Most gardeners probably have encountered Japanese beetles in their lawns and gardens. These insects leave their marks of destruction by the lacy, skeletonized leaves seen on the vegetation they attack. Although Japanese beetles aren't active at night, they fly and eat during the day. According to the Pennsylvania State University Extension website, adult Japanese beetles feed on about 300 plants with some of the most susceptible vegetation including roses, zinnias, marigolds and flowering cherry trees.
The Japanese beetle (Popillia japonica) belongs to the scarab family. Its body is oval-shaped and a metallic blue-green in color. It has forewings that are reddish-orange or brown and hair underneath the body that's white or gray. Five patches of setae (white hairs) run alongside the beetle's abdomen, and two clumps of white hair are on the rear of the body. The beetle's hard, leathery wings are copper in color.
A typical Japanese beetle is about ½ inch long, according to the Minnesota Gardening for Beginners' website. The grayish-white larvae of the insect are ¾ inch long and are shaped as the letter "C".
After overwintering in soil, the larvae move toward the surface of the soil as the soil grows warmer and spring approaches. From May to June, they mature and emerge as adults from the soil around late June through July. After mating, an adult beetle lives for 30 to 45 days and then lays 40 to 60 eggs, according to the Pennsylvania State University Extension website. Larvae hatch in about 10 to 12 days and feed on grass roots until the end of September, when the soil is cool enough to push larvae farther down, where they overwinter. It takes about one year for one generation to evolve.
History and Geography
The Japanese beetle, which originated in Japan, came to North America in the early 1900s. In 1912 Japanese iris bulbs arrived in the United States. Japanese beetles were noticed in 1916 on iris bulbs in New Jersey. These beetles, which live in woods, gardens and open meadows, are found throughout the United States except for the extreme southeastern region. They can be found as far north as Ontario, Canada.
Chemical insecticides such as sprays or granules can effectively control Japanese beetle larvae that live in soil, while insecticidal spays work on adult beetles. Golden Harvest Organics recommends using interplantings of flowers such as larkspurs, four o'clocks, white geraniums and buckeyes that have flowers able to attract and poison Japanese beetles. Another control method is to spread a sheet under infested plants and then shake the plant so beetles fall on the sheet to be dumped into a container of soapy water.
Several pests are often mistaken for the Japanese beetle. The false Japanese beetle resembles the Japanese beetle in both shape and size. Although its brown color is slightly metallic, the patterning is different. Several scarab beetles from the genus Anomala are similar in size and shape to the Japanese beetle with some even having metallic coloration. This beetle, however, does not have the shiny green coloration of the Japanese beetle.