Stenamma stictosomum, Branstetter, Michael G., 2013

Branstetter, Michael G., 2013, Revision of the Middle American clade of the ant genus Stenamma Westwood (Hymenoptera, Formicidae, Myrmicinae), ZooKeys 295, pp. 1-277 : 206-210

Stenamma stictosomum sp. n. Worker: Figures 157, 158; Map: Figure 159

Stenamma mgb47 Branstetter, 2012: phylogeny.

Type material.

Holotype worker. MÉXICO, Oaxaca: 20.6km SW Valle Nacional, 17.60404°N, 96.37786°W ± 60m, 1740m, 13 Aug 2009, cloud forest, ex sifted leaf litter (M. G. Branstetter, collection MGB1390) [USNM, specimen CASENT0605499]. Paratypes: same data as holotype [1w, UNAM, CASENT0605499], [1w, UCD, CASENT0605497].

Worker diagnosis.

Body color mostly black to dark brown, sometimes with a bluish glare in specimens with coarsely punctate sculpture; small- to medium-sized species (see HL, ML, PrW below); anterior clypeal margin broadly emarginate, with two blunt inner teeth (best viewed with mandibles open); basal margin of mandible sinuous, but without a basal notch or deep depression; setae on gastral tergites sparse, stout, and suberect, only sometimes with a few underlying short decumbent setae; eye relatively large (EL 0.15-0.18, REL 20-25), oval-shaped, with 8-9 ommatidia at greatest diameter; head and mesosomal sculpture densely punctate, densely carinulate, or carinulate-punctate, with carinulae merging into punctae; propodeal spines reduced to sharp angles or tubercles (PSL 0.09-0.11, PSI 0.9-1.2); frontal lobes well-developed, but not completely obscuring torular lobes in full-face view (FLD 0.15-0.22, FLI 23-28). Similar species: Stenamma vexator .

Geographic range.

Mexico (Atlantic slope) to Honduras.

Worker description.

(9 measured) HL 0.73-0.88 (0.88), HW 0.65-0.78 (0.78), FLD 0.15-0.22 (0.22), PCW 0.03-0.04 (0.03), SL 0.56-0.68 (0.68), EL 0.15-0.18 (0.18), ACL 0.51-0.61 (0.61), ML 0.93-1.11 (1.11), PrW 0.44-0.53 (0.53), PSL 0.09-0.11 (0.10), SDL 0.09-0.11 (0.11), PL 0.34-0.40 (0.39), PH 0.23-0.25 (0.25), PW 0.17-0.19 (0.19), PPL 0.20-0.24 (0.24), PPH 0.19-0.23 (0.23), PPW 0.20-0.23 (0.23), MFL 0.64-0.80 (0.77), MTL 0.51-0.65 (0.63), CI 86-94 (88), SI 79-92 (88), REL 20-25 (23), FLI 23-28 (28), PSI 0.9-1.2 (0.9), MFI 94-115 (101), ACI1 63-66 (63), ACI2 87-94 (89).

Small- to medium-sized species; general body color mostly black to dark brown, with appendages brown to orange-brown; setae dark golden brown; mandible with 6-7 teeth, consisting of 3 distinct apical teeth, a distinct basal tooth, and 2-3 teeth in between, which are often worn and indistinct; basal margin of mandible sinuous, but without a basal notch or deep depression; mandible mostly smooth and shining, with scattered piligerous punctae and striae; anterior clypeal margin broadly emarginate, with two blunt inner teeth (best viewed with mandibles open); surface of median clypeal lobe somewhat rough (irregular depressions, punctae), with a pair of faint longitudinal carinulae that diverge anteriorly, apex of lobe with a short transverse carinula, remainder of clypeus mostly smooth and shiny; posterior extension of clypeus between antennal insertions of moderate width (PCW 0.03-0.04), sides subparallel; frontal lobes moderately developed (FLD 0.15-0.22, FLI 23-28), but not completely covering torular lobes in full-face view; head subrectangular to slightly oval-shaped (CI 86-94), with posterior margin slightly to distinctly depressed medially; eye relatively large (EL 0.15-0.18, REL 20-25), oval-shaped, with 8-9 ommatidia at greatest diameter; head coarsely punctate (type population), or carinulate punctate, or mostly carinulate; in specimens with mainly carinulate sculpture, piligerous punctae are present in interstices, especially toward lateral margins; scape somewhat short (SI 79-92), not reaching posterior margin of head when laid back; scape surface mostly smooth and shiny (type population), or rougher, with dense piligerous punctae and carinulae; funiculus with a somewhat distinct 4-segmented antennal club; mesosoma sculpture variable, similar to head sculpture, either coarsely punctate (type population), carinulate punctate, or mostly carinulate, with carinulae mostly longitudinal in direction, but sometimes transverse on pronotal dorsum and propodeal dorsum, or arcuate on pronotal side; propodeal declivity always transversely carinulate; promesonotum in profile low-domed and roughly symmetrical; metanotal grove distinct to somewhat indistinct, of moderate to shallow width and depth; propodeal spines reduced to sharp angles or short tubercles (PSL 0.09-0.11, PSI 0.9-1.2); petiole and postpetiole robust, with nodes somewhat bulging; petiole of moderate length (PL/HW 0.45-0.58); petiolar node in profile usually subconical (type population), roughly symmetrical, with dorsum forming a well-defined apex that points vertically, but sometimes dorsum with a broadly rounded top that points slightly posteriad; postpetiole in profile subspherical, usually similar in same size to petiolar node (PPH/PH 0.79-0.93); petiole and postpetiole punctate, with anterior faces of nodes smooth and shiny; gaster mostly smooth and shiny, with scattered piligerous punctate; most of body dorsum with a layer of medium to short standing pilosity; scape with a uniform layer of subdecumbent to decumbent setae; gaster with a sparse layer of stout suberect setae, and sometimes a few underlying short decumbent setae; leg setae mostly appressed, with suberect setae on coxae and femoral venters.

