The USDA has a coordinated Federal-state program to control populations and limit at least the human propagated spread of the Gypsy moth from currently quarantined states into new areas. The Gypsy Moth quarantine currently includes the District of Columbia and the entire states of Connecticut, Delaware, Maryland, Massachusetts, Michigan, New Hampshire, New Jersey, New York, Pennsylvania, Rhode Island and Vermont. As well as spreading in concert with humans, populations can naturally spread by female moths flying to uninfested areas, or at the larval (caterpillar) stage, which are carried on the wind by their silk threads.
The government has developed another interesting control program which sprays effected areas with an engineered baculovirus, which is very effective in killing the caterpillars. The baculovirus works by changing the nocturnally-feeding caterpillars behavior, so that they remain high in the forest canopy instead of their usual return to daytime hiding places on the ground. When the virus then kills the caterpillar, the caterpillar's flesh dissolves and the virus rains down from the top of the tree and is widely spread to other caterpillars below.
The asian subspecies of Lymantria dispar, although similar to the European subspecies described above, has never become established in North America. Because it is a stronger flier than the European subspecies, and presumably could quickly spread throughout the US, it is considered a major threat and carefully monitored at likely entry pathways.
(Aphis-USDA 2003; Aphis-USDA 2011; Hamilton, 2011; Hoover et al. 2011; Liebhold 2003; McManus et al 1989)
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.
Biogeographic Regions: nearctic (Introduced ); palearctic (Native ); oriental (Native )
Other Geographic Terms: holarctic
- Munson, A., J. Hanson. 1981. Pest Alert: Gypsy Moth. St. Paul, MN: United States Department of Agriculture Forest Service.
- National Biological Information Infrastructure (NBII) and IUCN/SSC Invasive Species Specialist Group (ISSG). Lymantria dispar (insect). 49. Baltimore: Global Invasive Species Database. 2011.
Regularity: Regularly occurring
Type of Residency: Year-round
Regularity: Regularly occurring
Type of Residency: Year-round
Global Range: The gypsy moth is native to a vast area of Eurasia. The established North American population originated from near Paris, France. Introduction was at Medford, Massachusetts in 1869 (Ferguson, 1978). The North American range expands annually and maps showing generally infested areas are usually readily available from USFS. A map in Appendix G of the 1995 FEIS shows the predicted range as of 2010 within the USA to extend from northeastern South Carolina across eastern Kentucky and much of Indiana into eastern Illinois and eastern Wisconsin. If anything the advance may be running ahead of prediction at least northward. Spot introductions by human transport can occur almost anywhere in temperate North America. The eventual range of the gypsy moth in North America will almost certainly be all climatically suitable forested regions of southern Canada and virtually the entire eastern and central USA and probably much of the West.
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.
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.
Range length: 15 to 35 mm.
Range wingspan: 37 to 62 mm.
Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry
Sexual Dimorphism: female larger; sexes colored or patterned differently
- United States Department of the Interior National Park Service. Gypsy Moth. 2. Washington, D.C.: Integrated Pest Management Manual. 2009.
All stages are very easily recognized. There are probably hundreds of useful pamphlets etc. easily available from the U.S. Forest Service, state agencies or county extension agents in regions where gypsy moth is a concern, as well as websites. The Field Guide to Moths (Covell, 1984) also has good illustrations of adults and larvae. Given the extensive information available, identification should never be a problem.
The details of the markings are very diagnostic: the combination of blue thoracic and red abdominal dots is distinctive to the gypsy moth larva at least in North America. Also note that the head of late instar gypsy moth larvae is contrastingly paler than the body, with very prominent hair tufts immediately behind it. Head markings on older larvae are unique. No stage of the gypsy moth is similar to any other North American moth. There are of course other dark hairy caterpillars, but all differ greatly in details. The appearance of both sexes of the adults is unmistakable. No other such large egg masses have the dense fuzzy covering, although the much smaller egg masses of some tussock moths that (unlike gypsy moth eggs) are laid on the female's cocoon (usually on an old leaf), may have some hair.
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.
Habitat Regions: temperate ; terrestrial
Terrestrial Biomes: forest
Other Habitat Features: urban ; suburban
- 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.
Comments: Almost any natural or artificial situation with woody vegetation and a temperate climate can support gypsy moths, but outbreaks rarely occur except in forests where oaks (or other favorite food plants) comprise at least 15 to 25% of the stand (Nichols, 1980), usually higher. Forests comprised of over 50% oaks are especially susceptible to defoliation. The 1995 FEIS regards oak-hickory and oak-pine forest types as the most vulnerable and northern hardwoods as essentially the only immune type in most of the USA. Spruce-fir forests and others that are nearly pure conifers are also immune to the currently established European strain but the Asian gypsy moth is better adapted to conifers. Some immune types such as northern hardwoods support persistent populations but not outbreaks. Oak forests in New England, Pennsylvania and elsewhere were often nearly 100% defoliated for at least one season during the course of each gypsy moth population cycle in the mid and late 20th century and in some cases going back 100 years. In general, the degree of defoliation in peak years is directly correlated with the percentage of oaks and other highly favored species in a stand. Some good early discussions include Gerardi and Grimm (1979) and Mason, and Hicks and Fosbroke, both in Fosbroke and Hicks (1987) but usually the information in the 1995 FEIS or below should suffice. The larvae can feed on over 500 species of plants but avoid most herbs. While one sees statements to the contrary, there are many plant species including trees and shrubs that gypsy moth larvae never or rarely eat. Private operators commonly spray trees for gypsy moth control which the larvae do not normally, or never (e.g. tulip tree), eat.
