I use a multi-grain mixture with some skimmed milk powder added in. The various grains and seeds I use include: bran. wheat, oats, sunflower seeds, flax, ect....
I have found that this mixture produces awesome mealworms and superworms that are generally far healthier than insects that are raised on one or two types of grain. If you are only buying what you need for food in a few days, then a bran and oatmeal mixture is fine... but if you are actually breeding your own mealworms/superworms and want to have a nice big fat yummy worm for your pet, try using a multi-grain mixture.
Take care
Annie B. <:3 )~~