Queen.

Unknown.

Male.

Unknown.

Biology.

A rare species, Stenamma stictosomum is a cloud forest specialist known from a few samples of sifted leaf litter, a beating sample, and from quarantine in Brownsville, TX. The latter specimen was found on orchids being shipped to the United States from either Oaxaca or San Luis Potosí, México. Collections range from 1450-1750 m elevation. The presence of Stenamma stictosomum on orchids and on vegetation (beating sample) suggests that it may nest or at least forage arboreally. This would help explain why the species appears to be so rare, despite being rather widespread.

Comments.

Stenamma stictosomum may form a complex of species, as evidenced by the significant amount of morphological variation among populations. However, an adequate assessment of species boundaries is impossible because so little material has been collected of the species (10 specimens from 7 localities). Consequently, I describe a single species here, but discuss some of the among population variation below.

The type population (20.6km SW Valle Nacional) is the most distinctive, with the head and mesosoma entirely coarsely punctate and without well-defined carinulae (except for the propodeal dorsum and declivity). In the right lighting, these specimens give off a bluish reflectance from the surface sculpturing.

Variant 1 (Figure 158 A–C) is a specimen from quarantine, likely originating from Oaxaca or San Luis Potosí, Mexico. It is similar to the type population, but has reduced sculpture overall (less coarse, more polished) and carinulate punctate sculpture on the promesonotum.

Variant 2 (Figure 158 D–F) is from Guatemala (a single specimen). It is similar to the type population, except that the punctae are less coarse (more polished, somewhat effaced) and there are smooth patches of cuticle on the side of the head and pronotum. Also, the petiolar node in profile has a rounded dorsum that points slightly posteriad.

Variant 3 (Figure 158 G–I) is from Veracruz, Mexico (a single specimen) and is coarsely sculptured, but the sculpture is carinulate punctate, with the carinulae emerging out of the borders of the punctae. The carinulae on the promesonotal dorsum are indistinctly transverse in orientation and the carinulae on the pronotal side are arcuate.

Variant 4 (Figure 158 J–L) is from Hidalgo and San Luís Potosí, Mexico. All specimens are similar in that the sculpture is mainly carinulate or rugulose (mostly lon gitudinal in orientation), rather than punctate. Punctae are visible in the interstices, but they do not form the dominant sculpture type. Also, the petiolar and postpetiolar nodes are less bulging, appearing more average in form, with the postpetiole clearly smaller than the petiolar node.

Material examined.

GUATEMALA:Zacapa: 2km SE La Unión, 14.95284°N, 89.27655°W, 1450m, 14 May 2009 (LLAMA); MÉXICO:Hidalgo: [Tlanchinol], 43km SW Huejutla, [ca. 20.988°N, 98.662°W], 1500m, 14 Jun 1983 (S. & J. Peck); Oaxaca: Oaxaca or San Luis Potosí, 19 Apr 1961 (quarantine in Brownsville, TX); 20.6km SW Valle Nacional, 17.60404°N, 96.37786°W, 1740m, 13 Aug 2009 (M. G. Branstetter); San Luis Potosí: 20km W Xilitla, [ca. 21.293°N, 99.194°W], 1600m, 12 Jun 1983 (S. & J. Peck); Veracruz: 10km S Orizaba, 18.750°N, 97.083°W, 1500m, 19 Mar 1985 (P. S. Ward).