Waste management in leaf-cutting ants

Hygienic behaviour is an important aspect of social organisation because li ving in aggregations facilitates the spread of disease. Leaf-cutting ants f ace the additional problem of an obligatory dependency on a fungus, which i tself is also susceptible to parasites. In this study we provide evidence f or the importance of effective waste management in colonies of several Pana manian species of Atta and Acromyrmex leaf-cutting ants, differing in colon y size and typical mode of waste accumulation (external or internal dumps). We show that: (1) waste is dangerous for the ants, which die at a higher r ate in the presence of waste; (2) waste is dangerous for the mutualistic fu ngus because waste in field colonies is infected with the specialised funga l parasite Escovopsis; (3) the ants allocate considerable effort to active management of waste in order to reduce these dangers. This management follo ws a "conveyer belt" model according to which increasingly dangerous tasks are performed by older workers, who are less valuable to their colony. Our approach is kaleidoscopic, as different species of leafcutting ants are une qually suitable for direct observation and experimental manipulation, and s uggests that more in depth studies of waste management in attine ants would be highly rewarding.