Forest tent caterpillar

Distribution

Canada

Micro-habitat(s)

Leaf

Damage, symptoms and biology

Defoliation is caused by the caterpillar, which begin to feed on the new leaves as soon as they appear in May. Given this insect’s voracious appetite and gregarious behaviour throughout most of its development, its presence can be quickly detected. Older larvae devour entire leaves and, when the tree is completely defoliated, migrate in search of other sources of food. Larvae can also be observed in colonies on tree trunks sheltered from the sun’s rays.

During massive invasions, trees can be completely defoliated over large areas. Even when severely defoliated, trees withstand infestations relatively well. Infestations generally last no more than three consecutive years. However, on trembling aspen, radial growth loss and twig dieback occur. Denuded trees will produce another crop of leaves during the season.

In the fall, the presence of egg bands, which resemble spongy, brownish masses, can be easily detected on small branches and twigs. In late June, the female deposits between 150 and 350 eggs in masses that encircle the twigs. The embryo develops over the course of the season and overwintering takes place as a fully developed embryo within the eggshell.

Life cycle (East of the Rockies)

Other information

A species native to North America, the forest tent caterpillar is the most widespread defoliator of deciduous trees. Its range extends from coast to coast.

The insect has been known for many years and the first outbreak was recorded in 1791. Since then, the forest tent caterpillar has been reported at regular intervals in Canada.

Infestations are generally short and parasitoids are very important in the natural control of populations. The most important parasitoid is the large flesh fly, Sarcophaga aldrichi Parker, which acts quickly after the start of an infestation, and can destroy up to 80% of the pupal population.

In recreational parks or on ornamental trees, it is recommended that egg bands be removed in the fall. At that time of year, they are more visible because the leaves have dropped. In the spring, colonies of young larvae at rest can be removed by hand. On small trees, a water jet can be used to dislodge larvae from the foliage.

Main host(s)

Red oak, sugar maple, trembling aspen