As a follow up to Don Lewis' post a few days ago on Japanese Beetles, they seem to be active in large numbers now (July 14, 2009). I found hundreds of them on my Linden tree last night. They are also hitting some of the shrubs. Their arrival in central Iowa is fairly recent. It has only been the last four years that I have seen them in significant numbers.
Linden trees (Tilia spp) are a favorite of the Japanes Beetle. The picture below shows a Linden on Barrington CC in Chicago in 2008. The insects start feeding on the top of the tree and move down. They can defoliate a Linden if there are enough insects present and the tree should be treated with insecticide if the problem is bad enough.
The second picture show a Japanese Beetle on the left and a Masked Chafer on the right. I took this picture on Iowa State campus. Both species lay eggs in the turf that will hatch into larvae that damage the root system later in the summer. Fortunately, the Masked Chafer adult does not do significant damage to landscape plants.