Restricted Ingestion of Bacteria by Fire Ants

Fire ant queens and workers from colonies fed to repletion on Serratia marcescens, Bacillus thuringiensis, or Bacillus sphaericus were aseptically dissected, and homogenates of their thoracic and gastric guts were plated on appropriate media to determine whether bacteria were ingested. All three species of bacteria were effectively excluded from the gut of both queens and workers. A small, slow-growing, Gram-negative bacterium, noted in some of the test queens, was subsequently isolated from the gut of 8 (13.8%) of 58 queens from field colonies. This bacterium was partially characterized, but was not identified. Implications for microbial formicide research are discussed.