TreeHelp Product Suggestions: Safer's Japanese Beetle Trap
Close-up of a Japanese beetle USDA	Japanese beetles skeletonizing a leaf Ohio State University Extension Service

Distribution

The Japanese beetle (Popillia japonica Newman) is a highly destructive plant pest that can be very difficult and expensive to control. Feeding on grass roots, Japanese beetle grubs damage lawns, golf courses, and pastures. Japanese beetle adults attack the foliage, flowers, or fruits of more than 300 different ornamental and agricultural plants.

Japanese beetles were first found in the United States in 1916 near Riverton, New Jersey. Since then Japanese beetles have spread throughout most states the lie 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. Usually infestations in states west of the Mississippi River are eradicated before the Japanese beetle becomes established.

Hosts

Adult Japanese beetles feed on over 400 species of broad-leaved plants. The grubs will also feed on a wide variety of plant roots including ornamental trees and shrubs, garden and truck crops, and turfgrasses. They seem to prefer Kentucky bluegrass, perennial ryegrass, tall fescues and bentgrass.

Symptoms of Damage

Adult Japanese beetles are skeletonizers.  This means that they eat the leaf tissue between the leaf veins, but leave the veins behind. Attacked leaves have a lacey appearance, and soon wither and die. Adult beetles will often attack flower buds and fruit. The grubs can kill small seedling plants, but most commonly damage turf. The turf first appears off-color as if under water stress. Watering may help temporarily, but more often it will have no effect. The turf feels spongy under foot and can be easily pulled back like old carpet to reveal the grubs. Large populations of grubs kill the turf in irregular patches.

Life Stages of the Japanese Beetle
(from Ohio State University Extension Service)

The life stages of the Japanese beetle are typical of white grubs.

• Eggs: The white oval eggs are usually about 1/16 inch (1.5 mm) long and 3/64 inch (1.0 mm) wide. They are placed in the soil where they absorb moisture and become more roundish.

• Larvae: The larvae are typical white grubs that can be separated from other soil dwelling white grubs by the presence of a V-shaped series of bristles on the raster. First instar larvae are about 1/16 inch (1.5 mm) long while the mature third instars are about 1-1/4 inch (32 mm) long.

• Pupae: The pupae are first cream colored and become light reddish-brown with age. The average pupa is about 1/2 inch (14 mm) long and 1/4 inch (7 mm) wide.

• Adults: The adults are a brilliant, metallic green color, generally oval in outline, 3/8 inch (10 mm) long and 1/4 inch (7 mm) wide. The wing covers are copper-brown and the abdomen has a row of five tufts of white hairs on each side. These white tufts are diagnostic. The males have a sharp tip on the foreleg tibia while the female has a long rounded tip.

Life Cycle and Habits
(from Ohio State University Extension Service)

Larvae that have matured by June pupate and the adult beetles emerge from the last week of June through July. On warm sunny days the new beetles crawl onto low growing plants and warm for a while before taking flight. The first beetles out of the ground seek out suitable food plants and begin to feed as soon as possible. These early arrivals begin to release a congregation pheromone (odor) which is attractive to adults that emerge later. These odors attract additional adults to gather in masses on the unfortunate plants first selected. In cool weather, the adults may feign death by dropping from the plants but normally they will take flight. Newly emerged females release an additional sex pheromone which attracts males. The first mating usually takes place on turf with several male suitors awaiting the emergence of a new female. Mating also is common on the food plants and several matings by both males and females is common.

After feeding for a day or two, the females leave feeding sites in the afternoon and burrow into the soil to lay eggs at a depth of 2 to 4 inches. Females may lay 1 to 5 eggs scattered in an area before leaving the soil. These females will leave the following morning or a day or two later and will return to feed and mate. This cycle of feeding, mating and egg laying continues until the female has laid 40 to 60 eggs. About 95% of a population are generally laid by mid-August, though adults may be found until the first frost of fall.

If the soil is sufficiently moist, eggs will swell in a few days. Egg development takes only 8 to 9 days at 80 to 90 degrees F or as long as 30 days at 65 degrees F. The first instar larvae dig to the soil surface where they feed on roots and organic material. If sufficient food and moisture are available, the first instars can complete development in 17 days at 78 degrees F or as long as 30 days at 68 degrees F. The second instars take 18 days to mature at 78 degrees F and 56 days at 68 degrees F.

While this development is occurring, grubs may tunnel laterally in search of organic matter and fresh roots. This creates a very spongy feel to the soil and turf. Generally most of the grubs are in the third instar by early fall and are ready to dig into the soil to hibernate. The grubs burrow 4 to 8 inches into the soil as cold temperatures arrive. At this depth, the soil rarely gets below 25 degrees F and the grubs survive with no difficulty. If the soil begins to cool further, the grubs may dig deeper. The grubs return to the surface in the spring as the soil temperature warms. Generally the grubs can be expected to be active at the surface when the surface soil temperatures are about 60 degrees F, usually in mid-April. The grubs continue their development in the spring and the few second instars seem to mature in time to pupate along with the third instars. The mature grubs form a pre-pupa in early-June. The prepupa voids its gut contents and has a translucent appearance. The pupa is formed in the split skin of the pre-pupa in an earthen cell 1-to-3 inches in the soil.

Control Strategies

Control methods include using insect parasites such as parasitic wasps, winsome fly and nematodes. Bacterial Milky Disease has also been used as a biological control in some areas. Physical traps can also be effective against the Japanese beetle. Insecticides may also be used, but timing is important as females lay the majority of their eggs within the first 7-10 days of their lives.

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