Oldgardener, so you get these also. Here we call them green June beetles. They lay hundreds of eggs. They are normally satisfied to lay their eggs in the small woodland behind our house unless it's to dry there. They love moist compost rich ground as the larvae feed on the decaying material. So your garden is providing what they need. Grubs grow to 3 inches or more if well fead. Then when your garden begins to dry or they run out of organic matter to eat they go for the roots to survive. Dug up a rather newly planted rose that had perished (this never happens). I had gotten lazy and just improved the hole. I knew better but did it any way. So when digging I counted 30+ giant grubs in there with one big one hanging onto the last piece of root left. Now I keep a spot for the beetles if the weather has dried their habitat. A moist pile of decaying grass and leaves. After adult beetles leave I spread it out so it dries quickly in the summer sun killing the grubs. Amazing site to see. Hundreds of grubs piled on top of each other. Yuk!
