Insect Pests of Christmas Trees

Defoliators

Pine Webworm

The pine webworm, Tetralopha robustella Zeller, is an occasional pest of Christmas trees. It primarily attacks one- and two-year-old seedlings but may also infest older trees.

Description - The adult moth is dark gray with black on the basal and outer parts of its forewings. It has a wingspan of about 25 mm. Mature larvae, about 18 mm long, are light gray to yellowish-brown with two darker brown stripes on each side.

Damage - The first sign of infestation is usually a mass of brown frass pellets in a silken webbing on the twigs (Fig. 9). The masses enclose the needles on which larvae feed. At first the webbed mass may e only one or two inches long but may later become quite large and contain several larvae. Seedlings up to two feet tall can be defoliated by the larvae of a single nest. Infestations on larger trees cause partial defoliation, loss of growth and poor tree appearance. Life History and Habits - Pine webworms overwinter as pupae in the soil. Adults emerge in the spring, mate and lay eggs on the needles. On hatching, young larvae mine the needles. Older larvae feed on needles and construct the web mass. Larvae continue to feed within the expanding web until mature, then drop to the ground and pupate in a cell in the soil. As with many moths, the speed of develop-

Figure 9. Newly Started Pine Webworm Web.

Control - Controls generally are not necessary for light or extremely spotty infestations. Individual infestations can be destroyed by hand. The larvae are also easily controlled by labeled insecticides, but good spray coverage and pressure are needed to penetrate the webs.

Sawflies

attack single or small groups of trees, but outbreaks over extensive areas can occur. The red-headed pine sawfly, (Fig. 10) Neodiprion lecontei (Fitch), and others in the same genus are among the more common in Georgia. Description - Adults are small wasps. Females are reddish-brown to black, 6 - 9 mm long, with slender antennae. Males are smaller (5 - 6 mm), black and have feathery antennae. Larvae resemble caterpillars but are usually found without hairs and have five or more pairs of fleshy prolegs on the underside of the abdomen – caterpillars normally have only four pairs of prolegs. Sawfly larvae also have only one pair of simple eyes (ocelli) on their head capsule, while caterpillars normally have six pair. Larvae of the more common sawfly species vary from 15 to 25 mm in length, are greenish to dusky gray and have conspicuous stripes or spots.

Figure 10. Red-Headed Pine Sawfly Larvae.

Damage - Sawflies are gregarious feeders (commonly found feeding in large groups). Damage often is not noticed until the needles of a branch or tree are almost completely devoured or until the larvae are large and easy to see. Early-stage infestations are normally indicated only by discolored, straw-like needles or by frass accumulation on the ground beneath infested trees. Large branches or small trees may be defoliated by sawflies. When a tree is defoliated, the larvae move to neighboring trees to complete their development.

Life History and Habits - Adult females lay eggs on needles in the spring. Larvae hatch and feed on both new and old needles, usually defoliating one branch before moving to another. They seem to prefer to eat older needles. Larvae mature in three to six weeks. Fully grown larvae drop to the ground and spin silken cocoons in the litter or soil. They pupate within the cocoons. Some may remain in the cocoons for up to three years before pupating, although most complete their development in a much shorter time. There may be as many as three to five generations per year depending on species and location.

Control - Sawflies are relatively easy to control with insecticides when damage is noticed. Frequent inspection of trees is important to detect sawfly infestations before serious defoliation takes place. Spot or area spraying is normally all that is required. Pupae are highly prized by ground birds and rodents.

Bagworm

The bagworm, Thyridopteryx ephemeraeformis (Haworth), attacks a wide variety of trees including both conifers and hardwoods. It appears to prefer cedar and arborvitae but attacks other conifers, including pine, spruce and cypress.

Description - The case of the bagworm is a somewhat carrot-shaped bag, up to two inches long, comprised of silk and bits of whatever foliage the larvae feeds on inside the bag (Fig. 11). Mature larvae, 18 - 25 mm long, are dark brown with yellowish heads. Adult females are soft, yellowish-white and grub-like, with no functional eyes or appendages. They spend their entire lives inside the bags. Males are hairy, sooty-colored moths with clear wings which span about 25 mm. Damage - Injury is caused by larvae feeding on the foliage. Heavily infested trees may be defoliated and killed. If not killed, infested trees may be weakened and stunted. The

Figure 11. Bagworm on Cedar.

Life History and Habits - Bagworms overwinter as eggs inside bags attached to twigs. Eggs hatch in the spring and young larvae crawl to the nearest foliage and begin to feed. Each larvae constructs a bag around itself as it feeds, spinning silk and enlarging the bag as it grows. Larvae partially emerge and tow their bag with them when moving about. When mature, in late summer, larvae attach their bags to twigs with silk and pupate inside. The pupal stage lasts about four weeks. Male moths emerge in early fall, fly to the bags containing females and mate. ?Females deposit up to 1,000 eggs in or on the pupal case, drop to the ground and die. The eggs overwinter. There is only one generation per year.

Control - When infestations are light, hand destruction of bags during late fall and early winter will reduce or eliminate populations by destroying the overwintering eggs. Insecticide applications are effective but should be made when the bags and larvae are small. Older larvae are harder to control. Thoroughly wet the bags with insecticide sprays. Controls are best applied late in the day when bagworms are more active.

Pine Colaspis

The pine colaspis, Colaspis pini Barber, is an occasional pest of Christmas trees. It is known to feed on most species of Southern pines but rarely causes significant economic injury. Description - Adults are oval, convex, tannish to brown chrysomelid beetles with metallic greenish specks on their backs (Fig. 12). They are about 5 mm long. Mature larvae are yellowish-white, about 6 mm long, with a sparse covering of short hairs and clusters of longer hairs at the outer edge of each body segment. Damage - Adults feed on needles, chewing from the edges to the midrib. Badly damaged needles turn brown, Light feeding injury is often limited to the needles of new growth. In heavy infestations, needles over the entire tree may be

Figure 12. Pine Colaspis Beetles and Damaged Needles.

Life History and Habits - Pine colaspis larvae spend the winter in cells in the soil, then pupate in the spring. Adults emerge in late spring to early summer and feed on pine needles, mate and lay eggs in the soil. Larvae feed in the roots of grasses and other herbaceous vegetation until fall, when they move deeper into the soil to overwinter. There is only one generation per year.

Control - Controls are seldom needed. Insecticide treatments for tip moths and other pests normally provide adequate suppression. The beetles are easily killed by insecticide sprays if a problem does develop, although timing of sprays is critical. Many growers treat damage after the beetle is gone.

Pine Chafer

attacks various species of pine but does not appear to favor the ones commonly grown as Christmas trees. Description - Male beetles are 6 - 7 mm long. They have a greenish-bronze head and thorax, and dark tan to brown wing covers. Female beetles are dark tan and about 9 mm long. Mature larvae are dirty white with brown heads and are 9 - 12 mm long. Damage - Adult beetles feed mostly on new needles, cutting notches just above the needle sheath. This causes the needle ends to die and turn brown. Heavily infested trees look reddish-brown and fire-scorched. Damaged needles may continue to grow from their base but do not attain their normal length. Life History and Habits - The larvae spend the winter several inches deep in the soil, then pupate in the spring.

Pine chafer adult feeding on foliage. Note characteristic position of rear legs.

Control - The beetles can be readily controlled by available insecticides. Examine trees often to detect infestations early.

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