Lymantria dispar (Linnaeus)
GENERALLymantria dispar, the gypsy moth, is one of North America's most devastating forest pests. Etienne Leopold Trouvelot in 1868 accidentally introduced the gypsy moth, a native specie of Europe and Asia, into the USA. By the 20th century, the gypsy moth has spread over 20 states from its introductory state Massachusetts. In 1932 in Pennsylvania, the first gypsy moths were detected in Luzerne and Lackawanna Counties. By the 1980's, the infestation advanced into Centre, Blair, Huntingdon and Clearfield Counties. Ever since then, heavy defoliation has occurred along the mountain ridges. Several successive years of defoliation on plants result in mortality of the plants.
Most of the yearly cycle of gypsy moth is spent in the egg stage. The life cycle consists of the egg, larva (caterpillar), pupa, and moth. Female gypsy moths lay their eggs in large clumps called egg masses in July. The egg masses are covered by a dense coating of hairs from the abdomen of the female. As a result, the egg mass in the late summer and early fall appears to be a dark tan to light brown but as the egg mass weathers, later it looks light tan to gray in color. Each egg mass is around 0.5-1 inch long and contains between 500 to 1,000 eggs.
Eggs begin to hatch in late April through early May. The larvae of gypsy moth develop in stages known as instars. The male goes through five instars and the female six. First instars larvae that emerge from the eggs are mostly black and about 1/8 inch in length. The young caterpillars spin long silk threads and are covered with long buoyant hairs that are caught and carried by the wind. This method aids the caterpillars to disperse into new locations in search of food. Young larva feeds night and day.
Fifth and sixth instar larvae are about 2 inches long and are the most voracious feeders of any growth stages of the gypsy moth. These feed only during the night and seek shelter during the day in bark crevices or other protected sites. Late instar larvae develop five pairs of blue dots and six pairs of red dots along their backs. Larvae feeders are most active from May to July. The larva (caterpillar) stage for gypsy moth lasts for about 40 days.
Pupation takes place in mid June to early July. They remain in this stage for 7 - 10 days and emerging as adult moths. Pupae are 3/4 - 1 1/2 inches in length and attach to tree bark, stones, buildings and other similar sites. Adult moths emerge mid July through mid August. Adult moths do not feed and may live for only a few days to several weeks. Females are larger than the males and have a white to cream color, and the males are dark brown.
Female Gypsy Moth Male Gypsy Moth
Tree damage is caused by larva (caterpillar), which feeds on the foliage of the plant. Depending on the density of the population, larva may cause tree defoliation. Defoliation makes trees more vulnerable to disease organisms and other insects. Affected trees will eventually die after 2 - 3 years. A series of successive defoliation results in the death of the tree. This in long term may result in deforestation and affects in weather changes. Since 1980, the gypsy moth has defoliated over 1,000,000 acres (4,000 km2 ) of forest each year. In 1981, a record 12,900,000 acres (52,200 km2 ) were defoliated. This is an area larger than Rhode Island, Massachusetts, and Connecticut combined.
Clusters of trees killed following gypsy moth defoliation in central Pennsylvania
Gypsy moth larvae prefer hardwoods, but may feed on several hundred different species of trees and shrubs. Some of which include; oaks, apple, sweet gum, speckled alder, basswood, gray and white birch, poplar, willow, and hawthorn.
Some of the trees they avoid are ash, yellow poplar, sycamore, butternut, black walnut, catalpa, flowering dogwood, balsam fir, red cedar, American holly, and shrubs such as mountain laurel, rhododendron, and arborvitae. This list may change with the availability of preferred plants.
Temperatures below minus 20°F or colder during the winter will destroy exposed eggs. Freezing temperatures in May may kill many larva (caterpillars).
Natural enemies include parasitic and predatory insects such as wasps, flies, ground beetles, and ants; many species of spiders; several species of birds such as chickadees, bluejays, nuthatches, towhees, and robins; and approximately 15 species of common woodland mammals, such as the white-footed mouse, shrews, chipmunks, squirrels, and raccoons. These play an important role during periods when gypsy moth populations are sparse.
