Each Streptomyces±fungal challenge was replicated three times and done on Czapek yeast autolysate agar. The actinomycete was inoculated on Petri dishes and grown to a diameter of ,1.5 cm; fungal strains were then point-inoculated near the edge of the culture. Challenges were monitored every two days and growth inhibition of tested fungi was scored as a reduction of growth rate as compared with growth of fungal cultures in the absence of the Streptomyces, or as complete suppression of growth. We assayed possible antibiotic production speci®c to the specialized parasite Escovopsis in the same way that we assayed antibiotic production speci®c to other potential contaminants, except that each challenge to Escovopsis was replicated ®ve times. Four strains of Escovopsis isolated from the gardens of different Acromyrmex octospinosus colonies in Panama in 1997 were tested against Streptomyces. We also studied the production of antibiotics speci®c towards Escovopsis in other attine species, including Cyphomyrmex longiscapus, Atta colombica and Atta cephalotes. The presence of a zone of inhibition in bioassays indicates ®rst, the production of diffusible metabolites by the actinomycete, and second, the susceptibility of the test fungus to these compounds. As inhibition is dose dependent, the detection of partial inhibition implies the existence of a dose that could impart complete inhibition.Growth-promotion bioassays. Broth cultures of the attine fungus isolated from an Apterostigma colony were grown with extracts from the Streptomyces isolated from this species. Actinomycete extracts were obtained by growing Streptomyces in Czapek yeast autolysate broth for 2 weeks and then passing the broth through a low protein-binding, sterilizing ®lter unit (Millipore, Millex) to remove bacterial biomass. We replicated each bioassay ®ve times and used 50 ml Czapek yeast autolysate broth per bioassay.