Selectively Targeting of Gardeners and Symbiotic Fungus in Leaf-Cutting Ant Colonies Using Essential Oils

Social insect pests such as leaf-cutting ants challenge conventional pest management because effective control must disrupt colony-level organization rather than target individual insects. Colony persistence depends on the mutualistic association between gardener workers and their cultivated fungus, Leucoagaricus gongylophorus. Compounds that selectively impair these components while preserving forager-mediated bait transport may therefore offer strategic advantages. We evaluated the essential oils of weeping willow (Salix babylonica), Surinam cherry (Eugenia uniflora), weeping bottlebrush (Melaleuca viminalis), ginger (Zingiber officinale), and black pepper (Piper nigrum) against two leaf-cutting ant species, Atta sexdens and Acromyrmex subterraneus, after characterizing their chemical composition by GC-MS. The oils displayed distinct terpenoid profiles: bottlebrush oil, for instance, was dominated by 1,8-cineole and α-pinene, while ginger oil was rich in camphene and β-phellandrene. Forager and gardener workers were tested separately, along with their symbiotic fungus. Responses were generally concentration-dependent, although effects varied among oils and biological targets. Ginger oil exhibited strong fungicidal activity, but only at the highest concentration tested (100 mg mL^-1). Bottlebrush oil showed marked toxicity to A. sexdens gardeners at concentrations as low as 0.10 mg mL^-1, while effects on foragers were comparatively low. The remaining oils produced limited or inconsistent responses. These findings indicate that caste-selective toxicity and fungal suppression are achievable but not widespread among essential oils. Bottlebrush oil emerges as a promising candidate for further investigation, particularly regarding its constituent compounds and potential synergistic interactions for toxic bait development.