Mycetomoellerius holmgreni

This fungus-growing ant forms small soil nests in sandy soils. Their nest entrances are marked by a turret of grass, straw and sand. The architecture and demography of nests vary between season. In autumn, nests have fewer fungus chambers and many winged ants, while in the spring, there are more fungus chambers and a significant number of immature individuals. This indicates that T. holmgreni seems to invest in reproduction during the autumn and establishes new nests during the winter, which promotes growth during the spring and summer.

Identification
A member of the Iheringi species group. Mayhe-Nunes and Brandão (2005) - The most useful character to distinguish this species from the other members of the lheringi group is the shape of the lobes on the antennal scapes. Among the species that lack pilosity on the mesopleura, it also can be distinguished from Trachymyrmex pruinosus, which has triangular frontal lobes. It differs from Trachymyrmex tucumanus by the shape of the small projections on petiolar node, one or two spine-like pairs in T. holmgreni and one tooth-like pair in Trachymyrmex tucumanus.

Distribution
From Misiones Province in Argentina to northern Brazil.

Distribution based on Regional Taxon Lists
Neotropical Region: Argentina, Bolivia, Brazil, Paraguay.

Habitat
This is a widely distributed ant that has been found in savanna, forest, restinga and dune habitats.

Biology
Mayhe-Nunes and Brandão (2005) - The nest found at Santa Barbara do Monte Verde. Minas Gerais State, by one of us (AJMN) was excavated in sandy soil, in an area with few bushes and scarce low vegetation, about 1100 meters above sea level. The entrance hole was longer than broad (6 x 2cm) and in one of the sides had a tower of 1cm height, built with mixed grass straws and sand. The internal structure resembles that of nests of other Trachymyrmex species, such as Trachymyrmex pruinosus discovered by Gallardo (1916), as well as Trachymyrmex turrifex described by Wheeler (1907). The seven alternating spheroidal chambers found were vertically disposed, with the following approximate measures: first chamber (3 x 3cm) about 5cm deep, second (7 x 7cm) to 10cm, third (5 x 5cm) to 20cm, fourth (9 x 7cm) to 30cm, fifth (7 x 5cm) to 40cm, sixth (5 x 5cm) to 50cm, and seventh (7 x 5cm) to 60 cm. The grayish fungus garden was laminated and set vertically, an appearance characteristic of grass use as fungal substrate. The first chamber had several pupae and little fungus hanging from the roof, suspended by thin roots. In the second chamber, a bulky fungus garden was also hung from the roof by roots. Equally, in the three following chambers, the gardens were big, however rested in the bottom of the chambers. The queen was in the fourth chamber; in the last two chambers, small amounts of fungus were found. Besides these chambers, five more possible trash chambers were observed containing a dark brown material, but without ants corpses. During the excavation, the workers do not feign death, a common behavior of other Trachymyrmex. The appearance of the fungus garden and the use of grass straw to build the tower in the entrance of the nest corroborate Goncalves (1975) observations on T. holmgreni cutting fresh leaves of the grass Paspalum ancylocarpum.

Cristiano et al. (2018) - This fungus-growing ant forms small soil nests in sandy soils. Their nest entrances are marked by a turret of grass, straw and sand. The architecture and demography of nests vary between season. In autumn, nests have fewer fungus chambers and many winged ants, while in the spring, there are more fungus chambers and a significant number of immature individuals. This indicates that T. holmgreni seems to invest in reproduction during the autumn and establishes new nests during the winter, which promotes growth during the spring and summer.

Albuquerque et al. (2018) - A nest survey in Itapeva State Park (Rio Grande do Sul state, Brazil) collected nest attributes from 10 colonies and demographic information from 4 colonies. Colony sizes were: 294-581 workers, 20-107 pupae, 8-41 larvae, 0-27 males and 4-54 alate females. Dry and wet weight of the various castes were calculated and spatial aspects of the nest detailed (diameters of nest holes, chamber sizes, etc.). Colonies had a single nest entrance and typically had a small turret that was surrounding by a horeshoe shaped mound.

Nomenclature

 *  holmgreni. Trachymyrmex holmgreni Wheeler, W.M. 1925a: 37 (w.) BOLIVIA. Mayhé-Nunes & Brandão, 2005: 282 (q.m.).

Worker
Mayhe-Nunes and Brandão (2005) - TL 4.1-4.5; HL 1.12-1.34: HW 1.05-1.22; IFW 0.66-0.78; ScL 0.91-0.98; TrL 1.58-1.75; HfL 1.43- 1.58. Dark to reddish brown, sometimes with lighter head or darker gaster. Integument fine and indistinctly shagreened, opaque. Hairs moderately scarce on the body, short and erect or curved on appendages; hook-like mixed with oblique to decumbent hairs on gaster and other parts of body; fine pubescence restricted to funiculus.

Hlead in full face view little longer than broad (CI 95). Mandible smooth and shining except laterally on base where it is finely transversely striate, and near the masticatory margin, which bears the apical and 8 teeth gradually diminishing towards the base. Frontal lobe sub-triangular, moderately expanded laterad (FLI 65), backwards directed and laterally subdentate; anterior border straight; posterior border weakly concave. Frontal carina diverging caudad, fading out a little before the apex of scrobe. Front and vertex with weak longitudinal gulae. Posterior third of antennal scrobe weakly delimited by the frontal carina and extension of the preocular ones. Supraocular projection as bifid or truncated spine. Occiptal corner smoothly rounded full-face view, surmounted by stout tubercles. Occiput notched in the middle. Occipital tooth developed as a stout rather smooth spine-like projection. Inferior occipital corner with carina. Eye weakly convex, no more than 14 facets in a row across the greatest diameter. Antennal scape surpassing the occipital corner by nearly ¼ of its length, when laid back over head as much as possible; basal lobe perpendicularly enlarged, its inner projection bigger than the external ones, prolonged towards the head's middle when the scape is lodged in the scrobe: anterior surface surmounted by small tubercles and ridges.

