Avaliação da atividade de escavação de ninhos em Acromyrmex subterraneus (Hymenoptera, Formicidae): estímulos e divisão de trabalho

Abstract

(Evaluation of nest’s digging activity in Acromyrmex subterraneus (Hymenoptera, Formicidae): stimuli and division of labor). Leaf cutting ants from Atta and Acromyrmex genera are known by their social organization and ability to build nests with a complex architecture. Nest building has a great importance in the field because it alters the chemical and physical properties of the soil, contributing to the growth of vegetation. In addition, the excavation process allows us to understand fundamental behavioral patterns in social organization in cutting ants, constituting relevant basic ecological studies related to behavioral dynamics of group activities organized in eusocial insects. It is known that for some species of leaf-cutting ants, symbiotic fungus and offspring act as a stimulus for the excavation, exerting influence on the complexity of the emerging structures (tunnels and chambers). This study investigated what are the stimuli for digging behavior in Acromyrmex subterraneus during nest building, testing the hypothesis that the presence of the fungus garden and/or brood are stimuli for the excavation of tunnels and chambers. In addition, we investigated the division of labor to verify if the level of activity of workers for excavation task changes due to the presence of the fungus and brood. The experiment consisted in recording the frequency of excavation of individually marked workers placed in plastic cylinders filled with soil, in which were applied four treatments: FB - 30 medium workers, 5g of fungus garden and 30 brood items (larvae and pupae) FG - 30 medium workers and 5g of fungus garden, LP - 30 medium workers and 30 items of brood and WK - 30 medium workers without fungus garden and brood. After 24 hours we registered nest morphometric parameters (length and width of chambers and tunnels in cm) and the volume of excavated soil, as well as the excavation activity of each worker. In contrast to the expected, there was no change in the morphological structure, digging frequency or volume of excavated soil among the treatments. However, we verified differences among the activity level of the workers, leading to an unequal distribution of tasks with half of the most workers remaining inactive while the others performed the excavation intensely and repetitively.