Megalomyrmex wettereri

This is another Megalomyrmex that inhabits the nests of fungus growing ants, in a peculiar lestobiotic relationship.

Identification
Boudinot et al. (2013) - Worker Uniquely identified by (1) strongly reduced eyes, with at most 5 ocelli at maximum diameter; (2) katepisternum smooth. Queen Presumably identifiable similarly as worker (see comments section below). Male Identified by the following combination: (1) forewing 1m-cu present; (2) occipital carina obscured by vertex in full-face view; (3) scape about four to five times longer than pedicel; (4) petiolar sternum smooth and shining.

Characters which separate the workers of Megalomyrmex miri from Megalomyrmex wettereri are as follows: (1) smaller (HL 0.49–0.55 vs. 0.58–0.59); (2) scape longer (SI 90–96 vs. 84–85); (3) setae on scape appressed (vs. decumbent to subdecumbent); (4) katepisternum longitudinally costate (vs. smooth); (5) petiolar peduncle with a dorsolateral longitudinal carina extending about one-fifth the length of the node (vs. without); (6) posterior face of petiolar node meeting posterior petiolar collar at a distinct angle (vs. smoothly curving through petiolar collar to posterior petiolar margin); (7) petiolar sternum almost completely rugose (vs. smooth and “polished”); (8) first gastric tergum with long, relatively dilute decumbent to subdecumbent setae interspersed with shorter appressed setae; (9) setae on legs appressed (vs. subdecumbent to decumbent); (10) head with distinct appressed and subdecumbent setae (vs. setae grading from decumbent to subdecumbent). Queens share with workers at least characters 2, 3, 5, 6, 7, 8, 9, 10.

Males of M. miri may be separated from those of M. wettereri by the following gross morphology: (1) scape setae completely appressed (vs. appressed to decumbent); (2) setae on legs, excluding ventral faces, completely appressed (vs. appressed to subdecumbent); (3) petiolar and postpetiolar nodes stronger, taller; (4) petiolar sternum rugose; (5) postpetiolar sternum anteriorly dentate in profile view (vs. rounded). In addition to gross morphology, several genitalic characters separate the two closely related species: (1) dorsal margin of telomere concave; (2) apical segment of digitus thinner than digitus stem, linear; (3) apicodorsal margin of cuspis obscured by digitus stem; (4) apical margin of cuspis emarginate; (5) penisvalvar teeth distinctly separated; (6) ventral margin of penisvalva convex; (7) penisvalva shorter. Morphometrically, males of M. miri and M. wettereri differ only slightly. A larger sample size for the respective species may yield further discriminatory characters.

Distribution based on Regional Taxon Lists
Neotropical Region: Costa Rica, Panama.

Biology
Brandão (2003) - This is another Megalomyrmex of the silvestrii group that inhabits the nests of fungus growing ants, in a peculiar lestobiotic relationship. The type specimens were found inside a nest of Trachymyrmex bugnioni (Attini), collected by J. Wetterer, to whom the name of this species is dedicated, and inside a nest of Cyphomyrmex longiscapus in Panama collected by U. Mueller.

Adams et al. (1998-1999; 2000) described the finding of two colonies of this new species in Panama containing healthy fungus gardens of C. longiscapus, although no attines were present at the time of collecting. According to these authors, laboratory observations revealed that the Megalomyrmex "consume the fungus by cropping mycelium from the garden substrate. However, they do not forage for and add nutrient substrates, or otherwise tend the fungus garden; thus, when the garden becomes depleted, Megalomyrmex sp. must locate and usurp new gardens in other attine colonies". When presented with active colonies of C. longiscapus, workers of this new species displace "host" workers in mass raids, stinging and ultimately killing the apparent defenseless C. longiscapus. When presented with C. longiscapus larvae in the laboratory, M. wettereri workers strip them of the mycelium layer that naturally covers the cuticle, then place the larvae with their own brood. Adams et al. (1998-1999) considered this Megalomyrmex as a predator on C. longiscapus as they forcibly eject the resident attine to usurp their fungus gardens.

Adams et al. (2000) described in detail how this species conducts mass raids to usurp gardens of C. longiscapus, then lives in the garden and consumes the fungi. Megalomyrmex wettereri workers feed their larvae with attine brood only after removing the fungal mycelium that covers the attine larval integument, suggesting that this fungal coat may provide partial protection against predators.

Boudinot et al. (2013) - This species has been described as a guest ant or an agro-predator, depending on its host choice. It has been collected cohabiting with Trachymyrmex cornetzi by Jim Wetterer in 1993 in Costa Rica and from numerous usurped Cyphomyrmex longiscapus colonies in Panama (Adams et al. 2000; Brandão 2003; Longino 2010). When M. wettereri takes over a Cyphomyrmex colony the M. wettereri workers fill the typically open auricle with soil (fig. 248) allowing them to maintain the garden free of the fungus-growing host workers and stealing most of the fungus garden (fig. 249). Single queens have been collected within usurped gardens suggesting that they are able to infiltrate a colony without the help of workers (Adams et al. 2000; RMMA unpubl. data), but larger colonies with >60 workers and up to three queens are typical. An unmistakable behavior exhibited by M. wettereri during host colony infiltration and colony disturbance is gaster flagging (http://youtu.be/Wb8tSLHwcUA). This behavior is seen in many other Megalomyrmex but is most frequently observed and very obvious in this species.

