The effect of fire ant (Hymenoptera: Formicidae) venom on ecologically relevant bacteria

Fire ants, Solenopsis invicta Buren (Hymenoptera: Formicidae) and Solenopsis geminata (Fabricius), have evolved a variety of physiological and chemical defenses against microbe introduction and infection in their colonies. Compounds of most interest are the piperidine alkaloids found in S. invicta and S. geminata. Alkaloids are produced by the poison gland, stored in the venom sac, and released through the sting. These compounds have antibiotic, antifungal, antiparasitic, antiviral, and hemolytic properties. We hypothesize that fire ants alter the microbiome of their environment through the consistent use of these chemicals in and around their nests, affecting plant-microbe interactions and the rhizobia-legume nodulation process. In this study, S. invicta and S. geminata worker ant venom extracts were evaluated in disc-diffusion bioassays against the nitrogen-fixing soybean (Glycine max L.) (Fabales: Fabaceae) symbionts Bradyrhizobium japonicum (Kirchner) (Hyphomicrobiales: Nitrobacteraceae) and Bradyrhizobium elkanii Kuykendall and the microbial insecticide Bacillus thuringiensis Berliner (Bacillales: Bacillaceae). Venom extracts inhibited the growth of all tested microbes, with S. geminata extracts having a greater inhibitory effect than those from S. invicta.