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Managing Japanese beetles: Identification, impact, and control methods

Theme: Pest guides

Overview:

The Japanese beetle (Popillia japonica) is a species of beetle native to Japan. In the early 1900s, it spread to North America and is now considered an invasive species and pest in Canada and the United States. It has also spread to Europe in recent years. This pest causes damage to a huge variety of crops in both its adult and larval stages. Common crops affected by the Japanese beetle include vegetables like tomatoes and corn, and fruit trees like apples and pears. The larvae typically attack the roots of plants while adults attack leaves resulting in severe defoliation (leaf loss).

In this article, we will provide an overview of the Japanese beetle, including how to identify it, and how to control it using biological control methods.

What is the Japanese beetle?

The Japanese beetle is an invasive species that is present in Canada and the US and has recently spread to British Columbia. While Canadian beetles, such as the Mountain Pine Beetle, primarily affect specific types of trees, the Japanese beetle is notorious for its broad range of host plants, feeding on over 300 plant species. This pest produces one generation per year.

Grubs (larvae) spend winter underground and begin feeding on roots in the spring once temperatures rise. They continue to feed and progress through three developmental phases before pupating (transforming from larva to adult), resting for two weeks, and then emerging from the soil as mature adults. Adults typically emerge in late June or early July in Vancouver, though this differs elsewhere depending on the climate. Adults are active for roughly six weeks, and during this time they feed and mate and females lay roughly 40-60 eggs throughout July and August. The lifecycle is complete by September and adult beetles die off. The eggs hatch in about two weeks and the larvae feed on roots until the temperatures get too cold. Eggs are white and around 1.5 mm long.

What are the different types of Japanese beetles?

The term Japanese beetle refers to only one species: Popillia japonica.  

Adult Japanese beetle

Adult Japanese beetles are relatively small measuring around 1 cm in length. The adults are metallic green with copper-colored wing covers. They also have six distinctive white tufts of hair along each side of their abdomen and are capable of flight under the right conditions.

A close-up of an adult of the japanese beetle on a leaf
An adult of Japanese beetle (Popillia japonica) ©Theresa Cira, Minnesota Department of Agriculture

Larvae of Japanese beetle

Japanese beetle larvae are milky white with tan-brown heads and are found in the classic C shape. They are around 2cm long and are found at different depths in soil depending on season and climate.

A close-up of a larva of japanese beetle curled in a "C" shape in soil
A larva of Japanese beetle (Popillia japonica). Credit: David Cappaert, Bugwood.org

What is the impact of Japanese beetles?

Adult Japanese beetles feed on the leaves and fruits of a wide variety of plants. Shortly after they emerge from the soil, the adults prefer to feed on the lower leaves of plants but they feed higher up as the season progresses. They also have a general preference for feeding on leaves that are in direct sunlight. Adult Japanese beetles like to attack grapes but also feed on apple, pear, cherry, and peach trees, and vegetables including corn, tomatoes, soybeans, and peppers. Defoliation can lead to the death of the crop. Japanese beetle larvae feed on the roots of a wide variety of plants, but they cause particular damage to turf grass, which is commonly used for sporting surfaces including golf. Large digging predators of the larvae can cause further damage to turf grass.

The economic impact of Japanese beetles in Canada is significant, particularly in British Columbia. The British Columbia Ministry of Agriculture estimates that annual crop damage due to Japanese beetles is around $14.5 million and the cost to the golf industry is estimated at $13.6 million (Invasive Species Centre)​. The pest has been particularly problematic in the city of Port Coquitlam. As such, British Columbia is a highly regulated area for Japanese Beetles. Public awareness campaigns by the Canadian Food Inspection Agency (CFIA) (in collaboration with the Department of Agriculture) educate citizens on how to identify and report Japanese beetle sightings, particularly in regions designated as Japanese beetle-regulated zones.

Are they dangerous to humans?

Japanese beetles are not harmful to humans. They do not bite, sting, or transmit diseases to humans, and are not poisonous.

How do I know if I have a Japanese beetle problem?

Japanese beetle damage has some characteristics that make it easy to identify. Adults feed on leaf tissue between the veins. This results in a lace-like appearance of leaves after adult beetles have fed on them. On thinner leaves the damage can look like irregular shapes missing from the leaf. Damage to turf grass caused by Japanese beetle larvae can look like brown patches, and if there is enough damage the turf grass can fold upward like a carpet when pulled.

Three adults of japanese beetle on a rose leaf damaged by their feeding
Japanese beetle (Popillia japonica) feeding damage on a rose leaf. Credit: Melissa Schreiner, Bugwood.org

How do I get rid of Japanese beetles?

Fortunately, there are many options for controlling the number of Japanese Beetles. Chemical insecticides are still in use; however, they might also kill beneficial insects. Safer and more environmentally friendly methods such as biological control, pose a low risk to bees and beneficial insects and are gaining prominence.

Cultural control

Infrequent but deep watering can encourage root growth which can help to make plants more resistant to damage by Japanese beetle grubs. Good irrigation and drainage are also important as grubs prefer moist soil. To reduce damage by adult beetles, avoid planting young plants during times of peak beetle numbers (July and August). 

Mechanical control

Beetle pheromones can be added to traps to attract beetles and effectively reduce their numbers. However, some sources suggest that using pheromones and traps can lure beetles to your fields or garden. Therefore, traps should be placed at the borders of your property and away from plants that beetles are more likely to damage. 

Biological control

Microbials

These are tiny organisms like bacteria, fungi, and viruses that kill pests through various modes of action. For example, the bacteria Bacillus thuringiensis galleriae produces toxins that selectively kill pest larvae, including Japanese beetle grubs.

Macrobials

These are larger organisms that kill pests often by directly feeding on them. Nematodes are tiny worms that enter pest larvae and release bacteria which is fatal to Japanese beetle larvae.

Natural substances

These substances are taken from natural sources like plants. Neem oil is a natural substance that can be applied directly to plants and reduces Japanese beetle feeding and disrupts larval development. Many useful products contain ​​​​pyrethrin, which naturally occurs in certain flowers and has insecticidal properties.

Encourage natural predators

Encouraging predators can help control the numbers of Japanese beetles, however, it’s important to remember that these predators can impact turf grass quality.

Summary

Japanese beetles pose a significant threat in Canada, especially in British Columbia, where crop and turfgrass damage have a severe economic impact. Effective management of Japanese beetles combines cultural practices, such as deep watering, with biological controls, including beneficial nematodes and Bacillus thuringiensis bacteria. These methods offer environmentally friendly alternatives to chemical pesticides, reducing the impact on beneficial insects like bees. By integrating these strategies, it is possible to sustainably manage Japanese beetle populations and mitigate their economic impact on agriculture​. 

To find out about specific biological control products to control Japanese beetle numbers please visit the BioProtection Portal. For more general info on biological control check out our beginner’s guide

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