Protecting indoor plants from black flies
If the Ladybirds are showing no interest in the pest, it could be one they don’t eat! I suspect it could be Fungus fly or Scairid fly. These are little black flies that hatch out of the compost of your pot plants and Ladybirds are not likely to eat them. There are a couple of measures you could take to help tackle the problem. Firstly, hang up some Yellow Sticky Traps near the pot plants and if possible near the compost surface. These will catch the adult flies.
Secondly, you could apply the new predator from Harrod Horticultural called Mighty Mite. This can be applied to the compost surface and will eat the eggs and larvae of the Fungus flies. I hope this is of help.