“I have never purchased grain items that already had weevils in them.”
I did once. I opened some corn meal and there were weevils so I went to the store and bought a new bag got home, opened it and it had just as many. I just picked them out and used it anyway.
A flour sifter will help eliminate the bugs—and I believe that is what they were for in the first place—separating weevils from the flour.