Mycetagroicus

A genus of fungus growing ants. Mycetagroicus species seems to be quite common, although they are seldom collected. This may result from cryptic habits, enhanced by the peculiar soil-binding sculpture, and also probably as a result of the slow movements these ants show in the field. (Brandão & Mayhé-Nunes 2008)

Identification
Brandão & Mayhé-Nunes (2008) - Mycetagroicus species (Mycetagroicus cerradensis, Mycetagroicus triangularis, Mycetagroicus urbanus and Mycetagroicus inflatus share a peculiar sculpture (Brandão & Mayhé-Nunes 2001), with all body surfaces covered with regularly spaced, round, minute pits (better seen at relatively high magnifications, up to 70 times), bearing each a deeply set hair, one third the diameter of the pit, sometimes effaced by soil particles; antennal scrobes absent; preocular carinae straight at the eyes level, and evenly curving inwards posteriorly; pronotal shoulders as spine-like triangular projections; mesonotum without conspicuous projections anteriorly, with the posterior dorsal margin oblique to vertical or nearly so, in lateral view; compact petiole, with short to indistinct peduncle; postpetiole always larger and broader than the petiole; disk of tergum 1 of gaster covered by a net of coarse rugulae, more evident anteriorly, sometimes joining similar-sized hair pits.

Brandao and Mayhe-Nunes (2001) - Mycetagroicus belongs to an informal group of genera called by authors as the “higher Attini,” which includes most of the tribe, and the true leaf-cutting ants, the polymorphic Atta and Acromyrmex. Among the “higher Attini,” the species of Sericomyrmex clearly differ from Mycetagroicus by the abundant silky pilosity and by the heart-shaped head. Several species of Cyphomyrmex (belonging to the two recognized species groups) possess auriculated occipital lobes: workers of the strigatus group have relatively deep antennal scrobes, and the frontal lobes of the rimosus group species workers are largely expanded laterally. Both Cyphomyrmex species groups workers share with Mycetagroicus only the presence of a short petiole. The mesonotum of Mycetarotes is very thorny: the petiolar node has small but noticeable spines, and its species have occipital projections - characters never observed in Mycetagroicus.

In the notebooks of Kempf and Goncalves, we have found samples numbers 1492 and 482 registered as Mycetophylax and Mycetosoritis, respectively. Unlike the genus we are describing, however, workers of Mycetophylax have the whole integument smooth, their dorsal pronotal projections are low and blunt, and the preocular carinae is almost straight. Among the species of Mycetosoritis there is a considerable morphological heterogeneity, comparable only to that found in Trachymyrmex. Mycetosoritis and Trachymyrmex differ from Mycetagroicus by the presence of an antennal scrobe, and by the presence of tubercles or spines in the dorsum of the gaster.

Distribution
Jesovnik et al. (2013) - Three of the four species in the genus Mycetagroicus are found in the Cerrado; the fourth, Mycetagroicus inflatus, is so far known from seasonally flooded riverbanks in a region characterized as ‘‘dense alluvial forest’’ (Silva, 2007).

Biology
Brandao and Mayhe-Nunes (2001) - Workers of all three species of Mycetagroicus  have the integument almost completely covered by soil particles in a fashion similar to other myrmicine Basicerotini and Slegomyrmecini (Holldobler & Wilson, 1986), resulting in the same camouflage effect derived from the thin and continuous mud layer, enhancing the overall resemblance of the ants to the environment they live in. This effect is enhanced in relatively aged workers. supposedly the foragers. However, Mycetagroicus does not have specialized hair as in Basicerotini and Stegomyrmecini, but their bodies are mostly of a rough texture, and covered with regularly spaced pits, from which depart long, deeply set, unspecialized erect to suberect hairs. Based on the fact that mud particles are firmly attached to the ant’s body, it seems likely that the hair pits may produce some adhesive secretion to help hold soil particles in place. The mud layer is not an SEM artifact because: 1. The picture with the Mycetagroicus triangularis ventral worker head clearly shows the mouth parts devoid of any soil particles, although otherwise encircled by areas completely covered by dirt; if the coating was the result of long term storage, all body surface would have been evenly covered. 2. It is likely that the specimen from which we took the mouth apparatus picture represents an aged worker, considering the very much worn out mandibular teeth. At the same time we have pictures of two Mycetagroicus cerradensis paratypes, a relatively young worker from Rancharia, SP. Brazil, clean of any soil grains, and a more aged worker from Fazenda Itaquere, SP. Brazil, showing not only more worn out mandibular teeth, but with many soil particles attached to the integument.

Nomenclature

 *  MYCETAGROICUS [Myrmicinae: Attini]
 * Mycetagroicus Brandão & Mayhé-Nunes, 2001: 641. Type-species: Mycetagroicus cerradensis, by original designation.

Worker
Integument shagreened, opaque. The hair pits and the overall texture of the integument capture fine grained soil particles, that as the workers age, accumulate in a thin uniform mud camouflage layer. Triangular mandibles longitudinally striate on dorsal surface till the smooth flange from where the teeth arise; the maxillary palps covered by the labrum in all studied specimens, labial palpi two segmented; the mouth apparatus clean of any soil particle, contrary to all other body surfaces. Clypeus antero-mesially convex, always with a median seta arising from the limit of the anteclypeus and clypeal anterior margin, that bears a small median notch. Preocular carinae start at the level of a rounded projection that interrupts the lateral margin of the head in full face view, evenly curving inwards, ending at the level or behind the posterior margin of the compound eyes, and not reaching the frontal carinae: antennal scrobe absent. Interfrontal width scarcely surpassing one half of its maximum width across the eyes; supraocular projections represented by minute tubercles: occipital margin slightly notched; occipital corners rounded, without noticeable projections but also covered all over by minute tubercles similar to those of the supraocular region; compound eyes notably convex, surpassing the lateral margin of the head and placed anteriorly on the head capsule, closer to the mandibular insertions than to the occipital corners.

Pronotum dorsal and lateral faces meeting in a triangular acute projection (in Mycetagroicus cerradensis and Mycetagroicus triangularis the anterior and lateral faces of the pronotum separated by a carina): antero-inferior corners of the pronotum projected, angulated or ending each in a small blunt tooth; mesonotum without relatively high projections at the anterior dorsal surface, except for low tubercles; posterior face of mesonotum, when seen laterally, oblique or vertical; anepisternum and katepisternum always distinct, sometimes separated by a carina; small metanotum interrupting the dorsal margin of the alitrunk; basal face of propodeum with two longitudinal crenulated ridges; the meeting of dorsal and declivitous faces of the propodeum as two short triangular projections, in one species truncated and blunt; metapleura and declivity continuous, without noticeable ridges or carinae. Hind femora length shorter than alitrunk length.

Petiole without conspicuous peduncle and dorsal projections, at most a low posterior triangular tubercle; petiolar ventral process pointing forward, below the metasternum; postpelioie longer, twice as long as the petiole, and large, without dorsal projections; sides almost parallel. Rugulae on the gaster tergum I more conspicuous on the anterior half, the rugulae often linking hair pits to one another; tergum I of the gaster at anterior half marginated on the sides, sometimes vestigially: sternum I with a longitudinal median sagital carina, as long as half of its length.

Etymology
From latinized Greek Mycetus (myketus) = fungus: agroikus (agroikos) = of the country, in the sense of cultivation.