I have been breeding mealworms for quite some time. I have started out with just three tubs of 180 worms each and at this stage I don't even know how many 1'000's I have, maybe even millions!
So my recipe is quite easy.
I only use wheatbran as a substrate, I have found that oatmeal is too expensive and too course. Then I feed them all vegetable and fruit leftovers from the kitchen except POTATOES as all forms of potatoes have a natural cyanide. So if you feed your worms potatoes, guess what, you are actually slowly but surely killing your pets! Carrots are good as they are high in vit. C and beta carotene. I normally whizz the carrots through the food processor and then just add a t-spoon per box of worms. Bananas = magnesium, apple cores = lots of moisture.
Then I have the "adult" worms in a plastic tub with an inch of wheatbran. I check this box every day to remove the pupae. If you don't remove the pupae the worms will eat them for their moisture content.
The pupae are removed and placed in a seperate smaller tub also on a bed of wheatbran; just so that the beetles hatching have something to munch on and to make sure the pupae are at a warm temperature. This container do NOT get any fruit or veg, moisture will cause them to rot.
Then the beetles are removed from the pupae box and placed in a separate container. (100 beetles per box). The beetles are also kept on wheatbran and fed fruit and veg. I remove the beetles once every 2 weeks and place them in a fresh box. If you don't do this, the beetles will eat their own eggs.
The wheatbran with the eggs are left for another 2 weeks after I have removed the beetles to make sure all the eggs have hatched. Then using a very fine mesh I sift the wheatbran to make sure I get ALL the baby worms. Once I have the baby worms seperated from the frass (worm poo) I start back at stage 1.
While the worms are growing I also sift them once every 2 weeks to get rid of all the frass and place them on new and fresh wheatbran. In case you wondered, my worms are the healthiest and best looking worms I have ever seen when comparing to worms from pet stores. Not boasting, juts stating a fact.
My animals can't seem to get enough of them and my super worms. Super worms however are a completely different kettle of fish.