A couple of weeks ago I saw this on an exhibition viola bloom. A nightmare if at show time. These happened overnight, but just one hole renders the bloom useless on the show bench.
My first thought was earwigs as they were in the vicinity, but then looking behind the petals discovered a tiny green caterpillar .
I would guess it was probably a caterpillar from some moth.
By taking off all the blooms with these pinholes in them within two weeks no more damage.