We use this method to raise D. pachea stocks.
First take a piece of the Senita cactus (Cereus schottii) and let it get good and rotten for several days at room temperature. Next, stir up a vial of banana Opuntiafood. Then, add some of the rotten cactus and mix thouroughly. Grow the flies on this mixture and add in some pieces of wood (popsicle stick) or dental cotton (pre-soaked) for a pupation surface.