The following is a summary of the suitability of common trees and shrubs based mostly on the 1995 FEIS, Nichols (1980) and observations by this author (Dale Schweitzer). In general oaks are the most important food plants, with white oaks slightly favored. Other highly favored species include mockernut hickory (Schweitzer), aspens, willows, some birches, basswood, Malus spp., most hawthorns and witch hazel. These will probably be severely defoliated if oaks are. Others that are readily eaten at least by older larvae when they are growing with oaks include beech, sweetgum, most hickories, hemlocks, and blueberries. These and some others like red and sugar maples, white pine, or rarely flowering dogwood may be defoliated in severe outbreaks when growing with oaks. First instars strongly avoid it but older larvae sometimes defoliate sweetgum. Some forest species that will not be defoliated even in severe outbreaks include true ashes, tulip tree, sycamore, magnolias, persimmons, cedars, balsam firs, bald cypress, Lonicera spp., redbud, mountain laurel, some clones of poison ivy. Most, but not all, of these are completely avoided even by starving last instars but the 1995 FEIS Appendix G pages 2-4 suggests some of these may be eaten in extreme circumstances. Black huckleberry at least usually escapes heavy damage.
Appendix D of the 1995 FEIS ranks hundreds of species as susceptible, resistant or immune. Coverage is weak for Ericaceae and some other understory groups but very thorough for trees. Carya ovata and Pinus rigida should be changed from immune to resistant like their congeners. Various sources including the 1995 FEIS Appendix G note defoliation and sometimes mortality of hickories. C. ovata growing with oaks were severely defoliated widely in New Haven County, Connecticut in June 1981. Ridgetop P. rigida can be killed (Schweitzer, pers. obs.; Quimby, 1985). In most other situations though pitch pine is at low risk, e.g., in sandy coastal pinelands. White pine is much more often defoliated than other pines.
So while virtually any kind of woodland, shaded park, backyard, or forest is potential gypsy moth habitat, not all such habitats are at risk for outbreaks. In general risk of heavy defoliation is high in wooded area composed of 50% or more oaks or other highly favored trees. It is in these habitats where gypsy moth outbreaks and efforts to control them are most likely to be potential long-term ecological concerns to biodiversity-oriented managers.
Non-Migrant: No. All populations of this species make significant seasonal migrations.
Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).
Locally Migrant: No. No populations of this species make annual migrations of over 200 km.
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.
Plant Foods: leaves
Primary Diet: herbivore (Folivore )
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).
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 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.
Species Used as Host:
- Several hundred species of trees and shrubs are used as hosts by gypsy moths.
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).
- wasps (Hymenoptera)
- flies (Diptera)
- ground beetles (Carabidae)
- ants (Formicidae)
- spiders (Araneae)
- chickadees (Paridae)
- bluejays (Cyanocitta cristata)
- nuthatches (Sitta)
- towhees (Pipilo)
- robins (Turdus)
- white-footed mice (Peromyscus leucopus)
- shrews (Soricidae)
- chipmunks (Tamias)
- squirrels (Sciuridae)
- raccoons (Procyon lotor)
- Calosoma beetles (Calosoma semilaeve)
- cuckoos (Cuculidae)
- starling grackles (Onychognathus tristramii)
- red-winged blackbirds (Agelaius phoeniceus)
Anti-predator Adaptations: cryptic
larva of Eurithia connivens is endoparasitoid of larva of Lymantria dispar
Animal / parasitoid / endoparasitoid
larva of Eurithia consobrina is endoparasitoid of larva of Lymantria dispar
Animal / parasitoid / endoparasitoid
larva of Parasetigena silvestris is endoparasitoid of larva of Lymantria dispar
Animal / parasitoid / endoparasitoid
larva of Tachina grossa is endoparasitoid of larva of Lymantria dispar
Animal / parasitoid / endoparasitoid
larva of Thelymorpha marmorata is endoparasitoid of larva of Lymantria dispar
POPULATION AND POPULATION CYCLES: Established gypsy moth populations remain low for varying periods of time, sometimes permanently. During this phase, predators including especially native mice (Peromyscus spp.) among other vertebrates and invertebrates, as well as native and introduced parasitoids (Diptera, Hymenoptera) exert some degree of control (e.g. Doane and McManus, 1981, Nichols, 1980, FEIS, 1995, Weseloh, 1985, Weseloh et al., 1983) and numerous other publications). Introduced predatory beetles (Calosoma) tend to have more impact at higher densities. Despite predators and parasitoids, populations in vulnerable forest types can increase to a point where natural enemies no longer exert effective control. Populations then build up within about three years to outbreak levels. In peak years of severe outbreaks in oak dominated forests 100% defoliation of all favored to moderately resistant trees often occurs. White oaks and other highly favored species may incur substantial defoliation the year before the general outbreak. Severe defoliation generally occurs for one or two seasons followed by a crash. Occasionally populations will fail to collapse for longer periods, and moderate to severe defoliation may continue to occur locally after generalized outbreaks in neighboring areas have collapsed. Such persistence is (or at least was) most likely in areas recently invaded by the gypsy moth, but since about the late 1990s has been much less frequent than previously due to the fungus Entomophaga maimaiga (Richard Reardon, USFS, pers. comm.). Collapse is most likely after a season with near 100% defoliation of oaks.
