Japanese beetle: Recognize & combat the Asian pest

The Japanese beetle is a very voracious pest that we humans brought in from Japan. We show how to recognize and combat the Japanese beetle.

The harmful image of the Japanese beetle (Popillia japonica) includes subterranean root damage and skeletonization damage on leaves and buds. For horticultural companies of all kinds and also private gardens, it is a serious pest that should be kept under close scrutiny. Here you can find out everything you need to know about recognizing, fighting and reporting the Japanese beetle.

Where does the Japanese beetle come from and why is it a problem?

The Japanese beetle is a species of scarab beetle (Scarabaeidae). In its native country of Japan, the beetle is an insignificant pest, since natural enemies die Populations are suppressed and the terrain generally poor for larval development suitable is.

In the United States, the Japanese beetle was first discovered in 1916 at a nursery near Riverton, New Jersey. It is thought to have originated from imported Japanese iris (Iris ensata) was introduced. Even today, it is mainly distributed via global trade, for example via potted plants and turf. The beetle is currently spreading westwards with great success. In its newly conquered range, it can quickly become a significant pest of turf, ornamental and crop plants, especially when the vegetation and ground cover favor its development - they offer it better living conditions here than in its original homeland.
In July 2021 he was discovered in Basel, where he probably arrived on a freight train. In November 2021, a specimen was found in a pheromone trap at the Freiburg freight station, with which the Japanese beetle has apparently also arrived in Germany.
The Japanese beetle feeds on more than 300 plant species from 80 plant families and can occur in large numbers, making it a feared quarantine pest.

Tip: Organisms that must be prevented from entering new areas are classified as quarantine pests because they can cause significant economic and ecological damage.

Do you have to report Japanese beetles? This beetle is a reportable insect. Contact your state's crop protection service and be sure to capture the beetle so it can be identified. Write down the place and time of the find.

Identify Japanese beetles

The Japanese beetle resembles our native garden beetle (Phyllopertha horticola), but can be distinguished from it by a few clear distinguishing features.

On which plants can you find the Japanese beetle?

The Japanese beetle uses many plants. Favorite plants include roses (pink), Grapes (Vitisspec.), Linden (Tilia spec.), apples (penalty x domestica), decorative apples (penalty spec.), cherries (prunus spec.), plums (Prunus domestica) and other stone fruit trees, birches (Betula spec.), elms (Ulmus spec.), raspberries (Rubus idaeus), currants (Ribes spec.), basil (Ocimum basilicum), Hollyhocks (Alcea rosea), marigolds (Calendula officinalis), Corn (Zea mays), soybeans (Glycine soy) and many more.

appearance and lifestyle

In order to recognize the Japanese beetle, one must of course know what it looks like and where and when it can be found.

Japanese beetle eggs: The newly laid eggs of the Japanese beetle are about 1.5 mm long and elliptical in shape, translucent to pearly white. Eggs are laid just below the soil surface, singly or in small groups.

Japanese beetle larvae: The Japanese beetle larvae feed on fine roots and other organic material. The larvae go through three instars and constantly grow to 32 mm in length. These are the C-shaped, white grubs with a yellowish-brown head that are typical of scarab beetles. They have three thoracic segments and ten legless abdominal segments. They can be distinguished from other grubs by a V-shaped row of spines on the last abdominal segment.

Japanese beetle pupae:They are about 14 mm long, 7 mm wide and resemble the adult beetle but are initially colourless, then cream colored and finally colored like the adult specimens.

Imagos of the Japanese beetle: The imagos, i.e. the adult animals, appear between May and June. The adult beetle measures 12 cm in length and about 7.5 cm in width, has iridescent copper colored elytra and a metallic green thorax and head. There are five patches of white hair on the sides of the abdomen. The Japanese beetle is found particularly frequently on certain host plants: These include maple (acer spec.), horse chestnut (aesculus spec.), birch (Betula spec.), hazelnut (Corylus avellana), walnut (juglans spec.), apple trees (penalty spec.), roses (pink) and elm (Ulmus spec.). The Japanese beetle can be recognized by a special alarm behavior: When threatened, they spread a pair of legs to the side of the body.

Japanese beetle: risk of confusion
There is a risk of confusion with the garden beetle (Phyllopertha horticola), the little July beetle (anomala dubia), for untrained eyes maybe also with rose chafer (Cetoniinae), June beetle (Amphimallon solstitiale) and field cockchafer (Melolontha melolontha). The grubs in particular can easily be confused.

