Posted: 25/01/2015 at 11:38
You will need a microbial insecticide. Bacillus thuringiensissubsp.israelensis (Bti) it is unavailable through retail outlets as it is for commercial use only. Try Bayer and see if they have anything containing imidacloprid.
Nematodes will get rid of the Larvae and it's my prefered method. Keep doing the vinegar traps and allow the growing medium to dry between watering, especially the top 1 to 2 inches. This will decrease survival of any eggs laid and/or larvae hatching.
You can place a slices or wedges of potato into the growing medium. The larvae will migrate to the potato and start feeding within a few days and it can then be removed.