Octostruma balzani

Octostruma balzani is a widespread Central and South American species that is common in many localities. It occurs in a variety of forested habitats: wet to seasonal dry, second growth to mature, lowland to montane. It usually occurs from sea level to the lower edges of cloud forests, typically around 1400 m. The highest elevation record is 1650 m in Nuevo León, Mexico. Almost all collections are from Berlese and Winkler samples of sifted litter and rotten wood from the forest floor. In quantitative 1 m2 litter plot samples, within-sample abundance is tens of workers or fewer, but the species can occur in nearly every sample, suggesting a high density of small colonies. Dealate queens and intercaste workers often occur together with workers in litter samples. (Longino 2013)

Identification
Key to Octostruma workers

Distribution
Longino 1999 for what is called the balzani complex - Tropical Mexico south through Central and South America at low and moderate elevations to the Bolivian Andes and to Parana and Sao Paulo states in southeastern Brazil; Trinidad, Dominica, and probably other islands of the Lesser Antilles (Brown and Kempf 1960).

Distribution based on Regional Taxon Lists
Neotropical Region: Argentina, Belize, Bolivia, Brazil, Colombia, Costa Rica, Dominica, Dominican Republic, Ecuador, El Salvador, French Guiana, Greater Antilles, Guadeloupe, Guatemala, Guyana, Honduras, Jamaica, Lesser Antilles, Mexico, Nicaragua, Panama, Paraguay, Peru, Suriname, Trinidad and Tobago, Venezuela.

Nomenclature

 *  balzani. Rhopalothrix balzani Emery, 1894c: 217, pl. 1, fig. 10 (w.q.) BOLIVIA. Combination in Octostruma: Brown, 1949f: 92. Senior synonym of barberi, equilatera: Brown & Kempf, 1960: 194.
 * barberi. Rhopalothrix (Octostruma) barberi Mann, 1922: 42 (w.) GUATEMALA. Combination in Octostruma: Brown, 1949f: 92. Junior synonym of balzani: Brown & Kempf, 1960: 194.
 * equilatera. Rhopalothrix (Octostruma) equilatera Weber, 1934a: 52, fig. 10 (w.) NICARAGUA. Combination in Octostruma: Brown, 1949f: 92. Junior synonym of balzani: Brown & Kempf, 1960: 194.

Worker
Ferrugineo fusca, antennis pedibusque rufescentibus, vel tota ferruginea, opaca, creberrime punctata, capite lato, absque crista transversa, scapo valde dilatato, angulo basali subloformi, thorace convexo, sutra meso-metanotali distincta, metanoto spinis trigonis armato, pedunculi segmento 1° postice superne nodo parum latiore quam longiore. Long. 1 3/4 mm.

Brown and Kempf (1960) - TL 1.9-2.7, HL 0.48-0.58, HW 0.51-0.65 (CI 101-113), WL 0.50-0.65 mm; measurements based on 42 workers representing at least 18 separate nests from all parts of the range, including the holotype worker: HL 0.56, WL 0.60 mm, CI 102; head narrower than average for this species.

The general form of the head and alitrunk and petiole varies within limits individually and among different nest series. Occiput convex and anterior part of cephalic dorsum flat or shallowly concave; the meeting of these two surfaces often produces a feebly indicated, blunt ridge or rise crossing the head in an arc and corresponding to the carina found in rugifera and rugiferoides. Lateral occipital (postocular) angles obtuse to obsolete.

Mandibles of moderate length, their upper surfaces feebly convex, external margins weakly convex in outline; masticatory border and teeth very slightly depressed; usually 7 larger teeth, with 2-3 minute intercalary denticles. Basal tooth most commonly broad and bluntly rounded or subtruncate, filling or nearly filling the space between mandibles and clypeus at full closure. In occasional specimens from the northern part of the range (thus away from the range of the sibling O. stenognatha), the basal tooth is variably narrowed to a blunt point, but never to the extent of stenognatha. The compound eyes vary in size from small to very small, apparently allometrically corresponding to degree of gynecoidy.

Alitrunk often more convex above in outline; metanotal groove varying from reasonably distinct, or more feeble, to virtually obsolete on the dorsum. Propodeal teeth also somewhat variable in size and shape. Petiolar node varying to a much more rounded summit profile; as seen from above, node proper about twice as long as broad in most samples, rectangular. Postpetiole subreniform, broader than petiole (but not twice as wide) and about half or a little more as wide as the first gastric segment.

The stubby erect clavate hairs vary considerably in number present; the pattern is a common one, allowing for hairs broken off. Additional pairs of hairs added on head, alitrunk, postpetiole and gastric dorsum commonly accompany increase in size, and apparently represent a gynecoidal tendency. The alitrunk may have no erect hairs, but often 1, 2, or even as many as 3 pairs are present. On the dorsum of the first gastric segment, the number of hairs is usually between 6 and 12, but may reach as high as 20 or more, mostly concentrated on the posterior 2/3 of the segment in rows of 4 or 6. Ground hairs are generally appressed or reclinate and inconspicuous, but in some samples they are easily seen, though appressed, on clypeus, anterior part of head or gastric dorsum, or all three places. Sculpture densely and regularly punctulate. prevailingly opaque. Color varying shades of reddish-brown.

Queen
Caput et antennae fere ut in worker, spinae metanoti validiores, petioli nodus 1. superne trapezoideus, antice latior quam postice, circiter dimidio latior quam longior. Alae fuscatae. Long. 2 mm.

Brown and Kempf (1960) - Ergatoid females (gynecoid workers) are like the worker, but are larger and have ocelli. The alitrunk is proportionately a little longer, and sometimes the promesonotal suture is better-developed; erect hairs are more numerous and widely distributed. Female: TL 2.7-3.0, HL 0.58-0.63, HW 0.62-0.65 (CI 100-109), WL 0.75-0.80 mm (8 specimens from 5 localities).

Type Material
Brown and Kempf (1960) - Type localities: Districts of Coroico and Chulimani-Yungas, Bolivia; other locality, Salinas sul Beni, Bolivia. Types in MCSNG; worker from Coroico examined and here designated as lectotype.

Rhopalothrix (Octostruma) lutzi Wheeler, 1913. Bull. Amer. Mus. Nat. Hist., 32: 241, worker, female (part.). Type localities: Laudet and Long Ditton, near Roseau, Dominica, B.W.I. Lectotype, by present designation, the specimen (Long Ditton) so labelled in, examined. NEW SYNONYMY.

Rhopalothrix (Octostruma) barberi Mann, 1922: 42, worker. Type locality: Trece Aguas, Alta Vera Paz, Guatemala. Holotype in. examined. NEW SYNONYMY.

Rhopalothrix (Octostruma) equilatera Weber, 1934: 52, fig. 10, worker. Type locality: Tuli Creek, near San Miguel, Nicaragua. Syntypes in MCZC and NAW, examined. NEW SYNONYMY.

Additional References

 * Longino, J.T. 2013. A revision of the ant genus Octostruma Forel 1912 (Hymenoptera, Formicidae). Zootaxa 3699, 1-61.