An unusual and overlooked situation can persist for years in coastal plain southern New Jersey (especially in Cumberland County 1980s to about 1996 when Entomophaga ended the situation) and may recur farther south locally if that fungus is slow to establish. Key ingredients appear to be low density (5-20%) of canopy oaks and a lot of sweetgum. Early instars concentrate on the scattered oaks, which are defoliated in late May. Older larvae then disperse to sweetgums--which were unacceptable to early instars. The sweetgums may or may not incur moderate to heavy defoliation depending on their density and proximity to oaks. Larvae forced off oaks find abundant food, disperse sufficiently that they are no longer at high density, and tend to produce normal egg masses. Red maple and blueberry are also readily available alternate foodplants but sweetgum seems preferred. The percent stand defoliation remains low but individual oaks are defoliated repeatedly. Because of the greater number (often six or more) of heavy (60-100%) defoliations per decade these oaks on mesic to hydric soils had higher mortality in the 1980s and 1990s than oaks in some xeric sites with more normal crashes. A few sweetgums and hickories were also killed. The Nature Conservancy's Eldora Preserve is an example of this damage pattern and most mature oaks were killed in the 1980s. New Jersey's only significant stand of Quercus nigra south of Dividing Creek lost almost all mature trees of that species, but hundreds (possibly >1000) of saplings and pole-sized water oaks persist as of November 2002.
Heavy defoliation may occur in somewhat interrupted areas of several hundred thousand acres during the worst seasons and thousand acre outbreaks are not unusual. In June 1981 most oak and mixed forests from southern Maine to coastal Connecticut were heavily defoliated. Occasionally in sprayed areas (mainly older reports, e.g. Nichols, 1980) populations can rebound to outbreak levels in three years, but generally they remain low for five or more years once they crash. Prior to the emergence of Entomophaga in 1989 the general rule was an outbreak every six to 12 years in New England etc. In the southern New Jersey Pinelands region many oak-pine forests (especially in Burlington, Cape May and Cumberland Counties) were defoliated several times when the gypsy moth first invaded in the late 1970s-1980s, often with substantial mortality to subcanopy or even canopy oaks. Other similar oak-pine forests in Salem, Ocean, and Atlantic Counties have (as of 2002) never had an outbreak, in many cases without any control efforts. The 1995 FEIS and other sources report similar observations elsewhere. Failure of expected outbreaks to materialize was a problem in the Sample et al. (1996) field studies. Outbreaks often start in highly favored stressed sites such as ridgetops. Some old reports suggested they sometimes started at the edge of developed areas, perhaps due to increased shelter for pupae and reduced predator (Peromyscus) densities (e.g. due to housecats and habitat changes).
Outbreaks are not fully synchronized, so that there are almost always some areas of heavy defoliation in any given season at least along the leading edge of spread. There are years with none over vast areas behind the leading edge. Likewise, even in the worst years (1981 to date) there are always areas with no noticeable defoliation. In New England, eastern New York and northeastern Pennsylvania, outbreaks usually collapse after one to three seasons. Following collapse, it may be difficult to find any stage of the gypsy moth for a few years. This fact has hampered studies of low-level gypsy moth populations so there are some gaps in knowledge of their population dynamics. Since 1989 (see below) frequency of outbreaks in the Northeast has declined markedly and much of southern New England has been outbreak free (as of 2002) since 1981 or 1982.
NATURAL CONTROLS. Outbreak collapse usually involves death of an overwhelming majority of gypsy moth larvae due to some combination of gypsy moth neuclear polyhedrosis virus (NPV), or since 1989 the fungus Entomophaga maimaiga, or starvation. Both pathogens are introduced, although there is some uncertainty of the exact origin of the current fungus, and are generally the most important natural controls in outbreak conditions. The fungus can also provide excellent control in pre-outbreak conditions and has prevented outbreaks since 1989 in large areas of New England. It is now also an important mortality agent in low density populations. Mortality from parasitism can become very high or may remain low in outbreaking populations. It seems to be the consensus that the important cumulative impact of parasitoids and predators is to slow the rate of increase in low-level populations and thus to lengthen the period between outbreaks, more than actually ending or preventing outbreaks.
Several mostly non-native parasitoids utilize gypsy moth larvae and pupae. Some useful references for identification and basic information include Hoy (####), Nichols (1980) and Simons et al. (1979). Nichols regarded nine species as of some importance in Pennsylvania. None of the parasitic wasps sting humans. Weseloh (1985) and Weseloh et al. (1983) and some of the references therein are among the important studies of parasitoid impacts including in low level larval populations. At least two parasitoids are often noticeable in many states. A tiny introduced wasp, Ooencyrtus kuvanae, attacks the egg masses and has five or six generations per year, from about July to December. Due to its small size, it can only destroy eggs near the surface of the masses. Nichols reports 20 to 50% parasitism of eggs. They kill the highest percentage of eggs in the small egg masses laid in outbreak years. These wasps commonly find virtually 100% of egg masses in an area. Another small wasp Cotesia (formerly Apanteles) melanoscelus kills gypsy moth larvae in about the third instar. The larva dies near or attached to the small white cocoon made by the wasp larva. This tiny wasp is apparently a specialist on Lymantriidae (gypsy moth, satin moth, native Orgyia) (Wieber et al., 2003). Most gypsy moth larvae observed by the author in parts of Hamden, Connecticut in 1982 (the year after a massive outbreak) and about half at Eldora, Cape May County, New Jersey in the early and mid 1990s (a suboutbreak period) were killed by this parasitoid. In general though its impact is limited by a complex of hyperparasitoids ((Wieber, et al., 2003). Parasites of eggs and early instars are generally not considered to have a major impact on gypsy moth populations, especially at high densities, but probably do help slow increase of low density populations.
