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
Longino (2010) - 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.

Brandão (1990) - M. incisus shows intraspecific vanation in size, dental formula, sculpture and color. The Diamantino, MT, Brasil specimens represent an extreme in all these characters with the higher values in all morphometric characters taken, declivity with rogusities and yellow legs. In the Colombian samples the workers are bicolored with head and gaster darker than the body. Dental formula varies among the series with the masticatory blade with 5 to 7 denticles. The katepisternum may be smooth or completely sculptured. M. incisus can be distinguished from Megalomyrmex drifti by the lack of anterior clypeal teeth and the falcate mandibles.

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.

Biology
Brandão (2003) - With the help of J. Lattke and E. Cancello I collected a colony of M. incisus in a dead twig on the ground in Caripe, Monagas province, Venezuela (10°10’N, 63°34’W), in a very wet afternoon (October 30, 1986). Only adult ants occupied the small chamber under the bark of the twig. The sample includes one dealated female (undescribed) and 28 workers. From the IHVL, I studied a worker from Caquetá Salzano, Colombia.

From the MCZ, I studied a sample of M. incisus including one dealate gyne and seven workers collected at Windblow Ridge, Arima Valley, Trinidad (elevation 1800’) T-40, in May 15, 1988, collected by S. Cover and M. Moffett, “44 miles past end of Cooker Trace; secondary montane rainforest, about 20 years old, in rotten branch on forest floor”.

Nomenclature

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

Type Material


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.

Worker
Brandão (1990) - Falcate mandibles smooth with dental formula 2 + (5-6); anterior clypeal border round without median denticle: median area of clypeus may be depressed but it is never marked by lateral carinae or anterior teeth; frontal suture in general impressed; 16 ocular facets at compound eye largest diameter: occipital margin not raised; promesonotal suture obsolete at thorax dorsum: metanotal groove deeply excavated and completely sculptured at dorsum: katepisternum may present gross longitudinal rugosities; dorsal face and declivity of propodeum indistinct; dorsal face not depressed longitudinally; declivity may have 0-2 concentric rugosities over the foramen; propodeal spiracles laterally produced in an angle of 45° to the main axis of body; pedunculate petiole with petiolar node slope straight in side view; ventral face of petiole with anterior denticle originating a longitudinal translucid flange; postpetiole as broad as the petiole in dorsal view with ventral process globose.

Pilosity: two parallel rows of long hairs. (.2mm) from the frontal carinae to head vertex. Pronotum with 4 to 6 long hairs, which also appear at petiolar and postpetiolar node apexes and are uniformly distributed over the gaster. Small hairs (.I mm) at mandibles, cephalic vertex, legs and gaster apex.

Color: in general deep and bright reddish-brown, but head and gaster may be almost shiny black and legs may be orange-yellow.

Queen
Brandão (2003) - Three equally developed ocelli; mesonotum with parapsidal sutures but no notaulus; katepisternum smooth; propodeum dorsal face and declivity continuous, with only one rugosity over the foramen; petiole ventral face with an anterior denticle, otherwise smooth; the postpetiole posterodorsal face has one continuous rugosity just before the socket, although rugosities are absent from the ventral face.

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.