Lifestyle of the Japanese beetle:

The Japanese beetle forms one generation per year. The adult males use the sex attractant japonilure to attract females. After mating, they lay 40 to 60 eggs. The larvae hatch after a maximum of two weeks, after which development proceeds to the third larval stage in autumn. The grub feeds on plant roots. The Japanese beetle overwinters as a larva at a depth of 25 to 30 cm. It pupates in the spring and hatches out of the ground as a new beetle from mid-May.

damage picture

Usually you see the damage first and thus come across the beetles. You should take a closer look at the following observations.

Harmfulness of the Japanese beetle grubs:
The larvae of the Japanese beetle damage the roots of lawn grasses and garden plants. This can cause brown patches of dead or dying grass to form in the lawn. The weakened roots make it easy for you to rip out the lawn like a loose carpet. However, many other insect larvae also cause the same damage, so that in case of doubt you have to dig up the grubs and examine them for the typical hairline.

Harmfulness of the Japanese beetle:
The adult animals in turn feed on the leaves, flowers and fruits of many different plants. Japanese beetles skeletonize the leaves, feeding on the tissue between the leaf veins, giving them a lacy appearance. But other types of insects can also leave such damage, so you need to identify the bug by its appearance. The Japanese beetles are usually not far from damaged leaves, so inspect the plant carefully. Keep an eye on the soil below: if disturbed, the beetles may reflexively detach from the plant. Then you should check whether they have the typical white spots on the side of the abdomen and show the alarm behavior. By the way: As a rule, the Japanese beetle starts at the top of branches and plants with its skeleton feeding - so it doesn't hide very well.

Fight Japanese beetles

If you want to fight the Japanese beetle, there are a few simple ways to protect your plants from the ravenous beetle.

• Step 1 should always be catching the beetle and reporting it to the responsible plant protection service.
• Attractant traps with the pheromone Japanilure are not yet available in 2021, but could be included in the range of specialist retailers if they become more widespread. They are used to identify the beetles and to reduce them if they occur in large numbers.
• There are already attempts to use various bacteria, fungi and nematodes against the grubs in the soil. One possibility, for example, is to use our Plantura Bio-HB-Nematodes against vine weevil & grubs. They are an effective, biological crop protection agent and the nematodes used do not damage the soil or plants. Apply our HB nematodes in autumn under the affected plants or on the lawn, observing the required minimum soil temperature.

• Collecting the beetles: If the imagos appear between May and June, they can be collected. Japanese beetles live for 6-8 weeks so it is important to continue control until their numbers decrease. Since the beetles like to fall to the ground when threatened, you can spread a tarpaulin under the affected plants.
• In 2021, no pesticides against the Japanese beetle have yet been approved in Germany because the pest is still too new. In the future, however, it would be possible to use neem preparations, for example, which are also effective against related beetles such as the May beetle and the June beetle. In professional horticulture, however, so-called emergency approvals will probably come sooner because of the expected economic damage.

Prevent an infestation

Effective prevention is better than having to fight it. What you can do if the Japanese beetle spreads in your area:

• It is known that grubs of the Japanese beetle live in the garden is a near-surface cultivation of the soil makes sense in autumn, because this way they are transported to the surface and can be eaten by garden birds will.
• If the Japanese beetles fly and mate between May and July, you should avoid excessive watering of the garden, because moist soil is more attractive for laying eggs.
• Promoting biodiversity, especially among birds. A bird friendly garden will have fewer problems with the Japanese beetle.

• Protect your plants with fine netting that you place over your crops.
• When choosing new plants for your garden, consider those that are less interesting to the Japanese beetle. These include boxwood (boxy spec.), Clematis (clematis spec.), chrysanthemums (chrysanthemum spec.), many conifers, daylilies (Hemerocallis spec.), cranesbill (geranium spec.), ginkgo (Ginkgo bioloba), Japanese lilac (Syringa reticulata), forsythia (Forsythia spec.), lilac (Syringa spec.), magnolias (magnolia spec.), red and silver maple (Acer rubrum, Acer saccharinum), oaks (Quercus spec.), white poplars (Populus alba), European beech (Fagus sylvatica) and rhododendron (rhododendron spec.).

The larva of the Japanese beetle is a typical grub and can cause a lot of damage. In our special article you will learn how to successfully fight grubs in the lawn be able.