Japanese Beetles

Latin name: Popillia japonica Newman

Size: 1/2″ long

Color(s): Metallic green head, shiny brown wing covers with white hairs along outer edges.

Life Cycle: The adult female beetles lay eggs in the summer. The larvae, which are creamy C-shaped grubs with brown heads, will hatch and start feeding on plant materials. They go through two molts, then bury themselves below the frost line for the winter months. In the spring, they go through two more molts, then emerge as adult beetles in early summer to start the process all over again.

Symptoms of their activity: Holes in leaves, skeletonized leaves. Also brown, dead areas of lawn, which are signs of the grubs’ feeding.

Typically seen on: Ornamental plants such as perennial flowers and roses, trees, shrubs, annuals, berry vines and fruit trees (that about covers everything we grow, right?)

Controls: I have to admit that I’m not an expert on dealing with Japanese beetles because we don’t have them here in Eastern Washington state… yet. But I fear they will eventually adapt to our climate. However, I have done some research and learned some things you should know about. First of all, do NOT use Japanese beetle traps! These are based on pheromones (mating hormones) which will attract even more of the beetles to your garden. Consider hand-picking any time you see the beetles on your plants. 

Natural predators: Natural controls include the introduction of parasitic nematodes to control them in your lawn milky spore bacteria, and a strain of Bacillus thuringiensis (Bt).

Additional information: Japanese Beetles/University of Illinois Extension and Japanese Beetle/Colorado State University Extension.

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