Pogonomyrmex santschii, Johnson, 2021

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 : 172-177

Pogonomyrmex santschii NEW SPECIES

( Figures 84–86 )

Distribution—78C

Holotype worker [ MACN: CASENT0281099 ]: ARGENTINA, Mendoza: Departamento Malargüe, Rt 45 at 54.7 km W Bardas Blancas, 35º55.8’S 70º12.9’W, 6060’ (1835 m), 25 January 2008 (R.A. Johnson #4109) . Paratypes, same data as holotype: IFML (6 workers) , LACM (6 workers) , MACN (9 workers) , MCZC (3 workers) , MNNC (6 workers) , RAJC (17 workers) , UCDC (3 workers), USNM (3 workers) . Additional paratype series from the same locality and date–RAJ #4108: IFML (2 workers, 3 alate queens, 3 males), ( MACN (3 workers, 3 alate queens, 9 males), MCZC (3 workers, 3 males), RAJC (7 workers, 6 alate queens, 14 males).

Worker diagnosis. Workers of this species are uniquely characterized by the following combination of features: (1) first gastral tergum smooth and shining or striae present along base to extending over anterior one-third of segment, striae rarely extending over anterior one-half of segment; posterior margin smooth and shining, (2) head and gaster ferruginous orange to reddish-orange; mesosoma black, occasionally with a weak orangish to reddish infusion on pronotum, infusion rarely present on mesonotum, (3) superior propodeal spines long, length> 0.6× the distance between their bases, (4) posterior surface of petiolar node and dorsum of postpetiole with transverse rugae, (5) interrugae on cephalic dorsum strongly granulate, dull, with a beaded appearance, and (6) rugae on frontal lobes subparallel-parallel, medial rugae usually continuing onto frontal triangle ( Figure 84 ).

Measurements — holotype (n = 12). HL 1.52 (1.41–1.76); HW 1.60 (1.34–2.02); MOD 0.35 (0.33–0.41); OMD 0.35 (0.32–0.47); SL 1.19 (1.16–1.38); PNW 1.05 (0.91–1.24); HFL 1.63 (1.41–1.81); ML 1.88 (1.63–2.11); PW 0.38 (0.34–0.44); PPW 0.54 (0.49–0.65). Indices: SI 74.37 (67.33–86.57); CI 105.26 (94.81–119.53); OI 21.87 (19.80–26.28); HFI 101.87 (89.60–106.85).

Description. Head subquadrate to wider than long (CI = 94.81–119.53), widest just posterior to eyes; posterior margin flat in full-face view. Longitudinal rugae on cephalic dorsum prominent. In full-face view, medial rugae diverging toward posterior corners of head; interrugae strongly granulate, dull, with a beaded appearance. Posterior corners rugose, interrugae weakly granulate, weakly shining to smooth and shining. Anterior margin of clypeus moderately concave, dorsum with numerous subparallel, longitudinal rugae. Numerous long, curved, bristle-like, cream to light yellowish macrochaetae project from anterior margin of clypeus and basolateral margin of mandibles. Mandibles with six teeth; mandibular dorsum coarsely rugose. MOD ranging from 0.20–0.26× HL. In profile, eyes situated slightly anterior to middle of head, OMD = 0.88–1.21× MOD. In full-face view, eyes protruding slightly beyond lateral margins of head.Antennal scapes relatively long (SI = 67.33–86.57), reaching posterior corners of head or failing to do so by less than length of basal funicular segment. Antennal scapes with weak longitudinal striae, interstriae weakly shining; basal flange well developed with carinate margin. Psammophore well developed.

Mesosomal profile flat to weakly convex; all mesosomal surfaces with prominent subparallel-parallel, irregular rugae. In dorsal view, humeral shoulders of pronotum enlarged, weakly to moderately angulate. Dorsum of promesonotum with irregular, sometimes branching, longitudinal rugae; pronotum rugoreticulate or mesonotal rugae diverge anterad toward humeral shoulders of pronotum, medial rugae diverge weakly and continue to anterior margin of pronotum, rugae on anteromedial portion of pronotum strongly irregular to rugoreticulate; promesonotal suture weakly to moderately impressed. Irregular rugae on pronotal sides traverse ventrally or posteroventrally or rugoreticulate; rugae on mesopleura angle posterodorsally; irregular transverse rugae on propodeal dorsum traverse ventrally or anteroventrally on sides. Superior propodeal spines long, length> 0.6× the distance between their bases, tips bluntly acuminate, connected by well defined keel. Inferior propodeal spines wider than high, apex weakly rounded to bluntly acuminate. Propodeal spiracles narrowly ovate facing posterad. Interrugae on mesosoma weakly to strongly granulate-punctate, dull to weakly shining. Legs weakly shining to shining.

