Rose Chafer Beetles - Pesky little things...
There are a few pesticides that would work to kill these clumsy little bugs such as Bonide Eight Garden & Home Spray, Monterey Take Down Garden Spray, or Monterey All Natural Mite and Insect Spray. Unfortunately, however, due to the number of bugs, this fight tends to be futile and they come right back. Rose Chafers start as grubs in the soil where they overwinter then pupate once it warms up. You can treat your soil with a grub control starting in spring and throughout summer, however, this is not always an effective method of control because if your neighbors aren't doing the same, the bugs will still find your beautiful roses, peonies, and other large and light-colored flowers.
Our recommendation aside from pulling the bugs off by hand is to put out a large white bucket filled with dish soap and water. These bugs are attracted to light colors and will fly directly into the water where they will drown. The good news is that Rose Chafers only have a three to four week feeding period, so they will be gone soon! Happy Planting!