[All figures follow this article.]

The tent caterpillars lay eggs in masses, and shiny, dark brown or black egg mass encircles the stem or twig of a tree (Fig.1).

The newly hatched caterpillars are 3 mm long, black, and contain fur-like setae on the body (Fig.2).

The coloration, markings, and patterns on late stages of caterpillar vary by species. The Eastern tent caterpillar (ETC), late stage caterpillars are black with blue and white markings and a continuous white line on back background (Fig.3). The forest tent caterpillars (FTC) are similar in appeared as ETC, except they have a white dot instead of white continuous line on the background (Fig.4). The Western tent caterpillar (WTC) has a blue-white stripe on the with black bands (Fig.5).

In the spring and early summer, the most tent caterpillars build a tent-like structure with silken web on branches of trees (Fig.6). In contrast, forest tent caterpillars construct a silken mat on leaves. The newly hatched caterpillars built a tent on branches. The tent covers the larvae, protecting them from predators such as birds. It also helps shield them from harsh weather conditions by facilitating thermoregulation and assists with larval molting.

Life cycle

All the tent caterpillars have a similar life cycle. They complete one generation in a year. A single tent caterpillar adult female lays only one egg mass annually. An egg mass of 100-350 eggs encircles the twigs in mid-summer. Egg masses overwinter and hatch in April and July in the southern and northern US, respectively, which coincides with tree bud expansion.

Colonies of first instar caterpillars stay together and spin a silken web around a branch junction or on trunks. Instead of tents, the FTC produces a silken mat on branches or trunks where the caterpillars rest. The caterpillars from 1st to 4th or 5th stages are gregarious and feed on foliage. The size of the tent increases as the caterpillars grow. The tent serves as an area for the caterpillars to rest. They leave the tent during the day for food and return at night.

The last larval stage becomes solitary in habit, wanders off, and feeds individually. Tent caterpillars develop through 5-8 larval stages. Additional larval stages are added if they feed on poor-quality tree materials until they reach optimal size for pupation. Larval development is completed within 4-7 weeks.

Late-stage caterpillars pupate inside the silken cocoons at bark crevices, leaves, on the ground, and under any structure (Fig .7). Moths emerge from those cocoons in May or June/July in the southern and northern USA, respectively. The adult moths of tent caterpillars are yellowish in FTC (Fig. 8), brown in ETC (Fig. 9), and black to greyish in WTC (Fig. 10).

Damage

Tent caterpillars feed and defoliate, beginning from early April to late June. During pest outbreaks, defoliation (Fig .11) causes branch dieback growth reduction and occasionally kills the tree. If the population is abundant, tent caterpillars may strip the trees and migrate to new tree hosts. The tent, colonies of caterpillars (Fig. 12) and silken cocoons on trees and shrubs reduce the aesthetic appearance of landscapes.

Host range

Tent caterpillars have a wide host range. FTC feed on trees such as trembling aspen (Populus spp.), alder (Alnus spp.), birch (Betula spp.), cherry (Prunus spp.), sugar maple, oaks (Quercus spp.), elm (Ulmus spp.), basswood (Tilia americana L.), water tupelo (Nyssa aquatica L.), and blackgum (Nyssa sylvatica Marshall), sweetgum (Liquidambar styraciflua L.) and feed on shrubs such as willow (Salix spp.). Meanwhile, Eastern and Western tent caterpillars feed on black cherry, apple, crabapple, pear, and some other fruit trees. WTC also feeds on shrubs, including bitterbrush (Purshia tridentata), California lilac (Ceanothus spp.), mountain mahogany (Cercocarpus spp.), and some other ornamental shrubs.

Management

In ornamental landscapes, such as residential or commercial settings, tent caterpillars can be managed by destroying egg masses in the winter, as egg masses are visible on defoliated trees. Developing tents can be physically destroyed as new tents appear. The tent caterpillars can be trapped using a sticky collar wrapped around the tree trunk to capture migrating caterpillars. In residential areas, caterpillar colonies and cocoons can be dislodged by using high-pressure water sprays.

Several insecticides are effective on tent caterpillars.

Microbial insecticides such as BT product (Bacillus thuringiensis var. kurstaki), spinosad, and baculovirus are effective on younger stages of tent caterpillars.

Insect growth regulators, such as diflubenzuron, can used; however, it is not recommended near water, as it can negatively affect aquatic arthropods. Biorational insecticides, such as azadirachtin and insecticidal soap, effectively reduce tent caterpillar populations. Synthetic insecticides, such as organophosphates (malathion and acephate), pyrethroids (permethrin and bifenthrin), and carbamates (carbaryl) are also effective on larvae, and they can be spot-applied. Younger larvae are more susceptible to insecticides than caterpillars in late stages.

All insecticides should be used according to the label.