ARTICLES, NEWS      HOMEPAGE      EMAIL-CONTACT



Japanese Beetle, Popillia japonica, Grub worm
Invasive Species and Pest

The Japanese beetle, or Popillia japonica, was accidentally introduced as a pest in the United States. It may have arrived as grubs in nursery plant soil imported from Japan. They first appeared near Riverton, New Jersey in 1916 and by the year 2000 had spread rapidly to all states east of the Mississippi River except Florida, as well as the upper Midwest, and even into southern Canada. In Japan, this beetle does not pose a significant threat because of the lack of suitable habitat, and in Japan there are natural predators that keep it under control.

The situation in the United States is quite different. Here there is an abundance of moist grassland for the development of Japanese beetle eggs and larva along with many suitable food plants for the adults. The broad range of plants this invasive species eats further complicates the gravity of the situation. Adult Japanese beetles enjoy a wide variety of both wild and cultivated plants, eating leaves, flowers and fruit.

Japanese beetle with legs up defense
Japanese beetle with legs up defense


Japanese beetle pest invasive-species
Japanese beetle pest, invasive-species

Japanese beetle on finger, size
Japanese beetle on finger, size reference
Japanese beetle larva, or grubs, feed on the roots of grasses, vegetables, nursery seedlings and field crops. Between the two life stages of the Japanese beetle, nearly 300 plant species are targeted for their dinner. The beetle has no natural enemies in the U.S. making it a major source of damage, where the cost of controlling both the adults and the grub worm amounts to hundreds of millions of dollars per year.

Japanese beetle, Popillia japonica, pest
Japanese beetle, Popillia japonica, pest

Japanese beetle, legs up defensive posture
Japanese beetle, legs up defensive posture
Adult Japanese beetles are a metallic green color, with copper-tinged, brown forewings, or elytra. Their abdomens have five areas of white hairs on both sides, as well as a pair at the tip. Female Japanese beetles are slightly larger than males and better equipped for digging. Japanese beetle grubs are typical for the scarab beetle family. The grub worm bodies are c-shaped, and vary from creamy to gray in color, except for the end which appears dark from eating their food and some amount of dirt along with it. Japanese beetle grubs may reach a length of up to roughly 1.25 inches.

scarab grub worm
scarab grub worm

adult, Japanese beetle, Popillia japonica
adult, Japanese beetle, Popillia japonica
The life cycle of the Japanese beetle is one year. The female lays several batches of eggs, roughly 40 to 60 eggs in total during her lifetime. Japanese beetle grubs hatch within 2 to 3 weeks and start feeding right away. They dig deeper at the first frost and overwinter there. In spring, they feed again for 4 to 6 weeks, and then dig deeper to pupate in a cell lined with dirt. The first adults of the season emerge a few weeks later.





Japanese beetle, Popillia japonica
Japanese beetle, Popillia japonica
A few mammals, such as skunks, raccoons and moles, as well as some birds may dig up and eat the tasty Japanese beetle grubs. Some native insects feed on eggs and young grubs, while birds and fish may eat adults. In the 1920s and 1930s, numerous natural enemies to the Japanese beetle were imported from Asia and introduced into infested areas. Of those introduced, a few predatory insects have prospered including two species of parasitic wasp larvae that devour the beetle grubs, and one parasitic tachinid fly which prefers the adult beetles. Japanese beetle grubs also are susceptible to parasitic worms called nematodes, or threadworms, as well as a few pathogens including the milky disease bacterium, Paenibacillus popilliae.

Japanese beetle on grass, plant stem, pest
Japanese beetle on grass, plant stem, pest

Japanese beetle group on leaf
Japanese beetle group on leaf
The Japanese beetle, Popillia japonica, has firmly established itself on the North American continent and will remain a part of the natural landscape into the future. Most likely this invasive species will continue to increase its range as time goes by.

Andrew Williams / CritterZone.com
Literature cited
Carde, Ring T. 2003 Encyclopedia of Insects Academic Press pgs.609-610
The Japanese beetle, Popillia japonica, pictures on this page are available for commercial stock photography license. All text and photos that appear on this webpage are copyrighted and may not be copied or used in any way without permission from CritterZone.

CritterZone does not specifically endorse our advertisers, or their methods. We cannot control the ads that run on our articles. CritterZone advocates humane and respectful treatment of all creatures.

Japanese beetle with wings showing
Japanese beetle with wings showing