meadow katydids what do they eat?

I caught some meadow katydids yesterday and would like to know what they eat. I have kept them before but they never seem to last long. I have fed them crape mirtle leaves and apple and wild strawberries and a few other things and they seem to eat that but not very much. What do they eat in the wild or what do people feed them when they keep them?

also what do cone head katydids eat?