It seems like out trees are taking an awful beating from foliage-devouring insects, such as gypsy moth caterpillars, bagworms, eastern and forest tent caterpillars and webworms.

The gypsy moth is one of the worst. In the forests of Pennsylvania, New York and other northeastern states, these moths have defoliated hundreds of thousands of acres in the past several years.

Bagworms feed mostly on arborvitae, cedars and junipers, but no evergreen or deciduous tree or shrub is immune. Locally, they hatch during the first week in June. They spin a cocoon-like bag and move about freely to feed, carrying their bag with them.

In late summer they pupate and then transform into moths. The female remains in her bag and lays 200 to 1,000 eggs. Bagworms can be controlled by picking off and burning the bags during fall, winter or early spring.

The eastern tent caterpillar is another serious defoliator of deciduous shade trees: sometimes the entire countryside appears covered by silken tents this caterpillar makes.

Eggs are laid, 150 to 350 of them, in masses encircling small twigs. They hatch in spring, about the time wild cherry leaves appear. The best control is to get rid of the eggs during the winter or destroy the tents and tiny, caterpillars in spring.

Webworms attack mimosa and locust trees. There are two generations a year, so webworms are present from June until frost.

When a tree loses its foliage at any time other than the onset of the winter dormancy, it's seriously affected, according to Philip M. Wargo at the Northeastern Forest Experiment Station in Hamden, Connecticut. When insects consume part or all of a tree's foliage, normal growth and food-producing are distrubed or completely interrupted, he says.

Wargo has extensively studied the results of tree defoliation by gypsy moth caterpillars. The greater the amount of foliage eaten by the insect, the greater the adverse effects: the less leaf tissue, the less food produced.

A deciduous tree seems to tolerate as much as 50 percent defoliation a year without much difficulty. However, when defoliation exceeds that, it's very serious, especially if it's severe enough to cause the tree to refoliate in the same growing season. Refoliation may be necessary for the tree to survive, Wargo says, but it results in a significantly altered tree.

Bad weather contributes to the severity of defoliation. A tree may be more vulnerable to effects of defoliation the following year, and defoliation followed by attacks from secondary organisms may kill the tree. Because most dying trees are depleted in starch content, starvation also pays a role in mortality.

As for evergreen, they usually don't survive one defoliation. Q. Our poinsettia was outdoors for the summer and grew too tall. Can we cut it back ? A. If you cut it back, it may not bloom for Christmas. Bend the stems to shorten them. Select an internode (growth bud) on the stem four to six inches above the soil level: Pinch or squeeze the stem at this point to flatten it so you can bend the stem over.

At another point up the stem (half the distance you want to shorten the stem), repeat the flattening process. Then bend the stem and tie the part that is doubled with green string or plastic. In a few days the inverted leaves should right themselves.