Gypsy moths are insects that can cause extreme defoliation to trees when in their caterpillar stage.
Preferred tree species include alder, aspen, basswood, birch, hawthorn, oaks (especially chestnut and white), and willow. The least preferred tree species include American holly, ash, black locust, flowering dogwood, sycamore, and tulip.
The gypsy moth is one of the most destructive insects in North America. Most of the moth’s destruction occurs in the Northeast, but it’s spreading to southern and central states. Young caterpillars spin down on silken threads from treetops and move through wind currents. Mature gypsy moth caterpillars are identified by five pairs of blue spots followed by six pairs of red spots on their backs. After the caterpillars have pupated, adult gypsy moths emerge in mid-summer. These insects are ravenous feeders. For example, a single caterpillar can eat its way through 10 square feet of foliage during its development. Trees that are infested with gypsy moth caterpillars become weak and more susceptible to other problems. Within one year, complete defoliation can kill conifers and hardwoods. A female moth can lay up to 100 eggs. Egg sacs can be found on trees, rocks, walls, firewood, and underneath vehicles.
To control gypsy moths, two or three foliar treatments may be necessary because of the caterpillar’s long emergence period. Bt, a bacterial pathogen, is effective on caterpillars. Trees recovering from gypsy moth damage should also be fertilized to help the healing process.