Japanese beetles mate and lay their eggs the same day. The female lays from 40-60 eggs. The eggs pupate and burrow deep into the soil (about 12 inches) throughout the summer and fall. In the spring the grubs migrate toward the top of the soil, and in late June-early July, mature into adult beetles.
Some favorite plants of Japanese beetles are: river birch trees, roses, zinnias, hibiscus, bean and potato plants, bee balm, and petunias.
Control can be established in many ways: Chemical, through applications of grub control in the lawn in spring and fall; Mechanical, by shaking the beetles from the plants into a bucket of water with some dish detergent (best done in early morning or late evening when the beetles are less active); and by planting attractants away from areas that need to be protected, such as larkspur which poisons beetles. Bushes and trees can be protected by infusing insect controls (such as Bayer Tree and Shrub Insect Control) into the root systems in early spring. Invite crows and turkeys into your yard in the spring--they dine voraciously on beetle grubs. PLEASE AVOID USING JAPANESE BEETLE TRAPS! Research has shown that the beetles are attracted to the traps from as far as 5 miles away. The traps do not trap all of the beetles, so you now have attracted more beetles to your yard than you had to begin with. And, of course, the best control is to avoid planting the plants that they like best.
If anyone has other means of controlling these pests, please share!