Here are the culprits. Japanese beetles.

We immediately set out Japanese beetle traps, which caught beetles by the quart, but didn't seem to help the infestation in the vineyard. After further research we discovered that you need to place the traps farther away from the vineyard, as they attract the beetles to them. After a strategic redeployment of traps the problem was much more under control.

Who ya gonna call?

Jeff, the Beetle-Buster.