the 45x45x45 tanks are not really big enough for Leopard Geckos, i'd go for a 24" (2ft) tank as a minimum for Leo's.
If you mean "bug grub" then you feed that to the crickets (keeps them alive longer) along with some carrot or apple for extra vitamins and a water source (the better fed the crickets, the better they are for the Leo).
Then you should dust the crickets with something like Nutrobal in the manner Shele said, 2-3 times a week. 1-2 times a week you should dust them with Pure calcium powder (such as calypso) and also keep a small dish of pure calcium in the tank at all times.
Hope that helps
