I admit this is an impractical means of killing bugs, but you may find that some early 19th century horns are dark, somewhat greenish, in color. Soak the horn in copper acetate (nice blue chemical) an it becomes most unpalatable. Unfortunately also unesthetic to the modern eye.
Made one flat priming horn this way couple decades ago, for the late Loren Herrington. Left it soaking in a jar many many months and forgot about it. Loren was very polite when I mentioned it - meaning he had completely forgotten. Gave it to him, at that point couldn't charge him. Last I saw it was a nice green, being sold at Lapeer by his widow, Laura. No bug holes, though.