Megalomyrmex incisus

This species occurs in moist to wet forest habitats, from sea level to 1000 m elevation. It is most often encountered as workers in Winkler samples of sifted leaf litter. Colonies have twice been collected from dead wood on the forest floor (Brandão, 2003). Boudinot et al. (2013) - At least in Central America, M. incisus is a lowland species, having been collected from about sea-level to 870 m. Full colonies are rarely collected for this species. However, in March 2006, a single colony was collected with 10 ergatoid queens, 66 workers, 1 male and brood in a mushy wet log in Ecuador (fig. 244), and on 3 May 2013 a full colony with alate males, one ergatoid queen and about two-to-three dozen workers was collected in a folded leaf on the ground in a second growth rainforest in Gamboa, Panama (BEB000836-2, below). Gaster flagging behavior was often observed in the laboratory, prompted by minor disturbance. Many workers and all ergatoids were covered in unidentified mites in both Ecuadorian and Panamanian colonies. A winged female was collected by W.L. and D. E. Brown, 23–27 June 1971, Rancho Grande, 1100m, Estado Aragua, Venezuela. From the material available to us, only ergatoid queens were found in Central America and Ecuador.

Identification
Material from Central America and Venezuela is very similar in color and mandibular dentition. Workers are solid black, and the basal teeth of the mandible vary in size, the second from the base being much larger than the flanking teeth. As a result the mandible appears falcate rather than triangular. A collection from Colombia is distinctive, with the color lighter red brown and the basal teeth of the mandible of more uniform size. Other size and shape characters, including the highly distinctive petiole, are the same as other M. incisus. M. incisus has a range disjunction. It is moderately abundant in Winkler samples from Guatemala and southern Mexico, occurs in Panama and Venezuela, yet has never been collected in Costa Rica, in spite of extensive survey work there.

Boudinot et al. (2013) - Worker uniquely identified among Central American Megalomyrmex by the following combination of characters: (1) second or third basal mandibular tooth largest; (2) clypeus, between antennal insertions wider than maximum scape width; (3) eyes placed about midlength of head; (4) katepisternum costate. Additionally, the petiolar shape is unique, with a robust wedge-shaped node for which anterior face is steeper than posterior face. Queen. Ergatoid queens are identifiable similarly to workers but with larger gaster. Male Uniquely identified among Central American Megalomyrmex species by the 11-merous antenna, and the kinked and apically swollen metabasitarsus.

Distribution
Southern Mexico south to Peru, Venezuela, and central Brazil; absent in Costa Rica. Sea-level to 1000 m elevation.

Distribution based on Regional Taxon Lists
Neotropical Region: Brazil, Colombia, Ecuador, Guatemala, Honduras, Mexico, Panama, Paraguay, Peru, Trinidad and Tobago, Venezuela.

Nomenclature

 *  incisus. Megalomyrmex (Wheelerimyrmex) incisus Smith, M.R. 1947e: 102 (w.) PANAMA. Brandão, 1990: 451 (m.); Brandão, 2003: 157 (q.).

Boudinot et al. (2013) - The 11-merous antenna of the Megalomyrmex incisus male is unique at least within the named Central American representatives of the genus. Megalomyrmex male 01 from Mexico has the penultimate antennomere elongated and partially divided by a lateromedian suture, although this is likely a developmental aberration. It remains to be determined if the 11-merous state is consistent throughout the entire range of M. incisus. Workers, queens, and males of M. incisus have glabrous compound eyes.

We report an intense orange form of this species from Ecuador and Venezuela. Despite the striking coloration, which is similar to that of M. longinoi, the Ecuadorian workers are otherwise only slightly distinct from specimens from the Colombian and Central American populations. Male M. incisus specimens examined from Ecuador are markedly different from the Central American material; these specimens have a longer petiole with a less robust node, a more compact postpetiolar node, coarser setae, and a median clypeal bulge. Additionally, a distinct new species from Brazil, otherwise identifiable as M. incisus, was examined at the MCZ.

Queen
Boudinot et al. (2013) - Ergatoid. (n=3): HW 0.76–0.78, HL 0.76–0.80, SL 0.70–0.74, OMD 0.15–0.16, EL 0.24–0.26, ML 1.06–1.16, CI 97–10, SI 90–83, EI 32–33, OMI 61–66.

Similar to worker, but with alate-condition mesosoma, all three (minute) ocelli, wider petiole and postpetiole, and slightly coarser sculpturation.

Male
Boudinot et al. (2013) - (n=2): HW 0.67–0.70, HL 0.57–0.59, SL 0.32–0.34, EL 0.35–0.36, ML 1.10–1.18, CI 117–119, SI 56–58, EI 51–52.

Head Antennae with 11 antennomeres; antennomere 5 sigmoid; antennomeres 6 and 7 evenly curved, curve of 6 stronger than 7; antennomeres 8–11 distinctly clavate: shorter and broader than preceding antennomeres; scape length subequal to eye length. Basal half of scape infuscated; pedicel white; antennomeres 3–7 infuscated; 8–11 yellowed. Mandible strap-shaped, with basal and ectal margins subparallel; masticatory margin with four teeth, apical tooth about four times as long as subapical tooth; basal three teeth subequal in size. Dorsal face of mandible smooth and shining. Minimum distance between lateral ocellus and compound eye about two lateral ocellus lengths. Compound eye glabrous. Occipital carina not visible in full-face view. Mesosoma Mesosoma somewhat attenuate: propodeum elongated. Notauli absent. Parapsidal lines weak. Foraminal carina present, strong; with concentric dorsal carinula. Basitarsi not anteroposteriorly flattened; metabasitarsus kinked just basad midlength with dorsal portion swollen. Pterostigma well-developed. Forewing crossvein 1m-cu absent; submarginal cell length four to five times width; terminal abscissa of M branches from Rs+M distad 2r-rs. Metasoma Basipetiolar carina a very obtuse triangle. Ventrolateral longitudinal carina of petiole absent. Petiolar spiracle in anterior third. Petiolar and postpetiolar posterior margins without girdling carinae. Postpetiolar helcium subcircular. Postpetiolar spiracle placed near one third the length of the lateral tergal margin. Sternum of postpetiole with an anterior convexity in profile view. Postpetiolar tergum shallowly convex, weakly bilobed. Genitalia Abdominal sternum IX longer than broad, tapering to apex; apex not produced ventrally or distinctly sclerotized. Telomere triangular with a narrow and acutely rounded apex; dorsal margin concave, ventral margin convex; medial dentiform process absent; medial face subrectangular; ventral margin without sclerotized denticles. Cuspis apicodorsally and apicoventrally rounded; apical margin linear. Digitus broadened at midlength; dorsal margin strongly arched, ventral margin weakly arched; apex narrowly rounded; ventral margin slightly obscuring apicodorsal angle of cuspis. Valviceps height somewhat greater than half its length, ovate; dorsal margin produced dorsally in basal half, with apical half convex and sloping gently to meet the ventral margin which continues to the apex; ventral margin weakly convex but produced ventrally in the basal half; penisvalvar teeth miniscule, triangular, relatively wide-set.

Type Material
Holotype worker: PANAMA, Panamá: Barro Colorado Island, Jul–Oct 1943 (Zetek) (not examined).