Compsilura concinnata is an introduced tachinid fly whose larvae parasitize gypsy moth caterpillars and hundreds of other species including a few sawflies. Sometimes it reaches high levels in outbreaking gypsy moth populations, but it usually does not greatly impact them, probably because it is a multiple brooded generalist that quickly becomes limited by lack of alternate hosts which it may deplete (see Boettner et al. 2000). Its long-term impact on native summer feeding Lepidoptera has apparently been drastic reductions and state level extirpations of once widespread (Farquhar, 1934) summer species in New England. It does not appear to have greatly impacted any native spring feeders. As far as known, other gypsy moth biocontrols are not seriously impacting native species.
Life History and Behavior
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.
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.
Communication Channels: chemical
Other Communication Modes: pheromones
Perception Channels: visual ; ultraviolet; tactile ; chemical
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.
Development - Life Cycle: metamorphosis ; diapause
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.
Status: wild: 12 months.
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.
Mating System: polygynous
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.
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.
Key Reproductive Features: semelparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; oviparous
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.
Parental Investment: female parental care ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female)
- 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.
- 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 the Interior National Park Service. Gypsy Moth. 2. Washington, D.C.: Integrated Pest Management Manual. 2009.
Gypsy moth eggs overwinter and hatch during warm weather in spring, mostly soon after oaks begin to leaf out, but a few days later than many native spring caterpillars do. There is only a single annual generation in all parts of the range. First instar larvae usually disperse via the wind on warm, sunny days and commence feeding once they find an acceptable plant. The great majority of hatching is probably in a period of about a week (Schweitzer, pers. obs.; Doane and McManus, 1981, p 184-6), but it can spread over a month with egg masses in the sunniest places hatching earlier. Larval development is slower than most other spring feeding caterpillars (Schweitzer, pers. obs.) such as cankerworms (Alsophila, Bistonini), Malacosoma, Xylenini, most Catocala, spring Lycaenidae, Tortricidae. Most larvae hatch about early May and mature in late June or July in southern New England. Larval growth is substantially asynchronous, due largely to the variety of plants eaten, and a few larvae may still be found in late July. The pre-pupal and pupal stages combined last about 2 weeks, so moths are generally seen at least throughout July and early August in southern New England. All stages occur earlier southward (depending on altitude) with both sexes often near peak by the end of June in Cumberland and Cape May Counties, New Jersey. Males were well represented in blacklight samples from the State College, Pennsylvania pine barrens collected in September 1985 (Schweitzer, pers. obs.). Females usually lay their eggs in one mass on their first or second day and soon die. Females usually mate only once, and since males can mate several times and live a few days, males are effectively in surplus supply. Depending largely on the nutritional quality of larval food females lay from about 100 to1000 eggs. Fecundity is much lower in outbreaking populations, especially in areas of heavy defoliation, than at low densities.
Egg masses are generally within a few meters of the female's cocoon. They are often placed on tree trunks or the underside of limbs. They may be placed in bark furrows or behind loose or shaggy bark if available. They are also often laid on boulders, outdoor furniture, in or on outbuildings etc. Most are less than 5 meters off the ground. While most are somewhat sheltered many are not. Egg masses are generally fairly easy to find and egg mass counts are used to index the outbreak potential. Roughly a count of 500 or more per acre indicates a high potential for an outbreak that spring, unless they are small due to previous defoliation stress on the larvae. Be careful to count only current year egg masses.
Molecular Biology and Genetics
Barcode data: Lymantria dispar
Below is a sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species.
See the BOLD taxonomy browser for more complete information about this specimen and other sequences.
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Download FASTA File
Statistics of barcoding coverage: Lymantria dispar
Public Records: 32
Specimens with Barcodes: 223
Species With Barcodes: 1
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.
US Federal List: no special status
CITES: no special status
State of Michigan List: no special status
National NatureServe Conservation Status
Rounded National Status Rank: NNA - Not Applicable
Rounded National Status Rank: NNA - Not Applicable
NatureServe Conservation Status
Rounded Global Status Rank: G5 - Secure
Comments: While such claims are made, often to promote spraying, it is not true that unchecked gypsy moth infestation will result in deforestation of large areas. Or at least that failed to happen in the first 130 years. It is however quite likely that some trees will be killed during the first outbreak in an area and quite possible others will be in subsequent outbreaks. Mortality might include high quality canopy trees as well as many already stressed or weak individuals. It is also not true that every tree that refoliates a few weeks after an outbreak will recover. Many to most trees that die do so a year or more later often due to secondary agents such as two lined chestnut borer (a beetle) or Armillaria fungi (Dunbar and Stevens, 1975). As gypsy moth invades new areas the best case scenario (increasingly likely now due to Entomophaga) is that no serious defoliation will occur, the worst case probably is roughly 50% mortality to oaks and other highly favored trees when two or more severe defoliations coincide with drought. Such severe damage is much less likely in subsequent outbreaks.
