Pheidole debilis

Pheidole debilis occurs in wet forest leaf litter. It is most often collected in Winkler samples of sifted litter but is rarely collected at baits. Major workers may occur together with minor workers in Winkler samples. One nest was collected in soil, and one nest was collected from rotten wood. (Longino 2009)

Identification
Longino (2009) - With the morphometric profile of Pheidole gnomus, Pheidole mera, Pheidole sparsisculpta, and Pheidole sospes. Minor worker: face foveolate with overlying rugulae versus face uniformly foveolate, without overlying rugulae (mera, sospes) or with extensive smooth areas (sparsisculpta); lateral pronotum foveolate versus with smooth shiny patch (mera); minor worker of gnomus unknown. Major worker: vertex lobes weakly sculptured with faint foveolate sculpture versus vertex lobes with pronounced transversely arcuate rugae (gnomus), or coarsely reticulate rugose (sospes), or completely smooth and shining (sparsisculpta); head in lateral view normally convex versus with pronounced medial bulge on face (gnomus); lacking antennal scrobe versus with shallow but distinct antennal scrobe (mera, sospes); promesonotal groove present versus promesonotum evenly arched, with no trace of promesonotal groove (mera).

In Costa Rica, minor workers of this species can be distinguished from the common Pheidole harrisonfordi by more pronounced rugulae on the face and mesosomal dorsum, the slightly impressed promesonotal groove, and the lack of any longer setae above the short, subdecumbent pilosity on the hind tibia. However, these distinctions do not hold over the broad concept of P. harrisonfordi as a whole (see Comments under P. harrisonfordi). Minor workers are distinguished from the similar Pheidole beloceps by the foveolate side of the pronotum (smooth and shiny on P. beloceps). Major workers are distinguished from P. beloceps by having a relatively broader head and having the scrobe foveolate (small shiny patches on P. beloceps).

Distribution
This species is mainly known from the Barva Transect in Braulio Carrillo National Park, on the Atlantic slope of Costa Rica. It is moderately abundant across a range of elevations, from La Selva Biological Station to 1500m. Minor workers tentatively assigned to this species have been collected elsewhere in Costa Rica: Hitoy Cerere, the Monteverde area, and the southern Pacific lowlands. A collection of minor workers in a Winkler sample from the Osa Peninsula also contained a major worker that matches the typical form in most respects, differing in the lack of any clypeal gibbosity or carina, and the presence of shiny patches on the antennal scrobes. (Longino 2009)

This taxon was described, and is only known, from Costa Rica.

Nomenclature

 *  debilis. Pheidole debilis Longino, 2009: 23, fig. 4 (s.w.) COSTA RICA.

Worker
Minor Measurements (paratype): HL 0.52, HW 0.49, HLA 0.17, SL 0.42, EL 0.09, ML 0.60, PSL 0.06, PMG 0.00, SPL 0.03, PTW 0.09, PPW 0.14, CI 93, SI 86, PSLI 11, PMGI 0, SPLI 6, PPI 152.

Measurements (n=13): HL 0.46-0.55, HW 0.42-0.49, SL 0.36-0.46, CI 88-93, SI 84-95.

Clypeus smooth with 1-3 longitudinal rugulae; eye small, with fewer than 10 ommatidia; face densely foveolate, overlain with reticulate rugulae; margin of vertex flattened with weak median impression; occipital carina narrow, not visible in full face view; scape with abundant subdecumbent to suberect setae, mostly shorter than maximum width of scape; promesonotal groove weakly impressed; propodeal spines present; entire mesosoma foveolate, overlain with faint reticulate rugulae on promesonotal dorsum; abundant setae on promesonotal dorsum; dorsal (outer) margin of hind tibia with short decumbent pilosity, no long erect setae; first gastral tergum smooth and shining; gastral dorsum with moderately abundant suberect setae; color variable, light to dark red brown.

Major Measurements (holotype): HL 1.13, HW 0.94, HLA 0.30, SL 0.48, EL 0.14, ML 0.81, PSL 0.06, PMG 0.02, SPL 0.06, PTW 0.19, PPW 0.38, IHT 0.18, OHT 0.41, CI 83, SI 51, PSLI 5, PMGI 2, SPLI 6, PPI 204, HTI 43.

Measurements (n=11): HL 0.92-1.15, HW 0.80-1.04, SL 0.42-0.52, CI 81-88, SI 50-56.

Mandibles smooth and shiny; clypeus smooth and shallowly concave, with shallow anterior notch, and very weak posteromedian gibbosity or carina; face with longitudinal rugulae on cheeks and between frontal carinae, grading to faint foveolate sculpture overlain with reticulate rugulae on scrobe, fading to very faint foveolate sculpture on posterior vertex lobes; scrobe a faint, unbounded impression; head with abundant suberect setae projecting from sides of head in face view; scape smooth and shining, terete at base, with subdecumbent pubescence and scattered longer suberect setae; hypostomal margin flat; median tooth small; inner hypostomal teeth pointed, stout, closer to midline than to outer hypostomal teeth; promesonotal groove impressed; propodeal spines present; mesosoma with a mix of foveolate, smooth, and rugulose sculpture; dorsal (outer) margin of hind tibia with short decumbent pilosity, no long erect hairs; pilosity abundant on mesosomal dorsum; first gastral tergite smooth and shining, with abundant flexuous erect setae; color orange brown.

Type Material
Holotype major worker. Costa Rica, Heredia: 16km SSE La Virgen, 10.26667°N 84.08333°W, ±2000m, 1100m, 15 Feb 2001 (R. Vargas#01-RVC-015), unique specimen identifier INB0003622662.

Paratypes: major and minor workers. Same data as holotype; same locality as holotype but 17 Nov 2000 (J. Longino#4361) [,, , , , , , ].

Etymology
The name is in reference to the faint sculpture on the face of the major worker, compared to P. harrisonfordi and other common litter ants that have more heavily sculptured major workers.