Part 3

In the Northeast, the gypsy moth has a single generation per year, overwintering in the egg stage. Eggs hatch in late April and May and larvae are present for approximately two months. Full-grown caterpillars measure more than two inches long and are easily identified by the five pairs of blue spots and six pairs of red spots arranged in a double row along the back. The adult moths are active from late June to early September. Female moths, their bodies heavy with eggs, are unable to fly and must rely on a powerful sex attractant to lure male moths. This sex attractant has been chemically synthesized and is used as a trap bait in surveys designed to determine the presence of gypsy moths in areas suspected to be infested. Each female deposits from 200 to 800 eggs in a buff-colored mass which she attaches to any convenient surface including cars, trailers, and other vehicles.

During the past 75 years the gypsy moth has been the target of many large-scale control programs, and much money has been spent trying to reduce the impact of gypsy moth infestations. Current control efforts are handicapped by the unavailability of a safe and effective persistent chemical. In the North two predators and nine parasites have been successfully established to help control the gypsy moth. The greatest problem in controlling gypsy moth spread, however, lies in the fact that recreational vehicles transport egg masses and larvae from infested sites into uninfested areas.

HICKORY BARK BEETLE, Scolytus quadrispinosus (Say)

The hickory bark beetle is reported to be the most serious insect pest of hickory in the United States. Population explosions where thousands of trees were killed have been reported from New York, Pennsylvania, Maryland, Virginia, and recently from Georgia. Hickory bark beetles are distributed throughout the range of their host in eastern United States. All species of hickory are subject to attack, as well as pecan and possibly butternut. Adult beetles emerge in May and June in the southern portion of their range. They feed for a short time by boring into the petioles of leaves and into small twigs of the host. Dying leaves and twigs are the first evidence of attack. After feeding, the beetles fly to the trunk and larger branches of the host and bore into the inner bark to lay their eggs. Short, longitudinal egg galleries are etched into the sapwood and from 20 to 60 eggs deposited in small niches cut on either side of the gallery. As the larvae develop, their galleries radiate out from the egg gallery. Two generations per year have been reported from northern Mississippi. The beetle overwinters in the larval stage. With the coming of warm weather in the early spring, it changes into the pupal stage, and finally, in May, to an adult.

Outbreaks of this insect begin in periods of hot, dry weather and subside when rains commence.

SMALLER EUROPEAN ELM BARK BEETLE, Scolytus multistriatus (Marsham)

The smaller European elm bark beetle was first reported in the United States in 1909. Its presence in this country was given significance with the introduction of the Dutch elm disease in 1930. The beetle attacks all native and introduced species of elms and now occurs wherever the hosts are present. The feeding of the adult beetles in the spring is responsible for transmitting the Dutch elm disease from diseased to healthy trees. The Dutch elm disease is now our most important shade tree disease.

Adult bark beetles emerge in the spring from dead or dying elms and begin feeding on the twigs of healthy elms. The female then excavates an egg gallery in the bark of dead or weakened elms. Eggs are deposited along the walls of the gallery. The larvae, upon hatching, burrow into the bark at right angles to the egg gallery. Pupation occurs at the end of the larval tunnel. New adults tunnel to the bark surface and leave the tree through circular emergence holes. There are usually two generations a year. The beetles overwinter in the larval stage.

Chemical control and good tree maintenance are the two methods used to reduce bark beetle populations. Insecticides are used to prevent feeding by the adults in the spring. Tree sanitation involves removal and disposal of dead elms and elm limbs which eliminate breeding and larval development sites.

COLUMBIAN TIMBER BEETLE, Corthylus columbianus (Hopkins)

All hardwood trees in the eastern half of the United States are subject to attack by the Columbian timber beetle, but oaks, maples, birch, basswood, yellow-poplar, and elm are the preferred hosts in the South. The beetle causes two major types of damage: 1) physical damage caused by the 1/32″ to 1/16″ hole excavated by the adult into the sapwood, and 2) degrade caused by stain which may extend for a considerable distance above and below the gallery. Large diameter trees are preferred as hosts, but trees as small as one and one-fourth inches in diameter may be attacked.

There are two and sometimes three generations of this insect each year. Adults from the first generation emerge from late May through June and those from the second in October. The first evidence of attack is the white dust which collects at the entrance hole. Later, depending on the tree’s physiological condition, a sap-soaked area may develop around the entrance hole. The adult bores a horizontal hole into the sapwood of a healthy tree for a few inches and later constructs two or three shorter lateral branches. “Cradles” (or egg chambers) are then constructed for a short distance perpendicular to these galleries. The female deposits a single egg in each chamber. The offspring spend their entire developmental period within the cradles feeding on fungi which grow on the sapwood. It is this fungus which causes the extensive staining characteristic of Columbian timber beetle attack. Winter is spent in both the pupal and adult stages in the brood galleries.

