shasta marguerites: what eats the petals?

I think it’s tiny black pollen beetles, I had this last year.

It may be caterpillars, they do eat flower petals, or even aphids, although they cluster on the stems so you’d be able to see them. You could try spraying the plants with diluted washing up liquid?

I grew them for years and they were always ignored by slugs and snails. So I can't help, but I'm sure someone will be along who knows! They are lovely flowers!