Megalomyrmex milenae

Three colonies were baited with Keebler Pecan Sandies and excavated from the embankment of the La Seda creek off of Pipeline Road in Panama, two each with a single ergatoid queen. Worker numbers were estimated to be around ~187 in one colony and 273 workers and 9 males in the queenless subcolony. In 2013, several more colonies were collected, all of which were monogynous, and with worker numbers ranging from 25 to 462. The smallest colony had likely just migrated from its natal nest and was found in loose leaf litter. In larger colonies, the nest entrance is similar to that of M. foreli as an inconspicuous hole in the soil. (Kohout 2013)

Identification
Boudinot et al. (2013) - Worker uniquely identified among Central American Megalomyrmex by the following combination of characters: (1) masticatory margin of mandible with 5 robust, equally-spaced, subequal triangular teeth; (2) eye large (EL > 0.30 mm); (3) compound eye without ocular setae; (3) mesosternum without triangular processes. Queen similarly identifiable to worker, but with much larger gaster, ergatoid. Male unique among Central American Megalomyrmex for the hypertrophied compound eyes. Otherwise separated by the following combination: (1) forewing 1m-cu present; (2) wings infuscated; (3) propodeum distinctly depressed; (4) large (ML > 2.0 mm).

Males and both castes of females have glabrous eyes. The males have the largest compound eyes known for any Central American Megalomyrmex species.

In Central America, workers of M. milenae may most easily be confused with Megalomyrmex foreli, but differ as follows: (1) clypeus not produced anterodorsally in profile view; (2) mesosternal processes bulging, rounded (not denticulate); (3) petiole without a narrowed peduncle; (4) postpetiolar sternum without a pointed process; (5) first gastric tergum with long, relatively dilute setation. Further, M. milenae workers are separated from all leoninus- and modestus-group species by the following combination of characters: (1) dorsal face of mandible smooth; (2) anterior margin of clypeus without median denticle; (3) petiole without narrowed peduncle; (4) petiole with laminar tooth; (5) postpetiole rounded, without tooth; (6) femoral apices rounded.

Similarly to workers, males of M. milenae are most similar to M. foreli, but differ in the following: (1) occipital carina not visible in full-face view; (2) ocelli subequal in size; (3) compound eyes gigantic (4) minimum distance between lateral ocellus and compound eye less than one lateral ocellus length (vs. about two and a half); (5) wings infuscated (vs. hyaline) (6) propodeum distinctly depressed; (7) postpetiole shorter, more globose; (8) smaller (ML ~2.15 vs. ML ~2.75); (9) CI greater (CI 128–129 vs. CI 98–99).

Megalomyrmex milenae workers are most similar to those of the South American Megalomyrmex cupecuara, but can be separated by the following (M. cupecuara holotype examined, MCZ; measurements of M. cupecuara from Brandão 1990): (1) eyes larger, maximum diameter about three times longer than maximum supraclypeal area breadth (no measurements of M. cupecuara available, but maximum eye length about 1.5–2 times supraclypeal area breadth); (2) shape short, SI 125–128 (vs. SI 136–138); (3) dorsal mesonotal face short, about one-third length of posterior face (vs. long, subequal to length of posterior face); (4) dorsal and posterior faces of propodeum meeting at rounded angle laterally (vs. propodeum weakly tuberculate); (5) petiolar peduncle comparatively; (6) anterior face of postpetiolar node flattened (vs. anterior face of postpetiolar node strongly convex); (7) postpetiolar sternum rounded (vs. with weak denticle); (8) gastric setae somewhat sparse with single layer (vs. denser, bilayered).

Distribution
Panama; sea-level to 100 m elevation.

Distribution based on Regional Taxon Lists
Neotropical Region: Panama.

Nomenclature

 *  milenae. Megalomyrmex milenae Boudinot, Sumnicht & Adams, 2013: 45, figs. 10, 12, 14, 66, 73, 88, 131–135, 183, 198, 213, 228, 239 (w.q.m.) PANAMA.

Worker
(holotype): HW 1.26, HL 1.51, SL 1.93, OMD 0.38, EL 0.36, ML 2.17, CI 84, SI 128, EI 29, OMI 106. (n=10): HW 1.26–1.38, HL 1.51–1.62, SL 1.93–2.05, OMD 0.37–0.42, EL 0.35–0.38, ML 2.17–2.37, CI 83–86, SI 125–128, EI 26–29, OMI 99–123.

