I use neem oil as a foilar spray and I spray the top of the soil wheather its peat, hydroton, or soil; don't matter. Then I add this stuff called Natrol to the res. for a day. That gets everything gone, even other pests that you didn't know you had.
Personally, I use neem oil once a month until week 4 of flowering to maintain control of all pests. That stuff has plenty of trace elements and it makes the leaves real shiny. The plants love it! The Natrol will get rid of the larva in the medium and the neem will make it where the nats, mites, etc. can't reproduce.