Symbiotic partnerships and their chemical interactions in the leafcutter ants (Hymenoptera: Formicidae)

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Leafcutter ants are indigenous to Central and South America and the southern US and are noticeable for their active herbivorous behaviours, collecting mostly fresh plant parts to manure underground gardens of their Leucoagaricus gongylophorus fungal cultivars. These gardens contain a single clone of the cultivar but are also susceptible to pathogens, most notably the specialised mycopathogen Escovopsis. Pathogen pressure led to the evolution of intensive grooming behaviours assisted by antimicrobials produced in endocrine glands and by domesticated antibiotic-producing actinobacteria grown on the integument of workers. The most notable of these are Pseudonocardia species that are abundant in Acromyrmex but have been lost in Atta leafcutter ants. The leafcutter ant symbiosis represents a fascinating example of chemical warfare of which the details are becoming increasingly known. Here, we review recent progress in understanding the complex interactions that take place between the mutualistic and parasitic symbionts, particularly between the ants, their mutualistic fungal cultivars and cuticular actinobacteria, and their Escovopsis parasites.