Because of database limitations of the IMPACTS and some other fields, most discussion relating to impacts to native Lepidoptera from gypsy moths and past control programs is placed in this section. Obviously in North America, threats to gypsy moth populations are not of concern, but threats to other organisms due to gypsy moth outbreaks or, more often, control efforts are a major issue. At present the highly persistent (on foliage), highly lethal biocide Diflubenzuron (tradename Dimilinis the main known cause of concern for biodiversity effects. This biocide is highly lethal to at least immatures of any Arthropods (old, broad sense) that eat it, and also as a contact insecticide. The most serious threats and impacts from a biodiversity perspective in the past generally were related to control efforts (including biocontrols), although at least in terms of widespread species, threats from current programs are not comparable to those from practices in the 1950s through 1980s. Current threats which could have consequences persisting more than a few months include tree mortality, impacts to native fauna from gypsy moth outbreaks, impacts to native Lepidoptera from increased generalist parasitoids, and especially eradication of local Lepidoptera or other invertebrate populations by chemical biocides or less likely by BTK. Defoliation itself has many temporary effects to both terrestrial and aquatic environments (see 1995 FEIS) but few or none of these would threaten long term loss of native biota, although short term temperature changes could affect woodland stream fauna for a generation (often a year) or more.
Unlike for example balsam or hemlock woolly adelgids, out of control white tailed deer, or potentially several emerging oak pathogens, gypsy outbreaks may change species composition but will not fundamentally alter the forest or eliminate strata. If tree mortality does occur some species will likely increase and some will likely decrease. On harsh sites, oaks that are killed by gypsy moth are usually replaced by release of understory oaks. On "better" sites there is a greater chance of replacement by other genera such as maples, or on sandy sites by released understory pines. Despite defoliation and tree mortality, mixed forests will remain mixed forests and oak forest or woodland will usually remain oak dominated, as have millions of acres in New England. The forests at Medford and Melrose Massachusetts first experienced gypsy moth outbreaks around 1880 and in 1988 were still primarily oak or oak-hickory dominated on hotter slopes with more mixed hardwoods including some very large oaks in more mesic places (Schweitzer, personal observations). Oaks were reproducing in part because there were almost no deer there in 1988. Witch hazel, pines and hemlocks were common. Some outcrops and places that burned multiple times per decade were dominated by scrub oak and heaths. As Musika (1993) points out tree mortality is not the only effect of gypsy moth outbreaks that can alter stand composition. Herb and shrub species commonly benefit from the increased light. Stand changes are possible if tree mortality occurs and it is possible but undocumented that such could occur even without direct overstory mortality. This topic is complex and impact likely to be very variable with location, climate, and site conditions. Pre-gypsy moth stand composition also will usually not be really "natural". Impacts of stand composition change may not be great for arboreal herbivores (e.g. Lepidoptera, Orthoptera) overall because so many species are polyphagous among forest tree genera, although of course more specialized herbivores (e.g. Catocala moths) will be affected by changes in abundance of foodplant species or (usually) genus.
There was minimal concern for non-target impacts of gypsy moth control efforts as recently as the mid 1980s (e.g. see the near lack of coverage in the FEIS, 1985), especially not regarding biological control efforts. Therefore there was no systematic documentation of impacts at the time. This has changed since about 1990 at least in part due to US Forest Service sponsored research projects. Appendix G of the 1995 FEIS has extensive coverage of non-target risks.
Localized populations of spring feeding Lepidoptera can be completely eradicated by gypsy moth spraying including BTK. There now seems virtually no doubt that the skipper Pyrgus wyandot is extirpated in most of its range and imperiled in the rest due largely or entirely to gypsy moth spraying from about 1957 to 1989. The species was extirpated in New Jersey by about 1960 (records compiled by David Iftner). All of the populations mentioned by Schweitzer (1989) from 1985 and 1986 field work in West Virginia were apparently eradicated by 1990 from gypsy moth spraying as was the classic occurrence in Green Ridge State Forest, Maryland. It is unknown if any have been recolonized. Several conversations with Lepidopterists in western Maryland and West Virginia in the late 1980s suggested eradication of P. wyandot and drastic reduction (at least short-term) of other spring butterflies in sprayed areas to be the norm. Dozens of other Lepidoptera declined or disappeared with that skipper in the late 1950s in northern New Jersey. Some like Papilio cresphontes and Chlosyne nycteis are probably no longer resident in the state although much habitat remains for the former. While search effort has been inadequate and the species probably will be rediscovered at least in Virginia and maybe widely, the grasshopper Appalachia hebardi is now ranked globally historic by NatureServe with no known collections since most of its known range in Pennsylvania was sprayed with DDT or Carbaryl in the late 1950s to 1970s. It is also very unlikely that the regional collapse of Erynnis persius persius in and near New England during and after the 1950s could have been unrelated to massive multi-million acre gypsy moth spraying peaking in 1958. Based on specimens in older collections, that species was clearly of comparable abundance to E. baptisiae before the 1950s and it is now absent at almost all "suitable" sites. The uniquely (for their size) depauperate specialized moth fauna of the Rhode Island pine barrens is probably at least partly explainable by gypsy moth spraying from the 1950s into the 1980s (Schweitzer, pers. obs.).
Some have suggested the decline of the regal fritillary including the near extinction of the eastern subspecies Speyeria idalia idalia was related to gypsy moth spraying. Probably the multi-million acre spray programs in the late 1950s did eradicate some populations in and near New England and the last record in mainland Massachusetts was in 1958. However in most regions populations persisted for at least another ten to 25 years, and eventually died out even in unsprayed areas. Other factors were obviously involved. Compsilura (below) could have played a role but it must be noted that of the five eastern Speyeria, this one is the least associated with forests where that fly is most abundant. Also this fly generally hunts for hosts in trees and shrubs not leaf litter or forest floor herbs. Modest declines of the other three Speyeria in the Northeast appear easily explainable by other factors.
