250 adults will not eat much. Maybe a few cups? Why not skip the dog food altogether? Fruits and veggies and a little chicken every once in a while is plenty. They like leftover spaghetti too.

They're roaches, they thrive on pretty much anything. I had some in a cup in a cupboard and forgot about them for a MONTH, I took the cup down to see what was in it, and they were all alive. After a month with no food or water.