THE ROLE OF LEAF-CUTTING ANT WORKERS (HYMENOPTERA, FORMICIDAE) IN FUNGUS GARDEN MAINTENANCE

1. We studied the role of leaf-cutting ant workers (Atta sexdens (L.)) in fungus garden maintenance, by temporarily excluding workers from the garden. This increased its subsequent attractiveness, as expressed by an increase in the numbers of workers licking it. 2. The length of free mycelia on areas of the garden from which workers were excluded increased but was reduced again when workers were returned. Workers therefore removed hyphae from the garden surface. 3. The maximum 'isolation effect' was obtained by preventing ant access for 2-3 days, after which the effect declined. Removing staphylae from portions of garden kept ant-free for 4 and 6 days restored the effect, as the ants were not distracted by harvesting staphylae. Portions of garden kept ant-free for longer than this were no more attractive than non-isolated control garden. 4. Workers were highly efficient in detecting and removing contaminants from their fungus garden. Samples of garden could be isolated from workers for up to 12 days before major growth of contaminants occurred, and this contrasted with the maximum of 6 days for the isolation effect on licking. The isolation effect was therefore not a response to contaminant growths on the garden. 5. Workers on the garden surface may remove hyphae for nutritional reasons, or to 'prune' their fungus and stimulate its growth. In either case, the result is a regulation of fungal growth.