Gypsy moth
| Gypsy Moth | |
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| Adult male gypsy moth | |
| Conservation status | |
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Not evaluated (IUCN 3.1)
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| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Class: | Insecta |
| Order: | Lepidoptera |
| Family: | Lymantriidae |
| Genus: | Lymantria |
| Species: | L. dispar |
| Binomial name | |
| Lymantria dispar (Linnaeus, 1758) |
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| Synonyms | |
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The gypsy moth, Lymantria dispar, is a moth in the family Lymantriidae of Eurasian origin. Originally ranging from Europe to Asia, it was introduced to North America in the late 1860s and has been expanding its range ever since. It is also known as the Asian gypsy moth.
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Eggs
Gypsy moth egg masses are typically laid on branches and trunks of trees, but egg masses may be found in any sheltered location. During outbreaks, moths have been known to fly to ships in port and lay their eggs on the ships. Four to six weeks later, embryos develop into larvae.
The egg is the overwintering stage. After an acclimation stage, eggs can withstand freezing temperatures. The longer they are chilled in winter, the less heating is required for their hatch in spring.
Egg clusters are buff colored when first laid but may bleach out over the winter months when exposed to direct sunlight and weathering. As the female lays them, she covers them with hair-like setae from her abdomen. Many individuals find these hairs irritating, and they may offer the eggs some protection. Egg clusters contain from a couple of hundred to about 1,200 eggs, although some batches may be as small as 50 eggs.
Larvae
The hatching of gypsy moth eggs coincides with budding of most hardwood trees. Larvae (caterpillars) emerge from egg masses from early spring through mid-May.
Gypsy moths are dispersed in two ways. Natural dispersal occurs when newly hatched larvae hanging from host trees on silken threads are carried by the wind for a distance of up to about 1 mile, although most go less than 50 meters. Eggs can be carried for longer distances. Artificial dispersal occurs when people transport gypsy moth eggs thousands of miles from infested areas on cars and recreational vehicles, firewood, household goods, and other personal possessions. Females are flightless in most varieties, so these are the only means of spreading.
Larvae develop into adults by going through a series of progressive moults through which they increase in size. Instars are the stages between each molt. Male larvae normally go through five instars (and females, six) before entering the pupal stage. Newly hatched larvae are black with long hair-like setae. Older larvae have five pairs of raised blue spots and six pairs of raised brick-red spots along their backs, and a sprinkling of setae.
During the first three instars, larvae remain in the top branches or crowns of host trees. The first stage or instar chews small holes in the leaves. The second and third instars feed from the outer edge of the leaf toward the center.
When population numbers are sparse, the movement of the larvae up and down the tree coincides with light intensity. Larvae in the fourth instar feed in the top branches or crown at night. When the sun comes up, larvae crawl down the trunk of the tree to rest during daylight hours. Larvae hide under flaps of bark, in crevices, or under branches - any place that provides protection. When larvae hide underneath leaf litter, mice, shrews, and Calosoma beetles can prey on them. At dusk, when the sun sets, larvae climb back up to the top branches of the host tree to feed. When population numbers are dense, however, larvae feed continuously day and night until the foliage of the host tree is stripped. Then they crawl in search of new sources of food.
Full-grown caterpillars are 40–50 mm long (Porter, 1997).
Pupae
The larvae reach maturity between mid-June and early July. They enter the pupal stage. This is the stage during which larvae change into adults or moths. Pupation lasts from 7 to 14 days. When the population is spread out and running low, pupation can take place under flaps of bark, in crevices, under branches, on the ground, and in other places where larvae rested. During periods when population numbers are dense, pupation is not restricted to locations where larvae rested. Pupation will take place in sheltered and non-sheltered locations, even exposed on the trunks of trees or on foliage of nonhost trees. Usually the caterpillars create flimsy cocoons made of silk strands holding the leaf together, while others do not cover their pupae in cocoons, but rather hang from a twig or tree bark, like butterfly pupae do.
