Nest spatial structure and population organization in the Neotropical ant Azteca chartifex spiriti Forel, 1912 (Hymenoptera: Formicidae: Dolichoderinae)

Azteca chartifex spiriti is a dominant arboreal ant living in forests and agroforests in southeast Bahia, Brazil. This species is especially important as it is considered as one of the main agents of natural biological control in cocoa plantations. This ant builds carton structures following a polydomous nesting strategy. Our study aimed to characterize the spatial structure of its nests and population organization living in. Seven colonies of A. chartifex spiriti were studied. In each one, the main nest, as well as six satellite constructions of different sizes, were measured and their population studied. We randomly sampled 350 workers per colony, 50 from the main nest and 50 from each one of the six selected structures. The sizes of these constructions were negatively related to their distance from the main nest. This central nest is where the reproductive gyne is supposed to be and where brood is present, while in the more peripheral and smallest satellites (similar to 2 cm), workers are tending their mutualistic scale insects (Hemiptera: Coccidae). Practically only workers are found in nests of intermediate size. Workers of A. chartifex spiriti are weakly polymorph and their distribution by size category is not random within the colony territory. Workers are much more variable in the central nest compared to the peripheral structures, particularly in the smallest satellite constructions where minor workers are dominant. These characteristics are interpreted as a form of optimization of resource use by the ants.