CHOICE OF FORAGING TRAILS BY LEAF-CUTTER ANTS IN BIFURCATIONS: USE OF INDIVIDUAL AND SOCIAL INFORMATION

ELIZALDE, LUCIANA; FARJI-BRENER, ALEJANDRO G

Simposio; XX Symposium de Myrmecologia; 2011

Many ant species build trail networks that branch off to access different resources simultaneously. However, these branches represent a behavioral challenge for the ants that come out to forage since they must choose one of the two trails. At least two types of information can help in this situation: the information obtained during previous trips (prior experience or individual information) or the number of ants passing through a branch of the bifurcation (social information), which could indicate the quality of the resource at the end of that trail. We evaluated in Acromyrmex lobicornis leaf-cutting ant the use of individual and social information to decide which branch to follow at a bifurcation in the foraging trail. In 10 nests we marked ants returning from both branches of a bifurcation with a different color for each branch. The next day, using the color marks we estimated the degree of fidelity of ants to the branches that they had used previously. Then we put attractive baits (corn flakes) at the branch with less ant traffic and evaluated the degree of fidelity of ants to both branches. Prior to placing the bait a 71% on average of the ants were faithful to their branch. The inclusion of bait in the branch with previously less ant activity increased ant traffic from 30% to 73%. However, 31% (range 9–68%) of the ants were faithful to the branch in which they foraged previously but had less ant traffic. These results show that both individual and social information are used by ants to decide which branch to take in a trail bifurcation. Most of the ants used social information, changing to the other branch when it had higher traffic, but a significant percentage (30%) remained in the branch where they had previously foraged, using individual information. The use of both types of information can be beneficial for the colony to rapidly exploit new resources while maintaining the diversity of plant material entering the nest and necessary for the fungus culture.