Adults
The forewing of the male moth is 20–24 mm long, and that of the female 31–35 mm (Waring et al., 2003).
The brown male gypsy moth emerges first, flying in rapid zigzag patterns searching for females. The male gypsy moths are active throughout night and even daytime as well, unlike most moths, which are only nocturnal. When heavy, black-and-white egg-laden females emerge, they emit a pheromone that attracts the males. After mating, the female lays her eggs in July and August close to the spot where she pupated. Then, both adult gypsy moths die. The European and most Russian forms of the gypsy moth have flightless females. Although they have large wings, the musculature is not developed. However, the Japanese gypsy moth females do fly and are attracted to lights.
Gypsy moths (at least of the introduced American population) fly all day and night, with the possible exception of the late morning. They are most active soon after dusk and in the latter hours of the night (Fullard & Napoleone 2001).
Gypsy moths by country
New Zealand
Gypsy moth eggs are often found on inbound freight in New Zealand and a live moth was found in 2003. A spraying programme was carried out which eradicated the moth.
United States
The gypsy moth was introduced into the United States in 1868 by a French scientist, Leopold Trouvelot, living in Medford, Massachusetts. The native silk spinning caterpillars were proving to be susceptible to disease so Trouvelot brought over gypsy moth eggs to try to make a caterpillar hybrid, that could resist diseases. When some of the moths escaped from his lab, they found suitable habitat and started to multiply. Gypsy moth is now one of the most notorious pests of hardwood trees in the eastern United States.
References
- Barbosa, P. & Greenblatt, J. (1979): Suitability, digestibility and assimilation of various host plants of the gypsy moth Lymantria dispar L. (Lepidoptera, Lymantriidae). Oecologia 43(1): 111-119.
- Barbosa, P.; Waldvogel, M.; Martinat, P. et al. (1983): Developmental and reproductive performance of the gypsy moth, Lymantria dispar (L) (Lepidoptera, Lymantriidae), on selected hosts common to mid-atlantic and southern forests. Environmental Entomology 12(6): 1858-1862.
- Dwyer, G. & Elkinton, J.S. (1993): Using simple-models to predict virus epizootics in gypsy-moth populations. Journal of Animal Ecology 62(1): 1-11.
- Elkinton, J.S.; Healy, W.M.; Buonaccorsi, J.P.; Boettner, G.H.; Hazzard, A.M.; Smith, H.R. & Liebhold, A.M. (1996): Interactions among gypsy moths, white-footed mice, and acorns. Ecology 77(8): 2332-2342.
- Fullard, James H. & Napoleone, Nadia (2001): Diel flight periodicity and the evolution of auditory defences in the Macrolepidoptera. Animal Behaviour 62(2): 349–368. doi:10.1006/anbe.2001.1753 PDF full
- Gansner, D.A.; Herrick, O.W.; Mason, G.N. & Gottschalk, K.W. (1987) Coping with the gypsy moth on new frontiers of infestation. Southern Journal of Applied Forestry Research 11: 201-209.
- Gould, J.R.; Elkinton, J.S. & Wallner, W.E. (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.
- Porter, Jim (1997): The Colour Identification Guide to Caterpillars of the British Isles (Macrolepidoptera). Viking, London. Page 81.
- Rossiter, M.C. (1991): Maternal effects generate variation in life-history - consequences of egg weight plasticity in the gypsy moth. Functional Ecology 5(3): 386-393.
- Waring, P., Townsend, M. and Lewington, R. (2003): Field Guide to the Moths of Great Britain and Ireland. British Wildlife Publishing, Hook, UK. Page 211.
- Weseloh, R.M. & Andreadis, T.G. (1992): Epizootiology of the fungus Entomophaga maimaiga, and its impact on gypsy moth populations. Journal of Invertebrate Pathology 59(2): 133-141.