How do I eradicate them?
Japanese Rose Beetles
That is a loaded question! They are probably the toughest nastiest beetle known to man. I recommend a two pronged approach to get at both the adult beetles and the grubs in the soil. Spray the rosebushes with an insecticide that lists control of such beetles. Get some Bayer Tree and Shrub Granules and apply the product around the base of each rosebush working into the soils lightly. Water it in well once applied. The insecticide in the granules goes up through the root system and into the natural juices of the rose and gets at anything eating any part of the rose. Plus it kills the soils grubs that turn into more adult beetles. You never ever want to buy or use any of those Japanese Beetle Traps on the market! They actually attract more beetles to your roses than what you may be dealing with. The only way to use such traps is to place them a long ways away from your property so that the beetles go elsewhere and leave your roses alone. Just kidding on the traps locations but those traps are not a good thing at all if you love roses and have problems already.