For more information I will refer you to two insect notes. One on the adult at http://www.ces.ncsu.edu/depts/ent/notes/O&T/flowers/note44/note44.html

and the other on their juvenile form as one of the white grubs at http://www.cropsci.ncsu.edu/turffiles/ag366/ag366.html

Many people like the idea of the biological control offered by use of Bacillus popilliae (milky spore)which controls only the grubs of Japanese beetles. Unfortunately the adults are efficient fliers and control of grubs in your lawn is seldom sufficient to prevent adults from finding your grapes, roses, hibiscus, etc. You may achieve control of grub worms in your lawn but they seldom reach numbers to be a big problem there anyway. There has also been some work done on controlling them with entomogenous nematodes (microscopic roundworms), but so far results are not encouraging. If you want to try that, at least find out if the nematodes you purchase are fresh enough to be alive.

For dealing with adults, traps as employed by most of us are usually not effective either. In many cases the traps attract more beetles than they catch. They may actually make the problem worse. The problem will almost definitely get worse if the trap is not emptied every day or two (that persistence thing again). Dead decaying beetles release ammonia that repels other beetles who were attracted from afar by the sexual scent but found something more interesting when they got close to that smelly death trap.

Anecdotally, I once met a gentleman who hung a Japanese beetle trap low over a pond and removed the trapping apparatus. According to him, the beetles that dropped through the funnel hit the water where his bass found them tasty. I've never seen this work, so if you try it, I would like to hear what you observe.

Finally to consider the insecticide options I quote from the entomologists who wrote one of the publications cited above: "carbaryl (Sevin), malathion, imidacloprid (Merit) are good choices. Many of the newer lawn and garden multi-insect products are also effective. Pyrethroid containing chemicals are slightly more persistant. Spinosad and Neem based products give a little protection. Roses or shrubs may also be protected by covering with light netting. Handpicking adults from plants is an almost hourly battle. Homemade concoctions and blended beetle cocktail repellants are mildly effective, and may need reapplication every one or two days."

While even the most effective of the insecticides is not likely to last all season, you may have the pleasure of hearing dead beetles hit the ground. It's generally a bad idea to spray flowers. Most flowers attract insects that are also beneficial as pollinators and in controlling other insects. Indeed, even if you spray the outside of a rose bud this morning, you may find Japanese beetles feeding inside the opened flower this afternoon.

If you are handpicking, note that they tend to drop when disturbed. If you position your jar of soapy water beneath them, you may improve your catch. And they will die fairly quickly in the soapy water.

Good luck. Keep smiling.