This is food for your newly hatched mealworms. Check your cultures every week to make sure they aren't out of apples. They can also be bought. I record the date I start each culture on the top layer of paper. This strategy keeps me in plenty of worms.
Potatoes also work, but apples work better because they supply more moisture for the worms.
Set container out to room temperature for one day every week to allow the worms to feed.