Communication between the fungus garden and workers of the leaf‐cutting ant, Atta sexdens rubropilosa, regarding choice of substrate for the fungus

Abstract

SummaryBait made from orange peel, containing the fungicide cycloheximide, was initially harvested by workers of Atta sexdens rubropilosa (Forel) and incorporated into the fungus garden as substrate for the fungus. The bait was subsequently rejected by the worker ants days later. Exposure of the fungus to cycloheximide, in laboratory sub‐colonies, resulted in the fungus being ‘stressed’. By interchanging normal fungus garden with ‘stressed’ fungus garden, a change in the foraging behaviour of the workers was evident.–Two hypotheses to explain the behavioural changes were tested: a volatile semiochemical is produced by the fungus which affects the foragers directly, or contact between workers (and fungus garden) is necessary for information regarding fungal substrate to be transmitted through the worker force. When pairs of sub‐colonies were connected (one colony of each pair exposed to cycloheximide in the bait) and workers were initially prevented from passing from one colony to the other, one colony continued to forage on orange bait while the other did not. When both colonies were allowed to make full contact then both colonies failed to accept orange bait. This discounted the first hypothesis, but supported the second, as a highly volatile chemical should be able to diffuse between colonies. When large foragers were prevented from making contact with the second colony, the information may be communicated by smaller workers.