Japanese beetles can destroy so many blooms if you let them. They are very destructive for about a month and then usually die off for the season. Most flowers do okay, but dahlias often take a hit. 

It is tedious, but if they are particularly destructive one week, I’ll place organza bags over my blooms as they are just starting to open to protect them. I pull the strings tight and cut the bloom with the bag still on, removing it once it’s in the bucket. It’s tedious, but if I have an upcoming event or a wedding where I want specific dahlias, it’s what needs to be done. Luckily, in my zone, usually, my dahlias don’t bloom until late August anyway. The peak of Japanese beetles in my area is usually in July.