If you are going to use the seed only take out small amounts and keep that bag in the freezer. You don't want any of them flying around and laying eggs. Then you are going to have a problem. Kill them as fast as you see them.
Personally I would not use the bag to prevent a bug outbreak. They should exchange the food if they are reputable. I would find a new source for buying seed. Chances are they have a lot of old stock in the same condition.