Fungus-growing ants (Attini) of the genera Atta and Acromyrmex are severe pests of natural and cultivated plants in the Neo-tropics (see Cherrett, Chapter 2 and Fowler et al., Chapter 3). These ants culture symbiotic fungi (Basidiomycetes) on fresh vegetable substrate made of flowers and leaves harvested close to their nest. According to Weber (1972) the ants feed specifically on their fungus and can be considered "monophagous." On the other hand, Littledyke and Cherrett (1976) have shown that worker ants ingest sap from the leaves they collect. Therefore, from an ecological point of view, these ants should be classified as "polyphagous" (Cherrett 1972a) since they feed on a wide range of plants (Weber 1966; Cherrett 1968). It has also been shown that the attines exhibit preferences for certain plant species (Amante 1967; Cherrett 1968; Rockwood 1976, 1977; Fowler and Robinson 1977; Pollard et al. 1983; Pintera 1983). Within a group of plants, some species appear immune to attack while other closely related species are particularly susceptible.