If the fire ant problem has not resolved itself yet, you might want to try diatomaceous earth (D.E.) to kill them. I like to put the D.E. in a long necked bottle and puff it into the ant entrances. Ants groom each other, so quickly spread the D.E. The D.E. has to be reapplied whenever it gets wet, but some diligence with it will wipe out the whole colony.
