Nematodes have not proven very effective in controlling fire ants. Nematode strains tested to date cause ants to temporarily move away from the treated mound, but few colonies are actually eliminated. If nematodes are used, be sure to water the treated area fairly regularly. Areas treated with nematodes need to remain moist.
Here is an article from Florida on fire ant control using nematodes.
http://ipm.ifas.ufl.edu/applying/methods/biocontrol/antnematode.shtml
Here is a more recent article from eXtension about the use of parasitic nematodes to control fire ants.
http://www.extension.org/pages/Fire_Ant_Treatment:_Natural_and_Biological_Control
