruginous orange, concolorous or nearly so with gaster, (3) in profile, regular, subparallel-parallel rugae posterior to eyes curve medially rather than continuing to posterior margin, and (4) notauli absent ( Figure 77 ).

Measurements —(n = 9). HL 1.15–1.43; HW 1.15–1.38; MOD 0.40–0.55; OMD 0.15–0.27; SL 0.36–0.43; HFL 1.53–1.76; ML 2.18–2.44; PW 0.46–0.60; PPW 0.65–0.76. Indices: SI 27.41–33.59; CI 91.34–112.50; OI 33.33–40.74; HFI 122.46–136.29.

Additional material examined. ARGENTINA: Mendoza: 19.7 km W Villavicencio , 8860’, Jan 18, 2008 ( MCZC; RAJC) ; 31.5 km W Villavicencio , 8540’, Jan 18, 2008 ( RAJC) ; 33.9 km E Rt 39 on road to Los Berros , 8980’, Jan 19, 2008 ( IFML; RAJC) ; Quebrada Santa Elena , 7160’, Dec 30, 2005 ( MCZC; RAJC) ; Sierra de Uspallata , 8630’, Dec 30, 2005 ( RAJC) , 9590’ & 10,040’, Dec 30, 2005 ( CASC; IFML; LACM; MACN; MCZC; RAJC; UCDC; USNM) ; Quebrada de Cueva del Toro , 8850’, Dec 30, 2005 ( IFML; RAJC) ; Quebrada de Manantiales , 8230’, Dec 30, 2005 ( RAJC) ; Uspallata , Dec 29, 2005 ( RGPC) ; Departamento Uspallata, Estancia Yaguaráz , Jan 25, 2014 ( RGPC) ; Departamento Uspallata, Estancia Tambillos , Jan 25, 2014 ( RGPC) ( Figure 78A ).

Etymology. The specific epithet, rastratus (Latin, from rastrat = covered as if with longitudinal scratches), is derived from the very fine, dense, longitudinal striae on the first gastral tegum. As noted by Mayr, “anterior half of first abdominal segment with dense, shallow longitudinal striae (rastrato) that often diverge laterally toward the posterior in an irregular fashion”.

Discussion. Pogonomyrmex rastratus is not known to co-occur with any congeners. Pogonomyrmex rastratus is distinguished from all congeners except P. sanmartini by the following characters: (1) striae that extend over the anterior one-half or more of the first gastral tergum, posterolateral margin smooth and shining to weakly coriarious, dull to weakly shining, (2) for most to all workers in a series, rugae on dorsum of promesonotum well defined, regular to very regular, continuous, lacking short lateral branches, (3) anterodorsal margin of pronotum with one to several straight, strong, continuous, transverse rugae, and (4) superior propodeal spines consist of short triangular teeth to long spines, length> 0.5–0.6× the distance between their bases for some to all workers in a series. Pogonomyrmex rastratus can be distinguished from P. sanmartini based on coloration: the head and gaster are mostly light to dark ferruginous orange to reddish-orange in P. rastratus , whereas in P. sanmartini the head is reddish, reddish black, or black and the gaster is black.

The identity of P. rastratus has been one of the more confusing taxonomic problems among South American Pogonomyrmex , despite the fact that it was one of three species that Mayr (1868) described when erecting the genus (along with P. coarctatus and P. carbonarius ). At least three problems have confounded understanding the identity of P. rastratus : (1) Mayr gave two contrasting descriptions for this species, (2) Mayr appears to have been the only author to have examined syntypes of P. rastratus , which resulted in an erroneous synonymy and subsequent misunderstanding the identity of P. rastratus , and (3) Kusnezov misinterpreted the type locality.

The problem of contrasting descriptions was created by Mayr, who gave similar descriptions of P. rastratus in Mayr (1868) and Mayr (1870), but gave a contrasting description in Mayr (1886). Mayr (1868) noted that P. rastratus was “red-orange with mandibles, antennae, part of the pronotum before the collar (neck) and feet black”. In a key, Mayr (1870) again described P. rastratus as, “red except for black mandibles, antennae and legs, the ends of the tarsi brown, and the metanotum with two small spines which are longer than broad at the base”. These two descriptions coincided, but the description in his next paper ( Mayr, 1887) conflicted with the two previous papers, indicating “black or red, mandibles, antennae, and legs red-brown or black-brown ”. The conflicting description of color appears to have resulted from Mayr believing that fine, longitudinal striae on the first gastral tergum diagnosed P. rastratus . As such, the conflicting description of color in Mayr (1887) appears to have resulted in his placing P. carbonarius (the holotype is concolorous black with fine, dense, longitudinal striae on the first gastral tergum) as a junior synonym of P. rastratus without explanation (see also Kusnezov, 1951). This interpretation is supported by the labels on syntype workers of P. rastratus —one of which was determined to be a syntype of P. carbonarius because the locale on the label “Pampa del Sur” is the type locality for P. carbonarius (see discussion under P. carbonarius ).

