Like the tale of the sorcerer’s apprentice, the gypsy moth (Lymantria dispar) is an example of an experiment gone horribly wrong. The moth was brought to the United States in 1869 in a failed attempt to start a silkworm industry. Escaping soon after, the gypsy moth has become, over the past century, a major pest in the northeastern United States and southeastern Canada.
Egg masses appear as 1.5 inch (4 cm) tan or buff-coloured hairs on tree trunks, outdoor furniture, or the sides buildings.
Gypsy moth caterpillars change appearance as they grow. Young caterpillars are black or brown, and about ¼ inch (.6 cm) in length. As they grow, bumps develop along their backs along with coarse, black hairs. Each of the eleven sections of a developed caterpillar will have two coloured spots, the first five pairs, blue, and the last six, red. Mature caterpillars can be as long as 2 ½ inches (6.35 cm).
Gypsy moths are seen only in mid-summer. Males are grayish brown and can fly; females are larger, whitish with black marks, and cannot fly.
Tree damage is caused by the insect larvae, or caterpillars, which emerge from their eggs beginning in early spring and continuing through mid-May. The larvae move to the leaves of trees and begin to eat, mostly at night. During daylight hours, larvae generally seek shade from the sun but feeding can occur in daytime in heavy infestations. Gypsy moth larvae grow by moulting, five moults for males and six for females. Feeding occurs in the “instar” stage or period between each moult. As might be expected, a caterpillar’s appetite increases with each moult. Feeding continues until mid-June or early July, when the caterpillar enters the pupal stage emerging, finally, as a moth. Both male and female moths exist only to reproduce once; the male moths flying to find the females, who are too heavy to fly. The females lay their eggs from July to September, depending on location, then the moths of both sexes die.
Depending on the degree of infestation, tree damage ranges from light to almost complete defoliation. Most deciduous trees can survive a moderate degree of defoliation. Many can even survive one complete defoliation by the gypsy moth caterpillar. However, continuing attacks can fatally weaken a tree or leave it vulnerable to other insects or disease.
The gypsy moth caterpillar is not a fussy eater. It has a preference for the leaves of deciduous hardwood trees such as maple, elm, and particularly oak. Gypsy moths can also feed on apple, alder, birch, poplar, and willow trees. As it grows, it will also attack evergreens, like pines and spruces. Gypsy moths appear to dislike ashes, sycamores, butternuts, black walnuts, dogwoods, and balsams. However, during heavy infestations, competition for food will drive the caterpillar to attack almost any tree or shrub.
Recommended Steps to Control Gypsy Moth
The gypsy moth can be combated at the egg and larval (caterpillar) stages. Egg masses, when discovered, should be burned or soaked in water or kerosene. If the egg masses are unreachable, spray them with a strong dose of Horticultural Oil Insect Spray. Spray in the late fall as well as a few times in the early spring, before leaves begin to form on trees. To prevent the caterpillars from reaching the foliage, use a TreeHelp Bug Band. You should use a TreeHelp Bug Band to protect nearby trees as well.
Use Garden Insect Spray with Spinosad and Gypsy Moth Trap to control both the caterpillars and the moths. At the first sign of the caterpillars, spray the tree with the Garden Insect Spray with Spinosad and repeat the spraying every two to three weeks. At the same time, place Gypsy Moth Trap around your property, to capture the adult moths before they begin to reproduce.
If the trees are too tall to spray, in the spring treat potentially impacted trees with the Once-A-Year Insecticidal Drench w/Merit to provide protection against the larva and other insects through te full growing season.