Forest Pests: Insects, Diseases & Other Damage Agents

Leopard moth
Zeuzera pyrina (Linnaeus)

From: Solomon, J.D. 1995. Guide to insect borers of North American broadleaf trees and shrubs. Argic. Handbk. 706. Washington, DC: U.S. Department of Agriculture, Forest Service. 735 p.

Hosts. Elm, maple, ash, beech, walnut, oak, chestnut, poplar, willow, apple, pear, plum. Some host preferences depend on region; in New York, elms and maples preferred (Pike 1892, Seaver 1912). But attacks over 100 species of trees and shrubs (Britton and Crombie 1911). Except for evergreens, most woody plants of suitable size appear susceptible (Howard and Chittenden 1916).

Range. An introduced pest, probably from Europe, where it is a major problem in fruit trees (Britton and Crombie 1911). First reported from Hoboken, New Jersey, in 1882. Because female moths are extremely poor fliers, the spread has been slow. Now it is distributed mostly along the Atlantic seaboard from Philadelphia northward to Massachusetts (Commonwealth Institute of Entomology 1973, USDA FS 1985). Reportedly captured in Carson County, South Dakota (CIE 1973), but this occurence is unconfirmed.

Description

Adult. Black and white spotted moth; derives name from its spots. Wings semitransparent, white, and thickly dotted with distinctly tinged black spots of dark blue cast (Howard and Chittenden 1916). Wingspan of females ranges from 62 to 75 mm (USDA FS 1985). Females heavy bodied and much larger than slender bodied males. Thorax white with six large black spots and, near center, one small spot. White abdomen with dark crossbands (Howard and Chittenden 1916).

Egg. Oval, salmon, or orange yellowish, and about 1.5 mm long (Britton and Crombie 1911).

Larva. About 50 mm long, pale yellow, and often with a pinkish tinge when fully grown. Head, very prominent thoracic shield, and anal plate brownish black. Sparsely hairy body dotted with large, prominent dark tubercles on each segment (Howard and Chittenden 1916).

Pupa. About 30 to 40 mm long, dark brown, and characterized by sharp protuberance on head (Britton and Crombie 1911).

Biology. Adults emerge from May to September (Howard and Chittenden 1916). The heavy-bodied females seldom fly and often lay eggs near the sites where they emerged from the pupae. Moths eat nothing, live only a few days, and die soon after mating and oviposition. Females deposit 400 to 800 eggs singly or in small clusters in bark crevices or beneath plates of bark (Britton and Crombie 1911). Larvae hatch in about 10 days and begin boring into the wood, often entering the nearest bud, twig, or branch crotch. They bore into the pith of small stems and the heartwood of larger branches or trunks. Larvae move to larger branches when they grow too large for those in which they are feeding (Howard and Chittenden 1916, Seaver 1912). They grow to about 25 mm by the end of the first season. In fall, larvae bore tunnels that slant upward, 50 mm or more below the bark surface, where they remain dormant over winter. Larvae resume feeding the following summer, pass a second winter in dormancy, and begin pupation the second spring after the eggs hatch (Britton and Crombie 1911). Pupation occurs in small chambers near the bark. In 4 to 6 weeks, the pupae exit through the bark and move partially out of the tunnels. After the moths emerge, the pupal cases remain in the openings (Britton and Crombie 1911). A life cycle requires 2 years.

Injury and Damage. The earliest symptoms may be girdled or broken twigs and branches with yellow, wilted foliage. Larval tunnels in the wood and girdling burrows under the bark are visible at the ends of broken stems. Numerous partly broken branches with dead brown foliage hanging in tree crowns are characteristic of heavy infestations. Attacks on large branches and trunks are characterized first by fine, whitish frass in bark crevices and often by sapstained bark. Later, large quantities of frass--consisting mostly of small, cylindrical yellowish to brown excrement pellets--are expelled and can be observed in bark crevices and on the ground underneath an infested tree. Gallery entrances are usually kept covered with woven silklike webs. Large branches and trunks 10 to 15 cm may be girdled. Besides burrows under the bark, these insects construct galleries up to 12 mm in diameter and 5 to 15 cm long that slant upward into the wood. The shape and size of these galleries vary widely because larvae repeatedly vacate galleries and establish new ones. Boring and tunneling seriously damage infested trees. Large branches or even trunks of small trees are sometimes girdled and occasionally break in the wind. Ugly scars appear on the trunks of large trees where the bark dies, splits, curls, and eventually breaks away. Injuries in timber trees result in defects and degrade in sawn lumber. Seedlings and small trees are sometimes girdled and killed (USDA FS 1985).

Control. Birds, especially woodpeckers, are the most important natural control. Although four wasplike parasites have been found in Europe, only one species--Copidosoma truncatellum (Dalman)--has been reported in this country (Gordh 1979). Squirrels have been observed feeding on larvae (Howard and Chittenden 1916). Removal and destruction of infested branches are recommended, and heavily infested damaged trees should be destroyed. Planting species that are least susceptible to attack (species other than elms and maples) and spacing plantings so that the crowns do not touch discourage movement of the insect from tree to tree (Britton and Crombie 1911). The impact of injury may be reduced by maintaining trees in a vigorous condition. Chemical insecticides can be introduced into tunnels (Britton 1928).

Adult(s). James Solomon, USDA Forest Service.

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