Nylanderia austroccidua

Nests are frequently found under stones. It is suspected that N. austroccidua follows the reproductive flight schedule of other Nearctic species (Trager, 1984). They are commonly found in moist, mountainous regions of the southwest United States, frequently in forests dominated by oak, maple, and pine. However, there are also collections in arid central Mexico and Texas (fig. 206). This species apparently has the most southern distribution of any native Nearctic Nylanderia species, being known to occur as far south as Costa Rica, where it is a cloud forest inhabitant (Longino, 2010) (Kallal & LaPolla, 2012).

Identification
Kallal & LaPolla (2012) - Overall brown, sometimes bicolored with lighter mesosoma than head and gaster; in lateral view pronotal margin angular; bluish reflections visible on head and mesosoma under microscopic examination.

Compare with: Nylanderia bruesii, Nylanderia vividula, and Nylanderia terricola.

The bluish hue reflected by the cuticle of this species under microscopic examination is unique among Nearctic species (although some Nylanderia faisonensis may exhibit it weakly and Nylanderia species in other parts of the world do display a similar bluish hue). The angular pronotum viewed in profile distinguishes it from Nylanderia bruesii, Nylanderia terricola, and Nylanderia vividula. Overall body color is generally brown but varies across the range and is not diagnostic; the species ranges from light brown to dark, reddish brown. Bicoloration is also present, but infrequently observed in worker specimens. Mesocoxae and metacoxae are also known to be pale and whitish in some populations. Males have triangular parameres, unlike the more digitiform parameres of N. bruesii, to which this species may be confused, and have a distinct upturned point on the aedeagal valve not present in other species. Trager (1984) noted the presence of subbasal denticles in males, but we have not observed these structures.

Distribution
Mountains of southwestern US, Texas, Mexico to Costa Rica.

Distribution based on Regional Taxon Lists
Nearctic Region: United States. Neotropical Region: Costa Rica, Mexico.

Nomenclature

 *  austroccidua. Paratrechina austroccidua Trager, 1984b: 113, fig. 17, 20 (w.q.m.) U.S.A. Combination in Nylanderia: LaPolla, Brady & Shattuck, 2010a: 127. See also: Kallal & LaPolla, 2012: 11.

Worker
Kallal & LaPolla (2012) - Measurements (n=15) TL: 1.87–2.64; HW: 0.45–0.60; HL: 0.58–0.69; EL: 0.13–0.18; SL: 0.60–0.76; PW: 0.37–0.45; WL: 0.63–0.84; GL: 0.49–1.25; PH: 0.10–0.30; PFL: 0.47–0.61; PFW: 0.13–0.19. SMC: 2–9; PMC: 2–5; MMC: 1–4. Indices: CI: 82–90; REL: 21–28; SI: 109–114; FI: 81–96.

Brown in color, infrequently bicolored with mesosoma lighter brown than head and gaster; mandibles, scapes, mesocoxae, metacoxae, and legs yellowish-brown; cuticle smooth and shiny; cephalic pubescence dense; pronotal pubescence sparse to virtually absent on remainder of mesosoma; gastral pubescence sparse; on mesosoma notum macrosetae often with raised setal bases. Head relatively quadrate with slightly convex lateral margins; posterior margin slightly emarginated medially; scapes surpass posterior margin by first 3–4 funicular segments; median ocellus apparent, lateral ocelli often apparent. Pronotal anterior face greater than 45°; pronotal anterior face shorter than pronotal dorsal face; pronotal dorsal face with unique concavity; anterior margin of mesonotum continuous with posterior pronotal margin; propodeum with short dorsal face and long declivitous face, sometimes slightly dome-like in larger specimens.

Queen
Kallal & LaPolla (2012) - Measurements (n=2) TL: 3.73-4.26; HW: 0.75-0.67; HL: 0.76-0.79; EL: 0.27; SL: 0.77-0.83; PW: 0.88-0.95; MW: 0.82–0.85; WL: 1.25-1.27; GL: 1.71-2.21; PH: .41-0.42; PFL: 0.72-0.76; PFW: 0.20-0.21. SMC: 1-6; PMC: 6-8; MMC: 14-20; MtMC: 2-7. Indices: CI: 97-99; REL: 34-36; SI: 102-105; FI: 95-96.

Overall brown in color with mandibles, leg joints, and tarsi yellowish-brown; cuticle smooth and shiny; body with dense pubescence; macrosetae dark brown. Head as broad as long; scapes surpass posterior margin by length of first 3–4 funicular segments. Propodeum with short dorsal face and steep, long declivitous face.

Male
Kallal & LaPolla (2012) - Measurements (n=4) TL: 1.74–2.27; HW: 0.40–0.53; HL: 0.48–0.57; EL: 0.19–0.22; SL: 0.59–0.64; PW: 0.55; MW: 0.42–0.52; WL: 0.59–0.86; GL: 0.65–0.88; PH: 0.24–0.33; PFL: 0.47–0.54; PFW: 0.11–0.15; PL: 0.18–0.30. SMC: 0–4; MMC: 4–7; MtMC: 1–3. Indices: CI: 83–97; REL: 35–39; SI: 110–122; FI: 84–101.

Overall brown with mesocoxae, metacoxae, leg joints, and tarsi yellowish-brown; cuticle smooth and shining; cephalic pubescence moderate to dense; mesonotum with dense pubescence; gaster pubescence virtually absent; macrosetae dark brown. Head as broad as long; eyes weakly convex, slightly extending beyond lateral margins of the head in full face view; scapes surpass posterior margin by length of first two funicular segments; mandibles with long, straight inner mandibular margin; basal angle approximately 90°; smooth masticatory margin with a small subapical tooth and large apical tooth. Mesosoma enlarged to accommodate flight muscles; in lateral view, pronotal margin short and relatively straight with a small inflection towards mesonotal margin; propodeum with long dorsal face and short declivitous face. Genitalia: parameres short, relatively narrow, laterally oriented, and triangular; digiti angled ventrally at approximately half its length, with teeth at that angle where they meet cuspides; aedeagal valves triangular with small concavity at the distal end of the ventral margin, resulting a curved tip, teeth absent; ninth sternite somewhat rectangular, with thin lateral apodemes.

Additional References

 * Kallal, R.J. & LaPolla, J.S. 2012. Monograph of Nylanderia (Hymenoptera: Formicidae) of the World, Part II: Nylanderia in the Nearctic. Zootaxa 3508, 1-64.