Pogonomyrmex pichachen, 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 : 132-136

Pogonomyrmex pichachen NEW SPECIES

( Figures 63–64 )

Distribution—61C

Holotype worker [ MNNC: CASENT0922166 ]: CHILE, Bíobío: Bíobío Province, Rt Q-45 at Paso Pichachén , 37º27.2’S 71º07.4’W, 6750’ (2045 m), 22 February 2014 (R.A. Johnson #5244) . Paratypes, same data as holotype: IFML (3 workers) , LACM (6 workers) , MACN (12 workers) , MNNC (12 workers) , MCZC (6 workers) , RAJC (51 workers, 6 alate queens), UCDC (3 workers) , USNM (6 workers) .

Worker diagnosis. Workers of this species are uniquely characterized by the following combination of features: (1) striae on first gastral tergum extend over anterior one-third to one-half or more of segment, posterolateral margins mostly smooth and shining, (2) posterior surface of petiolar node and dorsum of postpetiole with transverse rugae, (3) head and gaster reddish-black to dark blackish-red, rarely reddish-orange, (4) longitudinal rugae on cephalic dorsum posterior to eyes irregular, often with secondary rugae, medioposterior margin with strongly irregular rugae to rugoreticulate, (5) interrugae on cephalic dorsum strongly granulate, dull, with a beaded appearance, (6) superior propodeal spines moderately long to long, length ranging from 0.3–0.6× the distance between their bases, and (7) restricted to the Patagonia region of Argentina and Chile ( Figure 63 ).

Measurements — holotype (n = 12 paratypes). HL 1.68 (1.47–1.69); HW 1.69 (1.48–1.73); MOD 0.39 (0.33– 0.38); OMD 0.39 (0.34–0.42); SL 1.27 (1.13–1.35); PNW 1.07 (0.98–1.17); HFL 1.49 (1.42–1.75); ML 1.97 (1.64– 1.98); PW 0.43 (0.37–0.47); PPW 0.59 (0.54–0.60). Indices: SI 75.15 (74.84–82.24); CI 100.60 (98.01–104.61); OI 23.08 (21.05–232.7); HFI 88.17 (95.95–108.07).

Description. Head subquadrate to quadrate (CI = 98.01–104.61), widest just posterior to eyes; posterior margin flat to weakly convex in full-face view. Longitudinal rugae on cephalic dorsum prominent, rugae posterior to eyes irregular, often with secondary rugae, medioposterior margin with strongly irregular rugae to rugoreticulate. In full-face view, medial rugae diverging or not diverging toward posterior corners of head. Interrugae on cephalic dorsum moderately to strongly granulate, weakly dull to dull, with a beaded appearance, medioposterior area sometimes entirely granulate; posterior corners rugose, interrugae smooth and shining to moderately granulate, weakly dull. Anterior margin of clypeus 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 0.21–0.24× HL. In profile, eyes situated slightly anterior to middle of head, OMD = 0.91–1.17× MOD. In full-face view, eyes protruding slightly beyond lateral margins of head. Antennal scapes (SI = 74.84–82.24) reaching posterior corners of head; scapes with longitudinal striae, weakly dull to weakly shining; basal flange well developed, flattened with carinate margin. Psammophore well developed.

Mesosomal profile weakly to moderately convex; all mesosomal surfaces with prominent irregular, subparallel-parallel rugae, often rugoreticulate on pronotal sides. In dorsal view, humeral shoulders of pronotum enlarged, anterolateral margins weakly to moderately angulate. Dorsum of promesonotum with weakly to strongly irregular longitudinal rugae that become strongly irregular to rugoreticulate on pronotum, or medial rugae occasionally continue to anterior margin of pronotum, lateral rugae diverge toward humeral shoulders of pronotum. Irregular rugae on pronotal sides traverse ventrally or posteroventrally or rugoreticulate; rugae on mesopleura angle posterodorsally; irregular transverse rugae on dorsum of propodeum traverse ventrally or anteroventrally on sides. Promesonotal suture usually present. Superior propodeal spines moderately long to long, length ranging from 0.3–0.6× the distance between their bases, spines connected by a well defined keel; inferior propodeal spines wider than high, apex broadly rounded. Propodeal spiracles narrowly ovate facing posterad. Interrugae on mesosoma weakly to strongly granulate, dull to weakly shining. Legs smooth and shining to weakly coriarious, weakly shining to shining.

Peduncle of petiole about 0.8× long as petiolar node, anteroventral margin with moderately to well developed rounded process that narrows posterad and continues subparallel-parallel to dorsal margin of peduncle of petiole. In profile, posterior surface of petiolar node weakly convex; node asymmetrical with anterior surface notably shorter than posterior surface, apex subangulate to angulate. In dorsal view, petiolar node longer than wide, widest near spatulate anterior margin, narrowing posterad. Posterior surface of petiolar node with regular to irregular, transverse to arcuate rugae. Dorsum of postpetiole convex in profile; in dorsal view, widest at or near posterior margin, narrowing to anterior margin, maximum width and length about equal. Transverse to oblique, regular to irregular rugae on dorsum of postpetiole finer, denser than those on posterior surface of petiolar node; interrugae on both surfaces smooth and shining to weakly coriarious, weakly shining. First gastral tergum with striae over anterior one-third to one-half or more of segment, posterior margin smooth and shining to moderately coriarious, weakly dull; posterolateral margins smooth and shining.

