Japanese Beetle Popillia japonica

Japanese beetles are a common and destructive invasive species in the U.S. Larvae feed on the roots of grasses and the mature adults feed on leaves, flowers and fruits. With abundant food and few natural predators the beetle is able to eat and reproduce freely.

Japanese beetles are, as their name suggests, originally found in Japan. Currently they are found in many countries such as Russia, China and the United States. They were first detected in 1916 in New Jersey and have spread since then. This map shows where Japanese beetles are found in the U.S and Canada.

Japanese Beetle Life History

Female beetles will burrow into the soil and lay eggs several times during the summer (40-60 eggs in total). The eggs will hatch and the grubs will feed on organic matter until winter. They will overwinter until temperatures rise again in the spring. The larvae will continue to feed on plant roots (in turn destroying the grasses above ground) until they are fully mature beetles. In cooler climates such as northern New York, mature adults will emerge from the soil in late June/early July. Japanese beetles have short life cycles typically only lasting one year. Once they emerge they must mate and females will lay eggs and the cycle begins once again.

Life cycle of Japanese beetle

Japanese beetle grubs (larvae) feed on the roots of lawn/turf grasses. This limits the grasses ability to take up water and survive hot and dry weather during the summer.

Adult Japanese beetles have been known to target over 300 species. But some of the most common host species are maple trees, elm trees, corn, roses, apples, blackberries and stone fruit such as peaches and plums.

Here you can see how easily Japanese beetles can feed on leaves and damage the plant. On a warm summer day, beetles can cause a lot of damage in a short period of time.

They often leave no more than a skeleton of the leaf. Leaves perform photosynthesis, a process that produces food and energy for the plant. When small plants can't photosynthesize, they will soon die. Larger plants, like trees, will appear brown from their loss of leaves. This removal of leaves is known as defoliation.

How to we slow the damage?

Because the Japanese beetle is so widespread and engrained into ecosystems, we can't completely kill all of them without also negatively impacting helpful species. We need tactics to manage the populations and reduce their damage so gardeners and farmers can protect their plants and crops. Combining methods to reduce populations is called Integrated Pest Management (IPM)

Have you ever seen one of these? If you have, there were probably some Japanese beetles nearby. This is a Japanese beetle trap. There is a lure at the top; the scent attracts beetles and they fall into the trap. It is commonly used as a way to see how large the beetle population is in an area. However it has also been shown to not be an effective solution to controlling populations because it only attracts more beetles.

Chemical Controls: There are a variety of pesticides available to farmers and gardeners to kill Japanese beetles. The results are fast and effective but they can have unintended side effects. Pesticides can kill beneficial insect species. They can also wash away with the rain and pollute water sources.

Using a natural control such as a parasite, bacteria, fungi etc. instead of chemicals that could damage the environment is called biological control. Biological controls only target their intended species.

This species of wasp, Tiphia vernalis Rohwer, is a parasite of overwintering grubs. Their larvae kill the overwintering beetle grubs, slowing their population growth.

Nematodes are another form of biological control. They are a microscopic, parasitic roundworm that eats insect grubs such as Japanese beetles.

Fun Facts About Popillia japonica

1. They love the sun! You are more likely to see beetles active on warm, sunny, summer days.

2. They prefer to eat with their friends. When one beetle starts feeding on a plant, they release a "congregation pheromone". This is something only other beetles can smell, and when they smell it they know someone has found a good place to eat. When beetles feed in groups, they can defoliate a plant very quickly.

3. The Japanese beetle is the most widespread and destructive turf-grass pest in the United States.

Sources for this page

Sophia Griffiths (2022)

Created By

Sophia Griffiths

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