If you have an insect problem with a mount the tanning of the skin was not done correctly.
I have several bird mounts from the 1970s and they look as nice today as they did back then.
One method you can do - big clear plastic bag like a Zip-Lock bag - they make some big ones. Insert your mount - spray a 2 second burst on the inside of the bag itself do not spray on mount or wet mount using a can of Raid House and Garden and seal the bag. Leave that sealed for 2 to 3 days.
That will surely fumigate.
But if yo ugot bugs take the mount back to your Taxidermist.
Safe Hunting is No Accident!