Assessing the effects of sodium on fire ant foraging in the field and colony growth in the laboratory

1. Sodium is an essential dietary element and preferential foraging for high concentrations of sodium by inland herbivorous and omnivorous ants suggests it may be limiting. If so, increased sodium availability through altered deposition and anthropogenic sources may lead to increased colony and population growth and cascading ecological impacts. 2. For red imported fire ants, Solenopsis invicta Buren, the present study tests: (i) whether colonies from coastal and inland sites differ in their responses to NaCl baits; and (ii) whether supplemental NaCl increases growth of fire ant colonies in the laboratory. 3. Fire ants in inland sites with low sodium deposition responded roughly an order of magnitude more strongly to high concentrations of NaCl baits than did fire ants in coastal sites with high sodium deposition. 4. Laboratory colonies of fire ants, however, showed no signs of sodium limitation or benefits of increased sodium. The link between behavioural responses to baits in the field and effects on colony growth deserves further investigation to assess the ecological impacts of altered sodium availability