Influence of biotic, chemical and mechanical plant defenses on the foraging pattern of the leaf-cutter ant (Acromyrmex striatus) in a subtropical forest

The diet of the leaf-cutter ant Acromyrmex striatus was used as indirect evidence for potential antiherbivore activity by the nectivorous ant Camponotus blandus and by chemical and mechanical plant defenses. Data on ant activity, plant abundance, and foliar material for analyses of chemical and mechanical plant defenses were collected during spring in a subtropical forest in the Argentinean Chaco. We found a negative relationship between the proportion of visits by C. blandus and leaf harvesting of A. striatus for the plant species that offer nectar. However, the most abundant plant species in the forest comprised the greatest part of the leaf-cutter diet. In general, no relationship was found between chemical or mechanical defenses and leaf-cutter diet for all the plant species of the forest. A few plant species with high levels of plant defenses suffered little or no harvesting by leaf-cutter ants. Our findings suggest two main reasons for the absence or low representation of nectar-offering plant species in the diet of A. striatus: nectivorous ant activity and low plant species abundances.