Pseudomyrmex hesperius Ward, 1993

Ward, Philip S., 1993, Systematic studies on Pseudomyrmex acacia-ants (Hymenoptera: Formicidae: Pseudomyrmecinae), Journal of Hymenoptera Research 2, pp. 117-168 : 157-158

Pseudomyrmex hesperius Ward , sp. nov.

(Fig. 4)

Holotype worker. - MEXICO Sinaloa: 15.9 mi. NE Concordia, Hwy. 40, 600m , 9.vi. 1967, D. H. Janzen XVIII, ex Acacia hindsii ( LACM). HW 0.66, HL 0.83, EL 0.36, PL 0.34, PH 0.26 .

Paratypes. - Same data as holotype: series of 11 workers ( BMNH, LACM, MCZC, MZSP, PSWC, USNM) .

Additional non-type material. - MEXICO Sinaloa: 14 km. S Mazatlan , 18. vii. 1965, R. R. Snelling, 15 workers ( LACM, MCZC, PSWC) .

Worker measurements (n=6). - HL 0.78-0.85, HW 0.65-0.69, MFC 0.028-0.043, Cl 0.79-0.83, REL 0.43-0.46, REL2 0.54-0.57, OOI 0.86-1.15, VI 0.75-0.82, FCI 0.043-0.062, SI 0.48-0.51, SI2 0.87-0.93,FI0.41-0.45,PDI 0.84-0.95, MPI 0.053- 0.066, NI 0.54-0.59, PLI0.73-0.77, PWI0.63-0.70, PPWI 1.41-1.56.

Worker diagnosis. - Small species (see above measurements) with elongate, subrectangular head and short eyes (REL 0.43-0.46, OI 0.61-0.65). Masticatory margin of mandible with five teeth, the fourth tooth (counting from the apex) separated by a gap of ca. 0.05 mm from the apicobasal tooth; MD8/MD9≈0.70; third and fourth teeth small, contrasting with the large subapical and apical teeth (the latter ca. 0.032 and 0.055 mm in length, respectively); mesial tooth on basal margin situated slightly closer to apicobasal tooth than to proximal tooth (MD 4/ MD 5≈0.65); palp formula 5,3; median clypeal lobe short, its anterior margin straight to weakly convex, sharply rounded laterally; minimum distance between frontal carinae subequal to or less than basal scape width; frontal carinae diverging anteriorly and fusing with the antennal sclerites; pronotum laterally rounded, without humeral angles; in lateral profile the mesonotum and basal face of propodeum slightly inclined anteriorly, separated by a well developed metanotal groove (Fig. 4); basal face of propodeum rounding into the longer declivitous face, the latter somewhat concave in profile; petiole short, apedunculate, shaped as in Fig. 4, with a prominent triangular anteroventral tooth; in dorsal view petiole very broad anteriorly (PWI 3 0.59-0.62); postpetiole broader than long, its anteroventral process small and inconspicuous. Mandibles finely striate; head punctulate on a smooth shining background, punctulae separated by one to several diameters on upper half of head, becoming denser towards the clypeus; mesosoma sublucid, with weak punctulate-coriarious sculpture; petiole, postpetiole and gaster shining, with very fine piligerous punctures. Standing pilosity common but short (<0.10 mm) on most parts of body, lacking on outer faces of tibiae. Appressed pubescence widely distributed, moderately dense on abdominal tergite IV. Dark brown; mandibles, appendages and fronto-clypeal complex tending towards a lighter brown.

Taxonomic comments. - This is a taxonomically isolated species, not belonging to any of the nine major species groups of Pseudomyrmex (see Ward 1989). The salient features of P. hesperius are small size (HW <0.72), reduced mandibular dentition and palp formula, short truncate median clypeal lobe, short eyes (especially obvious in lateral view, such that OI> 0.60), short apedunculate petiole with a broad attachment to the propodeum (PWI 3≈0.60), punctulate head sculpture, sublucid integument, and short standing pilosity. Some of these traits are shared with two other Mesoamerican Pseudomyrmex , P. fervidus (F. Smith) and a related undescribed species, but both of these are larger (HW> 0.70), with standing pilosity which is longer and more extensive (present on the outer faces of the tibiae).

Biology. - Although the type specimens of P. hesperius were collected from Acacia hindsii this species is not an obligate acacia inhabitant. The series from 14 km. south of Mazatlán was collected from dead branches of a woody plant, not Acacia (R. R. Snelling, pers. comm.).