Japanese beetle (Popilla japonica)

japanese beetle
 
 

Japanese beetles are metallic green and gold beetles that are known for gathering in large numbers and damaging plant leaves. The immature larvae (grubs) develop in the soil and can damage lawns by feeding on plant roots.

Description

Appearance

Adult Japanese beetles have copper colored wing covers and their head and thorax (area behind the head) are green. The abdomen (back area) has 5 tufts of white hair on each side and the end of the abdomen has two tufts of white hair. Adults are 1/3 - 1/2 inch long.

Japanese beetle larva are 1/8th – 1 inch long, are white with a tan head, and have small legs. They are found in the soil. They look similar to other insect larvae (grubs) found in the soil. 

Habitat

Adult Japanese beetles feed on more than 300 species of plants, including apple, birch, cherry, crabapple, elm, horse chestnut, linden (basswood), maple, mountain ash, oak, plum, and willow trees, as well as plants such as asters, grapes, hollyhock, roses, and Virginia creeper. Adults feed from late June through August. They feed between leaf veins, giving leaves a skeletonized look.

The larvae (grubs) of Japanese beetles feed on plant roots, especially grasses. They have been known to damage turfgrass in lawns.

Biology

Japanese beetles have three main stages in their life cycle: larva (grub), pupa, and adult. The larvae spend the winter in soil under grassy areas. In the spring, a Japanese beetle larva forms into a pupa which is the developmental stage between larvae and adults. Adults emerge from the pupae from late June to early July. Adults feed on leaves and are most noticeable in July and August but can remain active into September. In July and August, adult females dig small tunnels in the ground and lay their eggs. The larvae hatch from eggs after two weeks and spend the rest of the summer eating, focusing on the roots of grasses. When the weather gets colder, the larvae dig deeper into the soil and overwinter there. Find more information at the US Department of Agriculture website.

Origin and Spread

Japanese beetles are native to northern Japan. They were accidentally introduced to the U.S. and first found in New Jersey in 1916. Adult Japanese beetles can disperse by flying. Adults can be moved on plant material, and larvae can be transported in the soil of nursery stock or other soil movement.

Japanese beetles were first documented in Minnesota in 1968, but it wasn’t until the early 2000s that they reached such high numbers that they became more noticeable to residents. Japanese beetles have been confirmed in much of Minnesota. Refer to the Minnesota Department of Agriculture’s Japanese beetle distribution map and to EDDMapS Distribution Maps for current distribution.

Don’t be fooled by these look-alikes

  • False Japanese beetle (also called a sand chafer), Strigoderma arboricola (native) – False Japanese beetles have duller coloring than Japanese beetles. They have light white hairs, but the white hairs are not organized into the distinct tufts along the abdomen that Japanese beetles have.
  • Rose chafer, Macrodactylus subspinosus (native) – Rose chafers are pale green to tan in color with reddish‑brown or orange spiny legs.
  • European chafer , Amphimallon majale (invasive) – European chafers are tan throughout their body, they do not have the bright green head and thorax that Japanese beetles do. Similarly to Japanese beetle larvae, European chafer larvae can damage turf grass. Adult European chafers do not eat at all, so they do not cause leaf damage.
  • The University of Minnesota has an image of a variety of insects that get confused with emerald ash borer (Agrilus planipennis). Japanese beetles are one of the species on the document. Japanese beetles have copper-colored wing covers as opposed to the green wing covers of emerald ash borer. The image also shows how Japanese beetles compare in size and color to a variety of other insect species often encountered in yards.
 

Regulatory classification

Movement of Japanese beetles within Minnesota is not regulated. If you export products from Minnesota that main contain Japanese beetles, consult with the Minnesota Department of Agriculture for all applicable regulations, including Japanese beetle certification.

Threat to Minnesota

  • Adult Japanese beetles feed on more than 300 species of plants, including apple, birch, cherry, crabapple, elm, horse chestnut, linden (basswood), maple, mountain ash, oak, plum, and willow trees, as well as plants such as asters, grapes, hollyhock, roses, and Virginia creeper. Adults feed from late June through August. They feed between leaf veins, giving leaves a skeletonized look. It is thought that healthy trees are generally able to recover from Japanese beetle feeding, but trees that are stressed from other factors (such as drought) may not recover.
  • The larvae (grubs) of Japanese beetles feed on plant roots, especially grasses. They have been known to damage turfgrass in lawns.
  • Japanese beetles can damage soybeans and other agricultural crops.

What you should do

  • Keep a lookout for Japanese beetles and other invasive insects.
  • Take care not to move adults or larvae from site to site in soil or on vegetation.

Control methods

It has been found that Japanese beetle population numbers can vary dramatically from year to year. Generally, if plants are healthy, Japanese beetles do not kill them. Management methods include hand picking, protecting target plants, and chemical and biological pesticides. View the Japanese beetle information and management suggestions (University of Minnesota Extension) webpage and the US Department of Agriculture website for more detailed information on control.

Reporting

Report new occurrences by submitting a report through EDDMapS. If the report is from a county not known to have Japanese beetles on the Minnesota Department of Agriculture’s distribution map, you can email Report A Pest or call Report A Pest (1-888-545-6684).

Resources

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