Eastern Tent Caterpillar: The Landscape Harbinger of Spring

Throughout much of NJ during this week, the growing degree days (GDD) will be increasing consistently. By the end of the week, many areas will exceed 90 GDD, which means the eastern tent caterpillars will begin to hatch. Not all eggs will hatch at once since a staggered hatching period will potentially increase survival rates if the weather happens to cool again.

The photographs of the eastern tent caterpillar’s life cycle included in this blog were all taken during the spring of 2016 at the same site in Freehold, NJ. They are placed in chronological order covering a time span of 10 weeks from 1^st egg hatch on 3/23/16 to late pupation on 6/2/16. In 2016, central NJ experienced a relatively warm early spring that enabled the speedy first hatching.

 

 

 

 

 

 

 

 

 

The eastern tent caterpillar, Malacosoma americanum spp., is native to North America and found throughout the United States east of the Great Plains, and in the southern part of eastern Canada. This pest is one of the more significant defoliators of deciduous shade trees. Their preferred hosts include isolated, open-grown trees, especially wild cherry, crab apple, and apple. During outbreak years, which frequently occur at 8 to 10-year intervals, this pest will also occasionally attack pecan, hawthorn, beech, willow, and other shade trees.

 

 

 

 

 

 

 

 

 

 

Eastern tent caterpillars construct silk nests in the forks of trees, which are easily recognized during the spring months. The noticeable tents/nests cause an exaggeration of their impact as pests. Defoliation by this caterpillar will rarely cause tree mortality, as trees will re-foliate. The reduced aesthetic value of trees in urban & suburban areas is the primary harm created by the activities of this pest. Outbreak years also arouse much concern among area residents when the caterpillars migrate in mass across landscapes in search of new food or a place to complete their development. Nevertheless, unlike the gypsy moth, the eastern tent caterpillar has never been a major threat to the vitality of our forests and rarely reach large populations in ornamental trees.

 

 

 

 

 

 

 

 

 

Tent caterpillars spend the winter in brown masses of 150-350 eggs that the adult female attaches around small outer twigs. These shiny brown bands can be readily recognized and removed by hand. During the late 1800’s and early 1900’s, whole communities mobilized to combat the perceived threat of infestation by the eastern tent caterpillar. For example, in an early eradication campaign in Connecticut in 1913, more than 10 million egg clusters were destroyed when the extension service offered a $25 prize to the school child who collected the most. Such mechanical control efforts still overlooked as many as 20% of the eggs. Therefore, after larvae hatched in the spring and the silk tents formed, prize money was again awarded to school children in numerous towns for the number of tents they collected. In one such town, the children collected nearly 17,000 tents, weighing over half a ton. Then, usually with great vengeance and satisfaction, these tents were torched by flames or viciously stomped upon. Many of these same towns also offered a reward of 10 cents per quart filled with pupal cocoons of this insect. For instance, in 1899, at Glen Falls, NY, 1350 quarts containing the cocoons were turned in.

 

 

 

 

 

 

 

 

 

 

The simple mechanical methods of removing and destroying egg masses, tents, and pupal cases of tent caterpillars were and continue to be environmentally friendly ways of effectively suppressing their numbers in small, localized areas. However, even though these cultural practices should continue to be encouraged where they are practical, their limitations will always be evident.

 

 

 

 

 

 

 

 

 

 

Disease, natural enemies, and starvation are the primary environmental factors involved in the suppression of tent caterpillar species, which act to curb cyclical outbreaks of this insect. Since they are native caterpillars, numerous predators (i.e., spiders, ants, yellow jackets, assassin bugs, birds) and parasitoids (i.e., braconid wasps, ichneumonid wasps, tachinid flies) attack tent caterpillars, but in some years these beneficials do not arrive in time or in sufficient numbers to adequately control them every season. As a result, the 8 to 10 year intervals between outbreak populations has been a trend.

 

 

 

 

 

 

 

 

 

 

 

During tent caterpillar outbreaks, the higher competition invariably results in lower food quality and greater vulnerability to infection by viral (e.g., NPV), bacterial (Clostridium), and fungal (e.g., Entomophaga) diseases. Pupal parasitism of the caterpillar also increases with outbreaks of long duration. Finally, weather factors often play a key role toward the collapse of tent caterpillar outbreaks. For optimum survival, egg hatch in the spring is synchronized with the development of the leaves on the trees they typically feed upon. Observations have indicated over 99% mortality of tent caterpillars from starvation in regions where unusual weather patterns caused the forestalling of the development of the leaves on the trees.

 

 

 

 

 

 

 

 

 

 

Occasionally cultural and biological control strategies will fail to adequately keep their populations in check in specific areas. Environmentally friendly, biorational products such as horticultural oils and insecticidal soaps can suppress young larvae upon direct contact.  The bacterium (Bacillus thuringiensis) is the biological insecticide material of choice against young tent caterpillars less than 1-inch in size (i.e., first 3 instars). Acelepryn (chlorantraniliprole) is a reduced risk insecticide & has low negative impacts to beneficial insects. If applied as a spray treatment, it has translaminar properties. Tebufenozide (Confirm) is an insect growth regulator (IGR) & is classified as a reduced risk material by the EPA. Spinosad (Conserve) is OMRI approved & rounds out the list of the more biorational types of insecticides.

 

 

 

 

 

 

 

 

 

 

Do not use flaming torches when attempting to control. Instead, prune or rub out early in the morning/late afternoon or during rainy days when caterpillars are inside the nest. Most caterpillar species are relatively easy to kill with traditional contact insecticides. Penetrate the nest and control with carbaryl (Sevin) or one of the pyrethroids.

However, costly protection efforts to prevent damage to trees are rarely justified. Pesticide treatments may then be used as the option of last resort and then only on trees of high value or in areas having important recreational uses.

 

 

 

 

 

 

 

 

 

 

 

 

 

References:

Coulson, R.N. and Witter, J.A., 1984, Forest Entomology – Ecology and Management, Wiley-Inter-science Publications, New York.

Fitzgerald, T.D., 1995, The Tent Caterpillars, Comstock Publishing Associates and Cornell University Press, Ithaca, NY.

Penn State Cooperative Extension, 1991, The Eastern Tent Caterpillar, The Pest Sheet (G.A. Hoover and P.R. Haller, eds), Department of Entomology, Penn State College of Agriculture, University Park, PA.

USDA Forest Service 1990. The Eastern Tent Caterpillar. Maryland Department of Agriculture and USDA Forest Service, US Government Printing Office, Washington, DC.