I had never seen a Japanese beetle before this year. I first saw one at my daughter's. she had them on a small grape vine. I looked them up and that is what they were. Unfortunately I have also found them in my garden. Two of my roses are completely stripped of leaves. It must have happened so fast as I just noticed it yesterday.
below is one of many links I found when I googled 'how to control Japanese beetles'
This link is for a more natural approach. Not sure how well it will work, but is worth a try.

Here is a link that might be useful: JP control

I've never seen a live Japanese beetle, but after reading your post, I Googled "Japanese beetle damaged leaf" and it looks exactly like what was happening to the zinnias that I transplanted into my flower beds last week.

I kept checking for bugs but didn't see any, yet the damage kept getting worse every day.

I decided to spray the zinnias with a solution of Neem oil and there's been no further damage.

Don't know if it was Japanese beetles or some other bugs, but it worked.

they are prolific. In fact, they start their lives as grubs eating your grass. So if you spot those brown spots on your lawn early in the season, you can bet there might be grubs there.

you can spray with neem oil, handpick them, or use those beetle traps. Only thing with beetle traps is that they attract more beetles to it so don't hang it on a favorite plant. Set it some ways from your yard so they are drawn away.

A friend of mine in the States swears by a product called Milk Spore (I've also seen as Milky Spore). It is organic and safe but I have not seen it for sale in Canada. Japanese beetles love my roses :( but I just go around and pick them off and drown them in a bowl of soapy water. I heard the traps just attract beetles from miles around, so I would check into that before using.

I have JB too. Last year had only one or two. This year I have more but I planted more roses and apparently they love them especially yellow and white colored varieties (in my garden). As for Milky Spore; I saw it last year in Cosco in fall but didn't by (feel bad that didn't because it takes a few years to provide good result). Also I am not sure whether it work for our area because it seems to me that it is not effective in some areas (not sure if Ottawa is one of them). Here it is mentioned that nematodes can work too along with Milky Spore but I don`t know where you can buy them from.
Link: http://forums2.gardenweb.com/forums/load/organic/msg071018441954.html
General info about JB control: http://search.gardenweb.com/search/nph-ind.cgi?term=japanese+beetles+control&x=11&y=2