Bacterial microbiology of the red imported fire ant, Solenopsis invicta Büren (Hymenoptera: Formicidae)

Ants are capable of building close associations with plants, insects, fungi and bacteria. Symbionts can provide essential nutrients to their insect host, however, the development of new molecular tools has allowed the discovery of new microorganisms that manipulate insect reproduction, development and even provide defense against parasitoids and pathogens. In this study we investigated the presence of bacteria inside the Red Imported Fire Ant (Solenopsis invicta) midgut using transmission electron microscopy and molecular tools. After isolation and culture of these bacteria, the molecular analysis revealed ten unique profiles which were identified to at least the genus level. Three of these strains were genetically modified with the plasmid vector pZeoDsRed and successfully reintroduced into fire ant colonies. Strong fluorescence of DsRed was detected up to seven days after introduction. The transformed bacteria can still be rescued after pupal emergence; however most were passed out in the meconium. We further demonstrated that nurses contributed to the spread of the transformed bacteria within the colony by feeding the meconium to naive larvae. PCR results showed that Enterococcus sp., Kluyvera cryocrescens and Lactococcus garvieae are the most abundant species, but they are not consistently found in all sites throughout the southeastern United States. Antibiotic treatment of fire ant colonies under laboratory conditions confirmed that the entire bacterial community served as a symbiont, playing an important role in the queen’s ability to reproduce and affecting the colony fitness. These results are the foundation for a fire ant biological control program using endosymbiotic bacteria.