Chemical control is not practical for forest trees.

COTTONWOOD TWIG BORER, Gypsonoma haimbachiana (Kearfott)

The cottonwood twig borer is widely distributed throughout the entire range of eastern cottonwood, from Canada to the Gulf States and west to Missouri. The larvae of the cottonwood twig borer feed in the terminals of the host. This feeding results in reduction of terminal growth and forked and crooked trunks. Damage is especially severe on young trees.

The female moth lays eggs on the upper surface of leaves along the mid-rib, singly or in groups of two to eight. Hatching occurs in about five days and the young larvae cover themselves with silk mixed with trash, and then tunnel into the mid-rib. After the first molt, larvae leave the tunnels and bore into tender shoots. Larvae reach maturity in about 21-23 days and begin moving down the trunk of the tree where they spin cocoons in sheltered bark crevices, in litter, or between leaf folds. The adult moths emerge in eight or nine days. It takes from 40-45 days to complete the life cycle in mid-summer.

The most effective natural control is a potter wasp, Eumenes sp. which tears open tender cottonwood shoots and removes twig borer larvae from their galleries. Other wasps parasitizing the twig borer include Bracon mellitor (Say), Apanteles clavatus (Provancher) and Agathis sp.

COTTONWOOD BORER, Plectrodera scalator (F.)

The cottonwood borer is limited in range to the southern half of the United States. Hosts include cottonwood, poplars and willows. The adults feed on the tender shoots of young trees causing them to shrivel and break off. The larval stage of this insect tunnels in the inner bark and wood at the base of the tree and may kill or severely weaken it.

The adult beetles appear in midsummer. After feeding briefly on the tender bark of the terminals the adults descend to the bases of host trees where the female deposits her eggs in small pits gnawed in the bark. Eggs hatch in about three weeks. The larvae bore downward in the inner bark, entering a large root by fall. Larval feeding continues into the second year as the larvae bore into the inner bark and wood. The larvae transform into the non-feeding pupal stage and finally into an adult in the summer of the second year thus completing a two year life cycle. Adult beetles are 1¼ to 1½ inches long. They are black with lines of cream-colored scales forming irregular black patches.

The best control for the cottonwood borer is to maintain a vigorous, healthy stand. Slow growing, off-site plantings of host trees are the most severely damaged. While some systemic insecticides have shown promise, there is currently no registered chemical control method.

WHITE OAK BORER, Goes tigrinus (De Geer)

A recent survey of damage caused by various wood borers to three species in the white oak group revealed an estimated annual loss in the South exceeding 20 million dollars. One of the more important borers responsible for this damage is the white oak borer.

Usually the white oak borer attacks oaks one to eight inches in diameter. The damage, like that of other hardwood borers, is the result of larval feeding in the wood. Galleries up to one-half inch in diameter extend upward through the sapwood into the heartwood. The white oak borer takes three to four years to complete one generation. The mated adult female beetle lays her eggs singly in the inner bark through a small oval niche chewed through the outer bark. After about three weeks the eggs hatch and the larvae immediately bore into the sapwood. Later they bore upward into the heartwood. The boring frass ejected out of the entrance is evidence of an active infestation. Pupation occurs behind a plug of excelsior-like frass at the upper end of the gallery in the heartwood. In about three weeks, adults emerge by boring separate and perfectly round holes through the wood and bark. In the South, adults generally emerge in May and June and feed for a short time on oak leaves and the tender bark of twigs before the females lay their eggs.

Woodpeckers may destroy up to 25 percent of the larvae during the winter months, but this and the small toll taken by insect predators and parasites are not sufficient to keep the white oak borer population low enough to avoid serious economic loss.

RED OAK BORER, Enaphalodes rufulus (Hald.)

The red oak borer is a serious pest of trees in the red oak group. It ranges throughout eastern North America wherever host species grow. It is estimated that defects caused by larval tunnels in the sapwood and heartwood of host trees costs the hardwood timber industry millions of dollars each year.

Eggs of the red oak borer are laid during early and mid-summer in bark crevices or under patches of lichen on host trees. After hatching, larvae bore into the inner bark region where they feed until mid-summer of the next year. This feeding in the inner bark causes characteristic catfaces or bark pockets. Once larvae enter the wood they bore upward through the sapwood and into the heartwood and pupate behind a plug of excelsior-like frass. The larval galleries are from one-fourth to one-half inch in diameter, and six to ten inches long. Usually the galleries are within six inches of the center of the tree. The adult emerges at the lower end of the tunnel, using a hole cut through the bark by the larva just prior to pupating. Adults emerge in June and July. The timing of the two-year life cycle of the red oak borer is such that the adult population is greatest in odd-numbered years.