I have used parasitic nematodes for flea control. They work great, and also had some effect on fire ants the year I applied them to the lawn. There are other preditors of fire ants, but I do not know where you can buy them. Below is a link to where I bought the nematodes, and another link to an article that talks about other fire ant parasites.
Application of the nematodes requires a pump up sprayer that has NOT had any pesticides or herbicides in it. Plastic absorbs many chemicals, and those chemicals would kill the nematodes as well. Organic pesticides (pyrethrin) are still poisonous. The microscopic nematodes are shipped in a sponge. You place the sponge in water, and squeeze it gently a few times to dispurse the nematodes into the water. Load the nematode water into the sprayer and spray your lawn at once. If you have not had any rain in the past two days you should water the area you intend to spray before applying the nematodes. The nematodes make their way to the soil surface where they attack bugs that travel along the ground. They are not harmful to animals or people, and do not attack earthworms.