now that you mention coco... was it bagged coco, not bricks? I've seen several people having the same problem and all were using bagged coco, Bigsm0 had a terrible problem with them.
the issue not on the coco though, the issue along the side of fabric pots and down near bottom of pots where it gets damp or stays damp.. I treated the top.. and still am problem is sides of them fabric pots.I been spraying them as well, but doing nothing to stop them from coming back.