Japanese Beetles, Popillia Japonica

Close up of Japanese beetle on flower
Flickr user Ryan Hodnett (CC by SA license)

Is there a garden pest worse than the Japanese beetle? First, the beetle grubs destroy your lawn, and then the adult beetles emerge to feed on your leaves and flowers. Knowledge is power when it comes to controlling this pest in your yard.

Description

The Japanese beetle's body is a striking metallic green, with copper-colored elytra (wing covers) covering the upper abdomen. The adult beetle measures just about 1/2 inch in length.

There are five distinctive tufts of white hairs line each side of the body, and two additional tufts marking the tip of the abdomen. These tufts distinguish the Japanese beetle from other similar species.

Japanese beetle grubs are white, with brown heads, and reach about 1 inch in length when mature. First instar (a developmental stage between molting) grubs measure just a few millimeters in length. The grubs curl into a C shape.

Classification

Kingdom - Animalia
Phylum - Arthropoda
Class - Insecta
Order - Coleoptera
Family - Scarabaeidae
Genus - Popillia
Species - Popillia japonica

Diet

Adult Japanese beetles are not picky eaters, and that's what makes them such an impactful pest. They'll feed on both the foliage and flowers of several hundred species of trees, shrubs, and herbaceous perennials. The beetles eat plant tissues between the leaf veins, skeletonizing the foliage. When beetle populations get high, the pests may completely strip a plant of flower petals and foliage.

Japanese beetle grubs feed on organic matter in the soil and on the roots of grasses, including turfgrass. High numbers of grubs may destroy turf in lawns, parks, and golf courses.

Life Cycle

Eggs hatch in late summer, and grubs begin to feed on plant roots. Mature grubs overwinter deep in the soil, below the frost line.

In spring, grubs migrate upward and resume feeding on plant roots. By early summer, the grub is ready to pupate within an earthen cell in the ground.

Adults emerge from late June into summer. They feed on foliage and mate during the day. Females excavate soil cavities several inches deep for their eggs, which they lay in masses. In most parts of its range, the Japanese beetle life cycle takes just a year, but in northern areas, it may stretch to two years.

Special Behaviors and Defenses

Japanese beetles travel in packs, flying and feeding together. Males use highly sensitive antennae to detect and locate female mates.

Though Japanese beetles are despised for their voracious appetites for just about anything green, there is one plant that stops them in their tracks, literally. Geraniums have an odd effect on Japanese beetles and may be the key to defeating these pests. Geranium petals cause a temporary paralysis in Japanese beetles, rendering them completely immobile for as long as 24 hours. While this doesn't kill them directly, it leaves them vulnerable to predators.

Habitat

With such a variety of potential host plants, Japanese beetles are well suited to live just about anywhere. Popillia japonica inhabits forests, meadows, fields, and gardens.

Japanese beetles even find their way to urban backyards and parks.

Range:

Although the Japanese beetle is native to eastern Asia, this species was accidentally introduced to the U.S. in 1916. Japanese beetles are now established throughout the eastern U.S. and parts of Canada. Intermittent populations occur in the western U.S.

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