Taxonomy

Domain	Eukarya
Kingdom	Animalia
Phylum	Arthropoda
Subphylum	Hexapoda
Class	Insecta
Subclass	Pterygota
Infraclass	Neoptera
Superorder	Holometabola
Order	Lepidoptera
Superfamily	Noctuoidea
Family	Notodontidae
Subfamily	Phalerinae
Genus	Datana

Scientific Name

Datana integerrima

Common Name

walnut caterpillar

Description

Adult walnut caterpillars are moths with light-brown wings marked with dark-brown, transverse, wavy lines. The hind wings are lighter brown, without crosslines. A dark brown tuft of hair covers the back of the thorax. Moths have a wingspan of about 1 1/2 to 2 inches (37 - 50 mm). Immature larvae are reddish-brown, with narrow cream colored lines that extend the length of their body. Mature larvae are black, nearly 2 inches (50 mm) long, and thickly covered with long, dirty-white or grayish hairs.

Damage

Larvae feed in groups but do not form webs. They are capable of eating all the leaves on small trees or on individual limbs of large trees.

Seasonal History

The walnut caterpillar overwinters as a pupa in the soil. Moths emerge in the spring and deposit white eggs in masses on the undersides of leaves. In preparation for molting, the caterpillars move down to a large limb or to the trunk and form a compact mass. After shedding their skins, they migrate back toward the ends of branches and resume their feeding. Caterpillars molt several times during development. The first generation appears in June and July, and the second generation in late August and September.

When to Control

Control is necessary only when the insects are numerous in a grove, but it should be done when the larvae are small. Walnut caterpillars clustered on the trunk or limbs of a tree may be destroyed by crushing or burning

Originally compiled from

Datana integerrima

Importance

The walnut caterpillar feeds only on black walnut, pecan, hickory, and butternut. Defoliation may weaken the tree and make it susceptible to damage by wood borers. Tree mortality is rare, but may occur after 2 years of heavy defoliation.

Identifying the Insect

Eggs are spherical and pale green with white caps. They are laid in clusters of 120 to 800 on the underside of leaves. All larvae have black heads. Newly hatched larvae are light green and change to reddish brown with white stripes. Fully grown larvae are nearly black with white hairs. They are 1 to 2 inches (25 to 50 mm) long.

Pupae are 3/4 inch (20 mm) long and shiny, dark, reddish brown. The wing-span of moths is about 1 3/4 inches (45 mm). The front wings are dark tan with four rust colored lines. The hind wings are light tan.

Identifying the Injury

Young larvae skeletonize the upper leaf surface. As they grow, they feed on the entire leaf except the petiole. Individual branches, entire trees, or groups of trees may be completely defoliated.

Biology

Moths emerge in May and lay eggs. Eggs hatch in 8 to 10 days, and larvae feed until mature and pupate in the soil. Adults emerge in July and begin the second generation, which is the largest and most destructive. Larvae cluster together on tree branches or trunks and molt simultaneously, leaving a large mass of hairy cast skins adhering to the bark.

Control

Parasites, predators, and diseases are major factors influencing population levels. Cultural controls are: clipping foliage to destroy egg masses and larvae, removing clustered larvae as they gather to molt, and destroying pupae by shallowly disking the soil after larvae have pupated. Chemical control is usually not necessary because tree mortality is rare.

Gallery

References

Insects and Diseases of Trees in the South. 1989. USDA Forest Service - Forest Health Protection. R8-PR16. 98 pp. Taken from http://fhpr8.srs.fs.fed.us/forstpst.html