If you can't find the pests during the day, and the damage appears to be happening at night, then it probably is june bugs. There might be some chemicals you could use. There's a large toad population nearby, so I've periodically tried to lure some of them over by keeping small areas near the garden damp or flooded. I've heard people mention Sevin Dust, but I'm hesitant to use it due to the proximity of bee hives.
I've heard blacbird's suggestion several times for snails.
Doing well: tomato (all varieties), cucumber, garlic, thyme, mint, rosemary
So-so: oregano (purpling), zucchini, crookneck squash
Doing poorly: basil (yellowing), all chile plants (eaten by junebugs), cantaloupe, grape hyacinth (replanted)