Waste management in leaf-cutting ants

Hygienic behaviour is an important aspect of social organisation because living in aggregations facilitates the spread of disease. Leaf-cutting ants face the additional problem of an obligatory dependency on a fungus, which itself is also susceptible to parasites. In this study we provide evidence for the importance of effective waste management in colonies of several Panamanian species of Atta and Acromyrmex leaf-cutting ants, differing in colony 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 rate in the presence of waste; (2) waste is dangerous for the mutualistic fungus because waste in field colonies is infected with the specialised fungal parasite Escovopsis; (3) the ants allocate considerable effort to active management of waste in order to reduce these dangers. This management follows 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 unequally suitable for direct observation and experimental manipulation, and suggests that more in depth studies of waste management in attine ants would be highly rewarding.