Japanese Beetles

About Japanese Beetles

The Japanese beetle (Popillia japonica) is native to Japan, but has become common throughout much of the eastern U.S. since its accidental introduction in 1916. The adult beetles feed on the foliage, flowers, and/or fruit of more than 300 different plant species and are considered a major pest of many popular horticultural and agricultural plants. Adult Japanese beetles can cause significant damage to host plants because of their tendency to feed in large numbers.

Japanese Beetle Description

Adult Japanese beetles are approximately 3/8 inch in length, oval in shape and have clubbed antennae. They are metallic green in color with coppery-brown wing covers (elytra) and a row of five white hair tufts on each side the abdomen. The larvae are typical white grubs that can be distinguished from other species by the presence of a small V-shaped series of hairs on the underside of the last abdominal segment (raster). Newly hatched larvae are about 1/16 inch long, while the mature larvae are about 1 inch long.

Japanese Beetle Damage

Japanese beetles can damage plants during both the adult and larval stages, but the type of feeding injuries produced by each life stage is very different. Adult Japanese beetles are mainly leaf feeders that consume the tissue between leaf veins. Because the veins of the leaf are left intact, the damage is often referred to as skeletonization. In addition to leaves, beetles will feed on blossoms and ripe or damaged fruit when available. The larvae are a type of white grub that feeds below the soil surface on the roots of grasses and other plants.

Japanese Beetle Control

Control of the Japanese beetle is often difficult, because the adults and grubs cause different types of damage on plants. Moreover, adults are highly mobile and can infest new areas from several miles away, so controlling Japanese beetle grubs and/or adults in one area will not necessarily prevent new individuals from moving in and taking their place. Effective Japanese beetle control often requires an integrated pest management approach.

Cultural Control of Japanese Beetle

To avoid annual battles with Japanese beetles, it is important to select plant species that the insect does not consistently like to feed on. Certain plants are highly preferred by beetles and may be poor choices when replacing or adding to gardens and landscapes (see Table 1 below.)

Mechanical/Physical Control of Japanese Beetle

Hand removal can be an effective method for small-scale control of Japanese beetles. Beetles can easily be removed by shaking the plants or plant parts over a collecting container filled with water and a few drops of dish soap. The dish soap breaks the water’s surface tension so the beetles sink into the water and drown rather than escape. Studies have shown that removing beetles in the evening (around 7 p.m.) is particularly effective.

Commercial Japanese beetle traps have been recommended by some to control adult feeding damage. These traps usually employ two types of baits to attract beetles: a floral-based compound and a synthetic sex pheromone that mimics the odor the female beetle uses to attract mates. Although large numbers of beetles can be captured in these traps, they often attract more beetles than can be contained, and subsequently increase plant damage in their general vicinity. It is for this reason that trapping is not recommended for Japanese beetle control.

Chemical Control of Japanese Beetle

Numerous insecticides are labeled for use against adult Japanese beetles. Carbaryl (Sevin) and various insecticides in the pyrethroid (e.g., bifenthrin, cyfluthrin, fenpropathrin, lambda-cyhalothrin, permethrin, zeta-cypermethrin) and neonicotinoid (e.g., acetamiprid, clothianidin, imidacloprid, thiamethoxam) class of insecticides can be particularly effective for Japanese beetle control. Insecticides that are permissible in organic production include pyrethrins and neem-based products that contain azadirachtin. However, these products only act as a repellant and provide relatively short-term control.

Japanese Beetle Life Cycle

The Japanese beetle typically has one generation per year. Beetles begin appearing in June with adult activity often peaking in early July. Adult Japanese beetles prefer to feed in full sun at the top of plants, moving downward as the leaves are consumed. Aggregations of beetles are formed as a result of attraction to plant odors released during feeding. Essentially, feeding by initial beetles leads to more beetles arriving on a plant. Mated females alternate between feeding and egg-laying, typically entering the soil around a dozen times during their life span to deposit eggs among plant roots. Eggs hatch in approximately 10 to 14 days. The larvae will feed on plant roots until around the time of first frost, at which point the nearly full-grown grubs move deeper into the soil and remain inactive during the winter. As the soil warms the following spring, the grubs move back into the root zone and resume feeding until turning into pupae. The pupae transform into adults, which emerge from the soil to continue the next generation.

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