The Japanese beetle, Popilla japonica, is a serious insect pest of many plants found in yards and gardens in the Upper Midwest. Like the gypsy moth, Dutch elm disease, and white pine blister rust, the Japanese beetle was introduced into the United States from overseas. This pest was first described in New Jersey in l9l6 and is now established in most of the states east of the Mississippi River except Florida and Mississippi.
Minnesota has mounted an aggressive monitoring and eradication program to keep this pest from becoming established here. Because of its status as a threatened state, Minnesota is also subject to quarantines that restrict the movement of plant materials, soil, and sod that could be infested with any life stage of the beetle. Only certified pest-free plants and soil are allowed in.
Japanese beetles belong to the insect family Scarabaeidae (scarab beetles). The adults are stout, oval, ½-inch long metallic green beetles with coppery wing covers and five small tufts of white hair along both sides of the abdomen. The adults feed from late June through September on several hundred different types of plants, most commonly shrubs, shade trees, flowers, and fruits. The number of beetles peaks in mid-summer and feeding activities is heightened on warm sunny days. The feeding activity is more common on young leaves and is referred to as skeletonizing because the beetles consume all of the green tissue between the leaf veins, leaving only a tracery of the veins. Flowers and fruits are also consumed, and the beetles may feed in large numbers before moving on the their next plants.
Adult female beetles lay eggs in small clusters four inches underground in turf. The larvae, or grubs, which are grayish white with brown heads and grow ½ to l inch long, hatch within two weeks and feed on roots of grasses, vegetables, and herbaceous fruits. Feeding injury to turf roots by Japanese beetle grubs may be so severe that the turf can be rolled up like a carpet. Skunks and raccoons can also do a lot of damage to turf as they dig it up hunting for grubs underneath. Feeding continues until cold weather, at which time the grubs move farther down into the soil to overwinter. In spring the grubs resume feeding on plant roots, pupate, and emerge as adults from late June throughout the summer In Minnesota. There is one generation per year, but some beetles may mature over a two-year period.
The Minnesota Department of Agriculture conducts annual surveys for the Japanese beetle by placing traps at selected sites throughout the state. No beetles were trapped in the Brainerd area this summer. You can help by reporting any suspected life stages to the MDA; reporting extensive damage to lawns, roses, grapes, fruit or other preferred hosts to MDA; cooperating with MDA survey staff if they request permission to place traps on your property; and not importing soil or plants rooted in soil and sod from the eastern U. S. unless certified by state officials or treated to eliminate Japanese beetles. A new publication--Japanese Beetle Management for Homeowner--is also available from the MDA, 90 West Plato Blvd., St. Paul, MN 55107-2094, telephone 651-296-1348.