Diseases caused by bacteria, fungi, or viruses contribute to the decline of gypsy moth populations, especially during periods when gypsy moth populations are dense and are stressed by lack of preferred foliage.
Wilt disease caused by the nucleopolyhedrosis virus (NPV) is specific to the gypsy moth and is the most devastating of the natural diseases. NPV causes a dramatic collapse of outbreak populations by killing both the larvae and pupae. Larvae infected with wilt disease are shiny and hang limply in an inverted "V" position. It is suggested to leave dead infected larva in this position to help the spread of the virus to other larva.
Figure: Larvae infected by the nucleopolyhedrosis virus (NPV) hanging in an inverted "V" position
There are several ways to control the population of gypsy moth without applying chemicals. Some of these include:
Duct Tape and Tanglefoot
Wrap duct tape on a tree trunk at about chest height from the ground and smear tanglefoot, a very sticky substance in the center of the tape. When gypsy moth larva tries to climb the tree, they will get stuck to the tape. One can remove the tape with the moth or remove the moth from the tape and destroy them by placing them in a solution of water and dishwashing detergent. Do not apply tanglefoot directly to the tree, because it may damage the tree.
Burlap Folded Strips
Older gypsy moth larva feeds during the night and hides during the day. Burlap makes the perfect hiding place. Wrap the burlap at about chest height on a tree trunk and during the evening lift up the burlap and collect all larvae and put them in a solution of water and detergent. This will kill them. Repeat this process until the population seems to decline.
Gypsy Moth Trap
When gypsy moth reach the moth stage, the males can be trapped using a gypsy moth trap. The traps contain a bait inside their lid that smells like female gypsy moth pheromone, attracting males. Once the male gets into the trap they can not come out and they slowly die in the trap. This prevents the males from mating with the females, decreasing the number of eggs fertilized. As a result the next generation there will be fewer gypsy moths.
Destroy Egg Masses
The Gypsy moth spends most of its yearly cycle in egg stage. These eggs could be found attached to tree bark. Scrape the eggs off the bark and place them in a solution of water and detergent for about 24 hours. This eliminates hundreds and thousands of larva from hatching and eating the tree leaves.
Encourage birds to visit
Many birds prey on gypsy moth larva and birds feeding on the larva naturally decrease the population of gypsy moth. Place water and other bird attractive supplies around the property that will help birds come onto the property and prey on these pests.
Microbial and Biological Pesticides
Microbial and Biological pesticides contain living organisms that must be consumed by the Gypsy Larva. Microbials include bacteria, viruses, and other naturally occurring organisms; Biologicals includes manmade synthetics of naturally occurring organisms. These pesticides should be applied before the larvae reach the third stage of instar development. As they mature, larvae become more resistant to microbial pesticides and are, therefore, more difficult to kill. Example of the Microbial and Biological Pesticide is,
Dipel Thuricide - containing the active ingredient Bacillus thuringiensis (BT), is registered for aerial and ground application. It is available under a variety of trade names and is toxic to other moth and butterfly larvae. It can be used safely near water.
There are a variety chemicals that could be sprayed for effective management of Gypsy moth. This method is recommended for those with a very large population of infections. Applications should be made according to label directions after the majority of eggs have hatched during early to mid-May when larvae are small. Make sure small larvae have dispersed and they have begun to feed causing the characteristic shothole injury to host plant foliage. To maintain good plant health, applications should be made before serious defoliation occurs. Examples of some chemicals are:
Orthene-Registered for aerial and ground application, it is available under a variety of trade names. It's known to be toxic to bees and some gypsy moth parasites and is commonly used from the ground to treat individual trees.
Sevin-Registered for aerial and ground application and can be found under a variety of trade names. This chemical is known to be toxic to bees and gypsy moth parasites. At one time, it was the most widely used chemical in gypsy moth control programs.
Dimilin-A restricted-use pesticide that can be applied only by certified applicators. The same applies for other restricted chemicals.
Pesticides are poisonous. Read and follow directions and safety precautions on labels. Handle carefully and store in original labeled containers out of the reach of children, pets, and livestock. Dispose of empty containers right away, in a safe manner and place. Do not contaminate foliage, streams, or ponds.
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