I. Introduction: Japanese beetles (JB) were introduced into New Jersey on nursery stock from Japan in 1913. They are now seasonal pests in many eastern fruit growing areas. Larvae feed on roots of grass, herbaceous plants, and nursery stock, while adults feed on foliage and fruit.

II. Hosts: JB feed on over 275 plant species. This includes all deciduous tree fruits, many small fruits, vegetables, grasses, and weeds.

III. Description: Adults are 3/8 to 1/2 inch (10-13 mm) long, metallic green to greenish-bronze, with coppery red wings and small white tufts on the sides and tip of the abdomen (photo 1). Larvae are "C"-shaped, white to cream-colored grubs with brown heads, and 3/4 to one inch (19-25 mm) long when mature.

IV. Biology: JB has one generation per year. Grubs overwinter eight to ten inches (20-25 cm) deep in the soil. As spring temperatures increase, grubs move up in the soil to feed on grass and other small roots. They pupate in late May to June and adults start emerging in mid-June to mid-July. Adults, which live from 30 to 45 days, feed through late summer or early fall. Females lay eggs two to six inches (5-15 cm) deep in the soil during July and August, and grubs hatch in 10 to 12 days. Grubs first feed on decaying matter, but soon feed on roots as they move deeper to an overwintering site.

V. Injury: Adult feeding on apple foliage results in a "lace-like" appearance, as beetles consume the leaf tissue but not the veins (photo 2). Feeding on apple fruit is much less common, and usually occurs only if the fruit has been previously damaged or is over mature (photo 3). On stone fruits, feeding on fruit is the most common injury. Adults are gregarious and often feed in groups chewing large chunks from the fruit (photo 4). In the mid-Atlantic region most injury occurs during the last two weeks of July through the first week in August. Fruit is usually injured during the last two weeks before picking. Therefore injury is most common on varieties ripening during periods of JB abundance, e.g. `Redhaven', `Norman', `Glohaven', and `Loring'. Grubs feeding in the soil may cause injury to nursery stock.

VI. Monitoring: Attractant traps may be used to determine the beginning of adult emergence. Adults also may be monitored by quietly moving into the tree, jarring several branches, and observing how many fly off. Direct examination of foliage and fruit is the most effective way of assessing damage. On apple, watch for skeletonizing of foliage on trees (photo 2) in July and August. On stone fruits, examine fruit that is within two weeks of harvest for feeding injury. Since feeding may be "clumped" or unevenly distributed, care should be taken in looking at a representative sample before making a spray decision.

VII. Management: On mature semi-dwarf and standard size apple trees, control measures should be considered if foliage injury involves more than the top third of the tree. Dwarf and non-bearing trees should be treated more conservatively due to the smaller canopy volume. Control on stone fruits is justified if fruit feeding injury exceeds one percent.

Credits: Text prepared by H. W. Hogmire and S. S. Beavers, modified from the original text in the Mid-Atlantic Orchard Monitoring Guide (original text by D. G. Pfeiffer, L. A. Hull, D. J. Biddinger and J. C. Killian). Prepared in October, 1997.

Web Site Author: Alan R. Biggs
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