I think you have the pest. Beetle larvae look a lot like caterpillars, and are entirely capable of eating the leaf as shown in your first picture.
Some pests crawl down the plant in the day, to stay hidden in the soil. If these beetles do this, then you might be able to kill them there with either poisoned bait or spray.
You might be able to control them next year by spraying earlier, before the grapes are ripe, to catch the earliest larvae starting in on your plants, before they grow into adults.
At this time, not wanting to spray with toxins, you could try a couple of things.
1) Spray the plant with a pretty strong jet of water. Perhaps knock the beetles off, then spray them with something when they are on the ground.
2) Spray with something that does not affect the grapes. Perhaps a concoction of kitchen herbs (garlic, hot pepper, mint...)
3) Spray with something that is easy to wash off like insecticidal soap.
Trap the adults, especially if they stay on the ground through the day.
See if they are willing to go into a rolled newspaper to hide. Then remove the newspaper daily, and put out new ones.
