Japanese Beetle

Adults are about a centimetre long with a metallic-green body and coppery wing covers. A distinctive feature is a row of small white tufts of hair along each side of the abdomen, which separates them from similar scarabs. Larvae are typical white grubs: soft, C-shaped, with a brown head, found in the soil among roots.

The characteristic adult feeding pattern is skeletonization, in which the leaf tissue between the veins is eaten away, leaving a lacy network of veins. This, together with the white abdominal tufts, is a reliable field cue.

In much of its introduced range the beetle completes one generation per year. Adults emerge in summer, feed, and lay eggs in the soil, typically in moist grassy areas. Grubs hatch and feed on roots, move deeper to overwinter, and resume feeding before pupating the following season to emerge as adults.

Adults are attracted to plants already being fed upon and to certain volatile cues, which is why feeding often concentrates in patches. Soil moisture during egg-laying strongly influences grub survival and the following year’s adult numbers.

Adult feeding skeletonizes leaves and damages flowers and fruit, which can be significant on high-value horticultural crops and heavily fed field crops. Grub feeding severs and prunes roots, weakening grasses and, at high densities, causing turf and pasture to wilt, brown, and pull up easily. Both forms of damage vary greatly with local beetle density.

The adult host range is very broad; among cultivated crops it includes grape, apple, and soybean, along with maize silks and many other plants. Grubs are chiefly associated with the roots of grasses.

Adults are monitored by direct inspection of foliage and fruit for beetles and characteristic skeletonizing damage. Pheromone-and-floral-lure traps exist but can attract more beetles than they catch, so they are used mainly for detection rather than protection. Grub populations are assessed by digging and examining soil samples in grassy areas.

Management addresses both life stages and fits within integrated pest management, with attention to protecting pollinators when crops are flowering.

• Monitor adults and grubs separately and target the stage causing damage
• Conserve natural enemies and consider biological options such as insect-pathogenic nematodes and microbial agents for grubs where appropriate
• Manage soil moisture and turf where practical to influence grub survival
• Use physical protection such as netting on high-value plants where feasible
• Observe quarantine and reporting requirements in areas where the beetle is regulated