Competition between grass-cutting Atta vollenweideri ants (Hymenoptera: Formicidae) and domestic cattle (Artiodactyla: Bovidae) in Argentine rangelands

Abstract

Leafcutter ants are considered the most important herbivores in the Neotropics. Atta vollenweideri is a rangeland pest that competes with cattle for grass, reducing the carrying capacity of pastures. However, there is much controversy regarding their degree of herbivory, pest status and competition with cattle. Furthermore, their economic injury level (EIL) has not been determined. We studied A. vollenweideri in competition with cattle in a natural pasture in Argentina, quantifying primary productivity, as well as herbivory by ants alone and together with cattle. Productivity and herbivory by ants were contrasted with cattle dietary requirements under two grazing regimes. We estimated the first EIL for leaf-cutting ants in rangelands. Productivity was highly variable throughout the seasons. Competition between ants and cattle was evident during the low productivity periods, with evidence of ants being more affected by cattle unless ants store food during the productivity peak in summer and autumn. The EIL was 0.29 ant nests per hectare, although it likely overestimates the importance of these ants as pests. We discuss the shortcomings of a classic EIL formula for estimating the damage potential of social insects.