Head Palpal formula 4,3. Basal and masticatory margins of mandible distinct. Mandible with 5 robust teeth: apical tooth largest; basal four teeth subequal in size. Dorsal surface of mandible predominantly smooth except for setigerous punctures and striae near the masticatory margin. Clypeus convex in profile. Frons smooth and shining, with 2–4 weak, rounded carinae diverging from the posterior margin of the clypeus to the frontal carina. Antennal fossa with incomplete concentric carinulae. Malar area smooth and shining with setigerous punctures. Occipital carina short; visible in full-face view; curving abruptly onto postgenal bridge about 1/10 distance to hypostomal margin. Antennal club of three antennomeres. Mesosoma Mesopleuron smooth and shining; anepisternum separated from katepisternum by broad anterior fossa. Propodeum with distinct dorsal and posterior faces meeting at blunt, weakly produced angles; propodeum longitudinally depressed. Posterior face of propodeum with approximately 8 weak transverse carinulae. Foraminal carina entire. Mesosternal processes are rounded protuberances. Femoral apices rounded. Meso- and metabasitarsi circular to ovate in cross-section. MetasomaAnterodorsal face of petiole weakly concave, rising steeply to petiolar node apex. Posterior base of petiole smooth and posterior face of postpetiole with faint carinulae. Petiolar sternum with an anteroventral lamina. Postpetiolar sternum convex, without angular processes. Lancets of sting apparatus shorter than sting shaft, broad, slightly spatulate; sting shaft lancets, thin to pointed apex. Setation Subdecumbent to erect, somewhat dilute setae of variable length present on head, mesosoma, and metasoma; subdecumbent setae on scape of even length; setae on tibiae and tarsi decumbent to appressed. Lancets of sting apparatus slightly broadened at apex. Most of cuticle smooth and shining, except for piligerous punctures, and for short, shining, transverse carinulae along the midline of the ventral surface of the head. Head and antennae reddish-orange; mesosoma, petiole, and postpetiole orange-brown; gaster dark brown to black.

Queen
Ergatoid. (n=1): HW 1.40, HL 1.54, SL 1.84, OMD 0.35, EL 0.39, ML 2.34, CI 90.7, SI 120, EI 28, OMI 89.

Ergatoid. Similar to worker, except: postpetiolar sternum with a short, stout, anteroventrally-directed triangular process; sculpturation coarser, especially setigerous puncta which are elongate in the malar region, and on the petiole and postpetiole; setae on head and mesosoma coarse and dense; setae coarse, decumbent, and very dense on first gastric tergum.

Male
(n=3): HW 1.29–1.31, HL 1.01–1.02, SL 0.39–0.41, EL 0.76, ML 2.14–2.17, CI 128–129, SI 38–40, EI 58–59.

Head Antenna with 13 antennomeres, third antennomere apically kinked, and fourth antennomere curved; not forming club; scape length about half eye length (SL ~ 0.5 EL). Antenna brown, becoming light golden near apex. Palpal formula 4,3. Mandible triangular; masticatory margin with five teeth; apical tooth about twice as long as basal teeth; basal four teeth subequal in size. Compound eye glabrous. Occipital carina not visible in full-face view. Mesosoma Mesosoma attenuate; propodeum distinctly depressed. Notauli absent. Parapsidal lines distinct. Foraminal carina incomplete, but with 2–3 internal complete concentric carinae. Meso- and metabasitarsi tubular. Metabasitarsus neither kinked nor apically swollen. Pterostigma present, narrow and elongate. Forewing crossvein 1m-cu absent; submarginal cell 1 length about four times width; terminal abscissa of M branching from about midlength of Rs+M, becoming spectral after curving anterad, extending almost to apical margin. MetasomaBasipetiolar carina arc-shaped. Ventrolateral longitudinal carina of petiole present. Petiolar spiracle in anterior fifth of segment. Posterior margin of petiole and postpetiole without girdling carinae. Postpetiolar helcium approximately circular. Postpetiolar spiracle about midlength of lateral tergal margin. Sternum of petiole weakly bulging in anterior two thirds of sclerite. Postpetiolar tergum parabolic; apex slightly posterad midlength. GenitaliaAbdominal sternum IX about as broad as long; basolateral margins concave, forming “shoulders” basad the concave apicolateral margins, which form the acute apical lobe; apical lobe not strongly sclerotized or produced ventrally. Telomere short, triangular, bluntly rounded apically; medial dentiform process absent; medial face subquadrate; ventral margin without sclerotized denticles. Cuspis without an apicodorsal lobe; apical margin convex. Digitus somewhat broad; dorsal margin with a rounded angle posteroapically, ventral margin evenly curving until it becomes subapically linear; apex narrowly rounded; ventral margin obscuring apicodorsal angle of cuspis. Valviceps height somewhat more than half the length, subquadrangular; dorsal margin curving to linear apex; ventral margin sinuate, distinct at apex from dorsal margin; penisvalvar teeth close-set, long and narrow basally grading to fine and triangular apically.

Type Material
Holotype worker: PANAMA, Panamá: Pipeline Road, La Seda, 9.16°N 79.7449°W, 73 m, 27 May 2011 (R. Adams#RMMA110527-01) [CASENT0630042, ].

Paratype workers: (5) same data as holotype [CASENT0630983, ; CASENT0630984, ; CASENT0630985, ; CASENT0630992, ; CASENT0630993, ; CASENT0630994, ]; (3) same data as holotype except #RMMA1100527-02 [CASENT0631008, ; CASENT0631009, ; CASENT0631010, ]. Paratype queen: (1) same data as holotype [CASENT0630043, MCZ]. Paratype males: (3) same data as holotype except #RMMA1100527-02 [CASENT0631011, MCZ; CASENT0631012, INBC; CASENT0630869, MZSP].

Etymology
This species is named after Milena Elise Adams Antonova, daughter of R. M. M. Adams.