References based on Global Ant Biodiversity Informatics

 * Ahuatzin D. A., E. J. Corro, A. Aguirre Jaimes, J. E. Valenzuela Gonzalez, R. Machado Feitosa, M. Cezar Ribeiro, J. Carlos Lopez Acosta, R. Coates, W. Dattilo. 2019. Forest cover drives leaf litter ant diversity in primary rainforest remnants within human-modified tropical landscapes. Biodiversity and Conservation 28(5): 1091-1107.
 * Boudinot B. E., T. P. Sumnicht, and R. M. M. Adams. 2013. Central American ants of the genus Megalomyrmex Forel (Hymenoptera: Formicidae): six new species and keys to workers and males. Zootaxa 3732(1): 1-82.
 * Brandao, C.R.F. 1991. Adendos ao catalogo abreviado das formigas da regiao neotropical (Hymenoptera: Formicidae). Rev. Bras. Entomol. 35: 319-412.
 * Brandão C. R. F. 1990. Systematic revision of the Neotropical ant genus Megalomyrmex Forel (Hymenoptera: Formicidae: Myrmicinae), with the description of thirteen new species. Arquivos de Zoologia (São Paulo) 31: 411-481
 * Brandão C. R. F. 2003. Further revisionary studies on the ant genus Megalomyrmex Forel (Hymenoptera: Formicidae). Papeis Avulsos de Zoologia (São Paulo) 43: 145-159
 * Branstetter M. G. and L. Sáenz. 2012. Las hormigas (Hymenoptera: Formicidae) de Guatemala. Pp. 221-268 in: Cano E. B. and J. C. Schuster. (eds.) 2012. Biodiversidad de Guatemala. Volumen 2. Guatemala: Universidad del Valle de Guatemala, iv + 328 pp
 * Chacon de Ulloa P., A. M. Osorio-Garica, R. Achury, and C. Bermudez-Rivas. 2012. Hormigas (Hymenoptera: Formicidae) del Bosque seco tropical (Bs-T) de la cuenca alta del rio Cauca, Colombia. Biota Colombiana 13(2): 165-181.
 * Dattilo W. et al. 2019. MEXICO ANTS: incidence and abundance along the Nearctic-Neotropical interface. Ecology https://doi.org/10.1002/ecy.2944
 * Ettershank G. 1966. A generic revision of the world Myrmicinae related to Solenopsis and Pheidologeton (Hymenoptera: Formicidae). Aust. J. Zool. 14: 73-171.
 * Fernandes, P.R. XXXX. Los hormigas del suelo en Mexico: Diversidad, distribucion e importancia (Hymenoptera: Formicidae).
 * Fernández, F. and S. Sendoya. 2004. Lista de las hormigas neotropicales. Biota Colombiana Volume 5, Number 1.
 * Fichaux M., B. Bechade, J. Donald, A. Weyna, J. H. C. Delabie, J. Murienne, C. Baraloto, and J. Orivel. 2019. Habitats shape taxonomic and functional composition of Neotropical ant assemblages. Oecologia 189(2): 501-513.
 * Franco W., N. Ladino, J. H. C. Delabie, A. Dejean, J. Orivel, M. Fichaux, S. Groc, M. Leponce, and R. M. Feitosa. 2019. First checklist of the ants (Hymenoptera: Formicidae) of French Guiana. Zootaxa 4674(5): 509-543.
 * Longino J. T. 2010. A taxonomic review of the ant genus Megalomyrmex Forel (Hymenoptera: Formicidae) in Central America. Zootaxa 2720: 35-58
 * Longino J. T. L., and M. G. Branstetter. 2018. The truncated bell: an enigmatic but pervasive elevational diversity pattern in Middle American ants. Ecography 41: 1-12.
 * Longino J. et al. ADMAC project. Accessed on March 24th 2017 at https://sites.google.com/site/admacsite/
 * Longino, J.T. 2010. Personal Communication. Longino Collection Database
 * Silva R.R., and C. R. F. Brandao. 2014. Ecosystem-Wide Morphological Structure of Leaf-Litter Ant Communities along a Tropical Latitudinal Gradient. PLoSONE 9(3): e93049. doi:10.1371/journal.pone.0093049
 * Smith M. R. 1947. A new species of Megalomyrmex from Barro Colorado Island, Canal Zone (Hymenoptera, Formicidae). Proceedings of the Entomological Society of Washington 49: 101-103.
 * Vasconcelos, H.L., J.M.S. Vilhena, W.E. Magnusson and A.L.K.M. Albernaz. 2006. Long-term effects of forest fragmentation on Amazonian ant communities. Journal of Biogeography 33:1348-1356
 * Vásquez-Bolaños M. 2011. Lista de especies de hormigas (Hymenoptera: Formicidae) para México. Dugesiana 18: 95-133
 * Wild, A. L.. "A catalogue of the ants of Paraguay (Hymenoptera: Formicidae)." Zootaxa 1622 (2007): 1-55.