One minute oatmeal has already been processed to death, taking a lot of the nutrients with it. You could use it but not for long...Go ahead and put them in it, and add to it as soon as you can pick something up. If you have grape nuts cereal, flake cereal, or something along those lines, you could use that too. As long as you have something grain-based, without too many additives and sugar, you can substitute all you want. Meal worms eat grain, period...you don't have to follow someone's ingredient list to the letter. They're merely suggestions. I personally use oatmeal and powdered milk. Sometimes I use flake cereal or grapenuts if I have it.
As far as the pupae go, set up a second box with fresh bedding (oatmeal, etc.) and throw them in. When they emerge as beetles, they will mate and lay eggs in the grain. Within a couple weeks, you'll see teeny-tiny mealworms.
Some people lay a papertowel over the top to spray with water periodically. When I did it, I noticed that the beetles loved to hide in it...but I ended up with too much moisture and mold killed my culture. I also had that happen when I added carrots or potatoes for moisture. You'll have to experiement until you find what works for you, and it may be different at different times of the year. LOL! Good luck!
