Conditioning of scouts and recruits during foraging by a leaf-cutting ant, Atta colombica

Experiments using novel and familiar resources were conducted on colonies of the leaf-cutting ant, Atta colombica Guerin, in Costa Rica to determine the effects of prior experience on acceptability of plant resources. Two plant species, Aphelandra golfodulcensis and Caryocar costaricense, grew in the foraging territories of some but not all colonies tested. Artificial patches containing flowers of one or both species were presented to all colonies to study behaviour patterns of scouts and recruits, respectively. Scouts were significantly faster to show recruitment behaviour when encountering a patch containing familiar rather than unfamiliar resources. Workers recruited to a mixed patch by a single scout preferentially harvested resources encountered during travel on trails, regardless of the resource carried by the scout. Colonies treated the two resources differently when they were unfamiliar, accepting Caryocar but not Aphelandra after a delay of up to 24 h. This difference may be due to inherent differences in acceptability of the two resources. Colonies naturally harvesting Aphelandra continued to harvest this resource from artificial patches even after 48 h of exposure to Caryocar, suggesting that familiarity altered the relative ranking of the two resources. The results suggest that conditioning affects relative acceptability of resources to both scouts and recruits, and may be a partial explanation for the diversity of resources harvested by ant colonies. (C) 1996 The Association for the Study of Animal Behaviour