Humidity preference for fungus culturing by workers of the leaf-cutting ant Atta sexdens rubropilosa

The hygropreference of gardening workers of the leaf-cutting ant Atta sexde ns rubropilosa was investigated in the laboratory using a gradient of relat ive humidity. Gardening workers were placed, together with pieces of fungus garden, in small, interconnected nest chambers offering four different rel ative humidities: 33%, 75%, 84% and 98% RH. Workers were allowed to move fr eely between them and to relocate the fungus following their humidity prefe rence. While workers distributed themselves randomly in the nest chambers, they located the fungus gardens in the chamber with the highest humidity. T hese results indicate that gardening workers are able to sense differences in relative humidity, and that this ability is shown when they are engaged in fungus culturing. Humidity is discussed as one of the relevant variables that probably underlay the evolution of regulatory responses for the contr ol of fungus growth in leaf-cutting ants.