Cottonwood Leaf Beetle (Chrysomela scripta F.)

Taxonomy

Domain	Eukarya
Kingdom	Animalia
Phylum	Arthropoda
Subphylum	Hexapoda
Class	Insecta
Subclass	Pterygota
Infraclass	Neoptera
Order	Coleoptera
Suborder	Polyphaga
Infraorder	Cucujiformia
Superfamily	Chrysomeloidea
Family	Chrysomelidae
Subfamily	Chrysomelinae
Tribe	Chrysomelini
Genus	Chrysomela

Scientific Name

Chrysomela scripta

Common Name

cottonwood leaf beetle

Morris, R.C.; Filer, T.H.; Solomon, J.D.; McCracken, Francis I.; Overgaard, N.A.; Weiss, M.J. Insects and Diseases of Cottonwood. New Orleans, LA. U.S. Department of Agriculture, Forest Service; Southern Forest Experiment Station; State and Private Forestry Southeastern Area. Gen. Tech. Rep. SO-8. 1975. 41 p.

The cottonwood leaf beetle is one of the most serious pests of young trees in nurseries and plantations and occasionally causes severe damage in natural stands. In the nursery, the insect stunts height growth and reduces the yield of cuttings. First- and second-year plantations are weakened by early defoliation and may be overtopped by weeds. Continuing partial defoliation through the summer reduces tree growth and vigor. Serious damage occurs at the end of the growing season, when heavy populations feed on terminal tissues and buds, killing as much as 10 inches (25 cm) of the terminals. Lateral buds sprout below the injured terminals, and branches may grow above the dead terminal even before the season ends. These branches grow rapidly the next year, resulting in multiple-forked tops that have little potential for the production of quality wood for logs and pulpwood.

Often the sudden appearance of ragged foliage near branch ends and terminals of young cottonwoods will announce a leaf beetle attack. Some leaves will have brown patches where young larvae ate the green tissues. On other leaves, only the veins and midrib will remain. Heavy damage results in dead, black terminals from which the leaves and tissues are eaten. Other signs of the leaf beetle are black droppings on leaves and the unmistakable, pungent odor the larvae release when disturbed.

Adult beetles are oval, yellow, and about 1/4 inch (6 mm) long with slender black markings on their wing covers. Egg clusters are bright yellow, and newly hatched larvae are black. As they develop, they turn brown, and prominent white scent gland spots appear along their sides.

Adults spend the winter under fallen leaf debris or in clumps of weeds. In early spring they emerge and feed on unfolding leaves or on tender bark at the tips of twigs. The female lays a cluster of 15 to 75 eggs on the undersides of leaves. The newly hatched larvae feed side by side and skeletonize the leaves. Older larvae feed separately and consume the entire leaf except for the larger veins. At maturity they attach themselves to leaves, bark, or to weeds and grass beneath the trees to pupate. In 5 to 10 days they emerge as adult beetles. There are several generations per year, each lasting about 35 days.

The spring generation of the leaf beetle may be greatly reduced by the red lady beetle Coleomagilla maculata, which feeds on the eggs and pupae. However, as the season progresses, the ladybugs disperse to feed on aphids and other prey and do not affect later broods of leaf beetles. Several predaceous bugs feed on leaf beetle larvae, and a parasitic wasp also attacks them. Effective chemical controls are available.