Forest Tent Caterpillar

The forest tent caterpillar is broadly distributed throughout North America. As with all tent caterpillars, there is just one generation each year. The egg mass with its enclosed quiescent caterpillars is the overwintering stage. Eggs hatch and the first of the active larval instars appears in the early spring just as the buds of the host tree are begining to expand. The caterpillars grow rapidly and after feeding for about 2 months, spin cocoons and pupate. About 3 weeks later the adults appear and shortly thereafter the moths lay their eggs and die.

These tent caterpillars spend the winter in egg masses glued to twigs of the host plan.Prior to winter the insects transform to caterpillars and emerge from the eggs shortly after bud break. The newly emerged caterpillars move to crotches of branches and begin to produce a mass of dense silk.

Life cycle:The forest tent caterpillar has only one generation per year throughout its range. Overwintering larvae within egg masses begin emerging in early spring concurrent with the swelling and expanding of buds on host trees. In Florida, mass hatching of eggs commonly peaks during March, but has been observed as early as mid-February and as late as April. The young larvae are gregarious and initially feed together on the expanding buds, foliage, and flowers. As forest tent caterpillars develop through five larval instars, they eventually devour entire leaves. Late instar larvae tend to wander, individually traveling within, among or out of host trees, either in search of additional food or a place to pupate.

It is during the two to six weeks when caterpillars are noticeably present, particularly when they are approaching maturity, that the resulting circumstances create adverse situations for people, i.e., unpleasant encounters with caterpillars and their droppings. The pale-yellow pupal cocoons are variously located amongst webbed leaves, bark crevices, shrubbery and other somewhat protective places such as on the sides and under overhangs of buildings. Pupation takes 10 to 14 days, after which the adult moths emerge, mate and females oviposit egg masses on host trees. Although adult moths do not feed and live for only two to 10 days.Pharate larvae develop by fall and diapause through winter until emerging the following spring to begin the cycle again.

Damages:Trees that are fed upon by forest tent caterpillars are rarely killed by these insects because following complete defoliation, deciduous trees are able to produce another set of leaves during the same season. The main impact of forest tent caterpillar feeding on deciduous trees is a reduction in the rate of growth. Vigorously growing trees can tolerate up to two or even three consecutive years of heavy defoliation without suffering serious damage or mortality. If a prolonged defoliation cycle occurs, (four or more years), moderate to heavily defoliated trees may experience a reduction in growth, suffer branch dieback and could eventually be killed. A general rule of thumb is that complete defoliation can occur when an average of nineteen egg masses are found on an aspen tree that has a six inch diameter trunk at about four and half feet. When trees become stressed, such as during a drought, they are less tolerant of defoliation. A stressed tree can be injured or even killed in a much shorter time period than an unstressed tree. Protecting high value trees would be appropriate during forest tent caterpillar outbreaks when trees are under moisture stress.

Control: A wide variety of factors have been implicated in causing population declines, including several adverse environmental conditions. High levels of larval mortality have been associated with relatively low temperatures in the winter and spring (such as a late or hard freeze following larval emergence) and harsh weather when early instars are abundant. Harsh weather and extremely high temperatures may kill numerous adults later in the spring, and also reduce mating success and viability of offspring amongst survivors. Outbreak populations may also decline or collapse as a result of starvation, when larvae exhaust food supplies (i.e., host foliage) before completing development Natural enemies such as parasites, predators, and diseases may also exert important regulatory effects on Forest tent caterpillar populations.

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