A 3D model to illustrate the nest architecture of Acromyrmex balzani (Hymenoptera; Formicidae)

ABSTRACT For eusocial insects, the nest is a place where the main social interactions occur. The nest architecture ensures protection from predators and the environment, as well as suitable conditions for brood rearing, food storage, and in some cases the cultivation of fungus farms. Variations in nest architecture can occur, according to the environmental conditions. In order to elucidate the internal organization of nests, most studies use 2D schemes and photographs to illustrate the nest architecture models. However, 3D models can provide a different and more realistic view of the nest architecture. The aim of this study was to describe the nest architecture and colony size of the grass-cutting ant Acromyrmex balzani (Emery), using 3D models to illustrate these features. The structures of eight colonies were measured and the data were used to create a 3D model of each nest. Externally, the nests had one or more piles of loose soil and waste, with a single straw turret over the entrance. Underground, the nests had from 2 to 6 chambers, at a maximum depth of 122 cm. It could be concluded that the observed nest architecture of Acromyrmex balzani followed, at least in part, the pattern already reported in the literature. However, this is the first report of connection between two chambers made by two shafts, as well as the presence of the turret at the nest entrance/exit, regardless of the season of the year. These differences evidence that the nest structures may vary, depending on intrinsic or local environmental conditions.

Nest architecture development of grass-cutting ants

ABSTRACT Atta bisphaerica is a species of grass-cutting ants commonly found in the Cerrado biome. The Brazilian Cerrado (savanna) biome covers 2 million km representing 23% of the area of the country. It is an ancient biome with rich biodiversity, estimated at 160,000 species of plants, fungi and animals. However, little is known about their nest architecture development. This study investigated the architecture of fourteen A. bisphaerica nests from Botucatu, São Paulo, Brazil. Molds were made of the nests by filling them with cement to allow 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. As expected, there was a lateral development in the nests and increase in the number of chambers over time. Results showed that in nests with an estimated age of 14 months, the average depth was 1.6 ± 0.4 m; for those with 18 months it was 2.2 ± 0.7 m and at 28 months it was 2.5 ± 0.7 m. The number of chambers varied from 4 to 7 in 28-month nests, 2 to 4 in 18-month nests, and from 2 to 3 in 14-month nests. With respect to the dimensions of the internal tunnels, there were variations in their average width, increasing with time. The fungus chambers were located beneath the largest mound of loose soil. This study contributes to a better understanding of the so far unknown nest architecture development of A. bisphaerica grass-cutting ants.