The Origin and In Situ Identification of Uncultured Gut Bacteria in Fourth-Instar Larvae of the Red Imported Fire Ant, Solenopsis invicta (Hymenoptera: Formicidae)

Abstract

This study corroborated the findings of Lee et al. (2008) and relied on culture-independent techniques, particularly 16S rDNA sequencing. Results from the study demonstrated that ants in captivity completely change their gut bacterial diversity strongly supports the conclusion that fire ant gut bacteria are environmental in origin. Bacteria in the fourth-instar larvae were present because they were consumed with food sources. From molecular data, a differing list of bacteria from each colony with different branching and clustering among bacterial clades in the phylogenetic trees were found. Different bacterial diversity and evenness was found in all colonies, which provided evidence against the idea of the presence of obligate bactrial endosymbionts in Solenopis invicta guts. Obligate endosymbiont elimination through the use of broad-spectrum antibiotics did not significant affect ant mortality when compared to the untreated controls. This study did not find bacteriocytes in the midgut epithelium of fire ants. Microscopic observations did not locate any bacteriocytes in fourth-instar S. invicta larvae. All identified bacteria appeared to have been derived from the food or the environment. Though coadapted bacteria and specialized bacteriocytes were not found in the guts of fourth-instar larvae, such specialized organisms may be present elsewhere in the ant. Coadapted symbionts may exist in other parts of the larvae’s body or in other stages of development.

Keywords

• bacteria
• symbiosis
• Solenopsis invicta