Japanese beetles — a pest in Denver-area gardens in July and August — feast on a rose.Photo by Betty Cahill, Special to The Denver Post Most of us weren’t living in Riverton, New Jersey, in 1916, but that’s the place and year when Japanese beetles, Popillia japonica, first showed up in America. Back then they had no idea then that these rather attractively colored, half-inch long, metallic-green and copper beetles would turn out to be one of the most devastating landscape pests to lawns and scores of ornamental plants. It took them awhile, but Japanese beetles have made it to Colorado, and their summer feeding frenzy has gotten notice — lots of notice. The assumption is that Japanese beetle larvae from Japan hitchhiked on some nursery stock to New Jersey.