The effect of wilting on the selection of leaves by the leaf-cutting ant Atta laevigata

Abstract

Using field assays of leaf preference, we tested the hypothesis that wilting affects the selection of leaves by the leaf-cutting ant Atta laevigata (Fr. Smith). Detached leaves were left to air-dry until noticeably wilted. The area removed by the ants from wilted leaves was significantly greater than the area removed from fresh leaves, this effect being observed in several plant species, in leaves of different age, and in assays with different ant colonies. Leaves collected from water-stressed plants were also preferred to leaves from non-stressed plants. A. laevigata was found to employ a two-stage, size-related, strategy when cutting plants. Larger workers climbed the plant stem and dropped whole leaves to the ground by severing their petioles; smaller workers cut the lamina of the dropped leaves. The ants frequently left dropped leaves on the ground, until the next foraging day or even later, when they were harvested in a wilted condition in preference to newly-dropped leaves. It is possible that during wilting some repellent substances evaporate or become less effective, thus enhancing leaf palatability. Alternatively or in addition, changes in nutrient and water content may have rendered wilted leaves more palatable to leaf-cutting ants. © 1996 Kluwer Academic Publishers.