Selective fern herbivory by leaf-cutter ants of Atta cephalotes (L.) in Brazil

Abstract

Although leaf-cutter ants of the genus Atta are polyphagous, they discriminate between food plant species. Ferns represent the second largest group of vascular plants and are especially abundant in tropical forest understories, but seem to be avoided as food plants. We studied the leaf damage caused by leaf-cutter ants and its relation with water content, trichome density, alkaloids, triterpenoids, and total phenol and nitrogen content of nine fern species occurring in close vicinity to Atta cephalotes (L.) nests from rainforests in Brazil. Meniscium serratum Cav. presented the highest leaf damage with 32.3%, three other species had a leaf damage of less than 5%, and the remaining five species were undamaged. Food preferences of leaf-cutter ants were related with higher water content (> 70%), but independent of any other measured variables. Additional observations from Mexico and Costa Rica provided evidence that a larger number of ferns are attacked by leaf-cutter ants. We suggest that highly damaged fern species might serve them as an occasional, short-term, alternative diet when growing close to ant nests, whereas less damaged fern species might have some chemical components harmful for the fungus and detected a posteriori, because they were rejected after initial harvesting by leaf-cutter ants.