European Chafers are members of the Scarab Beetle family which is a big family of beetles that includes trhe Japanese Beetle, June bug, Rose Chafers, etc. What I have seen is that the European Chafer looks quite similar to the Rose Chafer which does damage plants much like the Japanese Beetle. The European Chafer does not eat anythiung as an adult while the adult rose Chafer does so if you have plant damage with a beetle that looks somewhat like that European Chafer that is probably the rose Chafer.
Control could start with an Insecticidal Soap spray and the best time to apply that is early in the morning while these beetles are still sluggush from the cooler night. Nem Oil products might be considered later along with pyrethrin based sprays or dusts, again best applied early in the morning.

dkgarber, I'm confused. I thought that your beetle had been identified as the Oriental Beetle, a known plant eater as an adult. Is this new problem yet another kind of beetle or the original pest?

Rhizo, I have both beetles (lucky me). The orientals mostly just fly around the house and fly at me..annoying indeed, but seem much less numorous that the chafers. But it was the chafers that were completely covering all my plants at night--I didnt' see a single oriental!!

Alas, they do eat. A lot.
I will post later some pictures of the European Chafer.

The European Chafer, or as I call it, My Enemy.

Here are some pictures of European Chafers, sometimes misnamed as "June Bugs"
link below.
I have witnessed those little bastards chewing on spearmint, as well as Sunflowers treated with a mix of Nicotine, Garlic, Soap, Canola oil and enough habanero to make you beg for mercy. They were eating it like candy.
After few tries, I went on to protect the Sunflowers with a dose of Sevin. I do not like to use pesticide, but I had no choice.
The sunflowers were for decoration only: one spray of Sevin. dose @ 20ml/gal (4tsp/gal)

Result: Still happily chewing.
Second dose @ day +2, Still enjoying the buffet...
Third dose at day +3, some result showing.

Then after, I read that the European Chafer was more resistant that the Japanese Beetle to insecticide.

They do eat, and they are voracious.
If anyone has some tricks to get rid of those little bastards, please let me know.
TIA
Steve

Here is a link that might be useful: {{gwi:1186844}}

erratum,
I stand corrected:
the picture is one of a Asiatic Garden Beetle.
I went to the Perdue university website and they confirm that adult European Chafer do not feed.

Spraying something as potent as carbaryl causes more damage then it cures. We should probably follow the lead of the Province of Ontario and not use any pesticide, herbicide, or fungicide just for cosmetic purposes. There is not much good reason to spray poisons that are harming our planet willy nilly just to prevent a few (of the some 8,000,000 insect species known only about 8,000 are pests) insect pests. Sionce the carbaryl and similar poisons are very broad spectrum poisons and kill off beneficials as well as the pests they can create, for you, more problems later because now you have no beneficials to help control the pests.