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Forest Tent Caterpillar

Malacosoma disstria


Trembling aspen, poplar and other trees and shrubs

Appearance and Life Cycle

Description of this image follows
Photo credit: Gerald J. Lenhard, Louisiana State University,

Description of this image follows
Egg masses with hatch occuring.
Photo credit: James Solomon, United States Department of Agriculture Forest Service,

Larvae emerge from egg bands in the spring, just as the foliage begins to appear on the trees. Larvae are dark brown with broad blue bands along each side and marked with a row of white key-hole shaped markings down the centre of the back. Contrary to their name, forest tent caterpillars do not construct a tent, but feed openly on the foliage. By mid to late June, the full grown larvae are 45 to 55 millimetres (mm) in length. The moths are present from mid-July to early August. After mating, the females deposit egg bands containing 100 to 200 eggs on twigs of host trees. The egg bands are 10 to 20 mm long and are covered with a foamy, dark-coloured, protective sub stance. The forest tent caterpillar completes one generation a year


Forest tent caterpillar damage can range from a thinning of the crown to complete defoliation. After a severe attack most trees will refoliate the same year. Trees may suffer top dieback or die if defoliated three or more consecutive years.


Natural factors such as disease, parasites, predators, starvation and adverse weather usually keep populations low. Where practical, some control can be achieved by removing the egg bands from the host trees late in the fall or early spring. For large shelterbelts, the larval stage may be sprayed with an insecticide such as malathion, acephate, carbaryl, deltamethrin. The biological insecticide Bacillus thuringiensis may also be used. Application of insecticides should be conducted in late May to early June while larvae are small and damage is light. Spraying will probably be required if the number of egg bands on the tree is greater than the trunk diameter in centimeters, measured at approximately 1.5 metres (m) above ground level.

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