Screening of native plants from central Argentina against the leaf-cutting ant Acromyrmex lundi (Guérin) and its symbiotic fungus

Abstract

Leaf-cutting ants are major agricultural and forestry pests in the New World. Attempts to control themhave most frequently involved the use of chemical insecticides, with mixed results. Among alternativemethods, botanical pesticides may provide a sustainable and efficient control of leaf-cutting ants. In thepresent study, we screened the activity of plant extracts derived from 89 species native to Argentina,against the leaf-cutting ant Acromyrmex lundi (Guérin) and its mutualistic fungus, Leucoagaricus gongy-lophorus, through a pick-up assay and bioautography, respectively. The pick-up assay revealed moderateto strong anti-foraging activity for just over 13.5% of the assayed species, including complete ant foraginginhibition for Aristolochia argentina, Flourensia oolepis, Gaillardia megapotamica, Lantana grisebachii andLithrea molleoides. Most plant extracts were well tolerated by fungi, with only 12.3% of the species testedshowing some degree of fungus growth inhibition. Among these, A. argentina, F. oolepis and Pterocaulonalopecuroides were the strongest inhibitors, whereas Baccharis flabellata, Dalea elegans and Zanthoxylumcoco revealed a more moderate activity. Only A. argentina and F. oolepis extracts showed strong antifor-aging effects and affected fungus growth at the same time. Values of IC50and MIC indicated that extractsinhibiting ant foraging at lower concentrations did not necessarily also inhibit fungus growth at lowerdoses. The active principle of A. argentina, on both ant foraging and fungal growth, was identified asargentilactone.