Part 2

The shiny black egg masses encircling the twigs of host trees can be seen during winter months. Small black, hairy larvae hatch out just as the leaves are beginning to unfold. They do not construct a tent, but make a silken mat on the larger branches or trunk of the tree on which they rest between feeding periods. When full grown, the larvae are about two inches long, brownish-black with distinctive white, keyhole-shaped spots down the middle of the back, and blue lines along the sides. Just before pupating, the larvae spin a whitish silk cocoon on the bark or leaf of the host. In about ten days the light brown moths emerge, mate, and the females begin laying their eggs.

Parasitic flies are one of the more important agents which normally keep this insect under control. Outbreaks occur with some regularity, however, and chemicals may be required to prevent defoliation.

FALL WEBWORM, Hyphantria cunea (Drury)

The fall webworm is not considered an important forest pest. However, ugly webs can seriously detract from aesthetic values. The preferred hosts in the South are persimmon, pecan, and sourwood, but it is also found on black walnut, hickory, cherry, sycamore, crab apple, and sweetgum. The insects range throughout North America.

The adult is a pure white moth about 1¼ inches long. The forewing is sometimes marked with blackish dots. The larva is about one inch long when full grown, generally pale yellow or greenish with a broad dark longitudinal stripe on the back and a yellowish stripe extending from black and orange warts. The insect has one generation per year in the northern part of its range, and two in the southern part. Moths of the first generation emerge from May to July and those of the second in July and August. Adult females lay 400-500 eggs in white cottony patches on the underside of the leaves of host plants. The eggs hatch in about a week, and the larvae form a web and begin to skeletonize the leaves by feeding in rows. As the larvae grow they expand the web to cover the colony. When the larvae are ready to pupate, they crawl or drop to the ground and form a brownish cocoon in the duff around the tree where they overwinter.

Natural enemies usually keep this insect under control. Webs can be pruned from high-value trees in scenic or recreation areas.

OAK LEAF TIER, Croesia albicomana (Clem.)

This oak leaf tier has been associated with the decline and mortality of several species of oak in the northeastern United States and southern Appalachians. An outbreak population in the mountains of West Virginia and Virginia in 1966-68 resulted in the loss of several thousand acres of scarlet oak. Usually such outbreaks coincide with periods of drought which increase the impact of defoliation on the host. Its hosts include northern red oak, black oak, scarlet oak, and pin oak. The latter two species seem to be hit hardest by this insect.

Croesia albicomana spends the winter in the egg stage. Eggs are glued to small twigs in the crown of the host tree. Hatch occurs from mid-April to early May. Young larvae, which emerge before bud-break, bore into and mine the expanding buds. When large numbers of this insect are present they can destroy most of the vegetative buds on a tree. Later the older larvae tie down a folded-over portion of a leaf and feed on it. Leaves fed on by the oak leaf tier appear to be full of shot holes. As the larvae near maturity they may tie the apical portion of two or more leaves together and feed on them. Mature larvae then drop to the ground to pupate in the litter. Adult moths emerge in June or early July, mate, and the female immediately begins laying eggs. The small, flat, oval eggs are deposited individually on small twigs, generally around nodes or leaf scars.

Little is known of the natural factors which regulate population levels of this insect, but undoubtedly weather is important.

VARIABLE OAK LEAF CATERPILLAR, Heterocampa maneto (Dbldy.)

The variable oak leaf caterpillar periodically defoliates extensive areas of hardwood forest in the eastern United States. Its range covers all of the southern and eastern states as far west as east Texas. The larvae feed primarily on oaks but will also feed on beech, basswood, birch and elm. Other defoliating insects may be associated with outbreaks causing additional damage. Young larvae skeletonize the leaf while older larvae devour the entire leaf except the primary veins. Infestations are generally more severe in the South, where the insect has two generations per year causing two periods of defoliation in a single year. While infestations usually subside before many trees are killed, heavy defoliation reduces the tree’s growth and vigor.

The variable oak leaf caterpillar overwinters as a non-feeding larva in a cocoon on the forest floor. It pupates and emerges as a moth the following spring. The female moth, gray in color and about 1¾ inches long, lays about 500 eggs singly on the leaves of host trees. The larvae feed on foliage for five or six weeks, drop to the ground to pupate, and emerge as adults in mid-summer. Larvae hatching from eggs laid by the second generation of moths defoliate the trees for a second time during late summer. By late October the mature larvae of the second generation have dropped to the forest floor to overwinter. The full grown larva is approximately 1½ inches long. Color varies among individuals. The head is generally amber brown with curved diagonal white and black bands. The body is usually yellow green with a narrow white stripe down the center of the back bordered by wider dark bands.

