Japanese beetles have made their annual emergence and the damage can be seen in many gardens. So far, we haven't heard reports of any large numbers of Japanese beetles in Northern Illinois. It's been believed that the numbers would be lower this year because of the harsh winter we had this season, and so far that is looking true. In my own yard I have only seen minor damage to my sweet potato vine and knock out roses, both preferred treats for the Japanese beetle.
Japanese beetles are chewing insects that destroy leaves, flowers and fruits of more than 276 plants. These beetles can completely skeletonize leaves, feed on corn silk and corn ear tips and are especially destructive to grapes, peaches and other members of the rose family. The grubs feed and cause damage on grass roots in lawns, parks, golf courses, and cemeteries.
The Japanese beetle has a one year life cycle, spending about 10 months as a grub in the soil and in late June, the first adults emerge with most present in July and August. Throughout the summer, adult beetles feed on a wide range of plants and deposit eggs in the soil. Eggs hatch about two weeks later and grubs feed on decaying matter and roots until temperatures cool in the fall. They move downward and overwinter as a partially grown grub and resume some feeding activity in spring. Pupation occurs in late spring and adults begin emerging in late June.
Every summer we always hear the same question; "How can I control Japanese beetles?" Unfortunately, there really isn't a great, easy solution. The most benign control method is to hand pick the beetles off of the plant. Dropping them in a bucket of soapy water will quickly drown the pests. Avoiding planting the preferred hosts of the Japanese beetle would be another alternative. Some gardeners like the idea of using traps to collect beetles. These traps are not recommended though because they will likely attract more Japanese beetles to the garden than were there previously. Various chemical treatments are also labeled for Japanese beetles and your local Extension office could give you the listing of those.
Learn more about the Japanese Beetle here: http://urbanext.illinois.edu/bugreview/japanesebeetle.cfm