Mycetomoellerius dichrous

Walter Kempf and his student Jorge Diniz discovered numerous nests of this species in recently burned cerrado.

Identification
Mayhé-Nunes & Brandão (2002) - This is perhaps the most aberrant species both in the entire genus and in the present species-group. Within the latter, the worker (and female) may be distinguished by the following features: bicolored, head dark brown, body and appendages brown; frontal lobes subtriangular, slightly expanded laterad, the interfrontal width not exceeding one half of head width; supraocular tumulus indistinct; antennal scrobe not delimited postero-laterally behind eyes, nor projecting posteriorly in a tuberous fashion; occiput rounded laterally; vertex lacking paired carinae; anterior half of sides of tergum I of gaster weakly to indistinctly marginate. The following characters are shared only with Mycetomoellerius compactus: occipital tooth absent; antero-inferior corner of pronotum rounded, not angular nor dentate; second and third pairs of mesonotal projections vestigial; postero-dorsal border of postpetiole broadly excised.

Specimens from Aguas Emendadas, northern Brasilia, have the propodeal teeth more developed than in the other samples.

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

Biology
Mayhé-Nunes & Brandão (2002) - We have found the following account by W. W. Kempf in the MZSP collection: “Recently, on October 21, 1975, at the beginning of the rainy season, Jorge Diniz and myself located several nests of this species in a small, already disturbed and recently burned ‘cerrado’ at the northern limit of the city of Brasilia. Although not prepared for a careful excavation, we tried nevertheless to dig out one nest with a small gardener's shovel. We were able to find the nest chamber with the fungus garden and to secure nearly the total population of the colony, although the chamber itself was destroyed before we could make out its size and shape, and verify if the fungus garden was a suspended one from rootlets, in the true Mycetomoellerius-fashion. The results of our findings may be summarized as follows:

The nest entrance was marked by a circular orifice of about 5 mm in diameter, around which the excavated soil had been heaped up in low and irregular mounds by the ants, not forming a regular crater. From the nest entrance, a vertical canal went down for nearly one meter, to open in the nest chamber with the fungus garden. 384 workers, 2 dealate queens, 23 alate males, 8 pupae and 39 larvae of different sizes and instars were retrieved from the nest, which probably represents the total population, inasmuch as at the moment of our digging no activity was going on at the outside of the nest, and we examined carefully any lump of earth taken out by our digging. The fungus-garden, secured only in somewhat smashed condition, seemed to contain cut-up stems of grasses or other plants. Probably there was no second chamber, because several visits to the excavation site after taking out the nest did not reveal any further activity.”

Castes
Known only from the worker caste.

Mayhé-Nunes & Brandão (2002) - In Kempfs notebook (# 11806) we found a mention to a complete series of this species, including workers, females, males, pupae and larvae, from Distrito Federal, Brasilia, northwestern city limit, 21.x.1975, W. W. Kempf & J. Diniz leg. (see detail in Biology). Despite several attempts we were not able to locate this sample, even with the help of Reginaldo Constantino at Universidade de Brasilia, where Kempf’s collection was deposited before being transferred to the MZSP, and of Jorge Diniz (Universidade de Goias), a student of Kempf at the time of his death.

Nomenclature

 *  dichrous. Trachymyrmex dichrous Kempf, 1967a: 126, figs. 7-9 (w.) BRAZIL.
 * Combination in Mycetomoellerius: Solomon et al., 2019: 948.

Worker
Mayhé-Nunes & Brandão (2002) - TL 4.5-5.1; HL 0.99-1.07; HW 1.03-1.11; IFW 0.51-0.57; ScL 0.93-1.07; TrL 1.51-1.70; WL mm; Hfl 1.49-1.70. Strikingly bicolored, head capsule deep brown, body and appendages medium brown or ferruginous. Integument finely but indistinctly shagreened, opaque. Long, dense, mostly curved or inclined hairs on head, alitrunk, and pedicel; same hairs but denser and less curved and more uniformly inclined on gaster, scapes and legs. Alitrunk hairs not arising from prominent tubercles which are lacking. Dense and much shorter pubescence of lighter color, inclined or appressed on head, pedicel, gaster and appendages. erect or suberect on thorax, never masking the integument.

Head. Mandibles smooth and shining except laterally on base where they are finely longitudinally striate; masticatory margin with apical tooth and approximately 8 teeth. slightly smaller towards the base. Frontal lobe triangular, little expanded laterad, interfrontal width scarcely or not at all surpassing one half of head width across the eyes. Frontal carinae diverging caudad, fading out at posterior fourth of head. Front and vertex inconspicuously tuberculate. Preocular carinae slightly curving mesad above eye but not intersecting the antennal scrobe, fading out shortly behind eyes. Posterior half of antennal scrobe indistinct, the apex not projecting in a tuberous fashion on occiput; supraocular tumulus vestigial. Occipital corners rounded and edentate. Occipital tooth absent. Occiput in full-face view distinctly notched in the middle. Vertex lacking paired carinae. Inferior occipital corner indistinctly marginate and rounded. Eyes moderately convex, with about 13 facets across the greatest diameter. Antennal scapes as long, or nearly as long, as head capsule, without prominent spicules, surpassing the occipital corner when laid back over the head as much as possible by one fifth of its length. All funicular segments distinctly longer than broad.

Alitrunk. Prominent piligerous tubercles lacking. Pronotum with indistinct humeral angles, its antero-inferior corners rounded and toothless. The lateral spines very low and tubercular. Mesonotum with a pair of high anterior conical spines, facing obliquely laterad, followed by two pairs of very low and little distinct denticulate tubercles, the posterior pair almost obsolete. AI trunk shallowly impressed at metanonotal groove. Basal face of propodeum narrow, lateral borders indistinctly marginate, bearing a few piligerous tubercles. Propodeal spines very short and inconspicuous. Hind femora about as long as alitrunk.

Waist and gaster. Petiole pedunculate, the node proper longer than broad, the dorsal armature obsolete; anterior ventral process developed as a small blunt spine. Postpetiole not much broader than long, flattened above, the postero-dorsal border broadly excised between the non-tubercular corners. Gaster opaque; tergum I with dense, minute and evenly distributed piligerous tubercles; vestigially marginate on sides in the anterior half.

Type Material
Mayhé-Nunes & Brandão (2002) - Holotype and 6 paratypes from type locality, one paratype from Brasil: Mato Grosso, Chapada dos Guimaraes, and one paratype from Brasil: Sao Paulo, Agudos at (examined).