Part 4

Generally, borers such as the red oak borer infest trees of poor vigor. It is possible, therefore, to reduce borer populations by maintaining vigorous stands and by removing cull trees.

CARPENTERWORM, Prionoxystus robiniae (Peck)

The carpenterworm bores in the wood of living hardwood trees, causing costly damage to commercial timber species. In the South, oak species are preferred hosts but black locust, maples, willows, and fruit trees are also attacked. The carpenterworm is distributed throughout the United States.

Adult moths emerge in late April to early June, mate, and the females lay groups of eggs in bark crevices or wounds. Each female lays 200 to 500 eggs during her one-week life span. After hatching, the larvae wander over the bark for a short time before boring into the inner bark where they feed until half-grown. The larvae then bore into the sapwood and heartwood, returning occasionally to feed in the inner bark. The larval period lasts from two to four years. Pupation usually occurs deep within the heartwood. Just prior to emergence, the pupa wiggles to the entrance hole where it remains slightly protruding until the adult moth emerges. The large winding tunnels constructed by the larvae in the sapwood and heartwood of living hardwoods serve as an entrance for wood-rotting fungi and insects such as the carpenter ant. In extreme cases, the tree may be structurally weakened and subject to wind breakage.

Some chemicals which have a fumigating action have proved effective in controlling this insect in shade trees, but no practical control has yet been found for forest trees.

PINE WEBWORM, Tetralopha robustela (Zell.)

Ugly, compact masses of brown excrement or frass pellets around the stem of pine seedlings mark infestations of the pine webworm. Rarely is the defoliation severe enough to kill the seedlings, but it undoubtedly has an impact on growth. Found throughout the eastern United States, the webworm commonly attacks red, white, jack, loblolly, shortleaf, and slash pines.

The adult moth has a wingspread of about one inch. The forewing usually is gray in the middle portion and darker at the base and tip. The hind wings and body are smokey gray. The full-grown larva is a caterpillar approximately ⅘ of an inch long. The head is tan with darker markings and the body light brown with dark longitudinal stripes running down each side.

Eggs are usually laid on seedlings, occasionally on larger trees, between May and September. After eggs hatch, the caterpillars live in silken webs surrounded by masses of frass, and feed on the needles. Generally each web contains one or two larvae but occasionally 25 or more may be found. After feeding is completed, the caterpillars drop to the ground and pupate below the soil surface. In the South, there are usually two generations each year.

In plantations, hand picking is an effective method of control. When high value nursery stock becomes infested, chemical control may become necessary.

BAGWORM, Thyridopteryx ephemeraeformis (Haw.)

The bagworm is distributed throughout the eastern half of the United States. It is generally recognized as a defoliator of conifers, particularly juniper, cedars, and arborvitae, but it is also found on many hardwood trees including maple, wild cherry, poplars, oaks, and apple.

The wingless, maggot-like adult female bagworms are present in September and October and spend their entire lives within the protective cover of the tough, silken bag which they construct as larvae. Males are quite agile fliers and can often be seen in the fall flying around infested shrubs in search of a mate. Mating takes place through the open end of the bag. Shortly thereafter the female deposits her egg mass containing 500 to 1,000 eggs in her pupal case. The eggs remain in the bag throughout the winter. In the deep South, hatching can occur as early as April, but occurs in May or June further north. During the early stage of development, the larvae, housed in their tiny bags, are quite inconspicuous. As they mature, the bags become quite noticeable, and the amount of foliage consumed increases rapidly.

Outbreak populations of bagworm are in most cases quickly reduced by low winter temperatures and a complex of several parasites. On shrubs and shade trees around a home, it is often practical to control bagworms by picking and destroying the bags.

PINE COLASPIS, Colaspis pini (Barber)

Colaspis beetles are found throughout the Southeast, but are more common in the Gulf states. They seem to prefer slash pine but have been found on many of the southern pines. The pine colaspis beetle is not a serious forest pest but feeding damage caused by large populations occasionally produces a spectacular browning effect of the needles similar to that caused by fire.

The adult beetles chew the edges of needles to produce an irregular, saw-like edge which turns brown. Occasionally only the tips of the needles show signs of the infestation. Later, however, the entire needle may die, causing the whole tree to become brown as though scorched by fire. Trees that have been attacked do not die, and little or no growth loss results. Attacks usually occur in early summer; by late summer the trees appear green and healthy again. This pest is sporadic in its occurrence and may not develop again in the same area for several years. The adult female lays her eggs in the soil during the summer. Larvae hatch and feed on roots of grasses and other vegetation, and overwinter in this stage. The larvae pupate in the spring; adults emerge in early summer to feed. There is only one generation a year.

Under forest conditions, no control measures are recommended for the pine colaspis beetle. On ornamentals and shade trees, insecticides can be used to prevent unsightly damage.

PINE SAWFLY, Neodiprion excitans (Roh.)

This pine sawfly is found throughout the southeast from Virginia to Texas. Loblolly and shortleaf pine are preferred hosts, but pond, slash, longleaf, and Sonderegger pine are also attacked. The larvae do not do well on the latter two species. As with most sawflies, the larvae feed in groups on the host needles. Generally the old needles are preferred, but all of the needles are eaten when large numbers of larvae are present. Three or four young larvae usually encircle a needle and, starting from the tip, consume all but a central core. When nearing maturity they eat the entire needle.

Four or five generations of this sawfly may occur each year. Adult females begin to lay their eggs in slits cut in the needles during late March. The eggs hatch in 10-21 days, and the larvae feed for about five weeks. When mature the larvae usually crawl to the ground and spin a cocoon in the loose litter at the base of the tree. Although all stages of the life history can be found at any time during the growing season, the peak adult emergence occurs in late summer. Larvae from this late summer generation are responsible for most of the damage which, although never directly responsible for mortality, may predispose the trees to attack by other insects (particularly bark beetles) and diseases.

Natural control factors generally bring outbreak populations under control after one season. Hogs, armadillos, mice, and shrews are reported as being of significant value in regulating the sawfly population. Insect parasites, predators, and disease are also effective control agents.

ARKANSAS PINE SAWFLY, Neodiprion taedae linearis (Ross)

Loblolly and shortleaf pines are the only trees attacked by the Arkansas pine sawfly. Periodic outbreaks of this insect over large areas in the south-central states cause substantial growth losses, but the insects seldom kill trees.

This insect has a single generation each year. In the spring, eggs which have overwintered hatch into tiny caterpillar-like larvae. The larvae feed in groups for 30-40 days (primarily on the older foliage) before crawling to the ground and pupating in the topsoil or litter. Adults emerge during warm days in October and November, mate, and the females begin laying eggs. Sawflies get their name from the manner in which the eggs are laid. The female is equipped with a saw-like “ovipositor” with which she cuts a slit in the needle into which the egg is inserted. From two to ten eggs are laid in a single needle. Each female deposits from 90 to 120 eggs.

An important natural control agent of this sawfly is a polyhedral virus disease that sometimes destroys large numbers of the larvae. Rodents destroy many cocoons. Several species of larval parasites are also known to exist. Of these, a parasitic fly, Anthrax sinuosa (Wied.) and an ichneumon wasp, Exenterus canadensis (Prov.) appear to be the most important.

VIRGINIA PINE SAWFLY, Neodriprion pratti pratti (Dyar)

The Virginia pine sawfly is found from Maryland to North Carolina, and west to Illinois. The insect prefers Virginia and shortleaf pine, but it will also oviposit and feed on pitch and loblolly pine.