I take apple cider vinegar and put it in a small condiment bowl with a drop of dish soap, cover it with saran wrap, and poke a bunch of holes in it. They fly in to get the acv and get trapped in or die in the acv/dish soap mixture. I keep them setting on top of my vivs because they tend to breed in there. They fly out and head for the vinegar mixture. I also wash all plants coming in my house, whether they go into the vivs or not, to try to get rid of any eggs in the soil and replant them.