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Lymantria dispar

By Aaron Wasserman

Geographic Range

Gypsy moths are native to southern Europe, northern Africa, central and southern Asia, and Japan. They have spread quickly since their introduction to the United States and Canada in 1869, and are especially prevalent in the northeastern United States. ("Lymantria dispar (insect)", 2011; Munson and Hanson, 1981)

Habitat

Gypsy moths are terrestrial animals that are only found in temperate forests or wooded areas (natural or artificial) in which their primary hosts comprise more than 20 percent of the total area. ("Lymantria dispar (insect)", 2011; McManus, et al., 1989)

Physical Description

Adult male gypsy moths are light brown with dark brown wings, which have a series of black bands down their lengths. Male antennae are feathery in texture and appearance. Adult females are slightly larger than males and are mostly white, also with a few dark bands on the wings. Female bodies are covered with tiny hairs and their antennae are thread-like in texture and appearance. Gypsy moths are 15 to 35 mm long on average, with a wingspan of 37 to 62 mm. There are three subspecies, which are European, Asian, and Japanese. Although all three are similar in appearance, Asian gypsy moths tend to have the largest larvae. ("Gypsy Moth", 2009; "Lymantria dispar (insect)", 2011)

Newly hatched larvae are black, hairy caterpillars, and as they age, they grow two rows of blue, then red, spots on their backs. Each spot has a patch of yellow or brown hair growing out of it. Legs of larvae are dark red. ("Gypsy Moth", 2009; "Lymantria dispar (insect)", 2011)

  • Sexual Dimorphism
  • female larger
  • sexes colored or patterned differently
  • Range length
    15 to 35 mm
    0.59 to 1.38 in
  • Range wingspan
    37 to 62 mm
    1.46 to 2.44 in

Development

There are four stages in the metamorphic life cycle of gypsy moths: egg, larva, pupa, and adult. Eggs are laid in July or August, on the trunks or branches of trees. After 4 to 6 weeks, the embryos develop into larvae. These larvae undergo diapause as eggs throughout the winter, and hatch in the spring of the following year, according to the budding cycles of the hardwood trees on which they are laid. As they grow older, larvae pass through a series of molting events, each one resulting in an increase in size. The stages in between molts are called instars. Gypsy moths typically undergo five or six instar stages before they become pupae, which happens in June or July. The pupa stage typically lasts 7 to 14 days. After pupation, males emerge first, usually 1 to 2 days before females. Mating occurs after adult females emerge, and then eggs are laid. Both parents die after the eggs are laid, and the cycle repeats. ("Gypsy Moth", 2009; McManus, et al., 1989)

Reproduction

Mating begins when female gypsy moths release a sex pheromone from their abdominal glands, which attracts males. Mating lasts approximately 30 minutes, and females lay their eggs within 24 hours of mating. Males are polygynous, but females mate with just one male because their pheromones cannot be released if multiple matings occur. ("Gypsy Moth", 2009)

Adult gypsy moths breed once per year, usually in July or August. Females typically lay about 1,000 eggs per breeding season on tree trunks and branches. Although it only takes about one month for larvae to develop inside of the eggs, they usually do not hatch for 8 or 9 months. After hatching, larvae are attracted to light, and move up their host trees by spinning silk threads. They spend much of their lives in tree canopies, until they reach the pupa stage, which is typically spent in a silk net on or near the host tree. After pupation, it only takes about about 2 weeks for adults to form, which is when the next mating cycle occurs. Overall, gypsy moths reach sexual maturity in about 11 months. ("Gypsy Moth", 2009; "Lymantria dispar (insect)", 2011)

  • Breeding interval
    Gypsy moths breed once yearly.
  • Breeding season
    Females lay their eggs in July or August.
  • Average eggs per season
    1,000
  • Average gestation period
    8 months
  • Range time to independence
    8 to 8 weeks
  • Average age at sexual or reproductive maturity (female)
    11 months
  • Average age at sexual or reproductive maturity (male)
    11 months

Adult gypsy moths only live long enough to ensure that the female's eggs are successfully laid on host tree trunks and branches. The female lays her eggs close to the spot where she pupated. Once the eggs are secure on the trees, both of the parents die. When the larvae hatch from their eggs, they are left to fend for themselves. (McManus, et al., 1989)

  • Parental Investment
  • female parental care
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female