Peduncle of petiole about as long as petiolar node, anteroventral margin with a triangular, broadly rounded process that narrows along posterior margin, then continues posterad subparallel-parallel to dorsal margin of peduncle. In profile, posterior surface of petiolar node weakly convex; petiolar node asymmetrical with anterior surface shorter than posterior surface, apex angulate to weakly rounded. In dorsal view, petiolar node longer than wide, widest near rounded anterior margin, narrowing posterad. Sides and posterior surface of petiolar node with regular to irregular transverse rugae. Dorsum of postpetiole convex in profile; in dorsal view, widest near posterior margin, narrowing anterad, maximum width and length about equal. Transverse rugae on dorsum of postpetiole finer, denser than those on posterior surface of petiolar node; interrugae on both surfaces weakly to moderately granulate-punctate, weakly shining to smooth and shining. First gastral tergum smooth and shining or striae present along base to extending over anterior one-third of segment, striae rarely extending over anterior one-half of segment; rest of segment smooth and shining

Erect white pilosity moderately abundant on head, mostly similar in length, most hairs 0.2–0.4× MOD. Moderately abundant suberect to semidecumbent pilosity on scapes; abundant decumbent hairs on funicular segments. Legs with moderately abundant suberect to decumbent whitish to light yellowish setae. Head, petiole, postpetiole, gastral terga with moderately dense, erect whitish to yellowish setae that are similar in length, most hairs> 0.5× MOD. Head and gaster light to dark ferruginous orange to reddish-orange, gaster sometimes slightly darker than head; mesosoma, petiole, postpetiole black, pronotum occasionally with a weak orangish to reddish infusion, infusion rarely present on mesonotum ( Figure 84 ).

Queen diagnosis. Queens of this species are diagnosed by the following combination of features: (1) castespecific morphology of the mesosoma related to wing-bearing and presence of ocelli on head, (2) fine striae cover more than anterior one-half of medial portion of first gastral tergum, (3) in profile, posterolateral and lateral margins of first gastral tergum smooth and shining; in profile, striae not visible or visible over a very limited part of more medial portions of segment, (4) head and gaster light to dark ferruginous orange to reddish-brown; pronotum, mesopleura, propodeum blackish to black; anterior and lateral portions of mesoscutum blackish to black, central and posteromedial portions of mesoscutum orangish-brown to reddish-brown, (5) superior propodeal spines moderately long, length approximately 0.3× the distance between their bases, (6) relatively small (HW = 1.43–1.87 mm; PNW = 1.15–1.42 mm; ML = 1.89–2.55 mm), (7) in posterodorsal view, medial rugae on cephalic dorsum continue to near posterior margin before diverging to posterior corners of head, (8) in posterolateral view, posterior margin of head with mostly longitudinal, regular to weakly irregular rugae that lack short lateral branches, and (9) transverse or oblique rugae cover posterior surface of petiolar node and dorsum of postpetiole ( Figure 85 ).

Measurements —(n = 12). HL 1.37–1.63; HW 1.43–1.75; MOD 0.30–0.37; OMD 0.33–0.39; SL 1.00–1.26; PNW 1.15–1.42; HFL 1.39–1.72; ML 1.89–2.36; PW 0.42–0.51; PPW 0.60–0.77. Indices: SI 66.89–79.74; CI 99.32–107.36; OI 20.27–24.50; HFI 93.92–106.85.

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 wider than long (CI = 99.32–107.36), broadest just posterior to eyes, posterior margin flat. Longitudinal rugae on cephalic dorsum prominent, wavy; interrugae moderately to strongly granulate, with a beaded appearance, dull to weakly shining; cephalic dorsum posterior to ocelli with regular rugae that usually lack short lateral branches; in full-face view, medial rugae not diverging to weakly diverging toward posterior corners of head; in posterolateral view, posterior margin of head with up to several regular medial rugae that traverse to posterior corners; posterior corners rugose, interrugae moderately granulate, weakly shining to smooth and 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 strongly irregular to rugoreticulate on pronotal sides; interrugae weakly to moderately granulate-punctate, weakly shining; superior propodeal spines medium-long, as long as to slightly longer than width at base, length approximately 0.3× the distance between their bases, tips bluntly acuminate; inferior propodeal spines wider than tall, apex rounded to angulate. Peduncle of petiole long, ventral surface flat or with a very weak, broadly rounded expansion. In profile, petiolar node asymmetrical with anterior surface shorter than posterior surface, apex subangulate to angulate. Posterior surface of petiolar node with wavy transverse rugae. In dorsal view, postpetiole slightly wider than long, dorsum with wavy, transverse rugae that are finer, denser than those on posterior surface of petiolar node; interrugae on posterior surface of petiolar node and dorsum of postpetiole weakly granulate-punctate, weakly shining. Fine striae cover more than anterior one-half of medial portion of first gastral tergum; in profile, posterolateral and lateral margins of first gastral tergum smooth and shining; in profile, striae not visible or visible over a very limited part of more medial portions of segment. Most body surfaces with moderately abundant suberect to erect, medium-length whitish setae, numerous hairs on head, mesosoma, and gaster> 0.3–0.4× MOD. Head and gaster light to dark ferruginous orange; mesopleura, propodeum blackish to black; anterior and lateral portions of mesoscutum blackish to black, often with an orangish tint ( Figure 85 ).

