Red Imported Fire Ant (Hymenoptera: Formicidae) Mortality Following Exposure to Sodium Hydrogen Carbonate (NaHCO₃)

Red imported fire ant, Solenopsis invicta Buren, worker responses to sodium hydrogen carbonate (NaHCO₃) placed on surfaces and in liquid food were evaluated in laboratory bioassays. The median lethal concentration (LC₅₀) of NaHCO₃ applied to surfaces on which workers were restricted was 7.11 mg per cm² at 7 days after initial exposure. Only 42% of workers feeding on sugar water containing 7.5% NaHCO₃ were killed; mortality was not increased with increasing concentration of NaHCO₃. Choice tests demonstrated that NaHCO₃ did not repel or deter feeding by workers. Whole-body pH of workers not exposed to NaHCO₃ was 6.97 (±0.08), while pH of workers exposed to 28 mg NaHCO₃ per cm² on surfaces was 7.90 (±0.21). This suggests a physiological shift in hydrogen ion concentration of ants exposed to NaHCO₃ and perhaps accounts for cause of death.