Japanese Beetle – Identification and Control

Last updated March 1, 2023

Japanese beetles are one of the most destructive garden pests. These beetles can damage plants by eating leaves, stems, flowers, buds, and fruits.

Identification

Japanese beetles have a metallic green head and thorax.
They have copper-colored hard shells covering their wings called elytra.
These garden pests are about 6/10 inches (15 mm) long.
These beetles have patches of white hair around the abdomen. These white patches are the main feature for identification of Japanese beetle.
When beetles sense danger, they tuck in their legs and drop down from the plant.
Japanese beetles larvae are C-shaped grub, greyish white with a brown head. These grubs live in the soil.

Lifecycle

Japanese beetles are most active during the summer months. The adult stage is when they become most destructive. The adult insects spend most of their time on the host plants, eating, and mating. Then the female will go to the ground and lay individual or a small cluster of 1/16 inch (1.5 mm) long, pearly white, and oblong eggs on the soil surface. After laying the eggs, she returns to the host plant to feed and mate again. Japanese beetle females can lay up to 60 eggs throughout their lifetime.

After about two weeks, eggs hatch into c-shaped larvae that will mainly feed on the roots of the grass but will also consume other organic materials. This beetle spends most of its life in the larvae stage. The larvae will go through a couple of instar stages until it pupates and then becomes an adult.

The adult beetle will start to feed on the host plant and spread pheromones. These pheromones will attract other beetles who will overwhelm the host plant.

Japanese beetles go through multiple stages in their life cycle:

Stage 1 – eggs
Stage 2 – larva (instar I, II, III)
Stage 3 – pupa (chrysalis)
Stage 4 – adults

Damage They Cause

The grubs of these pests will feed on the roots of the grass and can cause them to thin out.

Japanese beetles mate and feed in groups. These large groups can devastate the garden. Japanese beetles mainly feed on the leaves of their host plant, skeletonizing them in a matter of days. These beetles can feed on more than 300 plant species, eating leaves, flower buds, and petals. When Japanese beetles eat, they release pheromones, attracting more beetles into the area.

Plants They Attack

The larvae will feed on the roots of the grass. They are also known to feed on many other roots like ornamental plants, strawberries, corn, beans, and tomatoes.

Adult Japanese beetles feed on leaves, flower buds, and petals of many different varieties of fruits, vegetables, and ornamentals. Their favorites are:

Asparagus
Apple Trees
Blackberries
Blueberries
Beans
Cherry Trees
Corn
Grapes
Peas
Plum Trees
Rhubarb
Roses
Raspberries
Strawberries
Tomatoes

Live Biological Control

Introduce predator insects to your garden that will control adult beetles:

Parasitic wasps
Beneficial Nematodes

Some animals like shrews, moles, skunks, crows, and starlings will eat Japanese beetle larvae.

Organic Control

To control Japanese beetle grubs, use beneficial nematodes or milky spores.

To control adult Japanese beetle, use neem oil or pyrethrins.

Preventive actions

Select plant species that these beetles will not feed on.
Remove these garden pests by hand and throw them into the bucket with soapy water.
Knock Japanese beetles off the plants and crush them.
Avoid commercial beetle traps. They will lure in more than they will trap.
Reduce the feeding ground for grubs. Meaning, reduce or eliminate grass close to your plants.

More About Japanese Beetle

Japanese beetle is considered a destructive and invasive species everywhere apart from Japan. In there, they are just a minor pest.

The lifecycle of these pests can take from one to two years and is highly dependant on the temperature. The colder the temperature, the longer they take to develop.