Lifespan/Longevity

Gypsy moths are seasonal breeders, laying eggs approximately once per year. Therefore, life expectancy is 12 months. The egg stage lasts for approximately 8 to 9 months. Gypsy moth larvae live for about 2 to 3 months before entering the pupa stage, which lasts for approximately 2 weeks. Adults live for about 1 week before they lay new eggs. ("Gypsy Moth", 2009)

  • Average lifespan
    Status: wild
    12 months

Behavior

Gypsy moths remain on the same host tree throughout the instar stages. During the first three instars, they remain in the crowns of trees. During the last two or three instars, they crawl up and down the tree depending on the daylight cycle. At night, they feed on the leaves in the canopies. During the day, they crawl down the trunk in order to rest under bark or branches. Being closer to the ground makes them more vulnerable to predation. They will only leave their trees if they are dispersed by an outside force, such as wind. ("Lymantria dispar (insect)", 2011; McManus, et al., 1989; Munson and Hanson, 1981)

Pupae remain on the same host tree as the larvae, and can be exposed to or protected from predators depending on where they pupate. Once adult males emerge, they fly in zigzag patterns throughout the forest looking for females. Once females emerge, they emit pheromones that attract males, who will come to their host trees to mate with them. ("Lymantria dispar (insect)", 2011; McManus, et al., 1989; Munson and Hanson, 1981)

Although gypsy moths tend to remain in host trees for most of their lives, they are able to fly, as well as be transported by humans. Colonies typically move from place to place when they are in search of new forests to defoliate. Two of the subspecies differ in terms of their ability to fly. Asian gypsy moths are able to fly long distances, and can spread very quickly. European gypsy moths are incapable of flight, and therefore, take a long time to spread. Gypsy moth eggs can be inadvertently transported on vehicles, forest equipment, shipping containers, and lawn furniture. Larvae can also crawl or attach themselves to travelers and their possessions in order to move short distances. In addition, they can travel to the tops of trees, and allow the wind to carry them over great distances. ("Lymantria dispar (insect)", 2011; McManus, et al., 1989; Munson and Hanson, 1981)

Home Range

Gypsy moth larvae and pupae stay on the host tree where they hatched. Adults fly to different trees in order to mate. The exact size of their territories is not known. (McManus, et al., 1989)

Communication and Perception

Gypsy moths, like most other insects, perceive their environment by sight and tactile organs like legs and wings. In addition, gypsy moth larvae are able to perceive ultraviolet light from the sun. After they hatch from their eggs, they are attracted to this light and can move up their host trees. Eventually, they end up in the canopies, where they can be dispersed by wind. ("Gypsy Moth", 2009)

One way in which gypsy moths communicate with each other is by the use of chemical sex pheromones, which are released by the female abdominal glands in order to attract males. The pheromone released by female moths is known as disparlure (cis-7,8-epoxy-w-methyloctadecane). Sufficient research about its structure and function has been performed in order to allow it to now be synthesized in laboratories. ("Gypsy Moth", 2009)

Food Habits

Gypsy moths are herbivores that feed on the leaves of over 500 species of trees and shrubs. Their preferred sources of food are oak (Quercus), alber broadleaf trees (Alnus rubra), Douglas fir (Pseudotsuga), and western hemlock needle trees (Tsuga heterophylla). Because adults do not have fully-developed mouthparts, larvae are the only life forms that feed on their hosts. ("Gypsy Moth", 2009; "Lymantria dispar (insect)", 2011)

  • Plant Foods
  • leaves

Predation

When population numbers are low, gypsy moths have many natural predators. Some of these include wasps (Hymenoptera), flies (Diptera), ground beetles (Carabidae), ants (Formicidae), and spiders (Araneae). Birds like chickadees (Paridae), bluejays (Cyanocitta cristata), nuthatches (Sitta), towhees (Pipilo), and robins (Turdus) also consume and compete with them. In addition, mammals such as white-footed mice (Peromyscus leucopus), shrews (Soricidae), chipmunks (Tamias), squirrels (Sciuridae), and raccoons (Procyon lotor) are considered predators. When population numbers are high, additional predators are attracted to densely populated areas of gypsy moths. These include Calosoma beetles (Calosoma semilaeve), cuckoos (Cuculidae), starling grackles (Onychognathus tristramii), and red-winged blackbirds (Agelaius phoeniceus). (McManus, et al., 1989)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

