Mothproofing (not storage) advice, please

Among nine fedoras I regularly wear three gray felt ones (and one black felt one) but my favorite is a dark gray Knox still soft like new. Looks good, fits well, and keeps me warm in the winter. I feared it would be moth bait and after about eight months that seems to have happened. (I think it happened staying at someone's else house.) I think I covered the bite and scuff pretty well with a bit of starch. Now, to save this hat from a repeat performance, any advice on mothproofing? Any spray that will do the job?

The starch didn't do the trick. Lesson learned: never use a modern lint brush on a vintage hat. Tried putting a cotton swab in vegetable oil, rolling off the excess on a paper towel, and rolling the swab on the offending faded spot. We'll see.