Issue 2, May 19, 2023

Eastern Tent Caterpillar

Eastern tent caterpillars (Maclacosoma americanum) are native North American pests that can be heavy defoliators. They feed predominately on members of the rose family including crabapple, apple, cherry species, hawthorn, peach, plum species and many others. When feeding, the caterpillars chew from the margin of the leaf inward, leaving the midvein of the leaf behind.

Eastern tent caterpillars overwinter as eggs on host trees and young caterpillars hatch at bud break. Caterpillars are dark with a yellow-gold stripe down their back and blue spots along their sides. The caterpillars have short velvety hair covering their bodies with some sparse longer hairs along their bodies and can grow to be 2 inches long. The caterpillars create silk tents at the crotches of branches and venture out of the tents to feed on foliage. As the caterpillars grow, they will expand their tents. The tent provides protection from predators, parasites and pathogens. The tent also has a greenhouse effect, creating a warm, humid environment that is beneficial for caterpillar growth and activity.

Eastern tent caterpillars (Maclacosoma americanum; left), eastern tent caterpillar tent (right). Photos by Phil Nixon.

Eastern tent caterpillars can be differentiated from other tent building caterpillars like fall webworm by the location of their tents on the trees. Eastern tent caterpillars construct their tents at crotches or Y-intersections on trees early in the season, while fall webworms build their tents at the tips of branches later in the season. Eastern tent caterpillar populations vary from year to year, so we may find low population for multiple years and one year with a heavy population. When populations are heavy, feeding can lead to significant defoliation. Removal of tents or application of Bt treatments can limit further defoliation.

Cultural and Mechanical Controls

Removing tents by winding them around a stick and squashing the caterpillars is an effective means of reducing caterpillar populations quickly. By removing tents at night or on cloudy days, more caterpillars will be inside the tent when it is removed and more caterpillars can be controlled at once. When the tents are damaged or removed, the surviving caterpillars will be exposed to disease, parasites and predators. Inspecting branches and removing of egg masses from previously infested trees in the fall can help reduce caterpillar populations the following year.

Biological Applications

Bacillus thuringiensis kurstaki (Bt) treatments like Dipel or Thuricide are bacterial treatments that can be used to control caterpillars. Bt treatments are most effective when caterpillars are young. The caterpillars must consume the Bt treatment for it to be effective so applications to foliage are most effective.

Sarah Hughson

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