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Ants build underground nests to protect their colonies and to improve conditions for their offspring. The excavation of nests, by ants, modifies the soil structure, facilitating gas exchange and circulation, which needs further studies. Do initial nests modify the initial chamber soil matrix and gas exchange? The objective was to study the soil micromorphology of the wall of the chamber of initial nests of the leaf-cutting ant A. sexdens and how the CO2 diffuses into the soil matrix. The CO2 concentration in initial four-month-old A. sexdens nests was measured for 24 h using a respirometric system with a gas meter and closed nest holes (obliterated). After this period, they were opened and the CO2 concentration measured again. In addition, 15 cm deep holes were drilled into the ground 15 and 60 cm away from the ant nest hole. The CO2 was measured in these orifices and then they were sealed for 24 h and new ones made after this period. The contents of the nest chambers were removed, after the CO2 measures and the soil micromorphology of the walls of the initial chamber analyzed. The CO2 concentration in the nest chamber was greater than that in the soil at 15 and 60 cm distant from it. The CO2 accumulation did not increase with the obliteration of the nest entrance for 24 h. Coarse material, mainly quartz and charcoal fragments, besides fine material of clay, organic matter and iron oxides composed the soil of the wall of initial nests. The soil porosity in the chamber walls of the initial nests was lower than that of the matrix of the adjacent soil and differed between those of the nests. Initial nests of A. sexdens modifies the soil matrix of their walls, allowing to CO2 exchange between its chamber and adjacent soil. [ABSTRACT FROM AUTHOR]

The success of incipient colonies of leaf-cutter ants depends on multiple factors such as temperature, humidity, soil type, the queen's fertility and vigor, frequency of harmful microfungi, among others. Based on this observation, three factors related to Atta sexdens were characterized: (1) initial nest morphology (depth and volume); (2) queen oviposition rate; and (3) prevalence of Escovopsis (parasitic fungus) and other fungi in incipient colonies. Our observation showed a variation in chamber dimensions and volume, indicating differences in colony development rates. The oviposition rate of queens from nests of the same age showed a difference among queens. About microfungi prevalence, it was found that many are potentially deleterious. In particular, the parasite Escovopsis was present in 16.7% of the colonies. Our study shows positive correlations between queen condition and nest size/fungus garden size. These correlations collectively suggest that ecological factors such as plant availability can generate substantial variation between nests and thus shape the success of incipient colonies. [ABSTRACT FROM AUTHOR]

Research related to the comparative biology of phylogenetically close ant species has received little attention, although it is the basis for understanding the systematics of some sibling groups. The objective was to study the polygyny, oviposition, life cycle and longevity of the three subspecies of leaf-cutting ants. For that, we studied: oviposition rate - queens from three colonies were individually placed in plastic containers, and at 24-hour intervals, the laid eggs were quantified over a period of 96 hours; the workers' life cycle - the development of immature ants was observed every 24 hours and, as a result, the duration of each stage of development was determined; the workers' longevity - newly emerged adults were tagged and returned to the fungus chamber of their respective nests, and daily observations were made in each of the nest's chamber. Laying rates were variable in the three queens studied, with a mean of total eggs laid of 271 for Acromyrmex subterraneus brunneus, 113 for Acromyrmex subterraneus subterraneus and 119 for Acromyrmex subterraneus molestans.The incubation period was 21.2 days in A. s. brunneus, 22.8 days in A. s. subterraneus and 20.4 days in A. s. molestans. The larval phase and pupal phase lasted on average 22.5 and 21.2 days in A. s. brunneus, 22.8 and 15.8 days in A. s. subterraneus and 17.2 and 14.2 days in A. s. molestans, respectively. Life cycle was different in the studied taxa, from 62 to 77 days in A. s. brunneus, from 59-68 days in A. s. subterraneus and from 51 to 55 days in A. s. molestans. The workers' longevity varied between subspecies A. s. brunneus, A. s. subterraneus and A. s. molestans. [ABSTRACT FROM AUTHOR]

Atta capiguara is a grass-cutting ant species frequently found in Cerrado biome. However, little is known about the giant nest architecture of this ant. In this study, we investigated the architecture of three A. capiguara nests from a fragment of Cerrado in Botucatu, São Paulo, Brazil. Casts were made of the nests by filling them with cement to permit better visualization of internal structures such as chambers and tunnels. After excavation, the depth and dimensions (length, width, and height) of the chambers were measured. The results showed the shape of Atta capiguara nests consisting of mounds of loose soil with unique features resembling a conic section. The fungus chambers were found distant from the mound of loose soil and were spaced apart and distributed laterally at the soil profile. The waste chambers were located beneath the largest mound of loose soil. Both the fungus and waste chambers were separated and distant. Our study contributes to a better understanding of the so far unknown nest architecture of the grass-cutting ant A. capiguara. [ABSTRACT FROM AUTHOR]