Forest Pests: Insects, Diseases & Other Damage Agents

Defoliating Insects Hardwood Defoliators Forest Health Guide for Georgia Foresters Written by Terry Price, Georgia Forestry Commission Adapted for the web by the Bugwood Network

Many species of insects feed on the foliage of hardwood trees. Some are host specific and others are considered general feeders. Outbreaks can be quite extensive and may last for several years. The extent of defoliation and the time of year the defoliation occurs determine the severity of effects on trees.

Defoliation that occurs just as the leaves are expanding in the spring can deplete nutrition reserves needed for tree growth. Since leaves are the food factories for the tree, their removal early in the season delays the manufacture of new food. However, defoliation occurring in mid to late summer is not as damaging to a tree’s health as defoliation occurring in the spring. Some defoliators reach outbreak proportions periodically with outbreaks lasting 2-10 years.

Following are brief descriptions of some common hardwood defoliators in Georgia:

Oakworms in the genus Anisota, are common throughout Georgia and do considerable damage in forest and landscape trees. Common species are the orangestriped, pinkstriped and spiny oakworms (Figures 44 and 45). Defoliation is widespread throughout the hosts’ range.

Figure 44 - Orange striped oakworm photo by James Solomon

Figure 45 - Spiny oakworm photo by Gerald J. Lenhard

Figure 46 photo by Gerald J. Lenhard

The orangestriped oakworm feeds on various oaks and sometimes birch and hickory. Mature caterpillars are just over 1 ½ inches long, black with eight longitudinal orange-yellow stripes. They also have two black spines on the second thoracic segment and smaller spines on each succeeding segment. The greenstriped mapleworm, Dryocampa rubicunda, prefers maples but will feed on boxelder and oaks where they grow intermingled with maples. Full-grown caterpillars are about 1.5 inches long, pale yellow-green with cherry-red heads (Figure 46).

The buck moth, Hemileuca maia, feeds primarily on oaks. Full-grown caterpillars are about 2.5 inches long, brownish black and covered with small, yellowish dots; head is deep reddish brown (Figure 47).

The fall webworm, Hyphantria cunea, is a very common defoliator of pecan, sourwood, and persimmon. The caterpillars construct ugly nests of silk around the leaves they feed on (Figure 48). The caterpillars can be removed by hand on small trees, but larger orchard trees need to be sprayed using high-pressure equipment.	Figure 47 photo by James Solomon
Figure 48 photo by Ronald F. Billings	The oak skeletonizer, Bucculatrix ainsliella, feeds on oaks and chestnuts. Full-grown larvae are about .19 inch, pale yellow green with tan heads. Leaves are skeletonized by the larvae (Figures 49 & 50). Outbreaks are widespread over the range of chestnut oak. Based on GFC aerial surveys the oak skeletonizer was responsible for extensive
Figure 49 - Oak skeletonizer larva photo by G. Keith Douce	Figure 50 - Skeletonized leaf photo by James Solomon

The cherry scallop shell moth, Hydria prunivorata, feeds on black cherry. Full-grown caterpillars are about .8 inch, blackish above with 4 yellow lines. Outbreaks can be extensive over much of the range of black cherry (Cover Photo).

Figure 51 - Chestnut oak defoliation photo by Richard Jernigan

The forest tent caterpillar, Malacosoma disstria, feeds on water tupelo, sweetgum, blackgum, birch, elm, maple, oak and flowering fruit trees. Full-grown caterpillars are about 1.6 inches long, light blue heads; body is blackish with whitish hairs; each segment is marked dorsally with a white

keyhole-shaped spot (Figure 52). The adult moths are buff colored with two darker bands on the forewings. Caterpillars are present in early spring and upon maturity construct cocoons from folded leaves. The adults emerge in late summer and lay eggs in brown masses that encircle twigs. Eastern tent caterpillar egg masses do not encircle the twigs. The caterpillars make silken tents in host trees. In the 1980’s an outbreak occurred in southeast Georgia that involved several hundred acres of

