Weeding and grooming of pathogens in agriculture by ants

The ancient mutualism between fungus-growing ants and the fungi they cultiv ate for food is a textbook example of symbiosis. Fungus-growing ants' abili ty to cultivate fungi depends on protection of the garden from the aggressi ve microbes associated with the substrate added to the garden as well as fr om the specialized virulent garden parasite Escovopsis. Mie examined ants' ability to remove alien microbes physically by infecting Atta colombica gar dens with the generalist pathogen Trichoderma viride and the specialist pat hogen Escovopsis. The ants sanitized the garden using two main behaviours: grooming of alien spores from the garden (fungus grooming) and removal of i nfected garden substrate (weeding). Unlike previously described hygienic be haviours (e.g. licking and self-grooming), fungus-grooming and garden-remov al behaviours are specific responses to the presence of fungal pathogens. I n the presence of pathogens, they are the primary activities performed by w orkers, but they are uncommon in uninfected gardens. In fact, workers rapid ly eliminate Trichoderma from their gardens by fungus grooming and weeding, suggesting that these behaviours are the primary method of garden defence against generalist pathogens. The same sanitary behaviours were performed i n response to the presence of the specialist pathogen Escovopsis. However, the intensity and duration of these behaviours were much greater in this tr eatment. Despite the increased effort, the ants were unable to eliminate Es covopsis from their gardens, suggesting that this specialized pathogen has evolved counter-adaptations in order to overcome the sanitary defences of t he ants.