Moni

Ben, BT is baccillus thuringiensis (or something like that). Because it is so hard to say, everyone just says BT. Your garden center will know exactly what you are talking about. It is a bacteria that specifically targets certain insects and kills them. That is the beauty of it. It is very specific. There are different varieties of BT but they all target certain caterpillars/larvae. The version used for fungus gnat larvae is I believe the same version that is used to kill mosquito larvae in ponds, etc. It's great stuff. There are not many things that can be used on larvae in soil so this is just what you need. But what you are doing will work, too. It will just take a little longer because you are only killing one stage of the insects growth (adult). You will have to repeat what you are doing a couple more times to get all of the generations that go from larva to fly.
Moni