An even greater impact of past gypsy moth control programs was the drastic reduction or large-scale eradication of dozens of formerly common large summer moths. See additional topics for more detail. Almost all of the species were common or at least widespread (Farquhar, 1934) and not localized rarities or habitat specialists. There is disagreement as to how much long-term impact resulted from the spraying of about 12,000,000 acres (Doane and McManus, 1981) of forest with DDT or Carbaryl in the late 1950s versus impacts from the introduced tachinid Compsilura concinnata (Hessel, 1976; Boettner et al., 2000). It is reasonably clear that most of these species collapsed in or about the late 1950s at least in western Massachusetts and from Connecticut southward to central New Jersey. Virtually all Lepidopterists active from northern New Jersey to Massachusetts at the time considered the crashes immediate, not gradual, and blamed aerial spraying at least in part (e.g., see Hessel, 1976; Gochfeld and Burger, 1997; Schweitzer, 1988; also personal communications of this writer with Asher Treat, Charles Remington, Roger Tory Peterson, Joseph Muller, Sidney Hessel and others).
Most likely though an even greater long-term impact was the introduced parasitoid Compsilura concinnata. This fly could pose a serious threat of eradication of localized summer species in parts of western North America particularly in isolated canyons. Boettner et al. (2000) experimentally document extremely high mortality to H. cecropia and others from Compsilura. Early anecdotal reports of declines in Saturniid abundance, but not eradications, date back to soon after the introduction of Compsilura (see Boettner et al., 2000). While Boettner et al. tend to discount the impact of spraying, Compsilura alone seems an unlikely sole cause for immediate (vs. gradual) crashes in the late 1950s since it had been present nearly half a century, but there is little doubt this parasitoid has drastically impeded or completely prevented recoveries. Many of the most widely eradicated species (e.g. Citheronia regalis, Eacles imperialis, Sphinx drupiferarum, most Datana, and undoubtedly others) frequently remain as pupae for two or three years (Schweitzer, unpublished) and so could not be eradicated even by one year of 100% larval mortality over a large area.
Whatever combination of factors were involved, there is no doubt these crashes occurred within a few years of 1958, although it is a common myth that only Saturniidae and Sphingidae were affected. Gregarious Notodontidae such as Datana, Schizura, Clostera were also very scarce or absent in the affected areas in the 1960s, 1970s and at least into the 1980s and in some areas are still. Overall probably the most widely eradicated genera were Datana, Citheronia, Eacles, Sphinx, Lophocampa. The obvious common characteristics of all of these affected species are moderately to extremely large size, exposed (often gregarious) tree and/or shrub feeding caterpillars maturing from late July to October--precisely when large numbers of Compsilura females need native caterpillars. It is less clear why other Notodontidae, Lapara and smerinthine Sphingidae were not also widely eliminated, although some of them apparently were reduced at least in the 1970s. It is noteworthy that Anisota are difficult, but possible, for Compsilura to parasitize (David Wagner, pers. comm., 2001). Perhaps their granular cuticle makes Smerinthinae similarly difficult targets. While other Ceratocampinae (Eacles imperialis, both Citheronia) have disappeared from 99-100% of their former ranges on the New England mainland, two of the three Anisota and the related Dryocampa have not been widely eradicated. A. virginiensis and Dryocampa remain at least moderately common in many places, although they were apparently absent in parts of southern Connecticut in the mid and late 1970s (Schweitzer and Yale samples). Assuming old identifications are correct A. stigma has been eradicated from much of its New England range, becoming confined to Cape Cod region barrens. There however, it appears to be increasing in distribution since 1990 (Michael Nelson, pers. comm., 2001). A. stigma is the only one of the moths discussed in this section for which habitat loss (pine barrens) is a plausible major factor in its decline. The other large moths discussed here routinely utilize a variety of common habitats including dominant forest types, hedgerows, thickets, although a few probably do best in shrublands. Anisota senatoria now has a somewhat reduced range in New England being largely eradicated from the western half, but is still regular eastward and around Albany, New York. A. senatoria is/was itself an outbreak-crash late summer defoliator of oaks. Boettner et al., (2000) found moderate Compsilura parasitism in Hemileuca larvae, although Jennifer Selfridge also working in Massachusetts (email to Dale Schweitzer, September 2002) did not despite simultaneous high levels in A. polyphemus. There is no evidence of major impact to either Hemileuca species though. Although H. maia has disappeared with its habitat in many places, it still persists in all of the substantial pitch pine-scrub oak barren areas in Massachusetts, eastern New York, Rhode Island and probably Maine, but not in New Hampshire. H. lucina, an outbreak species of wet shrublands and powerlines increased drastically in abundance in the late 1970s and early 1980s, and expanded its limited range into Franklin County, Massachusetts, northeastern Connecticut, adjacent Rhode Island, and Vermont (Schweitzer, pers. obs.).
While the precise impacts of massive aerial biocide applications and an out of control biocontrol cannot be deciphered with certainty now, between these two impacts the genera Citheronia, eacles, Datana, tree feeding (but not shrub or herb feeding) Sphinx species, Lophocampa caryae, Manduca jasminearum and others have been eradicated from substantial portions, or all, of their New England range and parts of adjacent New York and Pennsylvania. Attacine Saturniidae and Automeris are greatly reduced. Most, but not Citheronia, have partially recovered (starting mainly in the 1990s) in northern New Jersey and by the early 2000s Datana were scarce but no longer absent in parts of Connecticut. Species in these groups for which suitable habitats are present appeared unaffected in the 1970s and 1980s on Block Island, Nantucket, Martha's Vineyard and extreme outer Cape Cod, areas long considered as poor habitat for Compsilura but also with reduced aerial spraying compared to the mainland, or on Block Island none at all.
