Pogonomyrmex meridionalis, Kusnezov, 1951

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 : 129-132

Pogonomyrmex meridionalis

( Figure 62 )

Distribution—61B

Pogonomyrmex meridionalis Kusnezov, 1951: 277 (worker). Holotype worker examined [IFML]. ARGENTINA, Santa Cruz: Bajo Caracoles, #5857 (N. Kusnezov leg.).

Worker diagnosis. Workers of this species are uniquely characterized by the following combination of features: (1) first gastral tergum lacking striae, moderately to strongly coriarious anterad, dull to weakly shining, (2) head and mesosoma blackish to black, gaster light to dark ferruginous orange, (3) longitudinal rugae on cephalic dorsum widely spaced, irregular, (4) rugae on pronotum weak to moderately coarse, (5) medial rugae on mesonotum usually continue to anterior margin of pronotum, and (6) in dorsal view, promesonotal suture usually weakly to moderately impressed ( Figure 62 ).

Measurements — n = 12. HL 1.63–1.88; HW 1.76–2.06; MOD 0.39–0.45; OMD 0.40–0.051; SL 1.20–1.48; PNW 1.12–1.27; HFL 1.68–1.97; ML 1.88–2.18; PW 0.41–0.48; PPW 0.57–0.66. Indices: SI 64.50–73.68; CI 103.89–120.83; OI 20.41–22.83; HFI 90.43–100.00.

Redescription. Head subquadrate to wider than long (CI = 103.89–120.83), widest just posterior to eyes; posterior margin flat in full-face view. Longitudinal rugae on cephalic dorsum prominent, widely spaced, wavy to irregular. In full-face view, medial rugae diverging toward posterior corners of head. In profile, rugae along dorsal margins of eyes continue posterad, usually converging with more medial rugae anteromedially to posterior corners, rugae along posterior and ventral margin of eyes not converging at posterior corners but rather continue medially over posterior margin. Interrugae on cephalic dorsum strongly granulate, dull to weakly shining; posterior corners rugose, interrugae weakly coriarious, weakly shining to smooth, strongly shining. Anterior margin of clypeus concave; dorsal surface with numerous subparallel, longitudinal rugae. Numerous long, curved, bristle-like, yellowish ammochaetae project from anterior margin of clypeus and basolateral margin of mandibles. Mandibles with six teeth; mandibular dorsum coarsely rugose. MOD ranging from 0.21–0.27× HL. In profile, eyes situated slightly anterior to middle of head, OMD = 1.00–1.28× MOD. Antennal scapes relatively short (SI = 64.50–73.68), failing to reach posterior corners by 0.5–1.0× length of basal funicular segment, strongly striate, interstriae weakly shining. Basal flange of scape moderately well developed with carinate margin. Psammophore well developed.

Mesosomal profile weakly convex; all mesosomal surfaces with prominent rugae. In profile and dorsal views, humeral shoulders of pronotum weakly enlarged, dorsolateral margin rounded. Dorsum of promesonotum with moderately coarse, irregular, longitudinal rugae that continue to anterior margin of pronotum, pronotal sides with subparallel, wavy to irregular rugae. Promesonotal suture usually weakly to moderately impressed. Mesopleura with wavy to irregular rugae angling posterad to posterodorsally, sometimes continuing onto sides of propodeum. Dorsum of propodeum with irregular longitudinal rugae to rugoreticulate. Superior propodeal spines long, length> 0.6× the distance between their bases; spines connected by weakly defined keel; tips blunt to acuminate. Inferior propodeal spines triangular, wider than tall, apex weakly rounded to angulate. Propodeal spiracles narrowly ovate facing posterad. Mesosomal interrugae moderately to strongly granulate, dull to weakly shining. Legs weakly coriarious, weakly shining to smooth and shining.

