Amen! clones, potting mix, and any other new introductions to the garden/ grow room can be possible sources. Went organic, was doing passive hydroponics w coir/perlite mix. Too wet, along with some other problems.  Cleanliness really is next to godliness. Or for you atheists it's KEY.  Some call them FILTH flies.  It go's back to the clecha that. An oz of prevention is worth a metric ton of cure. And the insecticide is systemic, so I avoid treating after the budding light cycle commences.  I have had good success so far. Also, do not leave tents open more then needed.