It is far from certain whether major Compsilura impacts will continue to spread. Obviously Compsilura will occupy suitable areas of North America where it was intentionally released and at least eastward it will spread. However, established Compsilura does not necessarily mean obliteration of large native summer feeding moths. This fly has long been present in southern New Jersey but at modest levels and with no obvious impacts at the population level to large moths. Saturniidae and Datana are still among the most common moths at lights for example.
Observations of possible Compsilura impacts and south and west of the Poconos region are equivocal. Datana, Eacles, Citheronia and other Saturniidae do not seem to be abnormally scarce now in central and southern Pennsylvania based on collecting by Stephen Johnson and to some extent this author through 2002. Indeed Callosamia promethea seems abnormally abundant in central Pennsylvania with caged females sometimes assembling over 100 males (Johnson) and Citheronia sepulcralis is at least widespread. Nor were such big moths at all scarce in the 2000 Great Smokey Mountains National Park BioBlitz. Except for a lack of Sphinx species Schweitzer noted reasonable to good numbers, especially of Eacles and Datana, in 1988 samples from Prince William Forest Park in Virginia. However Saturniidae, Sphingidae and some others were remarkably scarce in the 1999 USFS samples around Highlands, North Carolina (Adams, 2001). The extent to which Compsilura concinnata threatens North American Lepidoptera is unclear at present. Given its host breadth and the size of the US Lepidoptera fauna, thousands of species are potential casualties and it has apparently drastically reduced or eradicated formerly widespread or even common large summer moths from several states. This suggests it could have greater impacts in places like forested western canyons where equivalent summer moths are much more localized than their eastern counterparts. There is probably nothing preserve managers can do to mitigate Compsilura impacts. Probably of even greater concern are the impacts of Compsilura on native parasitoids of Lepidoptera, especially native Tachinidae.
Besides its lasting impact on native summer Lepidoptera, Compsilura probably should be credited with the near eradication of the introduced brown tailed moth, formerly a pest in and north of Massachusetts, from most of New England. Farquhar (1934) noted it was already declining by then and today its refugia are similar to those for severely impacted native species: extreme outer Cape Cod, various offshore islands and headlands, and far northern New England.
Impacts, if any, from an established biocontrol are generally unavoidable and long term whether such impacts be control of the target species or reduction or eradication of native non-targets. Not all impacts of introduced species on native species are significant at the population level. Hajek (1995) documented that some native Lepidoptera in several families can become infected by Entomophaga maimaiga under extreme laboratory conditions not meant to mimic field exposure. However, Hajek et al. (1996) found only two cases of infection (Malacosoma disstria (Lasicocmpidae), Catocala ilia (Noctuidae)) among 1790 native caterpillars in one large random study with high rates of infection among gypsy moth larvae. These authors also note that E. maimaiga is known only from gypsy moth in its native Japan. In other samples though they did find low to moderate infectivity in native Lymantriidae (Hajek et al., 1996; Hajek et al., 2000; Hajek et al., in press;) especially if the larvae spend time on the ground or in the leaf litter. The highest field incidence for any native species was 36% for Dasychira obliquata during a peak gypsy moth year. In most years no infected native Lymantriidae were recovered (Hajek et al., 1996; Hajek et al., in press). They also found single cases of infection in a Gelechiid (n=84) and in the noctuid Sunira bicolorago (n=20) among 358 caterpillars in samples from in and near forest leaf litter (Hajek et al., 2000). Low to moderate levels of mortality in extreme years should be easily absorbed by populations of common forest moths and probably have less impact than gypsy moth outbreaks. An ability to infect native species at levels too low to threaten their populations could be an extremely useful feature allowing the fungus to better maintain itself when gypsy moth larvae become scarce for long periods. Non-target impacts from Entomophaga maimaiga do not appear to pose any conservation concerns in terms of native Lepidoptera including Lymantriidae. This increasingly successful biocontrol will probably eventually occupy essentially the same range as the gypsy moth at least in humid eastern North America.
Since about 1990 gypsy moth control has taken a more focused Integrated Pest Management (IPM) approach. Potential biocontrols are getting some level of screening for non-target effects, but it is still possible another damaging species could be released and established. Under Cooperative Suppression Programs, spraying does not occur unless gypsy moth densities exceed certain thresholds. Completely unwarranted private spraying still occurs though and unscrupulous or ignorant operators deceive gullible neighborhood associations into annual spraying. Massive indiscriminant aerial spraying such as in the 1950s to early 1970s no longer occurs (FEIS, 1995), although hundreds of thousands of acres were sprayed some years, mostly with Diflubenzuron, in West Virginia and adjacent Maryland in the 1980s. Even by the mid 1970s or early 1980s such massive biocide use had ceased in Connecticut and became more spotty elsewhere in the Northeast where gypsy moth was well established. At current scales of biocide applications, eradication of common or widespread species at least among dispersive insect groups in areas with substantial forest would not be expected, and has not been reported. The potential for local eradications of native fauna is probably much higher for parts of the Midwest where forests are reduced to 10-100 acre scraps in a sea of agriculture. Mortality levels even from BTK could be sufficient to cause eradications in such small habitat islands and recolonization could be difficult even for some common species on such landscapes.
