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 cm(2) 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 NaHCO, did not repel or deter feeding by workers. Whole-body pH of workers riot exposed to NaHCO3 was 6.97 (+/-0.08), while pH of workers exposed to 28 mg NaHCO3 per cm(2) 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.