Control Gypsy Moths

Gypsy Moth Caterpillar

Gypsy moth larvae eating leaves.
Gypsy moth larvae eating leaves. | Source

Gypsy Moth Control Overview

The gypsy moth, Lymantria dispar, is one of North America's most devastating pests. The insect originated in Europe and Asia and has existed in those regions for a very long time. The gypsy moth was accidentally introduced into the U.S. around the New England area during the mid 1800s. The larvae can defoliate and kill trees if infestations are large and reoccurring. The damage caused since its introduction has been severe and control is somewhat limited. Damage reduction is key, but elimination is nearly impossible by now.

Understanding and recognizing the stages of the gypsy moth metamorphosis allows for better control. Traps, pesticides, natural resistances, and natural predators can reduce damage done to trees. Homemade traps can be assembled quite easily and are used to trap and larvae. Pesticide applications and other biological controls can be used to decrease the population within a certain area. Each method needs to be carefully considered and applied correctly.

Gypsy Moth Lifecycle

Adult Stage
The moth is the adult stage of the insect. The moth cannot feed and only lives long enough to mate and lay eggs.The male moth is capable of flight but the female is not. The female moth lays her eggs in masses of 600 to 1000 eggs.

Egg Stage
The mass is then covered with tiny hairs from the body of the female moth. The hairs give the mass a fuzzy appearance that is very distinct and easy to recognize. The eggs hatch in spring and the destructive caterpillars begin their quest into the treetops for food.

Larval Stage
The caterpillars hatch from the eggs in mid-May. They feed in the tree tops, but crawl down onto the ground every afternoon starting in June to hide from predators. The caterpillars return to the tree tops in the evening to begin feeding again. Pairs of colored dots are on the center of the caterpillars back. Red dots are towards the back end and blue dots are towards the head. Bristly hair covers the whole body of the caterpillar and may cause rashes to appear by those who handle the caterpillars with bare hands.

Pupal Stage
The pupal stage of the gypsy moth begins in late July and lasts until August. The caterpillars enter this stage after they have grown about an inch long. The caterpillar finds a suitable area and begins to shed its skin. The new skin forms into a hardened dark brown shell. The pupa is immobile for a week or two before emerging as an adult moth capable of reproduction.

Gypsy Moth Lifecycle

Gypsy moth lifecycle
Gypsy moth lifecycle | Source

Parasitic Wasp

Parasitic wasp laying eggs on gypsy moth larva.
Parasitic wasp laying eggs on gypsy moth larva. | Source

Natural Resistances and Predators

Cultural Resistances
Proper cultural practices such as watering and fertilizing helps build resistance to Gypsy moth feeding and other types of damage. A healthy tree may be able to withstand several outbreaks, but unhealthy trees may be killed after a single outbreak. Healthy trees are not a preventative measure against gypsy moth caterpillars, but outbreak reduction is key.

Gypsy Moth Predators
Some small mammals, birds, and insects may prey upon gypsy moth caterpillars. These types of predators usually do not severely impact the population due to the sheer numbers of gypsy moths and larvae during outbreaks. Parasitic wasps are becoming established in some regions and are effective against the caterpillars of gypsy moths. The wasps lay eggs on the caterpillars in order to reproduce. The eggs grow and begin to feed on the body of the caterpillars, eventually killing the caterpillars.

Plastic Bug Band

Gypsy Moth Caterpillar Traps

Barrier Bands
Barrier bands are sticky and entangle or deter caterpillars from moving upwards into the foliage. Caterpillars that have traveled to the top of trees will travel back to ground during the afternoon, and they often fall and will need to ascend back up the tree. The barrier bands will help prevent fallen caterpillars from traversing back into the foliage.

Barrier bands can be made using duct tape and sticky pest barrier material that is available in garden centers. Wrap a broad band of duct tape a foot or so from the base of the tree. Cover the tape with sticky pest barrier material. Do not apply the sticky material directly onto the tree. Place the sticky bands in April and remove in August when burlap collection bands are applied.

Collection Bands
Wrapping burlap or cloth near the base of trees will trap females as they look for a place to lay eggs. Bands should be applied before June and July. The caterpillars will travel down the trunk during the day to hide from predators. The bands provide hiding and collection of caterpillars is easy.

  1. Cut a strip of material that is 12 to 18 inches wise and long enough to wrap around the tree.
  2. Wrap the material at chest height, which is usually a few feet up the trunk.
  3. Tie string or twine 6 inches from the top edge.
  4. Let the material above the string flop and overlap itself. This will form a double tiered skirt for the caterpillars to hide in.
  5. Check the bands daily in mid-afternoon and around 6 P.M. Use a knife or stick to flick the caterpillars into soapy water. Handling the caterpillars with bare hands may cause a rash!
  6. Throw the caterpillars in the trash once they have died.

Female gypsy moth laying egg mass
Female gypsy moth laying egg mass | Source

Destroy Gypsy Moth Eggs

Killing egg masses is the most effective physical method of gypsy moth caterpillar control. It is also the best method to ensure an effective kill of future outbreaks. Each egg mass can contain between 600 to 1,000 future caterpillars. Egg masses are often found in cracks, nooks, and crannies in nature and in man-made structures. Loose bark, playground equipment, and shutters are examples of ideal hiding places for gypsy moth egg masses. Check and eradicate egg masses in August to prevent outbreaks when spring arrives.

Kill Egg Masses with Oil Sprays
Egg masses can be sprayed with horticultural oils designed to prevent eggs from hatching. These oils penetrate the egg mass and prevent gases from being exchanged which ultimately suffocates the eggs.

Remove Eggs by Hand
Remove egg masses by scraping them off trees and dropping them into a solution of soapy water for a day or so. This suffocates the eggs just like oil applications. Do not throw the egg masses onto the ground or back into nature. The eggs still have a possibility of hatching when spring arrives, so throw them in the garbage instead.

Diverse Plantings

Variety within a landscape will prevent total losses if infestations are massive. Lots of trees that are predominantly oak can suffer heavy damage from gypsy moth caterpillars. Increasing the amount of trees that are undesirable to the caterpillars such as maple and ash will reduce caterpillar damage in wooded areas.

Susceptible Trees
Gypsy moth larvae prefer some trees over others. Oaks, aspens, willow, apple, crabapple, tamarack paper birch, witch hazel, mountain ash, basswood, and linden are susceptible to gypsy moth caterpillars.

Prevent Gypsy Moth Hitch-Hiking

Gypsy moths often relocate to new locations via outdoor materials like firewood, camping materials, boats, campers, and other outdoor equipment. The egg stages are the most apt to be carried to a new location. Inspect outdoor equipment in late fall and early spring before moving the equipment. This type of control is used to help slow emerald ash borer as well. Use firewood native to the site instead of traveling with firewood from a distant location.

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