Also try running really hot (but not boiling) water down into the soil. This is my remedy for soil bugs of all kinds. And a layer of sand on the topsoil will work by cutting through the larve. Good Luck!

I have to admit that I've not seen a fungus gnat since I changed my potting mix. I find that the Saintpaulia seem to require a slightly more damp mix than my other houseplants, but with a mix of lots of perlite, some bark fines, and a bit of peat, I can keep a mix that drains well, holds enough water to keep their fine roots happy, yet doesn't stay wet for days to hold gnats.

I completely stopped using the mosquito stuff - it worked great, but I love not using anything!

Diatomaceous Earth kills most insects with exoskeletons, and larvae. I've effectively used food grade DE to rid my houseplants of pests.

Fungus gnats like a moist environment, so if you keep things a bit drier, it will definitely help.