Bug of the Week April 6, 2009

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In what has become an annual right of spring, it is time to announce the return of eastern tent caterpillar and, thereby, provide an excuse for all gardeners in the Washington area to get out and inspect their prized cherry, apple, and crab apple trees for early signs of this pesky caterpillar. A few weeks ago when forsythia’s bright yellow blossoms first appeared, tiny caterpillars hatched from dark Styrofoam-like egg masses attached to small branches of cherry trees and some of their close relatives. Eggs were deposited by female moths last summer and their spawn marked time as eggs last summer, autumn, and winter. With the return of warm weather over the past weeks, dozens to more than 300 hundred larvae hatched from each egg mass. After hatching, caterpillars moved to buds and waited for tender young leaves to unfold. At the same time, larvae built small silken tents over buds and the surrounding branch. From this bivouac, they move along silken trails to expanding leaves and munch nutritious foliage. As larvae grow during March and April, their tents enlarge and are relocated to the crotches of ever-larger branches near the center of the tree. Eastern tent caterpillars are a rather chummy lot and brothers and sisters from the same egg mass often participate in group activities such as communal foraging and enlarging their remarkable tent. This silken home provides protection from predatory and parasitic insects. Tents may also help caterpillars conserve moisture and elevate body temperatures for more rapid growth and development during chilly spring days. These hairy caterpillars have voracious appetites. They can totally strip even large trees of leaves when many tents are present. After caterpillars have completed development, a mass exodus from the tree transpires and larvae wander the land seeking protected spots beneath logs, leaves, stones, or man-made structures to spin yellowish-white, silken cocoons. Adult moths emerge from cocoons in June or July. At this time you may spot the tawny moths at your porch light. Adults mate and the female lays eggs on small branches of rosaceous trees. These eggs house the next generation of caterpillars that will emerge with the bloom of forsythia next spring. How do you know if you are likely to have a problem with eastern tent caterpillars? The best predictor of a problem this year may be the problem you had last year. The images for this Bug of the Week came from a small stand of wild cherry trees that are perennially infested with eastern tent caterpillars. If you had a cherry, apple, or purple plum with tent caterpillars last spring, now is an excellent time to carefully inspect the small branches and points where branches join the trunk of the tree. Now and as the tents enlarge and move to the crotches of the tree, tents and their inhabitants can be removed with a gloved hand on a cool day, placed in a bag, and destroyed. The old school remedy of “burning them out”, though dramatic, went out with the storming of Frankenstein’s castle. Flames are very damaging to the bark of a tree and flaming should not be used to remove these or any pest from a living plant. If left unchecked, tall trees festooned with tents may be totally stripped of leaves. While trees may recover and produce a second flush of leaves, repeated defoliation reduces the vigor of trees. If you have a tall tree from which you cannot safely remove eggs or tents, you may want to seek the help of a professional certified arborist. Entomologists believe that eastern tent caterpillar populations run in cycles. After a few years of caterpillar plague, natural enemies such as predators, parasites, and pathogens reduce tent caterpillars to innocuous levels. The last several years have been quite good for these rascals. With so many other indicators trending downward, perhaps Mother Nature will send a tent caterpillar relief package and give us a break from these noisome creatures.

For more information on eastern tent caterpillars, visit the following web sites.

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