And sanding that wing with superfine (400-600) sandpaper for extra grip would not work? Very fine sandpaper will not ruin the surface, but allows the acrylic paint to set.
Always make a try-out on a piece that you don´t need, Ok?
I take it that that butterfly wing is made out of polystone?
And has a smooth surface?
(Resin mixed with mineral elements as chalk to give it a stony look, but with a very reduced weight)