Gypsy moths are defoliators of trees and forests. They are dependent on host trees for survival, and increased dependency results in increased defoliation. The preferred host for the moths is oak trees (Quercus), but most species of trees (especially hardwoods) and shrubs are inhabited. However, they are not found on ash trees (Fraxinus), tulip poplars (Liriodendron tulipifera), or sycamore trees (Platanus), and rarely found on black walnut trees (Juglans nigra). ("Gypsy Moth", 2009; "Lymantria dispar (insect)", 2011; McManus, et al., 1989; Munson and Hanson, 1981)

When gypsy moths continuously feed in one area, outbreaks can occur in four-phase population cycles. The innocuous phase is characterized by very low population levels, and can last for multiple years. The release phase lasts 1 to 2 years and results in rapid increases of moths. Next, the outbreak phase leads to high levels of tree defoliation for 1 to 2 years. Finally, starvation and disease lead to the decline phase, and population levels drop back to those of the innocuous phase. ("Gypsy Moth", 2009; "Lymantria dispar (insect)", 2011; McManus, et al., 1989; Munson and Hanson, 1981)

Gypsy moth populations are also subject to disease. Wilt disease, caused by the nucleopolyhedrosis (NPV) virus, kills moths in both the larva and pupa stages. It is the most harmful natural disease of gypsy moths. (McManus, et al., 1989)

Species Used as Host
  • Several hundred species of trees and shrubs are used as hosts by gypsy moths.

Economic Importance for Humans: Positive

Gypsy moth defoliation can benefit humans by opening up forest canopies and by reducing overcrowding of trees on homeowner's properties. ("Lymantria dispar (insect)", 2011)

Economic Importance for Humans: Negative

Gypsy moths are notorious for their ability to defoliate almost any kind of tree. If more than 50 percent of the crown of a tree is destroyed, it will probably die. Some hardwoods can survive one or two defoliation events, but additional ones are usually fatal. Gypsy moth defoliation is harmful because the process of refoliation involves a heavy consumption of energy by the rebuilding tree. In addition, weakened trees are more susceptible to attack by viruses and parasitic insects. ("Gypsy Moth", 2009; "Lymantria dispar (insect)", 2011; McManus, et al., 1989)

Extreme defoliation leads to lost revenue due to lack of timber harvesting, cost of dead tree removal, and decreased property values in certain areas. In addition, defoliation eventually leads to deforestation, which can lead to flooding and loss of biodiversity. It is estimated that gypsy moths have destroyed 30 million hectares of forest in the United States since 1970, and this damage costs the forest industry millions of dollars per year. Unfortunately, the defoliation is getting worse over time. Gypsy moths already cover most of the eastern United States, and spread anywhere from 3 to 10 miles per year. At this rate of dispersal, they are expected to cover half of the entire United States by 2015. Finally, gypsy moths can also have direct impacts on humans. Some people are allergic to the hairs found on larvae, and exposure can lead to unpleasant side-effects. ("Gypsy Moth", 2009; "Lymantria dispar (insect)", 2011; McManus, et al., 1989)

  • Negative Impacts
  • crop pest

Conservation Status

Gypsy moths are not endangered, vulnerable, or threatened. In fact, they are such major pests that there are extensive efforts to eradicate populations from parts of North America. Programs have been created to trap adults and larvae, destroy egg masses, and apply insecticides to locations where the moths are major defoliators. ("Gypsy Moth", 2009)

Contributors

Aaron Wasserman (author), University of Michigan-Ann Arbor, Catherine Kent (editor), Special Projects.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

Palearctic

living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

World Map

arboreal

Referring to an animal that lives in trees; tree-climbing.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

chemical

uses smells or other chemicals to communicate

colonial

used loosely to describe any group of organisms living together or in close proximity to each other - for example nesting shorebirds that live in large colonies. More specifically refers to a group of organisms in which members act as specialized subunits (a continuous, modular society) - as in clonal organisms.

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

diapause

a period of time when growth or development is suspended in insects and other invertebrates, it can usually only be ended the appropriate environmental stimulus.

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

female parental care

parental care is carried out by females

folivore

an animal that mainly eats leaves.

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

herbivore

An animal that eats mainly plants or parts of plants.

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

holarctic

a distribution that more or less circles the Arctic, so occurring in both the Nearctic and Palearctic biogeographic regions.

