Pogonomyrmex striatinodus

Known from high elevation cloud forest, little is know about the biology of P. striatinodus. (Fernandez and Palacio 1998).

Identification
Johnson (2015) - Within the P. sylvestris-group, the combination of: (1) seven mandibular teeth, (2) eyes lacking hairs between ommatidia, (3) clypeus with prominent medial carina, and (4) in profile, anterior margin of postpetiole meeting helcium at a smooth continuous angle uniquely characterize this species.

Pogonomyrmex striatinodus and Pogonomyrmex sylvestris are the only congeners known to inhabit midelevation mesic forests. Pogonomyrmex striatinodus is diagnosed by: (1) lack of hairs between ommatidia, (2) seven mandibular teeth, and (3) in profile, anterior margin of postpetiole meeting helcium at a smooth, continuous angle; Pogonomyrmex stefani has: (1) several hairs between ommatidia, (2) six mandibular teeth, and (3) in profile, the anterior margin of the postpetiole is truncate and does not meet the helcium at a smooth, continuous angle. Pogonomyrmex striatinodus is separated from P. stefani by its sometimes weakly striate procoxae and absence of hairs between ommatidia; in P. stefani, the procoxae have prominent transverse striae and hairs are present between the ommatidia.

Pogonomyrmex naegelii might occur in open, drier habitats proximate to areas occupied P. striatinodus. Pogonomyrmex striatinodus is distinguished from P. naegelii by: (1) an elongate, triangular postpetiole, (2) in profile, the petiolar node is flattened with a crest or tooth on the anterior margin that is elevated above the posterior surface, and (3) head and mesosoma with numerous, long, flexuous hairs (longest hairs >MOD). In P. naegelii: (1) the postpetiole is nearly globular with length and width similar, (2) in profile, the petiolar node is convex and lacks a crest or tooth on the anterior margin, and (3) head and mesosoma have numerous short, relatively stiff hairs (longest hairs shorter than MOD). Pogonomyrmex striatinodus might also occur in areas proximate to Pogonomyrmex theresiae; P. striatinodus lacks a well-developed psammophore and has long superior and inferior propodeal spines, whereas P. theresiae has a well-developed psammophore and lacks superior and inferior propodeal spines.

Distribution based on Regional Taxon Lists
Neotropical Region: Colombia, Ecuador.

Biology
Johnson (2015) - Very little is known about the biology of P. sylvestris-group species. All three species are discussed together because they likely share a similar biology. Stray foragers comprise most collections for these three species. Few nests have been located: nests of P. stefani consisted of a small exposed entrance (Lattke, 2006), one nest of P. sylvestris was in a rotten log (Lattke, 2006), and nests of P. striatinodus are unknown. Diet and the sexual castes are unknown (except for the male of P. stefani) for all three species.

The P. sylvestris-group and P. sylvestris-group are sister groups that together form a clade that is sister to all other Pogonomyrmex (C.S. Moreau & the author, unpub. data). Consequently, obtaining information on the biology of P. sylvestris-group species (including diet, colony size and structure, phenotype of males and especially queens) would facilitate understanding the early evolution of the genus; queens would be especially interesting to collect given that Pogonomyrmex mayri has ergatoid queens. It is predicted that biology of these species is similar to that of P. mayri, which suggests that colonies are small (no more than several hundred workers) and that their diet consists of mostly dead arthropods and plant parts, but relatively few seeds (Kugler, 1979, 1984; Kugler & Hincapie, 1983).

All three species are known to occur only in northern South America (Venezuela, Colombia, and Ecuador), and they comprise the small group of South American congeners that inhabit mesophilic forests. Pogonomyrmex sylvestris and P. striatinodus are mid-elevation species—P. sylvestris has been collected only in premontane cloud forest habitats of Venezuela at elevations from 1000–1300 m, and P. striatinodus is only known from mesic forests at elevations from 1000–1525 m. Pogonomyrmex sylvestris occurs in the La Costa Xeric Shrublands and Venezuelan Andes Montane Forest ecoregions, and P. striatinodus occurs in Northwestern Andean Montane Forest ecoregion as defined by Olson et al. (2001). Alternatively, P. stefani is only known from two locations in the mesic lowland forests at elevations from 165–470 m, and its geographic distribution may be restricted to the Orinoco watershed of Venezuela (Lattke 2006); it occurs in the Llanos and Pantepui ecoregions as defined by Olson et al. (2001). None of these three species are known to occur proximate to one another.

