Nasturtium leaf compounds, diphenyl disulfide and lyral, against Atta sexdens (Hymenoptera: Formicidae) and their symbiotic fungi.

Abstract

Social insect pests, particularly leaf-cutting ants, present a considerable challenge in terms of control. Leaf-cutting ants are significant agricultural, forestry, and pasture pests, and understanding their behavior and defense mechanisms is essential for managing their colonies effectively. While toxic ant baits are a primary control method, the limited availability of effective insecticides and concerns over their hazardous nature has spurred the search for alternative solutions, particularly natural compounds, which aligns with the goals of forest certification groups. In the light of previous evidence demonstrating the efficacy of nasturtium leaves (Tropaeolum majus L. (Brassicales: Tropaeolaceae)) in suppressing leaf-cutting ant colonies, this study investigates 2 active components of nasturtium leaf extracts: diphenyl disulfide and lyral. We tested their impact on Atta sexdens (L.) (Hymenoptera: Formicidae), the most prevalent leaf-cutter ant species in Brazil, and their symbiotic fungus, Leucoagaricus gongylophorus (Möller) Singer (Agaricales: Agaricaceae). We conducted experiments with increasing concentrations of diphenyl disulfide and lyral, assessing their effects on the symbiotic fungus and on forager workers and gardeners of A. sexdens colonies. Our findings revealed no fungicidal activity, and ant mortality was minimal in both topical and ingestion bioassays with the exception of gardeners topically exposed to diphenyl sulfide. Furthermore, the compounds did not affect leaf ingestion, but diphenyl disulfide did increase interactions among foragers. These results suggest that neither diphenyl disulfide nor lyral are the primary contributors to the suppression of leaf-cutting ant colonies by nasturtium leaves. However, they may enhance the formicidal activity of other compounds present in nasturtium leaves.