What I use is Ortho systemic insect spray. If you can't find Ortho, try another systemic product that mixes with water. I will see an occasional jap. beetle, but then he's usually laying on his back with feet up the next day...
These roses are so easy to grow because of the lack of care they require with fungicides, molds, etc. but you have to watch out for the insect pests.
I told another ponder about a product called diatomaceous earth for the control of slugs. In checking this a little further, I realized that it can control other ground insects such as ants, worms, that attack a plant from the ground up. The tiny bodies of dead diatoms (Diatomaceous earth consists of fossilized remains of diatoms, a type of hard-shelled algae.) are laying in the soil, and when an insect moves across the dirt it slices the bodies (shells of ants and other hard bodied insects) and they die naturally. Some people even put this around the foundations of their homes if they have an ant infestation and the ants just disappear.
Let me know what you end up using and how it works for you.