Alitrunk. Pronotum with marked humeral angle; antero-inferior corner armed with a triangular and flattened spine-like projection; lateral spines long; median projections as two separated small truncated, bifid or simple spines. First pair of mesonotal projections similar to pronotal lateral ones; two longitudinal rows bearing three small teeth; the second and third pairs vestigial. Mesopleurae practically without hairs; blunt teeth-like projection on superior border of katepisternum. Alitrunk weakly constricted dorso-laterally at the shallowly impressed metanotal groove. Basal face of propodeum narrow, laterally delimited by a row of small teeth; slender propodeal spines longer than other dorsal projections of alitrunk.

Waist and gaster. Petiole shortly pedunculate, the node proper as long as broad, with one pair of small spines backwards directed, inserted near the posterior border; subpetiolar process vestigial. Postpetiole as long as broad, shallowly excavated above; posterodorsal border straight; postero-lateral corner without projections. Gaster opaque with minute piligerous tubercles randomly distributed in the tergum 1.

Queen
Mayhe-Nunes and Brandão (2005) - TL 5.6-5.9; HL 1.42- 1.51; HW 1.28-1.34; IFW 0.77-0.82; ScL 0.92-0.95; TrL 2.02-2.11; HfL 1.52-1.62; FWL 5.91-6.09; HWL 3.95-4.09. With the same general distinguishing characters of the workers, with the following differences: Thre ocelli on vertex, the lateral ones smaller. Pronotum with a pair of strong and acute scapular spines, directed out and forwards, and with a pair of inferior spines pointed down and forwards, smaller than the scapular ones. Mesoscutum surmounted by conspicuous tubercles, but without notable dorsal projections. With the alitrunk in dorsal view, very shallow parapses delimited by the parapsidial furrows; mesothoracic paraptera more or less impressed, with a narrow median portion; scutellum ending in a pair of moderately stout and acute spines, directed backwards, with the sides converging obliquely inwards; metathoracic paraptera concealed by the scutellum in dorsal view; propodeal spiracle orifices visible. Two strong acute spines on propodeum, longer than pronotal ones. First gastric tergite with a longitudinal ridge on each side; disk with two longitudinal series of small piligerous tubercles, absent in the middle of the segment.

Wings pale brown, completely covered by microtrichia. Fore wing with 5 closed cells (sub-median, median, costal, sub-marginal and marginal); anal vein turned up and fused with cubito-anal, not prolonged beyond the junction. Pterostigma conspicuous, although not pigmented. Hind wing with 5 complete veins, and 1 closed cell; 10 hamuli on anterior margin.

Male
Mayhe-Nunes and Brandão (2005) - TL 5.3-5.6; HL 0.83-0.95; HW 0.94-1.02; IFW 0.34-0.38; ScL 0.85-0.88; TrL 1.82-2.03; HfL 1.63-1.77; FWL 5.27-5.55; HWL 3.50-3.86. Dark brown, with antennae and legs ferruginous brown. Hairs moderately long and inclined, mixed with short and strongly curved hairs, conspicuous on head, dorsum of alitrunk and first segment of the gaster. Head. Mandibles finely striated on dorsal surface; masticatory margin with five teeth, gradually diminishing towards the base external margin s lightly sinuous. Median border of clypeus convex, with a large anterior notch; dorsal disk of clypeus without projections, but with one weak longitudinal carina on each side, between the base of frontal lobes and its anterior margin. Frontal lobes rounded and directed forwards, leaving part of the antennal insertions exposed. Frontal carinae subparallel, not reaching the occiput. Preocular carinae distinct, fading out at the posterior border of eyes. Compound eyes big and convex, filling some 1/2 of the head sides. Three prominent ocelli. Antennae with 13 segments; scape clearly surpassing the occipital corners, nearly three times longer than funicular segments I-III combined, with a basal lobe weakly projected; funicular segment I longer than II. Occipital corners rounded, with small spines and tubercles visible in frontal view. Occipital margin gently concave in the middle between the lateral ocelli.

Alitrunk: Pronotum with a scapular spine moderately long and acute. Scutum narrow with superficially impressed Mayrian furrows; parapsis shallowly impressed; parapsidial furrows conspicuously marked. Mesothoracic paraptera in dorsal view, slightly narrowed in the middle, where it is impressed and presents a series of short longitudinal keels, without side projections. Scutellum without dorsal projections, ending as two obsolete tubercles. Metathoracic paraptera backwards projected, partially visible in dorsal view. Propodeum with a pair of minute spines between basal and declivous faces.

Waist and gaster: Dorsum of petiole without projections. Postpeliole a little broader than petiole in dorsal view, superficially impressed above, with the posterior border concave. First gastric tergite without lateral ridges or piligerous tubercles, basally with a superficial impression on each side.

Wings similar as described for the female above; the unique noticeable difference is the 1Cu vein of the fore wing, much shorter in the male.

Type Material
Mayhe-Nunes and Brandão (2005) - Probably in the Royal Museum in Stockholm; not examined.