What is eating the petals off my Gold and Bronze Coreopsis and Shasta Daisy's?
Petals Pulled Off or Eaten on Plants
Certified GKH Gardening Expert
That can be hard to say without seeing the pest responsible. There are several things that you can do to prevent this from happening, though. Many natural solutions are very effective against a broad range of insects.
This collection of articles will give you ideas on how to make your own pest control, along with many other very useful tips: https://www.gardeningknowhow.com/special/organic