Pseudomyrmex subtilissimus

Identification
A moderately elongate head (broader than Pseudomyrmex tenuissimus, more elongate than Pseudomyrmex spiculus and Pseudomyrmex villosus), short petiole, and light brown color (with banded gaster) characterize P. subtilissimus (Ward 1989).

Distinguishable from all other acacia-associated Pseudomyrmex by its small size (HW < 0.60), elongate head (CI < 0.66), apedunculate petiole, and scarcity of standing pilosity (Ward 1993).

Distribution
Costa Rica and Nicaragua.

Distribution based on Regional Taxon Lists
Neotropical Region: Costa Rica, Mexico, Nicaragua.

Biology
Ward (1989) - This species has been collected only in, or on, swollen-thorn acacias, in association with Pseudomyrmex flavicornis (F. Smith). The collection records suggest that it is an obligate, non-aggressive acacia ant which somehow manages to coexist with P. flavicornis.

Nomenclature

 *  subtilissimus. Pseudomyrma subtilissima Emery, 1890b: 65, pl. 6, fig. 7 (w.q.) COSTA RICA. [Also described as new by Emery, 1894k: 53.] Combination in Pseudomyrmex: Kempf, 1972a: 224. See also: Ward, 1989: 432; Ward, 1993: 161.

Worker
measurements (n=17, except for FI where n=16). - HL 0.86-0.95, HW 0.55-0.59, MFC 0.020-0.032, CI 0.60-0.65, OI 0.52-0.59, REL 0.49-0.54, REL2 0.80-0.87, OOI 0.38-0.89, VI 0.79-0.88, FCI 0.035-0.055, SI 0.41-0.47, SI2 0.50-0.57, FI 0.44-0.53, POI 1.60-1.88, MPI 0.015-0.039, NI 0.52-0.66, PLI 0.65-0.75, PWI 0.56-0.68, PPWI 1.18-1.35.

diagnosis. - Similar to Pseudomyrmex spiculus (q.v.) except as follows: smaller, head more elongate (HW 0.55-0.59, CI 0.60-0.65), eyes shorter, not reaching the level of the median ocellus (REL 0.49-0.54); basal face of propodeum flatter, meeting the decIivitous face at a more distinct angle; petiole shorter, higher (PLI 0.65-0.75). Most of body uniformly light brown; gaster dark brown, with contrasting light brown band on anterior half of abdominal tergite IV.

Type Material
Syntype workers, one dealate queen, Alajuela, Costa Rica (Alfaro) [Examined]. One syntype worker here designated as LECTOTYPE.