Male diagnosis. Males of this species are diagnosed by the following combination of features: (1) first gastral tergum lacking striae, (2) head dark brown; gaster dark ferruginous orange; mesosoma black, occasionally with a brownish infusion anterad, (3) erect hairs lacking on first gastral tergum, (4) in profile, longest hairs along posterolateral margin of first gastral tergum> 0.5× as long to approaching length of longest hairs on first gastral sternum, and (5) notauli absent ( Figure 86 ).

Measurements —(n = 12). HL 0.98–1.28; HW 1.14–1.28; MOD 0.42–0.47; SL 0.31–0.42; HFL 1.30–1.63; ML 1.82–2.32; PW 0.37–0.52; PPW 0.63–0.71. Indices: SI 24.22–34.43; CI 102.52–120.75; OI 34.43–40.35; HFI 106.56–139.47.

Additional material examined. ARGENTINA: Mendoza: 4.5 km NE Las Leñas , 7680’, Dec 6, 2003 ( CASC; MCZC; RAJC) ; eastern peak of Valle Hermosas , 8700’, Dec 6, 2003 ( RAJC) ; Valle Hermosas , 7430’, Dec 6, 2003 ( RAJC) . CHILE: Maule: Rt 115 at 0.6 km W Paso Pehuenche, 8320’, Mar 3, 2014 ( RAJC) ( Figure 78C ).

Etymology. This species is named to honor Dr. Felix Santschi, who was one of the most prolific ant taxonomists. Santschi described more South American forms of Pogonomyrmex (17) than any other person.

Discussion. Pogonomyrmex santschii might occur with several P. rastratus -group species. This species might be confused with several species because striae can be present or absent on the first gastral tergum. For workers lacking striae on the first gastral tergum, P. santschii is diagnosed by having head and gaster ferruginous orange, mesosoma black, occasionally with a weak orangish to reddish infusion on pronotum, infusion rarely present on mesonotum. Pogonomyrmex araucania , P. intermedia , P. maulensis , P. spinolae might be confused with P. santschii , but all of these species have a lighter reddish to reddish-brown mesosoma. For workers with striae on the first gastral tergum: (1) head and gaster ferruginous orange, mesosoma black, and (2) striae on first gastral tergum occur along base to extending over anterior one-third of segment, striae rarely extending over anterior one-half of segment, posterior margin usually smooth and shining. The only species with these characters are P. bolivianus and P. vermiculatus . Pogonomyrmex santschii is separated from P. bolivianus by: (1) superior propodeal spines long, length> 0.6× the distance between their bases, (2) inferior propodeal spines taller than length of superior propodeal spines, and (3) mesosoma blackish to black. In P. bolivianus : (1) superior propodeal spines consist of denticles to short triangular teeth with height less than width at their base, (2) in profile, inferior propodeal spines taller than length of superior propodeal spines, and (3) mesosoma dark ferruginous orange to orangish-brown. Pogonomyrmex santschii is separated from P. vermiculatus by its ferruginous orange head and gaster. In P. vermiculatus , the head is dark red to reddish-black and the gaster black.

Biology. Pogonomyrmex santschii workers are solitary foragers. Nests of P. santschii most commonly are placed under a rock or in a clump of Stipa sp. (Poaeceae) or other shrub. The nest entrance ranges from a hole in the ground to a tumulus up to 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 January 25, indicating that mating flights occur during the austral summer.

Pogonomyrmex santschii occurs at elevations from 1835–2635 m, near the border of Chile and Argentina, and it occurs in the Southern Andean steppe and Valdivian temperate forests ecoregions, as defined by Olson et al. (2001) ( Figure 78C ).

Figures

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.

FIGURE 84. Photographs of Pogonomyrmex santschii holotype worker: (A) frontal view of head, (B) lateral view of body, and (C) dorsal view of body (CASENT0281099). Photographs by Shannon Hartman from www.AntWeb.org.

FIGURE 85. Photographs of Pogonomyrmex santschii paratype alate queen: (A) frontal view of head, (B) lateral view of body, and (C) dorsal view of body (CASENT0922093). Photographs by Michele Esposito from www.AntWeb.org.

FIGURE 86. Photographs of Pogonomyrmex santschii paratype male: (A) frontal view of head, (B) lateral view of body, and (C) dorsal view of body (CASENT0281106). Photographs by Shannon Hartman from www.AntWeb.org.