Still not enough info. As many details as you can if you want good help. We don't even know how old the culture is yet. Is it just one culture or has it been a repeating problem? Do you have experience culturing flies or is this your first attempt. How soon after mixing the media did you spike the flies?
im pretty sure its a mite problem. but i had 2 cultures from Joshs Frogs and i was using those to make more cultures. but i think ive only made about 4 other cultures so yes im new to this. I would wait prolly 45 minutes to an hour to put the flies into the media mix. i would wait 10 ish days and they would make the larvas on the wall but it seems like they would then just die within a few days.