Metarhizium anisopliae and Trichoderma viride for control of nests of the fungus-growing ant, Atta cephalotes

The leaf-cutting ant, Atta cephalotes, is an economically important pest in tropical and subtropical agricultural and forestry ecosystems. These ants use leaf fragments to cultivate Attamyces sp., a symbiotic fungus on which they feed. In this study, baits (wheat bran and orange juice) containing the entomopathogenic fungus, Metarhizium anisopliae (strain M-137), or the antagonist fungus, Trichoderma viride (strain T-26) to Attamyces sp., or a combination of both entomopathogenic and antagonist fungi were applied to control A. cephalotes nests in the laboratory and field. In the laboratory, control of the ant nests treated with any fungal treatment proved 100% effective. Under field conditions, the fungal baits were compared to the chemical Pirimiphos methyl, which was applied with an air pump. The ants did not detect the fungal agents contained in the baits that they introduced into their nests and, therefore, no detectable defensive behaviors were evident. The mortality of the bait-treated nests was 100% with M. anisopliae and the combined fungal treatment, and 80% mortality in the treatment with T. viride, whereas the mortality with Pirimiphos methyl was effective in 60% of the nests. Additionally, a week after application of these treatments, changes in the ants’ behavior were observed, reflected mainly in the absence of foraging activity. Thus, M. anisopliae and T. viride were effective in controlling A. cephalotes nests under laboratory and field conditions, and superior to the chemical Pirimiphos methyl.