Your retailer probably has Indian meal moths.
He doesn't need to refridgerate his entire grain stock, he needs to freeze it
-- but only temporarily. Freezing will kill the larva and eggs. I believe
the recommended time is 72 hours. (someone give us a sanity check, here)
You need to make sure to get the center of the bag below freezing and hold
it. Once he gets passed the existing stock, he can make a practice of
freezing new stock as it comes in before it hits his shelves. He can
probably accomplish this with a chest freezer in his back room if he isn't
running a walk-in.
Also, sanitation is important. Shelves need to have all the spilled flour
vacuumed out of cravasses. Make sure the pasta section gets a good cleaning,
too; and don't neglect the back room.