Megalomyrmex adamsae

This species is typically found in Trachymyrmex Forel nests

Identification
Diagnosis. Worker differing from Megalomyrmex symmetochus as follows: (1) setae on the mesosomal and gastral dorsum relatively stout and stiff (Fig. 3B); (2) scape relatively long (SI 94–98 vs. 90–93 in symmetochus); (3) ventral keel of petiole fading posteriorly, not connected to the two short subparallel carinulae at posterior margin (Fig. 3D), vs. ventral keel Y-shaped, splitting posteriorly to form two divergent carinulae at posterior margin (Fig. 3C).

Distribution based on Regional Taxon Lists
Neotropical Region: Panama.

Biology
Megalomyrmex adamsae is a specialized predator of Attini, like its close relative M. symmetochus. Colonies cohabit nests with their attine hosts as "agro-predators," feeding on fungal mycelia and perhaps attine brood. Megalomyrmex adamsae and M. symmetochus differ in host preference: M. adamsae is typically found in Trachymyrmex Forel nests, M. symmetochus in Sericomyrmex Mayr nests (Adams, pers. comm.).

Megalomyrmex adamsae and M. symmetochus are very similar species. There is molecular evidence that the two are probably sister taxa (Adams, pers. comm.). The characters differentiating them in the diagnosis are consistent in Central America and the concordant molecular, morphological, and behavioral characters strongly support the existence of two sympatric species in central Panama. I examined three collections from near Manaus, Brazil, and one collection from Peru that are in the symmetochus complex but do not cleanly fall into either adamsae or symmetochus. They vary in coarseness of pilosity and are somewhat in between the states of adamsae and symmetochus, the scape is long like symmetochus, the ventral petiolar keel is more like adamsae than symmetochus, they nest with Trachymyrmex. Molecular evidence weakly alligns them with adamsae (Adams, pers. comm.). Other South American examples of the symmetochus complex have been reported. Brown observed a colony from near Manaus, Brazil (reported as silvestrii in Kempf & Brown 1968; reidentified as symmetochus by Brandão 1990). He reported "The colony ... was found in a small rotten log in rain forest on 26.VIII.1962, in a small chamber with a small species of Trachymyrmex. The ants of both species were found throughout the fungus garden of the chamber, but off to one side in a small chamber was found a group of the Trachymyrmex clustered with a small piece of fungus garden unoccupied by Megalomyrmex. ... the situation suggested that the M. silvestrii colony had successfully attacked and moved into the attine nest, and was in the process of plundering it." Brandão (1990) reported a collection from Belem, PA, Brazil, from a nest of an unidentified Trachymyrmex.

Nomenclature

 *  adamsae. Megalomyrmex adamsae Longino, 2010: 41, figs. 3B, 3D, 7AH (w.q.m.) PANAMA.

Description
Measurements (holotype): HW 0.846, HL 0.898, SL 0.885, EL 0.257, ML 1.287, CI 94, SI 99. Measurements (n=6): HW 0.816–0.895, HL 0.875–0.957, SL 0.851–0.918, EL 0.243–0.274, ML 1.287–1.391, CI 93–96, SI 96–99. Palp formula 3,2; mandible generally with 6 teeth, apical largest, subapical next largest, 4 basal smallest and subequal in size (basal teeth vary from 4–6, and right and left mandible of same individual can vary in basal tooth number); dorsal surface of mandible coarsely striate; clypeus bulging; compound eye set in slight concavity of head capsule, most evident posterior to eye, ventral margin of concavity delimited by small carina (concavity and ventral carina of variable strength); occipital carina thin and not visible in full-face view; face and clypeus largely smooth and shining, with about 10 longitudinal linear carinulae on clypeus, coarse carinulae on malar space between compound eye and mandible, frontal carina fading into 2–3 longitudinal carinulae posteriorly, extending to about mid-length of compound eye, variable longitudinal etching elsewhere on face, 1–2 concentric carinulae around antennal fossa; ventral surface of head smooth and shining, anterior ends of occipital carina extend about 1/3 distance to hypostomal margin; mesosoma generally smooth and shiny; anepisternum, katepisternum, and lower sides of propodeum overlain with longitudinal carinulae (of variable strength on katepisternum); dorsal surface of propodeum concave; juncture of dorsal and posterior faces concave medially, forming blunt angles laterally; posterior face of propodeum with about 5 transverse carinulae; foraminal carina entire; dorsal petiole, postpetiole, and gaster smooth and shining, petiole and postpetiole with a few transverse posterodorsal carinulae; ventral keel of petiole in the form of a low translucent flange, forming a short angular tooth anteriorly, splitting and becoming two small subparallel carinulae posteriorly; posterolateral petiole with longitudinal carina, delimiting posteroventral concavity between lateral carina and ventral keel; ventral margin of postpetiole with short tooth; femora, tibiae, scapes, and dorsal surface of mandible covered with abundant subdecumbent setae; face, dorsal mesosoma, dorsal petiole and postpetiole with moderately abundant suberect coarse setae; dorsal gaster with dense suberect coarse setae; general body and appendage color orange, gaster darker, dorsal setae amber. Measurements (n=3): HW 0.939–1.023, HL 0.929–0.950, SL 0.905–0.945, EL 0.336–0.341, ML 1.529–1.578, CI 101–108, SI 92–96. Palp formula 3,2 or 4,3, with variable or partial fusion of terminal segments; general shape, sculpture, and pilosity characters, including mandibular dentition and sculpture, similar to worker; parapsidal lines barely visible; wing venation as in Fig. 7H. Measurements (n=1): HW 0.898, HL 0.891, SL 0.759, EL 0.525, ML 1.643, CI 101, SI 85. Palp formula 4,3; mandible with 5 distinct teeth, apical largest, diminishing in size basally; dorsal surface of mandible striate; antenna with third segment bent, creating a kink; clypeus and face with longitudinal carinulae; head capsule with concavity around compound eye, like worker; fused notaulae present anteromedially, parapsidal lines distinct; wing venation similar to queen; ventral margin of petiole a more delicate version of condition in worker and queen; abundant coarse suberect setae on dorsal head, mesosoma, and metasoma; color orange with darker gaster, lighter appendages, antennal segments 2–4 nearly white. This species is named for Rachelle Adams, whose extensive field and laboratory work has greatly advanced our understanding of the genus Megalomyrmex
 * Worker.
 * Queen.
 * Male.
 * Etymology.