Sequential load transport during foraging in Acromyrmex (Hymenoptera Formicidae) leaf-cutting ants

The complex social organization of leaf cutter ants is closely linked with intricate patterns of division of labor in the worker force. For instance, foraging might involve division of labor between cutters and carriers, as well as task partitioning during leaf transport. However, little is known about division of labor during foraging in Acromyrmex, particularly under field conditions. The goal of the present study is to investigate the behavior of Acromyrmex leaf-cutting ants on trails of different lengths in order to elucidate the effect of foraging distance on the occurrence of transport chains under field and laboratory conditions, and to discuss the hypotheses to explain the occurrence of transport chains. In Acromyrmex crassispinus (FOREL, 1909) and Acromyrmex subterraneus subterraneus (FOREL, 1893), cutting and carrying of fragments were clearly separated activities performed by distinct worker groups differing in body size. In addition, the behavior of foragers of both species differed significantly according to variation in trail distances. On short trails (1 m), cutters frequently transported the fragments directly to the nest, whereas on long trails (more than 10 m), most cutters transferred the fragments to other workers. Transport chains happened more frequently when workers harvested plants far from the nest. These results demonstrate that Acromyrmex species display both division of labor between cutters and carriers, and task partitioning during leaf transport, with trail lengths showing marked effects on the likelihood of sequential transport. Furthermore, the results of this study provide support for the hypothesis that the behavioral response of transferring fragments in Acromyrmex species would have been selected for because of its positive effect on the information flow between workers.