The second problem arose because neither Forel nor Kusnezov examined syntypes of P. rastratus . Consequently, Kusnezov based his concept of P. rastratus on specimens from Alto Pencoso, San Luis Province, Argentina, that Forel had misidentified as P. rastratus . These specimens were actually those of the undescribed species P. propinqua (see above). To his credit, Kusnezov (1951) was aware of possible problems with the identification noting that IFML contained “abundant material (more than 400 workers) from the type locality (surroundings of Mendoza) that do not correspond in all details to the original description of P. rastratus ”. This use of misidentified specimens also resulted in Kusnezov (1951) erroneously placing P. weiseri and P. weiseri var. neuquensis as junior synonyms of P. rastratus .

Lastly, Kusnezov (1951) appears to have misunderstood the type locality for P. rastratus . In his description of P. rastratus, Mayr (1868) indicated that the type locality was the area surrounding Mendoza, but explicitly stated that it was in the mountains near the city of Mendoza in a plain called Pampa de Canota–this plain is approximately 40 km northwest of the Mendoza at an elevation of approximately 3000 m. However, Kusnezov (1951) referred to the type locality as the “surroundings of Mendoza ”, even though he had quoted the locality from the original description (in Latin) in the previous paragraph. This misunderstanding created a problem because P. propinqua inhabits low desert areas surrounding the city of Mendoza, which is the area that Kusnezov assumed to be the type locality for P. rastratus . However, P. rastratus is a montane species that occurs at elevations well above those inhabited by P. propinqua .

Mayr (1887) described the male of P. rastratus from one specimen without workers, and he gave the collecting locale as “ Argentina ”. I did not find or examine this male, but the description given by Mayr does not match that of males collected from nest series by the author. All males collected from nest series had: (1) 3–4 teeth in contrast to 5 as described by Mayr, (2) rugae on the head anterior to the ocelli were longitudinal and regular, but the interrugae lacked the reticulations described by Mayr, (3) wavy to regular rugae were present on the thorax (= mesosoma), with none of the males displaying the rugoreticulate or granulate sculpture described by Mayr, and (4) wavy to regular transverse rugae covered the posterior surface of the petiolar node, with none of the males displaying the rugoreticulate sculpture described by Mayr. Thus, it is doubtful that Mayr (1887) described the male of P. rastratus .

Biology. Pogonomyrmex rastratus workers are solitary foragers. Nests of P. rastratus are located in open, exposed sites, under shrubs, and at the edge of rocks. Nests are most common in gravelly soils, but they also occur in loose, silty soils. The nest entrance consists of a tumulus that ranges from 5–15 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 on December 30, indicating that mating flights occur during the austral summer.

Pogonomyrmex rastratus appears to be restricted to the Pre-Cordillera at elevations that range from 2170–3045 m. This species occurs in the Southern Andean steppe and High Monte ecoregions as defined by Olson et al. (2001) ( Figure 78A ).

Figures

FIGURE 75. Photographs of Pogonomyrmex rastratus worker: (A) frontal view of head, (B) lateral view of body, and (C) dorsal view of body (CASENT0103268). Photographs by April Nobile from www.AntWeb.org.

FIGURE 76. Photographs of Pogonomyrmex rastratus alate queen: (A) frontal view of head, (B) lateral view of body, and (C) dorsal view of body (CASENT0922458). Photographs by Michele Esposito from www.AntWeb.org.

FIGURE 77. Photographs of Pogonomyrmex rastratus male: (A) frontal view of head, (B) lateral view of body, and (C) dorsal view of body (CASENT0172673). Photographs by April Nobile from www.AntWeb.org.

FIGURE 78. Geographic distribution of: (A) Pogonomyrmex rastratus, (B) P. sanmartini, and (C) P. santschii. The large black circle in each panel denotes the type locality.