Erect, short to medium-length, white 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 white setae. Mesosoma, petiolar node, postpetiole, gastral terga with moderately dense, erect, white setae, longest on mesosoma and petiolar node about 0.8× MOD. Head reddish-black to dark blackish-red, rarely reddish-orange; mesosoma black, rarely with a faint reddish infusion anterad; anterior portion of first gastral tergum dark brown to blackish or black, becoming lighter posterad, color of other terga similar to posterad portion of first gastral tergum with a darker transverse band along posterior margin of terga; antenna, mandibles, and legs blackish to black, mandibles often with reddish infusion ( Figure 63 ).

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) striae extend over more than anterior one-half of first gastral tergum, medioposterior one-quarter to one-third or more of first gastral tergum (including posterolateral margins) smooth and shining, (3) head dark reddish-black to blackish red; mesoscutum, mesoscutellum, axillae, pronotal sides, anepisternum black, (4) in posterodorsal view, posterior corners rugose, interrugae granulate-punctate, dull, (5) medial rugae along posterior margin of head strongly irregular to rugoreticulate, and (6) transverse or oblique rugae cover posterior surface of petiolar node and dorsum of postpetiole ( Figure 64 ).

Measurements —(n = 7 paratypes). HL 1.51–1.66; HW 1.61–1.70; MOD 0.34–0.37; OMD 0.33–0.43; SL 1.18–1.39; PNW 1.20–1.30; HFL 1.64–1.76; ML 1.97–2.33; PW 0.41–0.48; PPW 0.66–0.69. Indices: SI 71.76– 82.74; CI 99.38–111.26; OI 20.24–22.22; HFI 98.80–106.21.

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 = 99.38–111.26), widest just posterior to eyes, posterior margin flat to weakly convex. Longitudinal rugae on cephalic dorsum prominent, wavy to strongly irregular. In full-face view, medial rugae diverging toward posterior corners of head; medial rugae along posterior margin of head strongly irregular to rugoreticulate-vermiculate; posterior corners rugose; interrugae on cephalic dorsum and posterior corners moderately to strongly granulate-punctate, weakly dull to dull, usually with a beaded appearance. Mandibles with six teeth, dorsal surface coarsely rugose. Psammophore well developed.

All mesosomal surfaces except pronotal sides with regular to wavy, subparallel-parallel, rugae, becoming irregular to rugoreticulate on pronotal sides; interrugae smooth and shining to weakly granulate-punctate, weakly shining; superior propodeal spines moderately long, bluntly acuminate, length> 0.5× the distance between their bases; inferior propodeal spines wider than tall, apex broadly rounded to subangulate, height less than length of superior spines. Peduncle of petiole long, anteroventral margin with a weak to moderate sized, broadly rounded triangular process. 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 to oblique 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 petiole and dorsum of postpetiole weakly granulate-punctate, weakly shining. Striae extend over anterior one-half or more of first gastral tergum, medioposterior one-quarter to one-third or more of first gastral tergum (including posterolateral margins) smooth and shining. Most body surfaces with moderately abundant suberect to erect, medium-length, whitish setae, one to two longer hairs along posterior margin of head approach to exceed MOD. Head dark reddish-black to blackish red; mesoscutum, mesoscutellum, axillae, first gastral tergum dark brownish-black; rest of body black ( Figure 64 ).

Male. Unknown.

Additional material examined. None.

Etymology. The specific epithet, pichachen , is derived from the type locality, Paso Pichachén, which is at the border of Chile and Argentina.

Discussion. Pogonomyrmex pichachen is distinguished from all congeners by: (1) first gastral tergum with striae over anterior one-third to one-half or more of segment, posterolateral margins smooth and shining, (2) head and gaster reddish-black to blackish-red, rarely reddish-orange; mesosoma black, (3) longitudinal rugae on cephalic dorsum posterior to eyes irregular, often with secondary rugae, medioposterior margin with strongly irregular rugae to rugoreticulate, (4) interrugae on cephalic dorsum strongly granulate, dull, with a beaded appearance, (5) superior propodeal spines moderately long to long, length> 0.3–0.6× the distance between their bases, and (6) occurring in the Patagonia region.

Biology. Little is known about the biology of P. pichachen other than that workers are solitary foragers. Partial excavation of the type nest indicated that colonies contain at least 1000–2000 workers. The type nest was under a stone in sparsely vegetated alpine habitat with scattered large rocks; soil consisted of a mixture of lava tuff and coarse gravelly soil. Sexuals (alate queens only) were collected on February 22, indicating that mating flights occur during the austral summer.

Pogonomyrmex pichachen appears to be a mid-elevation species, with the type colony occurring at an elevation of 2045 m. Pogonomyrmex pichachen undoubtedly occurs in both Argentina and Chile given that the type colony was collected along their border. This species occurs in the Valdivian Temperate forests ecoregion, as defined by Olson et al. (2001) ( Figure 61C ).

Figures

FIGURE 61. Geographic distribution of: (A) Pogonomyrmex maulensis, (B) P. meridionalis, and (C) P. pichachen. The large black circle in each panel denotes the type locality.

FIGURE 63. Photographs of Pogonomyrmex pichachen holotype worker: (A) frontal view of head, (B) lateral view of body, and (C) dorsal view of body (CASENT0922166). Photographs by Michele Esposito from www.AntWeb.org.

FIGURE 64. Photographs of Pogonomyrmex pichachen paratype alate queen: (A) frontal view of head, (B) lateral view of body, and (C) dorsal view of body (CASENT0922171). Photographs by Michele Esposito from www.AntWeb.org.