Figure 52 photo by Ronald F. Billings

Eastern tent caterpillar, Malacosoma americanum, feeds on cherry, apple, and plum. Full-grown caterpillars are about 1.6 inches long; coloration varies but in general they have black heads, bodies marked with a mid-dorsal white stripe down the length of the back and yellow lateral stripes between each pair of which occurs a blue dot (Figure 53). The adult moths are light brown with two diagonal white stripes across the forewings. Silken tents usually occur in tree forks. The larvae lay trails of silk from the communal tent to wherever they are feeding. Long trails of larvae can be seen migrating along the silken path between the tent and leaves. Eggs are laid in masses on twigs (Figure 54). Egg masses can be pruned from twigs during the dormant season and destroyed. Caterpillars can be handpicked from the communal tents. Bt should be used on flowering trees to control young caterpillars. Bt is not harmful to pollinating bees.

Figure 53 photo by Tim Tigner

Figure 54 photo by Terry Price

Catalpa sphinx, Ceratomia catalpae, feeds on catalpa. Full-grown caterpillars are about 3 inches; black horn near the end; body marked with black and yellow (Figure 55).

Figure 55 photo by John H. Ghent

Figure 56 photo by Forrest L. Oliveria

The walnut caterpillar, Datana integerrina, feeds on walnut, butternut, pecan and hickory. Full-grown caterpillars are about 2 inches; black body with yellowish stripes covered with long, white to gray hairs (Figure 56). Younger larvae are reddish brown with longitudinal yellowish stripes. The adult moths lay eggs on the undersides of leaves beginning in May or June. Trees can be completely defoliated during outbreaks. Defoliations of two or more years can result in tree death. The pupae overwinter in the soil and there is one generation per year.

Variable oakleaf caterpillar, Heterocampa manteo, feeds on oaks, birch, elm, apple and other hardwoods. Full-grown caterpillars are about 1.5 inches long with variable coloration. They are greenish with white and yellow stripes. The head has a purplish brown band on each side (Figure 57). Adults emerge in May and larvae are present from July to fall. The young larvae skeletonize leaves by feeding on the undersides. Older larvae consume entire leaves except for the veins. Severe defoliation can occur in outbreak years. The insect overwinters in the soil as a prepupa. There is only one generation per year.

Figure 57 photo by Gerald J. Lenhard

Figure 58 - Adult gypsy moths, male-left, female-right photo from USDA APHIS PPQ Archives

The gypsy moth, Lymantria dispar, feeds on most hardwood species preferring oaks (Figure 58). Full-grown caterpillars are from 1.5-2 inches long and have a series of blue and red dots along the back (Figure 59). The gypsy moth is a serious spring defoliator of forest and shade trees. The destructive stage is the caterpillar, which feeds on several hundred species of trees and shrubs. This moth was brought to the United States in 1869 and has become established in at least 12 northeastern states. Long distance spread of the gypsy moth occurs when unsuspecting people move egg masses, caterpillars or pupae from infested areas (Figure 60).

Figure 59 photo by John H. Ghent

Figure 60 - Female gypsy moths and egg masses photo from USDA Forest Service Archives

The Georgia Forestry Commission (GFC), in cooperation with USDA Forest Service, has eradicated three infestations of the gypsy moth since 1991. The GFC in cooperation with the USDA APHIS conducts a comprehensive trapping program every year to detect the presence of the moth in the state (See Figure 177).

The locust leafminer, Odontota dorsalis, causes extensive defoliation every year throughout the range of black locust. The adult beetles feed on newly expanding leaves in the spring by skeletonizing the undersides of the leaves and chewing small holes in them. Eggs are then deposited on the undersides of the leaves. The larvae hatch and begin to mine the leaves. Outbreaks are spectacular, but trees are seldom killed (Figure 61).

