- Where does the Japanese beetle come from and why is it a problem?
- Recognizing Japanese Beetles
- Fighting Japanese Beetles
- Prevent an infestation
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The Japanese beetle is a very voracious pest that was brought from Japan by us humans. We show how to recognize and fight the Japanese beetle.
The Japanese beetle (Popillia japonica) damage pattern includes underground root damage and skeletal 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 will find everything you need to know about recognizing, controlling 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 a minor pest because natural predators suppress populations and the terrain is generally unsuitable for larval development.
In the United States, the Japanese beetle was first recorded in 1916 at a nursery in the Discovered near Riverton, New Jersey. It is believed to have been introduced via imported Japanese iris (Iris ensata) rhizomes. 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 - which offer it better living conditions here than in its original home.
In July 2022 he was discovered in Basel, where he probably arrived on a freight train. In November 2022, a specimen was found in a pheromone trap at the Freiburg freight station, which means that the Japanese beetle has now 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 dreaded quarantine pest.
Tip: Organisms classified as quarantine pests must be prevented from entering new areas because they have significant economic andecological 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.
Recognizing Japanese Beetles
The Japanese beetle is similar to 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 (Rosa), grapes (Vitis spec.), lime trees ( Tilia spec.), Apples (Malus x domestica), Ornamental Apples (Malus spec.), cherries (Prunus spec.), plums (Prunus domestica) and other stone fruit trees, birches ( Betula spec.), Elm (Ulmus spec.), Raspberries (Rubus idaeus), Currants ( Ribes spec.), Basil (Ocimum basilicum), Hollyhocks (Alcea rosea), Marigolds ( Calendula officinalis), corn (Zea mays), soybeans (Glycine soja) and many more.
Appearance and lifestyle
In order to recognize the Japanese beetle, you have to know what it looks like and where and when you can find it.
Japan Beetle Eggs: The newly laid Japanese beetle eggs 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.
Japan Beetle Larvae: The Japanese beetle larvae feed on fine roots and other organic matter. 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 approximately 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, that isthe 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 ( Malus spec.), roses (Rosa) 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
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 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
You usually see the damage first and then come across the beetles. You should take a closer look at the following observations.
Pests of 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 others also produce the same type of damageInsect larvae, so if in doubt you have to dig up the grubs and examine them for the typical hairline.
Painful image of the Japanese beetle:
The adult animals in turn feed on the leaves, blossoms 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 eating skeletons at the top of branches and plants - so it doesn't hide very well.
Fighting 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 appropriate crop protection service.
- Attractant traps with the pheromone Japanilure are not yet available in 2022, but could be included in the range of specialist retailers if they become more widespread. They are used to recognize 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 weevils and 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 place a tarpaulin under the affected plantsspread.
- 2022 we have not yet approved any plant protection products against the Japanese beetle, 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 probable economic damage.
Prevent an infestation
Better than fighting it is effective prevention. What you can do if the Japanese beetle spreads in your area:
- If you know that Japanese beetle grubs live in the garden, it makes sense to work the soil close to the surface in autumn, because this will bring them to the surface and garden birds can eat them.
- 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 egg laying.
- Promotion of biodiversity, especially among birds. A bird friendly garden will have fewer problems with the Japanese beetle.
- Protect your crops with fine nets placed over your crops.
- When choosing new plants for your garden, consider those that are less interesting to the Japanese beetle. These include boxwood (Buxus spec.), clematis (Clematis spec.), chrysanthemum (Chrysanthemum spec .), many conifers, daylilies (Hemerocallis spec.), cranesbill (Geranium spec.), ginkgo (Ginkgo bioloba ), Japanese Lilac (Syringa reticulata), Forsythia (Forsythia spec.), Lilac (Syringa spec.), magnolia (Magnolia spec.), red and silver maple (Acer rubrum, Acer saccharinum ), oak (Quercus spec.), white poplar (Populus alba), common 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 control grubs in the lawn.