Pogonomyrmex species groups

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The following is based on Johnson, R.A. 2015. A taxonomic revision of South American species of the seed-harvester ant genus Pogonomyrmex (Hymenoptera: Formicidae). Part I. Zootaxa 4029: 1–142. doi:10.11646/zootaxa.4029.1.1

Pogonomyrmex bispinosus-group

Workers in the P. bispinosus-group are diagnosed by the following characters: (1) psammophore well-developed, (2) first gastral tergum lacking striae, (3) posterior surface of petiolar node with transverse rugae or rugoreticulate, and (4) dorsum of postpetiole lacking rugae. Queens have: (1) psammophore well-developed, (2) weak transverse, but usually incomplete rugae on dorsum of postpetiole, and (3) short, delicate hairs along the lateral margin of propodeal declivity.

Pogonomyrmex coarctatus-group

Workers in the P. coarctatus-group are diagnosed by the following characters: (1) first gastral tergum lacking striae, (2) large (HW = 1.97–3.99 mm), sometimes polymorphic, (3) numerous small, hair-bearing foveae scattered across cephalic dorsum (best viewed at > 50x magnification), (4) part to all of cephalic dorsum with very fine, dense, longitudinal striae, (5) antennal scapes short, extending less than one-third the distance from posterior margin of eye to posterior corner of head, and (6) posterolateral margin of head with a carina that is much coarser than rugae on cephalic dorsum. All of these characters also diagnose queens, which are larger than those of all South American congeners (HW = 2.91–4.06 mm).

Pogonomyrmex cunicularius group

Workers in the P. cunicularius-group are diagnosed by the following characters: (1) psammophore poorly-developed, consisting of short to medium-length hairs scattered across ventral side of head, (2) first gastral tergum lacking striae, (3) head elongate (CI < 90.0), (4) femur long (HFL > 2.05 mm; HFI > 118.0), (5) scapes long, surpassing posterior corners of head; entire scape with pronounced longitudinal striae, (6) eyes small, ranging from 0.15–0.19x HL, and (7) anterior margin of clypeus flat to weakly convex, apron lacking clypeal teeth.

Queens are diagnosed by: (1) ergatoid, with morphology similar to workers except for presence of ocelli and slightly larger size compared to workers, (2) psammophore poorly-developed, consisting of short to medium-length hairs scattered across ventral side of head, (3) first gastral tergum lacking striae, (4) mesosoma weakly to moderately enlarged, mesosomal segments fused, metanotal groove weakly to moderately impressed, (5) head elongate (CI < 94.0), and (6) femur long (HFI > 116.0).

Pogonomyrmex laticeps-group

Workers in the P. laticeps-group are diagnosed by the following characters: (1) first gastral tergum lacking striae, (2) head broader than long, (3) interrugae on cephalic dorsum and dorsum of mesosoma smooth to moderately coriarious, weakly shining to shining (granulation and/or punctation absent) or rugae incised, interrugae about as wide as rugae, (4) superior propodeal spines well-developed, and (5) inferior propodeal spines poorly-developed or lacking. The mostly smooth interrugae appear to be the best character to diagnose Pogonomyrmex laticeps and Pogonomyrmex tinogasta. All three species have brachypterous queens, diagnosed by: (1) poorly-developed mesoscutum, its anterior margin barely surpassing the humeral shoulders of pronotum, (2) pronotum enlarged, and (2) in profile, the pronotum rises at an approximately 45° angle to meet the mesoscutum.

Pogonomyrmex mayri-group

Pogonomyrmex mayri is a monotypic species-group in which all three castes are easily diagnosed. Workers are diagnosed by: (1) striae on first gastral tergum, (2) psammophore poorly-developed, consisting of numerous short hairs scattered across ventral side of head, (3) deeply incised sculpturing on head and mesosoma, (4) antennal scapes densely granulate-punctate with strongly flattened base, (5) superior and inferior propodeal spines long, acuminate, (6) posterior surface of petiolar node flattened, and (7) anterior margin of clypeus concave with a small medial tooth. Queens are diagnosed by: (1) ergatoid, with ocelli not visible or absent, (2) striae on first gastral tergum, (3) postpetiole enlarged (PPW > 1.20 mm), wider than long, (4) anterior clypeal margin with medial tooth, and (5) anterior surface of petiolar node striate.

Pogonomyrmex naegelii-group

Workers in the P. naegelii-group are diagnosed by the following characters: (1) first gastral tergum lacking striae or striae restricted to base or rarely extending beyond the base, (2) small (HW = 1.06–1.33 mm), (3) psammphore poorly-developed, consisting of short to medium-length hairs scattered across ventral side of head, (4) superior and inferior propodeal spines well-developed, inferior spines >0.5–1.0x length of superior spines, (5) in profile, ventral process of postpetiole large and bulbous, its height much greater than its length, and (6) concolorous tannish-brown, occasionally with blackish gaster. Queens in the P. naegelii-group are diagnosed by: (1) first gastral tergum lacking striae or with faint to moderately strong longitudinal striae near base that sometimes extend over anterior one-half of tergum, (2) small (HW < 1.30 mm), (3) psammophore poorly-developed, consisting of short to medium-length hairs scattered across ventral side of head, (4) inferior propodeal spines triangular, moderately to well-developed, (5) in profile, ventral process of postpetiole large and bulbous, its height much greater than its length (for only alate queens), (6) concolorous tannish-brown, occasionally with blackish gaster, and (7) anterior margin of clypeus flat.

Pogonomyrmex sylvestris-group

Workers in the P. sylvestris-group are diagnosed by the following characters: (1) first gastral tergum lacking striae, (1) anteroventral margin of peduncle of petiole with acuminate spine, (2) in dorsal view, postpetiole triangular, longer than wide, (3) superior and inferior propodeal spines long, (4) in dorsal view, petiolar node elongate; in profile, petiolar node flattened with crest at anterior margin that is elevated above posterior surface, (5) eyes small, situated anterior to middle of head, (6) psammophore poorly-developed, consisting of numerous short hairs scattered across ventral side of head, (7) mesosoma with several or more long, flexuous hairs, (8) propodeal spiracles circular, and (9) anterior margin of clypeus with medial tooth, sometimes very small, indistinct. Queens are unknown for all species; males are known for only Pogonomyrmex stefani.