Gypsy Moth Pupae US Forest Service	Gypsy Moth Larva US Forest Service

Introduction

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.

What do they look like?

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 11 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.

What does it do?

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 with the male moths flying to find the females who are too heavy to fly.  After the females lay their eggs from July to September, depending on location, moths of both sexes then 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.

What tree species are affected?

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.

How Can I Control the Gypsy Moth?

Prevention
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. To prevent the caterpillars from reaching the foliage, use TreeHelp Bug Band.  You should use TreeHelp Bug Band to protect nearby trees as well.

Control
To control gypsy moth infestations, use BTK Biological Insecticide or the newer and more effective Gypsy Moth Traps.

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