The beetles in your photo with a patterned back are in the family Dermestidae. They do not feed on plants other than occasional visits to flowers to feed on pollen, which does not harm the plant. I cannot be sure what has caused the holes on the leaves of your plant in the photo. The extent of damage does not appear to be severe enough to threaten the health of the plant. Unless, there are more severely damaged plants that you did not include pictures of, I would recommend that you take no action at this time. If you don't see caterpillars or other insects feeding on the leaves during the day, you could try looking for something eating the plants at night. Certain caterpillars (e.g. cutworms) and beetles (e.g. flea beetles) feed on plants at night. Slugs are also notorious for coming out at night to chew holes in our garden plants. 

Thanks for these thoughts.I  never suspected cutworms but that could be one of my problems. The coneflowers look damaged, but they flower all summer in spite of that so I'm grateful for that. This gives me a place to start. I have looked for bugs at night or at dawn but they are hard to find. I know there are slugs. If there are cutworms, I think the eggs stay in the soil over the winter. Should I till the soil in the fall or spring to get rid of them?

Cutworms can be challenging, but usually the best approach is to protect the plants by maintaining open soil or using some other kind of barrier around the plants. Tillage is not usually an effective management for cutworms. This article from MSU Extension has some other ideas that you might find helpful: https://www.canr.msu.edu/news/cutworms_in_the_vegetable_garden