Foraging and grass selection by the grass-cutting ant Acromyrmex landolti fracticornis (Forel) (Hymenoptera: Formicidae) in habitats of introduced forage grasses in Paraguay

Colony densities of Acromyrmex landolti fracticornis (Forel) were found to vary in habitats of introduced forage grasses in central Paraguay. Colony densities were found to be positively correlated with basal grass coverage and the amount of grazing damage. The ants preferentially harvested tender grass blades that showed little or no previous damage by other invertebrates. Colony densities and the amount of grazing damage by the ants showed negative correlations with the amount of grazing damage by other invertebrates. Preferences were determined for 13 species of exotic forage grasses. In both laboratory and field tests, Digitaria smutsii and Panicum maximum were selected significantly more often than other species, and Pennisetum purpureum , P. ciliare and Brachiaria decumbens were selected significantly less often. The preferences observed in the laboratory were also observed in field colonies. The importance of these factors in determining colony density and their practical implications on the Paraguayan cattle industry are discussed.