Foraging activity of two species of leaf-cutting ants (Atta) in a primary forest of the Central Amazon

The foraging activity of the leaf-cutting ants Atta sexdens and A. cephalotes was studied observing two colonies of each species in a primary forest of the Central Amazon. These two ant species utilize chemically and visually marked trunk trails, and it was show that foraging is centered on these trails. The number of new foraging sites was inversely reated to the distance from existing trails. As a consequence, the area effectively exploited by the studied colonies was only 15 to 23% of their respective foraging ranges. Both species attacked large trees (stem diameter >20 cm) in a proportion higher to the available one and this preference seems to be related with quality of the harvested material and with the "area restricted search" strategy employed by these ants. Although these ants were able to exploit a wide range of plant species, harvest activity was concentrated on only a few. New leaves was the main item foraged by A. cephalotes whereas A. sexdens did not show a pattern of plant part preference. A. sexdens also presented a higher temporal variation in foraging rates, and this variation was partiallly related to the type of plant part harvested. It is suggested that the more generalistic behaviour presented by A. sexdens is one of the factors that contributes to its diverse habitat distribution as compared to A. cephalotes. © 1990 Masson