Castes
Known only from the worker caste.

Nomenclature

 *  striatinodus. Pogonomyrmex striatinodus Fernández & Palacio, 1998: 1650, figs. 1, 2 (w.) COLOMBIA.

Worker
Johnson (2015) - (n = 2 + 3 paratypes). HL 1.75–1.91; HW 1.58–1.68; MOD 0.28–0.32; OMD 0.37–0.42; SL 1.40–1.71; PNW 1.06–1.17; HFL 2.08–2.59; ML 2.20–2.34; PW 0.29–0.31; PPW 0.53–0.55. Indices: SI 88.05–103.01; CI 85.48–90.32; OI 16.67–19.28; HFI 130.82–156.97. See also Fernández and Palacio (1998).

Head elongate (CI = 85.48–90.32), widest just posterior to eye; posterior margin weakly concave. Cephalic dorsum, sides, and vertex rugoreticulate. Cephalic interrugae smooth, shining to strongly shining. Anterior margin of clypeus weakly convex with medial tooth that continues as a medial carina on dorsum of clypeus, dorsal surface with several subparallel, longitudinal rugae. Mandible with seven teeth; mandibular dorsum coarsely rugose. Up to several moderately long, curved, bristle-like, yellowish hairs project from anterior margin of clypeus. Eyes small, MOD = 0.15–0.17x HL. In profile, eyes situated anterior to middle of head, OMD = 1.19–1.45x MOD; no hairs project from between ommatidia. Antennal scapes long (SI = 88.05–103.01), surpassing vertex by slightly less than length of basal funicular segment; entire scape with moderately coarse, longitudinal striae, dull. Basal flange of scape well-developed with carinate margin. Psammophore poorly-developed, consisting of numerous short to moderately long hairs (similar in length to slightly shorter than those on cephalic dorsum) scattered across ventral side of head.

Mesosomal profile strongly convex; all mesosomal surfaces rugoreticulate to vermiculate. Superior propodeal spines long, acuminate, bases not connected by well-defined keel, spines about the same length as distance between their bases. Inferior propodeal spines well-developed, acuminate, length similar to that of superior spines but with a wider base. Interrugae on mesosoma smooth, shining. Propodeal spiracles circular facing posterad. In profile, procoxae with very weak, irregular to discontinuous transverse rugae, weakly shining. Legs moderately coriarious, weakly shining.

Peduncle of petiole about 0.4x length of petiolar node, anteroventral margin with acuminate spine. In profile, petiolar node asymmetrical with anterior surface approximately one-third the length of posterior surface, apex forming acutely tipped crest or tooth elevated above posterior surface; posterior surface flattened; anterior surface smooth and shining to moderately coriarious, weakly shining; lateral surface smooth and shining anterad, posterior one-half to two-thirds with coarse vertical rugae. In dorsal view, petiolar node elongate (length >2.70x width), weakly convex posterad, nearly vertical near center, and concave anterad, anterior one-third narrowing to subangulate tip; posterior surface with moderately coarse transverse rugae, interrugae weakly to moderately granulate-punctate, weakly shining. Dorsum of postpetiole convex in profile, anterior margin curving gradually to meet helcium at a smooth, continuous angle; in dorsal view, nearly triangular, widest near posterior margin, narrowing to nearly straight anterior margin; dorsum weakly coriarious, shining to smooth and strongly shining. First gastral tergum weakly coriarious, shining to smooth and strongly shining.

Short to long, flexuous, yellowish hairs abundant on head; medium to long hairs abundant on mesosoma, petiolar node, postpetiole, and gastral terga; longest hairs on head and mesosoma >MOD. Scape with abundant medium to long suberect hairs; abundant decumbent hairs on funicular segments. Legs with moderately abundant, long, suberect setae. Head and mesosoma dark reddish-brown to dark brown; petiolar node, postpetiole, legs, gaster slightly lighter orangish-brown.

Type Material
Johnson (2015) - Holotype worker UNCB (not examined). COLOMBIA, Nariño: Municipio de Barbacoas, Corregimiento de Altaquer, Reserva Natural Privada Río Ñambí, 1200–1400 m (Carlos Sarmiento leg., 14 July 1995). Paratypes examined, same data as holotype: 1 worker, 1 worker, , 1 worker , 2 workers.

Etymology
The specific epithet, striatinodis (from Latin—striare = striate, and nadus = node) refers to the transverse striae on the dorsolateral surfaces of the petiolar node.