Your substrate has to be where they're coming from & rather than risk my snakes (from the side effects of PAM) I'd bake the substrate to kill them off
before using it. Or just toss it outside in the garden & buy something else to use. If you're determined to use the same substrate, you might have more
luck from a different supplier? I would never ever use PAM (or any other pesticide) just to eradicate harmless wood mites...