You are correct, Seedfork. the holes in the centerof almost all the foliage of my yellow zinnias looked like someTHING took a big bite only from the center. . the edges weren't touched and there were no "munch" trails either. MWhatever it was, they apparentky didn't like the taste of my Zahara zinnia, as they were untouched!
On the far right of my distant pic, one can see the upright PVC pipe (screwed into the fence pole for support) of my DIY ground-level irrigation system. By having this upright section, I could walk over and stand upright to screw in my water hose and water from below. . . thus avoiding a known problem from watering frm above.
But the gnawed-out centers are totaly unknown to me. How do you stop / prevent flwea beetle damage??