If you store it in the freezer, it will help kill some of the bugs that eventually comes from it. Baking it kills the bugs better, freezing I think kills some while others just go dormant. But it's better then just leaving it sit out.
LOL, they are little tiny bugs. Sometimes you will get some that fly, almost like fruit flies. They won't invade your house, but they will get in the torts enclosure from the substrate. They don't hurt anything. You can boil or bake the substrate before you use it and then it takes a really long time before they show up, if they do at all. Freezing helps, but you will for sure eventually get some bugs. With the baking or boiling you have a good chance of them not showing up.