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FS ShieldForest Health Protection, Southern Region


Malacosoma disstria Hbn.

Importance.- Outbreaks occur periodically on oaks, tupelo gum, and other hardwoods over wide areas of the eastern half of North America. Growth loss and dieback occur, but trees are seldom killed unless they sustain 3 or more successive years of complete defoliation.

Identifying the Insect. - The larvae have pale bluish lines along the sides of a brownish body, and a row of keyholeshaped white spots down the middle of the back. They are sparsely covered with whitish hairs, and reach 2 inches (50 mm) at maturity. Adult moths are buff-brown, with darker oblique bands on the wings. Egg masses of 100 to 350 eggs encircle the twigs and are covered with frothy, dark brown cement.

Larvae - note keyhole shapes on back

Larvae - note keyhole shapes on back.
(Click for detail. JPG 38K).

Identifying the Injury. - The first noticeable signs of attack are sparse crowns and falling frass. Caterpillars often cluster on the lower trunks of infested trees. Single trees or complete stands may be completely defoliated during the spring.

Large areas are often defoliated

Large areas are often defoliated.
(Click for detail. JPG 41K).

Biology. - Eggs hatch in early spring. Caterpillars feed for 4 to 6 weeks on the opening buds, foliage, and flowers. Despite its name, this species does not form tents. Pupation occurs in yellowish cocoons and lasts 10 to 14 days. Moths emerge from late May to July, mate, and deposit their eggs. There is one generation per year.

Control.-Natural control agents include insect parasites of eggs, larvae, and pupae. Predators and viruses and fungus diseases, as well as high and low temperatures, also kill forest tent caterpillars. Starvation is common when populations exceed the food supply. Several chemicals and a microbial insecticide are registered for control.