I bought and tried a product called Surrender--contains 75% Acephate. Applied it yesterday after the sun came out.
Less than 1 day later, I have mounds full of dead fire ants. Not empty mounds--mounds with dead ones--thousands and thousands of dead ants.
Down side--it stinks like the dickens. I mean STINKS! I could smell it thru the unopened can when I was on my way home from the hardware store and had to stop and put it in the back of the truck. Had to hold the can down wind when I was spooning it out on the mounds. It ain't cheap, but it seems to work.
(not for crop areas, and I don't think I would use it where cattle could get to it, but that's just me.)
Did I say it stinks?