Megalomyrmex acauna

Megalomyrmex acauna is the only species of this group to be found in cerrados.

Identification
Occipital margin visible in head frontal view; head largest diameter at vertex; non-pedunculate petiole with a round posterior face; anterior slope of postpetiole round.

Brandão (1990) - M. acauana is close to Megalomyrmex balzani from which can be separated by the characters listed in the diagnosis.

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

Biology
This species was described from two samples collected in Gustavo Dutra and another locality in the Chapada dos Guimarães, near Cuiabá, Mato Grosso state, Brazil. Dr. Antonio Mayhé-Nunes visited the area recently and discovered that Gustavo Dutra was actually the name of an Agricultural School. The small village is now known as São Vicente, and is located in the county of Santo Antonio do Leverger, some 100 Km East of the state capital, Cuiabá.

Megalomyrmex acauna is the only Leoninus group species recorded in the "cerrados". The Leoninus group is otherwise an entirely Amazonian group. In fact, Prof. Marcelo Tavares sent me recently a sample from the Indian Reserve Tadarimana, Rondonópolis, state of Mato Grosso state, Brazil (16°28'S, 54°38'W). I collected in May 6 to 29, 1996, two colonies of M. acauna in Uruaçu, northwestern Goiás, Brazil (14°17'06"S, 48°55'01"W). Both localities are situated within the "cerrado" biome. The ants live in fairly large colonies that occupy spaces among stones, in a way that is very similar to the most closely related species, M. balzani. In both cases the colonies were found along gallery forests and all attempts to rear them in the lab failed.

Nomenclature

 *  acauna. Megalomyrmex acauna Brandão, 1990: 429, figs. 39, 56 (w.) BRAZIL. Brandão, 2003: 151 (m.).

Worker
Mandibles smooth; anterior clypeal border straight with median denticle; 3-segmented an­ tenna! club; frontal suture impressed; 18 ocular facets at com pou nd eye largest diameter; promesonotal suture impressed dorsally: mesos­ternum and metasternum without acrotergites; propodeum dorsum not depressed; declivity smooth; epipetiolar carina complete; non-pedun­culate petiole with anteroventral denticle; dorsal margin of petiole in side view straight; ventral face of postpetiole without process; genual plate acuminate.

Male
Brandão (2003) - From, I received a male of M. acauna (undescribed) collected by F.S. Truxal in June 13, 1956, in a locality 24 Km East of Formoso (13°37'S, 48°54'W), Goiás state, Brazil.

Clypeus smooth without anterior denticle; cephalic integument smooth next to the compound eyes: first funicular segment similar in size to scape, second and third smaller; mesonotum with parapsidal furrows impressed, but no notaulus; epipetiolar carina complete; dorsal face of propodeum smooth; petiole compressed dorso-ventrally; petiolar spiracles laterally produced; petiolar and postpetiolar nodes almost indistinct; postpetiole without ventral process; genual plates rounded.

Type Material
Gustavo Dutra, MT, Brasil (14°43'S, 55°39'W); Chapada, MT. Brasil, (15°26'S, 55°45'W).

Holotype (G. Dutra) and  10  paratypes  (1 from Chapada, 9 from G. Dutra) at Museu de Zoologia da USP; 2 (G. Dutra) paratypes at Museum of Comparative Zoology, Harvard; 6 paratypes (G. Dutra) at Museu Nacional  do Rio de Janeiro.

The types  from  Gustavo  Dutra  have  been collected by the late Dr. Cincinnato R. Gorn;:alves in October. 25, 1953. The paratype from Chapada has been collected by C. Aman in July. 1960.

Etymology
The specimen choosen as holotype bears a labels saying "Megalomyrmex nigricornis, sp. n., Borgmeier det." Accordingly I select the name acauna, meaning black horns in the Tupi lan­guage, due to the black scapes of the antennae, that differentiate this species from all others in the group.