Figure 61 - Life stages of locust leaf miner photo by Bruce W. Kauffman

Figure 62 - Sweetgum defoliation photo by Terry Price

A sweetgum defoliator, Paectes abrostaloides, was recorded as defoliating sweetgum across the South in 1977. Specimens collected from Georgia were sent to the Smithsonian Institution where they were identified as the same species occurring in other southern states. The outbreak lasted one season and there hasn’t been any activity reported since (Figure 62).

The larger elm leaf beetle, Monocesta coryli, causes widespread defoliation of native elm species throughout the South. Other trees attacked are river birch, pecan, hawthorn and Asian elms. Adults are about 7/16 inch in length, dull-yellowish brown head with large greenish patches at the tip of each elytra. Mature larvae are about the same length as the adults and are of a metallic reddish-brown color (Figure 63). The larvae overwinter in the soil. The adults emerge in May at which time eggs are laid on the undersurfaces of the leaves. Upon hatching the larvae feed together between the veins of leaves. The larvae skeletonize the leaves. There is one generation per year.

Figure 63 photo by Gerald J. Lenhard

Figure 64 photo by Bruce W. Kauffman

The elm leaf beetle, Pyrrhalta luteola, is about ¼ inch long and yellowish to dull green, with a black stripe on the edges of the elytra, with three dark dots behind the head. Mature larvae are about 7/16 inch long and are yellowish with two lines of black dots along the back (Figure 64). Unlike the larger elm leaf beetle, this beetle overwinters as an adult in protected places such as attics. In May the adults emerge and lay eggs in May to June. The larvae feed on the undersides of leaves and pupate at the base of trees. There are two generations per year.

The Japanese beetle, Popillia japonica, is a very destructive foreign pest that entered the United States over 80 years ago. By 1972 the beetle had been reported in 22 states east of the Mississippi River. Since then it has continued to spread into Wisconsin, Oregon and California. Adult beetles feed on the foliage and fruits of several hundred species of fruit trees, ornamental trees, shrubs, vines, and field and vegetable crops. Adults leave behind skeletonized leaves and large holes in leaves. The grubs live in the soil, feeding on the roots of plants and grasses and often destroying turf in lawns, parks, golf courses and pastures. The beetle is about ½ inch long with a shiny, metallic-green body and bronze outer wings (Figure 65). Control of the insect is best achieved by targeting the adults and grubs.

Figure 65 photo by E. Bradford Walker

Figure 66 - O. calceatus damage photo by Lacy L. Hyche

The yellow-poplar leaf-mining weevil, Odontopus calceatus, periodically causes partial defoliation of yellow poplar throughout the State (Figure 66). Affected trees really look “sick” but in time appear to recover well. However, weevil damage to transplanted trees and other landscape trees can reduce their aesthetic value. Adult weevils damage the leaves by feeding on the undersides near the midrib and the females damage leaves by chewing oviposition pits in the midrib. Larvae feed together between leaf surfaces causing the leaves to turn brown and die. Damaged leaves may stay on the tree until fall or they may drop prematurely. The adult weevils become active in early spring and egg laying occurs between March and May. Eggs hatch from 4-14 days. The larvae can be found from April to June. New adults emerge in May and feed on the foliage until mid-June. At this time the adults migrate from trees to ground duff and stay there until the following spring.

The spring cankerworm (SC), Paleacrita vernata, and fall cankerworm (FC), Alsophila pometaria, are often confused. They feed on elm, ash, hickory, birch, beech, apple, maple and oak. Adult females of both species are wingless gray moths. They are about 7/16 inch long. The males have tan wings. Mature larvae are ¾ inch long and vary in color from green to reddish brown to black, with one or more stripes of white, green or black (Figure 67). The SC has two pairs of prolegs while the FC has three pairs. The FC emerges from the soil as an adult moth in the fall. Mating takes place, the eggs are laid and the adults die. The eggs hatch from April to May at about the time the host buds are opening. SC pupae in the soil do not emerge as adults until early spring. Both species’ eggs hatch at about the same time. There is one generation per year. Outbreaks of both species often last for several years before declining.

Figure 67 - Fall cankerworm, dark phase photo by John H. Ghent

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