My fire ants only go away with Pyrethrim. Great thing about pyrethrim is that it biodegrades very quickly and is a "natural" product, i.e. comes from a plant source though there are man made ones call pyreth- something (omg now I can't remember exactly). But sprinkled liberally on the garden where I want to run them off, it works nicely, and doesn't render my crops inedible nor do I have to wait more than a few days to eat whatever is there - though I don't grow root crops, that could be different.
My fire ants laugh at Amdro and all other baits. They love a nice dusting with DE, I think it's invigorating for them. The kind of poisons that you sprinkle all over and 6 feet out, then water in? No more effective than pyrethrim. Cuts their numbers but doesn't kill out the nest. Boiling water and flooding makes them hide a while. But nothing eradicates them. At least though, I can keep their numbers down some and move them out of vegetable garden areas.
What DE does do very well for me is get rid of the flies in the coop. But for ants - it does nothing. Only kills the beneficials around them.
Oh and the ants being on the beans - what they are doing is "farming" the aphids. They don't eat the aphids themselves, the adult ants eat the honeydew that comes out of the aphids behind. It is very sugary and a great source of energy for them. You can kill aphids with lots of things, even just knock them off the plants with a strong stream of water, but until the ants are under control, they will keep coming back, and quickly.