Peduncle of petiole about as long as petiolar node, anteroventral margin flat or with a weakly developed, broadly rounded process that continues posterad more or less parallel to dorsal margin of peduncle. In profile, posterior surface of petiolar node weakly convex; node asymmetrical with anterior surface notably shorter than posterior surface, apex angulate. In dorsal view, petiolar node longer than wide, narrowest at posterior margin, gradually widening to spatulate anterior margin; dorsum and sides with moderately coarse, irregular, transverse, or arcuate rugae to rugoreticulate. Dorsum of postpetiole convex in profile; in dorsal view, widest near posterior margin, narrowing to rounded anterior margin; maximal width about equal to length; dorsum and sides with wavy to irregular, transverse rugae that are finer, denser than those on posterior surface of petiolar node, interrugae on both surfaces moderately granulate, weakly shining. Anterior one-third to two-thirds of first gastral tergum moderately to strongly coriarious, dull, posterior portion smooth and strongly shining to weakly coriarious, weakly shining.

Erect, short to medium length, whitish pilosity moderately abundant on head. Moderately abundant suberect to decumbent pilosity on scape, abundant decumbent hairs on funicular segments. Legs with moderately abundant semidecumbent white setae. Mesosoma, petiolar node, postpetiole, gastral terga with dense, erect setae, mostly similar in length, longest usually approaching MOD. Head, mesosoma, petiolar node black; postpetiole orangishblack to blackish-orange; gaster dark ferruginous orange ( Figure 62 ).

Queen. Unknown.

Male. Unknown.

Additional material examined. ARGENTINA: Chubut: Rt 20 at 25.2 km NW turnoff to Facundo, 1780’, Jan 28, 2011 ( IFML; LACM; MCZC; RAJC; UCDC; USNM); Cerro Dragón , 385 m, Jan 9–14, 2013 ( RAJC) ( Figure 61B ) .

Etymology. The specific epithet, meridionalis (Latin, from meridional –for southern) was undoubtedly derived from Kusnezov collecting the syntype worker in Santa Cruz Province, which is second most southern province in Argentina.

Discussion. The black head and mesosoma, dark ferruginous orange gaster, and lack of striae on the first gastral tergum separate P. meridionalis from all congeners except P. pronotalis and P. mendozanus . Pogonomyrmex meridionalis is separated from P. mendozanus based on: (1) longitudinal rugae on cephalic dorsum irregular, widely spaced, and (2) medial rugae on mesonotum usually continue to pronotal collar. In P. mendozanus , (1) longitudinal rugae on cephalic dorsum regular, narrow, subparallel, and deeply incised, and (2) medial rugae on mesonotum diverge toward humeral shoulders of pronotum, often with one to few transverse rugae along anterior margin of pronotum. Pogonomyrmex meridionalis is separated from P. pronotalis based on: (1) larger size (HW = 1.76–2.06 mm), (2) first gastral tergum moderately to strongly coriarious, dull to weakly shining anterad, (3) rugae on pronotum weak to moderately coarse, (4) medial rugae on mesonotum usually continue to anterior margin of pronotum, and (5) promesonotal suture usually weakly to moderately impressed; P. pronotalis is: (1) smaller (HW = 1.61–1.81 mm), (2) first gastral tergum weakly coriarious, weakly shining to smooth and strongly shining, (3) rugae on pronotum coarse, (4) medial rugae on mesonotum diverge or become transverse to rugoreticulate on pronotum but do not continue to anterior margin of pronotum, and (5) promesonotal suture usually absent.

Biology. Little is known about the biology of P. meridionalis other than that workers are solitary foragers. Partial nest excavations indicated that colonies probably contain about 500– 700 workers. The two nests located by the author were in sandy-gravelly soil and had a tumulus that was 10–15 cm in diameter. Pogonomyrmex meridionalis appears to be a lowland species that inhabits elevations from 385– 540 m. This species occurs in the Patagonian steppe ecoregion, as defined by Olson et al. (2001) ( Figure 61B ).

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 62. Photographs of Pogonomyrmex meridionalis worker: (A) frontal view of head, (B) lateral view of body, and (C) dorsal view of body (CASENT0914368). Photographs by Michele Esposito from www.AntWeb.org.