Nomenclature

 *  wettereri. Megalomyrmex wettereri Brandão, 2003: 155, figs. 1-4 (w.q.) COSTA RICA.

Worker
Mandibles smooth, except for the coarse rugosities at the external area near the base (Fig. 1), dental formula 2+6; palp formula 3:2 (?); anterior clypeal border without median denticle; compound eye with 5 ocular facets at its largest diameter; occipital margin not raised; promesonotal suture not impressed dorsally (Fig. 2), mesonotum undistinguished from pronotum; metanotal groove longitudinally rugose; katepisternum smooth; propodeum spiracles laterally projected in an angle of 45° from the main axis of the body; base with divergent carinae at the meeting with propodeum sides, declivity smooth; epipetiolar carina not complete over the foramen; dorsal profile of petiole, in side view, evenly curved till apex of node, ventral face with a pronounced anteromedian double denticle (Fig. 3) originating in a non-translucent short longitudinal flange; dorsal margin of petiolar node, in frontal view, round; ventral process of postpetiole produced in a sharp tooth.

Color: uniformly bright yellow; apex of segments reddish.

Queen
Three equally developed ocelli; mesonotum with notaulus; katepisternum distally rugose; propodeum dorsal face and declivity meeting in an angle similar to that of the conspecific workers; petiole and postpetiole also similar in shape and sculpture to the con-specific workers.

Male
Boudinot et al. (2013) - (n=3): HW 0.46–0.50, HL 0.47–0.52, SL 0.23–0.25, EL 0.24–0.26, ML 0.88–0.89, CI 96–99, SI 47–51, EI 52–53.

Head Antenna with 13 antennomeres; no antennomeres kinked, although apical antennomeres may shrivel asymmetrically when dried; apical antennomeres not forming a club; scape length slightly less than eye length.

Entire antenna pale yellow-brown. Palpal formula 3,2. Mandible triangular; masticatory margin with 5–6 teeth; apical tooth about three times as long as subapical tooth; basal teeth approximately equal in length. Dorsal face of mandible finely and densely striate. Minimum distance between lateral ocellus and compound eye about 4 to 5 times one lateral ocellus length. Compound eye with sparse short ocular setae. Occipital carina not visible in full-face view. Mesosoma Mesosoma robust. Notauli absent. Parapsidal lines weak to indistinct. Foraminal carina complete; posterior face of propodeum without additional distinct carinae or carinulae. Basitarsi tubular. Pterostigma well-developed. Forewing crossvein 1m-cu present; submarginal cell 1 about one fourth as wide as long; terminal abscissa of M present, branching slightly distad 2rs-rs. Metasoma Basipetiolar carina a shallow arch. Ventrolateral carina of petiole present, weak. Petiolar spiracle in anterior fifth. Posterior margin of petiole and postpetiole without girdling carinae. Postpetiolar helcium subcircular. Postpetiolar spiracle slightly anterad midlength of tergal lateral margin; without a lateral bulge. Sternum of postpetiole weakly bulging. Postpetiolar tergum convex. Genitalia Abdominal sternum IX tapering to long acute triangular lobe at apex; apical lobe not sclerotized or produced ventrally. Telomere short, evenly rounded apically; medial dentiform process absent; medial face weakly crescentiform; ventral margin without sclerotized denticles. Cuspis with distinct apicodorsal process; incised between apicodorsal process and convex apical margin. Digitus narrowed subbasally, broadening to apicodorsal bend; dorsal margin produced dorsoapically, as arched as ventral margin; ventral margin not obscuring posterodorsal angle of cuspis. Valviceps height somewhat more than half length, wedge-shaped; dorsal margin rounding evenly through apical margin to ventral margin; anterior two thirds of ventral margin almost linear, very weakly convex; penisvalvar teeth close-set, longest near base.

Type Material
Megalomyrmex wettereri, worker, gyne. Type Loc.: Costa Rica, Heredia, La Selva (10°26'N, 84°01'W), "em ninho Trachymyrmex bugnioni" (18 workers), collected by J. Wetterer in March 2,1993, 50-150 m, INBIO-OET; Panama, Panama Prov. Km 7 of El Llano Carti Suitupo Road, in June 07, 1998 (09°18'02"N, 78°57'31"W), Ulrich Mueller 980607-01 (one gyne – funiculus missing, two workers) "NMNH 2014315".

Holotype and five worker paratypes (La Selva) deposited at MCZ, Harvard; five paratypes (La Selva) and two paratypes (worker and gyne from Panama) deposited at the MZSP; five worker paratypes (La Selva) and one worker paratype (Panama) deposited at the USNM; two worker paratypes (La Selva) deposited at the BMNH.