Anything that has high acidic levels is not a good thing to feed your feeders... for example, onions, peppers (even bell peppers), garlic, and yes, i would say fruit aswell...
Just stick to things like carrots, kale, lettuce, romaine, potatoes, etc, and i think you'll do just fine. I would not feed your insects just anything in your fridge just to get rid of it (not you personally, but in general)