Japanese Beetles

- A pest of lawns and landscape plants -

Summary: The larvae, or white grubs, of Japanese beetle feed on the roots of grasses while the adult beetles feed on a wide variety of landscape plants. These beautifully ornate beetles can be an extremely destructive turf and landscape pest.

Jack DeAngelis, PhD

OSU Ext. Entomologist (ret.)

What are Japanese beetles?

Japanese beetles (right) are important turf and landscape pests in the eastern US. The adults are roughly 3/8" long with coppery wing covers, metallic green back and a row of white tufts along the sides. Adults feed on a wide variety of plants where they "skeletonize" leaves (remove leaf tissue between the veins). Japanese beetles belong to a large family of ornate beetles called scarabs (Scarabidae).

Japanese beetle larvae, or white grubs, are typical of other scarab larvae. Larvae live in the soil where they feed on plant roots and can do serious damage. Larvae are white with a brownish head capsule and three pairs of legs (see the white grub article for a picture). The "tail" end is usually packed with ingested soil particles and larvae are generally bent into a characteristic "C" shape as well.

common misspelling: Japanese beatle

Japanese beetle adult ~ 3/8" long; photo by David Cappaert, www.forestryimages.org

Life history of Japanese beetles

Adult beetles emerge from the soil in mid-summer. Adults feed for a few days then female beetles begin to lay eggs back in the soil. Larvae develop in the soil during the fall and spring, feeding on roots, ready to emerge as adults the following summer. Root feeding is a major but unseen part of the damage from these beetles.

Can I control Japanese beetles?

Adult beetles can be hand-picked from plants and dropped into soapy water. Plant foliage can be treated with insecticide to prevent feeding and larvae can be treated with a special microbial insecticide applied to the soil (see below). Since Japanese beetle has only one generation per year it is possible to significantly reduce their population in a given area with proper treatments.

Least-toxic insecticides and traps

Botanical insecticides can be used to treat landscape plants against Japanese beetle feeding, and neem oil insecticides are also effective feeding deterrents but must be re-applied every few days for as long as beetles are present

Milky Spore controls white grubs like Japanese beetle larvae

Japanese beetle larvae and other white grubs can be controlled with a bacterial insecticide called "Milky Spore". Milky Spore is applied to the soil where, over time, the bacteria build up and infect larvae. Milky spore is very safe and does not infect other organisms. Milky spore may take several years to become effective but should be a part of your arsenal if this pest is an ongoing problem in your landscape.

Related Articles

Least-toxic Botanical (Plant-based) Insecticides

Using Neem Oil Insecticides in the Garden

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