Pogonomyrmex stefani

An inhabitant of mesic lowland forests.

Identification
Johnson (2015) - Worker Within the P. sylvestris-group, the combination of: (1) six mandibular teeth, (2) eyes with hairs between ommatidia, (3) in profile, anterior margin of postpetiole not meeting helcium at a smooth, continuous angle, (4) in profile, procoxae transversely striate, (5) femur and tibiae smooth to weakly coriarious, weakly to moderately shining, and (6) medial clypeal region between antennal insertions with 9–12 fine, closely-spaced, longitudinal rugae, interrugae dull to weakly shining uniquely characterize this species.

Male This caste is diagnosed by: (1) first gastral tergum lacking striae, (2) small (HW < 1.10 mm; ML < 2.00 mm), (3) in dorsal view, posterior surface of petiolar node strongly coriarious, (4) in profile, petiolar node angulate, (5) pronotal sides granulate with a beaded appearance, (6) in profile, inferior propodeal spines broad, well-developed, acuminate or nearly so, and (7) notauli present. Note that males are unknown for Pogonomyrmex striatinodus and Pogonomyrmex sylvestris.

Pogonomyrmex stefani is the only P. sylvestris-group species known to occur in mesic lowland forests. The prominent transverse striae on the procoxae separate P. stefani from both P. striatinodis (procoxae sometimes very weakly striate, mostly smooth and shining) and P. sylvestris (procoxae imbricate, dull).

Pogonomyrmex naegelii is the only congener that might occur sympatrically with P. stefani, but the former species would occur in open, drier habitats than those occupied P. stefani. Pogonomyrmex stefani is distinguished from P. naegelii by: (1) hairs project from between the ommatidia, (2) an elongate, triangular postpetiole, and (3) in profile, the petiolar node is flattened to weakly convex with a crest or tooth on the anterior margin that is elevated above the posterior surface. Pogonomyrmex naegelii: (1) lacks hairs between the ommatidia, (2) the postpetiole is nearly globular with width and length similar, and (3) in profile, the petiolar node is convex and lacks a crest or tooth on the anterior margin.

Distribution based on Regional Taxon Lists
Neotropical Region: Venezuela.

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. striatinodis 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. striatinodis 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. striatinodis 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. striatinodis 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.

Nomenclature

 *  stefani. Pogonomyrmex stefani Lattke, 2006: 53, figs. 1  4 (w.m.) VENEZUELA.

Worker
Johnson (2015) - (n = 1 paratype). HL 1.29; HW 1.29; MOD 0.23; OMD 0.25; SL 1.02; PNW 0.89; HFL 1.38; ML 1.39; PW 0.29; PPW 0.42. Indices: SI 79.07; CI 100.00; OI 17.83; HFI 106.98. See also Lattke (2006).

Head quadrate (CI = 100.00), widest just posterior to eye; posterior margin weakly concave. Longitudinal rugae on cephalic dorsum coarse, wavy to irregular medially, becoming more irregular to rugoreticulate laterally. Cephalic interrugae moderately granulate-punctate, weakly shining. Anterior margin of clypeus weakly convex with very small medial tooth; dorsum between antennal insertions with 9-12 fine, closely-spaced, longitudinal rugae, interrugae dull to weakly shining. Mandible with six teeth; mandibular dorsum coarsely rugose. Up to several moderately long, curved, bristle-like, yellowish hairs project from anterior margin of clypeus. Eyes small, MOD = 0.18x HL. In profile, eyes situated anterior to middle of head, OMD = 1.09x MOD; several hairs project from between ommatidia. Antennal scapes long (SI = 79.07), surpassing vertex by less than width of basal funicular segment; entire scape with moderately coarse, longitudinal striae, dull to weakly shining. Basal flange of scape well-developed with carinate margin. Psammophore poorly-developed, consisting of numerous medium to long hairs scattered across ventral side of head.

Mesosomal profile strongly convex; all mesosomal surfaces with prominent rugae. Promesonotum with irregular longitudinal rugae medially, dorsum of propodeum with irregular transverse rugae, all other mesosomal surfaces rugoreticulate to vermiculate. Superior propodeal spines long, acuminate, bases connected by poorly-defined keel, spine length greater than distance between their bases. Inferior propodeal spines well-developed with broad triangular base, length less than 0.5x that of superior spines. Propodeal spiracles circular facing posterad. Interrugae on mesosoma weakly shining. In profile, procoxae with fine, subparallel, transverse striae. Legs smooth and shining to weakly coriarious, weakly shining.

Peduncle of petiole about 0.7x length of petiolar node; anteroventral margin with acuminate spine. In profile, posterior surface of petiolar node weakly convex; in profile, petiolar node asymmetrical with anterior surface slightly less than one-half the length of posterior surface, apex forming a bluntly tipped crest or tooth elevated above posterior surface; sides with wavy to irregular longitudinal rugae, posterior surface weakly rugoreticulate. In dorsal view, petiolar node elongate (length >1.90x width), sides subparallel, anterior portion narrowing to subangulate tip; interrugae with weaker secondary rugae, weakly shining. Dorsum of postpetiole convex in profile, anterior margin truncate, not meeting helcium at a smooth, continuous angle; robust in dorsal view, trapezoidal, widest near posterior margin, narrowing to rounded anterior margin; lateral margins wider ventrally at posterior margin; dorsum smooth and strongly shining to very weakly coriarious, shining. First gastral tergum smooth and strongly shining to weakly coriarious, shining.

Long, flexuous, yellowish to golden 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 to semidecumbent setae. Head, antennae, mesosoma, petiolar node, and postpetiole dark brown; mandibles, legs, and gaster brown.

Male
Johnson (2015) - (n = 1). HL 1.04; HW 1.01; MOD 0.43; OMD 0.14; SL 0.24; HFL 1.27; ML 1.88; PW 0.31; PPW 0.51. Indices: SI 23.76; CI 97.12; OI 42.57; HFI 125.74. See also Lattke (2006).