Destruction!

This is my white rose bush! Every single flower that opens is almost immediately devoured by these rose chafer beetles. Then they hang around where the flower was for some days. Now the beetles are eating my other roses too, plus irises, and various other flowers.
Any advice that doesn't involve spraying with poisonous chemicals?

Really warm today... just like summer. Too hot to do much on the garden or even have much of a walk. Had a very pleasant and quite long afternoon swim at the local beach with the usual swimming friends.