Preventive Soil Care

So I got roots soil and I know their known for their fungus gnats. So I got all my ingredients for my super soil mix and was about to start mixing and then I thought I would ask the community a quick question before I begin. What could I add to my soil mixes that would kill fungus gnat eggs and larvae before they even make it to the surface? Would mixing spinosad powder in with my super soil/other soil mixes prevent me from getting gnats? Looking for a reliable preventive ingredient I can just add to the mix and not have to really worry about doing drenches etc. Ty!

Dunks bt i crumbling them up in the soil . Should work i tried it in hydro not soil just tossed one in the res it didnt seem to work at first then they were gone one day .about two weeks to an month we had fliers that why i assumed it didnt work.then they just disappeared fans helped also we watered the hydroton from top with the bt i since it was drip lines. Every day once.