Outbreaks of the variable oak leaf caterpillar may be severe but generally subside before serious tree mortality occurs. Parasites and predators are not effective in controlling rising populations of the insect. Mice and predaceous beetles feed on the resting larvae and pupae in the litter and soil of the forest floor. While no chemical is currently registered for control of this insect, chemical spraying has been effective and safe in controlling closely related insects.

LOCUST LEAFMINER, Xenochalepus dorsalis (Thunberg)

The locust leafminer is a destructive pest of black locust and honey locust in both the adult and larval stages. It is found throughout the range of these trees in the eastern half of North America. The adults also feed on other species of trees.

The adult beetles overwinter in crevices in the bark of trees and under litter on the forest floor. The beetles emerge and begin feeding in the spring, usually after mid-April. After feeding for a short time they deposit eggs on the undersides of leaves, piling them one upon another, somewhat shingle-like. Eggs are covered with brownish fecal matter. Larvae soon hatch and eat into the leaf tissue to form a mine. Newly emerged larvae feed gregariously in a single mine for a short time. They then construct new mines where the insects live singly. Several mines are constructed before the larvae reach maturity. The larvae pupate in the mines and emerge as adults in July to begin the second generation. The adult beetles are foliage feeders, eating irregular holes in leaves. When sufficient in number they may defoliate host trees.

Under forested conditions no control is recommended. Rarely do trees die from attacks by this insect. Damage is objectionable mostly from an aesthetic viewpoint.

COTTONWOOD LEAF BEETLE, Chrysomela scripta (F.)

Willows, poplars, aspens and alders are attacked by the cottonwood leaf beetle in the eastern United States. Cottonwood is the most important host in the South. Damage has been especially severe in Louisiana and Mississippi where thousands of acres of cottonwood plantations are intensively managed. Adult beetles and larvae feed on the foliage. Damage is most critical during the first three years after the cottonwood is planted. Adults chew holes in the leaves and may attack the terminal shoots causing reduced growth or stem deformity. Young larvae skeletonize the foliage but older larvae consume all foliage except the leaf midribs. Damage may become severe enough to cause mortality.

The cottonwood leaf beetle overwinters in the adult stage. Eggs are laid in the spring. The female lays a cluster of about 75 yellowish eggs on the underside of a leaf. As the larvae mature they become yellow with black spots. After about nine days in the larval stage the beetle transforms into the non-feeding pupal stage which lasts five to ten days. The adult is about ¼-inch long and has a black head and thorax. The wing covers are yellow with longitudinal black stripes. The life cycle is completed in 25 to 30 days and several generations occur in a single year.

Control may be needed in a plantation only during the first three years. Chemical sprays have been successful in the past but at the present time no insecticides are registered for cottonwood leaf beetle control.

WALKINGSTICK, Diapheromera femorata (Say)

The walkingstick is a defoliator of broadleaved trees in North America. The black oaks, basswood, and wild cherry are the most common preferred hosts but numerous other hardwood species are attacked. This insect is widely distributed over the United States east of the Rocky Mountains as well as Manitoba and Ontario in Canada. At times, populations build in sufficient numbers to defoliate trees over large areas.

These slender, wingless, stick-like insects are pale green when young, but gradually change to a dark green, gray, or brown at maturity. The adult female measures up to three inches in length and is more stout-bodied than the male. Mating usually takes place in August and egg laying begins six to ten days later. The eggs are dropped to the ground where they overwinter in the leaf litter. In the northern part of the walkingstick’s range the eggs take two years to hatch. In the South, walkingstick eggs hatch the summer after they are laid, usually starting in mid-May. The newly hatched walkingstick looks like a miniature adult.

Parasitic wasps and flies are active against the immature walkingsticks but are not efficient enough to cause a substantial population reduction. Flocks of robins, blackbirds, and grackles have a much greater impact, however. The defoliation caused by walkingsticks generally occurs on upland sites in stands which are not of high value or intensively managed. For this reason there has been little interest in control.

GYPSY MOTH, Porthetria dispar (L.)

The gypsy moth is an introduced forest insect. It was brought into this country from Europe in 1869 and has been restricted to the Northeast. The gypsy moth feeds aggressively on oak, alder, apple, basswood, willow, and birch. As the caterpillars reach maturity they will also feed on hemlock, cedar, pine, and spruce.