World Map

Found in northern North America and northern Europe or Asia.

introduced

referring to animal species that have been transported to and established populations in regions outside of their natural range, usually through human action.

metamorphosis

A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

oriental

found in the oriental region of the world. In other words, India and southeast Asia.

World Map

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

pheromones

chemicals released into air or water that are detected by and responded to by other animals of the same species

polygynous

having more than one female as a mate at one time

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

semelparous

offspring are all produced in a single group (litter, clutch, etc.), after which the parent usually dies. Semelparous organisms often only live through a single season/year (or other periodic change in conditions) but may live for many seasons. In both cases reproduction occurs as a single investment of energy in offspring, with no future chance for investment in reproduction.

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

suburban

living in residential areas on the outskirts of large cities or towns.

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

urban

living in cities and large towns, landscapes dominated by human structures and activity.

visual

uses sight to communicate

References

United States Department of Agriculture. Diseases of the gypsy moth: How they help to regulate populations. 539. Washington, D.C.: Agriculture Handbook. 1979.

United States Department of the Interior National Park Service. Gypsy Moth. 2. Washington, D.C.: Integrated Pest Management Manual. 2009.

National Biological Information Infrastructure (NBII) and IUCN/SSC Invasive Species Specialist Group (ISSG). Lymantria dispar (insect). 49. Baltimore: Global Invasive Species Database. 2011.

United States Department of Agriculture. The homeowner and the gypsy moth: Guidelines for control. 227. Washington, D.C.: Home and Garden Bulletin. 1979.

Barbosa, P., J. Greenblatt. 1979. Suitability, digestibility and assimilation of various host plants of the gypsy moth Lymantria dispar L.. Oecologia, 43/1: 111-119.

Elkinton, J., W. Healy, J. Buonaccorsi, G. Boettner, A. Hazzard, H. Smith, A. Liebhold. 1996. Interactions among gypsy moths, white-footed mice, and acorns. Ecology, 77/8: 2332-2342.

Gould, J., J. Elkinton, W. Wallner. 1990. Density-dependent suppression of experimentally created gypsy moth, Lymantria dispar (Lepidoptera, Lymantriidae), populations by natural enemies. Journal of Animal Ecology, 59/1: 213-233.

Hajek, A., P. Tobin. 2009. North American Eradications of Asian and European Gypsy Moth. Dordrecht, Netherlands: Springer.

Jones, C., R. Ostfeld, M. Richard, E. Schauber, J. Wolff. 1998. Chain reactions linking acorns to gypsy moth outbreaks and Lyme disease risk. Science, 279/5353: 1023-1026.

Liebhold, A., J. Halverson, G. Elmes. 1992. Gypsy moth invasion in North America — a quantitative analysis. Journal of Biogeography, 19/5: 513-520.

McManus, M., N. Schneeberger, R. Reardon, G. Mason. 1989. Forest Insect and Disease: Gypsy Moth. Washington, D.C.: United States Department of Agriculture Forest Service.

Munson, A., J. Hanson. 1981. Pest Alert: Gypsy Moth. St. Paul, MN: United States Department of Agriculture Forest Service.

Redman, A., J. Scriber. 2000. Competition between the gypsy moth, Lymantria dispar, and the northern tiger swallowtail, Papilio canadensis: interactions mediated by host plant chemistry, pathogens, and parasitoids. Oecologia, 125/2: 218-228.

Reineke, A., C. Zebitz. 1998. Flight ability of gypsy moth females (Lymantria dispar L.) (Lep., Lymantriidae): A behavioural feature characterizing moths from Asia?. Journal of Applied Entomology, 122/6: 307-310.

Roden, D., W. Mattson. 2008. Rapid induced resistance and host species effects on gypsy moth, Lymantria dispar (L.): Implications for outbreaks on three tree species in the boreal forest. Forest Ecology and Management, 255/5-6: 1868-1873.

Rossiter, M. 1991. Maternal effects generate variation in life-history - consequences of egg weight plasticity in the gypsy moth. Functional Ecology, 5/3: 386-393.

Timms, L., S. Smith. 2011. Effects of gypsy moth establishment and dominance in native caterpillar communities of northern oak forests. Canadian Entomologist, 143/5: 479-503.

Work, T., D. McCullough. 2000. Lepidopteran communities in two forest ecosystems during the first gypsy moth outbreaks in northern Michigan. Environmental Entomology, 29/5: 884-900.

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