Fungus knat larvae in seedlings

Hi does anyone know how to stop fungus knat larvae killing my seedlings? Unfortunately some house plants bought for the kitchen infected my seedling pots and I did not realise until I had already moved the seedlings to the greenhouse. Kitchen flies dispatched with a glass of red wine as a trap but what can I pour or spray onto the seedling's compost to kill the white larvae that will not also kill my seedlings?