April 20, 2018

Japanese Beetle

Suzanne Wold-Burkness, Department of Entomology, University of Minnesota

Japanese beetle, Popillia japonica (Coleoptera: Scarabaeidae), feeds on nearly 300 species of plants, including fruits, vegetables, ornamentals, field and forage crops and weeds. This insect was first detected in New Jersey in 1916, and is thought to have been introduced from the soil surrounding plants imported from Japan. Japanese beetles have spread throughout most states east of the Mississippi River. However, partial infestations also occur west of the Mississippi River in states such as Arkansas, Iowa, Kansas, Minnesota, Missouri, and Oklahoma.

Identification

Biology & Life Cycle

Japanese beetle overwinter as late-instar larvae in the soil. In the spring when the soil begins to warm, larvae move toward the surface where they continue to feed and pupate. New adult beetles emerge from the ground in June and July and begin feeding upon foliage. Eggs are laid in the soil in July and August in grassy areas. Larvae begin to hatch in late July and go through three molts before fall. In August, young grubs begin feeding on plant roots. Grubs continue to feed and grow until cold weather provides the cue for them to tunnel 3 to 12 inches down in to the soil and make overwintering cells. There is one generation per year.

Damage

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Japanese beetle adults (E.C. Burkness, U of MN)

Adult beetles can be identified by their brilliant metallic green, with copper-brown forewings that do not entirely cover the abdomen, five lateral brushes of white hairs on each side of the abdomen, and two brushes of white hair on the last abdominal segment. Eggs are approximately 0.10 cm in diameter and are laid in grassy areas near vineyards. Larvae are typical white grubs, c-shaped, and are limited to feeding only on the roots of grass and weeds.

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Feeding damage from Japanese beetle (T.L. Galvan, U of MN)

This pest can be a problem particularly in new vineyards using grow tubes. The adults are skeletonizers, in that they eat the leaf tissue between the leaf veins but leave the veins behind, giving the leaf a lace-like appearance. Leaves fed upon by Japanese beetles soon wither and die.

Management

Monitoring/Trapping

Japanese beetle traps are sold in many garden centers. Commercially available traps attract the beetles with two types of baits; one mimics the scent of female beetles and is highly attractive to males while the other bait is a sweet-smelling food-type lure that attracts both sexes. This combination of ingredients is very powerful and can attract thousands of beetles in a single day. These traps can be used as an indicator of Japanese beetle presence; however, some researchers discourage the use of the traps because they believe that they actually bring more beetles into the vineyard, thus increasing the potential for feeding damage.

Biological Control

Japanese beetle larvae are subject to attack by a bacterium, Bacillus popillae (milky spore disease). This biological control agent can protect grassy areas from large larval populations, but it is ineffective against adults entering the vineyard.

Chemical Control

There is no proven economic threshold on the number of Japanese beetles or amount of damage that requires treatment. However, if a susceptible variety is being grown and growers have previously experienced high populations of Japanese beetles, then it is recommended that an insecticide be applied when Japanese beetle feeding is apparent on most vines, and skeletonized leaves are found. Spot treatments are adequate in some cases. Several insecticides provide good control of Japanese beetle, and can be found in the Midwest Small Fruit Pest Management Handbook.

References

Dami, I., B. Bordelon, D.C. Ferree, M. Brouwn, M.A. Ellis, R. N. Williams, and D. Doohan. 2005. Midwest Grape Production Guide. The Ohio State University Extension Service. 155 pp.

Ellis, M. D. Doohan, B. Bordelon, C. Welty, R. Williams, R. Funt, and M. Brown. 2004. Midwest Small Fruit Pest Management Handbook. The Ohio State University Extension. 125-129. http://ohioline.osu.edu/b861/

Krishik, V. and D. Masar. Japanese Beetle Management in Minnesota. 2001. http://www.extension.umn.edu/distribution/horticulture/DG7664.html

Minnesota Grape Growers Association. 1999. Growing Grapes in Minnesota. MN Grape Growers Association, Lake City, MN.

USDA-APHIS. 2007. Japanese Beetle ID Card. http://www.aphis.usda.gov/publications/plant_health/content/printable_version/jbidcard5-07.pdf.

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