For several years I've grown Nitoctiana sylvestris, which I raise in the
greenhouse till it's about 2ft tall, because it is very susceptible to
slugs.

I don't really like having it in the greenhouse, because it's a magnet
for whitefly.

This year, I have an invasion of sciarid fly (the little black flies
that swarm around the top of pots). They don't cause problems to most
things. but their larvae do eat fleshy roots, including cacti. I've
moved over from soilless to soil based compost to deter them, and taken
to putting a layer of sand on the top of all pots.

When I went to remove a Nicotiana which has just come into flower, I
realised it was covered in hundreds of sciarid flies which had become
stuck to its sticky leaves, and which were totally dead (unlike
whitefly, which can land on and take off from Nicotiana with impunity).
So maybe I should revise my thoughts, and start growing Nicotiana as a
biological sciarid fly control?
--
Kay