I have used Japanise Bettle traps and handpicking and dropping them into soapy water... since I have gotten Chickens I dont seem to have as many...they eat the larva and the adult...safer soap spray may help
I take a coffee cup of water outside and drop/pluck the beetles into the cup. When I have had enough fun, I take the cup full of beetles to my chickens and pour them into a dish. They love them. Last year when the supply began to lessen, I swear the chickens were sad about it!! We aren't in Japanese Beetle season yet, but it won't be long now...
I tried to feed the beetles to my chickens last year- I dropped them into a baggie of water. They really were lukewarm about them. A couple of them ate some of them, but not really a big favorite. I was thinking of getting one of those plastic bag beetle traps with the attractant hanging it on the fence of the chicken coop and cutting the bottom out of the bag- the beetles hit the lure, fall through the bag, are momentarily stunned and the girls would eat them. When I discovered the girls really didn't like Japanese beetles, I scrapped that plan. I ended up just hand picking them off plants and putting them in the beetle bag.
If you have kids around you can do what we did when we were kids. Catch the beetles in our cupped hands, shake them up and throw them on the ground and squish them before they can fly away.
I think my mom may have taught us this "game" to keep them off the roses.
If you are using one of those hanging traps, make sure to locate it as far as possible from the plants you are trying to protect. Because the traps contain an attractant they can actually INCREASE the number of japanese beetles in your garden! Honestly I'm not sure they're worth it.
Handpicking is the way to go. Best arrangement is to bribe children to collect them for you, into a bucket or jar filled with soapy water. I did pretty well off this arrangement when I was a kid
i asked an aunt of mine and she said to spray water on the plant, then put self rising flour on it. when the beatles eat it they expand and explode b/c of the flour. we're doing to do a combo of that and seven dust.