The best, easiest and least expensive way I've found to prevent beetles from destroying maple is to spray the boards about once a year with lacquer thinner. I buy the cheapest thinner I can find, put it in a back-pack sprayer, and spray all of my blanks every spring. Even though the beetles have invaded some of the buildings in the neighborhood, they have never gotten in any of my stock blanks stored in the top of the garage. Apparently, they don't like the taste of the thinner treated wood, and the thinner does no harm at all to the wood when making it into a gunstock.