Acromyrmex crassispinus and Acromyrmex heyerii are two of the leaf-cutting ants found in Uruguay. These ants are dominant herbivores in the Neotropics and constitute an economically important pest in agriculture and forestry, causing severe defoliations in very young plants. Although Metarhizium anisopliae and Beauveria bassiana are well-known entomopathogens, the main aim of this study was to evaluate the use of these fungi together with lower doses of chemical products for insect control. This combined application of entomopathogenic fungi with insecticides for reducing ant populations under field conditions could be a more environment-friendly solution. The effect of different commercially available insecticides on conidia viability in vitro was also evaluated. Under field conditions spores of B. bassiana and M. anisopliae were assayed in ant nests with a previous application of fipronil and sulphluramid. The loss of nest activity after 1 or 2 weeks showed the effectivity of the conidia formulation and the fipronil and sulphluramid doses in Eucalyptus plantation.