Anecdotally re Jap beetles, --have you ever grown four o clocks? There's a rumor they are toxic.
I usually have several wild Evening primrose plants and found they seemed a great trap plant. I would have JBs eating on them all the time.
Bear in mind, I have never grown many roses, most years none so I may not have the same kind of temptation for the JBs that others have. And maybe my low level mole problem helped. Thats the problem with these anecdotal reports, conditions can vary.
I love 4 O' clocks! Their aroma...ahhhhh...to die for!! Unfortunately, they don't grow well here in my yardens. At a recent bug talk I gave to a garden club, one lady said she found an old blender at a yard sale, poured soapy water JBs in it, mixed it up, and used that concoction as a lure to trap other JBs!! Bug juice!