Tuesday, December 12, 2006

Insight on the strategy of seed elaiosome collection by workers of Atta sexdens rubropilosa (Hymenoptera: Formicidae)

Ethel F. O. Peternelli, ethel@insecta.ufv.br, Terezinha M. C. Della Lucia, tdlucia@ufv.br, Luiz Alexandre Peternelli, peternelli@dpi.ufv.br, Neliane C. Moreira, nelianealex@yahoo.com.br, and Lucas M. Souza, lucasmachadodesouza@gmail.com. Višosa Federal University, Campus universitario - Višosa, MG. 36570-000, Brazil, Višosa, MG, Brazil

Workers of Atta sexdens rubropilosa, commonly known as leaf-cutting ants, can collect different parts of the plant, including fruits and seeds. When they collect seeds with elaiosome, a nutritive appendage on the seed, they use only this appendage; later the seeds are discarded. Why do they collect the entire diaspore if only the appendage will be used? Would this behavior be a strategy to maximize resource entrance in less time? To answer these questions three behavioral experiments were performed in laboratory with seeds of Mabea fistulifera (Euphorbiaceae). In the first experiment free seeds were offered in the arena. In the second, they were offered glued, so that only the elaiosome could be removed. In the third, the leaf-cutting ant workers would be exploring the seeds in the presence of Pheidole sp. (competitor) or Solenopsis invicta (predator) workers. The interactions between these species with leaf-cutting ant workers were analyzed separately. The results indicated that leaf-cutting ant workers treated the seeds they found differently depending on how they were found. The presence of a competitor and a predator had an influence on exploring, cutting and harvesting times. In conclusion, workers of A. sexdens rubropilosa prefer to transport diaspores that are bearing elaiosome, even if only this appendage is their goal, because such behavior is faster, safer and more efficient. Small ants are not exposed to the external factors when the elaiosome is removed inside of the colony. The workers of A. sexdens rubropilosa did not compete for the seeds with other species in this study. The removal of the elaiosome from the seeds is done essentially, by small workers inside the colony.

Species 1: Hymenoptera formicidae Atta sexdens rubropilosa (leaf-cutting ant)