Japanese Beetles

Japanese beetles are an invasive species that feed on the leaves, flowers & fruit of more than 300 species of plants. Japanese beetle grubs are pests on turfgrass. They chew grass roots, causing the turf to brown and die. Grub-damaged turf pulls up easily from the soil, like a loose carpet. There are both nonchemical and insecticide options for managing Japanese beetle adults and grubs. Below, I'll go into Japanese Beetle history in America, their life-cycle, and treatment methods. TLDR: treatment methods for various life-stages are at the bottom :)

Japanese Beetles (Popillia Japonica) were first found in the United States in 1916, after being accidentally introduced into New Jersey. Until that time, this insect was restricted to Japan where it is not a major pest. This pest is considered to be an invasive species. It is now found throughout the eastern U.S., except for Florida, and continues to move westward.


How to Identify Japanese Beetles

  • Approximately 1/3 to 1/2 inch long

  • Metallic green head and thorax (the area behind the head) with copper-brown wing covers

  • Sides of abdomen have five white patches of hair, and tip of abdomen has two patches of white hairs on the underside of the abdomen

  • Japanese beetle grub (C-shaped white to cream-colored grubs with a distinct tan-colored head)

  • From 1/8 inch up to about one inch long

  • Japanese beetle grubs look like other white grubs and can only be positively distinguished by examining the pattern of spines and hairs on the underside of the tip of the abdomen

Life Cycle

Japanese beetle grubs spend the winter underground in the soil of lawns, pastures, and other grassy areas. In spring, grubs move up near the soil surface to finish feeding and pupate into adult beetles. Adult beetles start to emerge from the ground in late June or early July. They can fly up to several miles to feed.

Adults feed primarily in July and August, although some may be active into September. Beetle-damaged leaves emit feeding-induced odors that attract other beetles (like sharks to blood). This often results in large clusters of beetles feeding and mating on particular plants while neighboring, equally attractive plants are only lightly infested.

Virgin females produce a sex pheromone for mating that is highly attractive to males. After mating, females tunnel one to three inches underground to lay eggs. Females will lay eggs several different times during July and August, totaling as many as 60 eggs. Dry soil conditions can reduce egg survival, resulting in fewer adult beetles the following year. The eggs hatch in about two weeks and the grubs feed mainly on the roots of lawn grasses.

As the soil starts to cool in the fall, the nearly mature, full-sized (third instar) grubs dig deeper in the soil, where they spend the winter.

Recommended Treatments in Colorado

Organic Options:

  • Kill the grubs by treating the lawn with Bio Advanced Complete, Grub X or Grub-Gone. Treat the turf 3x’s a season…spring, summer, and fall for best grub control. You won’t get rid of the beetle but you will save your grass and reduce the numbers. If your neighbor doesn’t do this they soon will once the brown patches show up in their yard!

  • To kill adult beetles but not the bees, use beetle-gone. It uses a bacteria to kill the beetle and not other insects. A spreader sticker is recommended to use along with beetle-gone so it won’t wash off as quickly.

Beetle-Gone recipe

1qt water, 6 TBS Beetle-Gone powder, 1oz Neptunes Harvest Rose & Flower or Tomato &Veg, combine all 3, shake well and spray!!

Other treatment methods:

  • You can treat the plants that they like best with products containing permetherin , sevin, or malathion.

  • Beetle traps are not recommended because they bring more into your yard than you can catch.

  • Remember insecticides kill insects, including bees.