Long term to permanent impacts, if any, of current suppression programs in extensively forested regions should be limited to species occurring in localized colonies in special habitats, such as Pyrgus wyandot. For this reason care needs to be taken not to spray large portions of shale barrens, pitch pine-scrub oak barrens, and other habitats likely to harbor specialized spring feeding Lepidoptera even with BTK. Another species of concern in Appalachian gypsy moth eradication and suppression projects recently has been Phyciodes batesii maconensis. A major global consideration for Speyeria diana in the 1980s was the potential for massive impacts from large-scale gypsy moth spraying to this known BTK-sensitive species, such as occurred (largely using Diflubenzuron) just north of its range in West Virginia in the late 1980s when the species was placed on the USFWS Candidate (C2) list. For a variety of reasons such threats did not materialize since indiscriminant large scale spraying of US Forest Service and National Park Service lands did not occur and does not now seem likely under current IPM based policies.
A shift from chemical biocides to BTK should benefit summer feeding species and insensitive to moderately BTK-sensitive spring species by preventing defoliation and parasitoid buildup. It is distinctly possible that BTK based suppression efforts have been a factor in the partial recovery of Saturniidae, Datana, Lophocampa etc. in places like northern New Jersey during the late 1980s and 1990s. Actual data on this topic would be interesting.
Threats from gypsy moth outbreaks to native species are generally moderate or less and short term (FEIS, 1995. Appendix G). But on closer consideration severe short term to long term impacts are likely to a few Lepidoptera and other herbivores in some situations. Tree mortality and large-scale starvation of native herbivores in outbreak years are probably the direct effects most likely to have long-term impacts, if either occur. If tree mortality occurs there could be potential for increased invasion by understory exotic plants. Large-scale starvation of spring feeding caterpillars such as most Xylenini, Orthosia, the earlier Catocala species, Bistonini, is unlikely in most forest types (but see below) because most spring caterpillars mature before defoliation typically occurs. Most summer tree feeders (Notodontidae, Ceratocampinae, some Limacodidae) reared by Schweitzer have one or both of two life history traits that would prevent outright loss of a population to starvation form a single defoliation. For about 40% of species 5% to 60% of pupae overwinter more than once so there is always a reserve. For about half eclosion is staggered over 30 to 70 days starting near the time of peak defoliation so later larvae would have at least low quality refoliated leaves even in severe outbreaks. A few spring feeders such as Feralia major and Psaphida rolandi also sometimes overwinter two or more times as underground pupae, but most spring feeders overwinter as eggs or adults which can only do so once.
Synchronized early summer species beginning their larval stage at the time of maximum defoliation or during the next three to four weeks (longer if hatchlings cannot use young foliage) are obviously at high risk of starvation when defoliation is severe. Examples could include hatchlings of Hypomecis, Lytrosis, Euchlaena, Hyperaeschra georgica, and Hyperstrotia in June. The potential for starvation is also high for Nadata gibbosa, Actias luna and Antheraea polyphemus both to early larvae present with gypsy moth larvae and to more numerous later larvae hatching during the period trees are leafless.
There are also a few spring feeding species whose late instars develop slowly that are at risk during the defoliation period. Extreme examples are Morrisonia confusa (often on oaks, see also Wood and Butler, 1991), an oak feeding Hydriomena (probably H. pluviata), and Lambdina "turbataria". All of these start feeding in April or May but remain as larvae until late August to October in Cumberland County, New Jersey (Schweitzer, pers. obs.). It is unclear how, or if, these species survive severe outbreaks. The four species of the Catocala amica group mature later than most other spring oak specialists, about when or just after defoliation typically occurs in New Jersey and Connecticut and so are at risk. A few hickory-specialized Catocala also linger as larvae (Sargent, 1976; Schweitzer, pers. obs.) and are at high to extreme risk of starvation in severe outbreaks. Such species include C. habilis, C. robinsoni, C. vidua and C. obscura. The BTK assay data in Peacock et al. (1998) imply at least two of these should fare better with a BTK application than in severe defoliation. Buckmoth larvae (Hemileuca maia) cannot complete development before defoliation but if they can reach late penultimate instar (which most can in southern New Jersey) mortality appears low. Somehow many survive and mature quickly when refoliation occurs. They may find some alternate food, perhaps Gaylusaccia leaves, or they may simply survive three weeks or so without food. By direct observation of captive larvae, 8 days of starvation has little, if any, lasting effect on last instar buckmoth larvae.
Scrub oak feeding Lepidoptera and other insects on xeric ridgetops and west slopes are at high to extreme risk of starvation, which could eradicate them if they do not occur in other microhabitats. For example Schweitzer observed on West Rock ridge, New Haven Connecticut that oak defoliation was virtually 100% on May 25, 1981 on the crest and west face but on the lower east slope did not reach that level until June 11. This difference should have a huge impact on survival of spring feeders, as most (sleeved and wild larvae of Xylenini and some Catocala) were observed to mature during that interval. As Gall (1984) observed survival on the west face would have been virtually impossible for many Catocala, and not all could have matured even by June 11. Indeed both of us observed many small Catocala adults there in July 1981. Specimens at Yale and elsewhere indicate two species of scrub oak habitats, Erynnis brizo and Chaetaglaea tremula, occurred on West Rock Ridge in the 1960s. Neither did in 1975-1982 (Schweitzer, pers. obs.) after outbreaks such as in 1971. Both species are larvae in spring. In an even more extreme incident at Hopkinton, Rhode Island on 16 May 1986 Dale Schweitzer observed nearly 100% defoliation of scrub oak buds in a small (<100 acre) sand plain pine barren by first and second instar gypsy moth larvae obviously blown in from adjacent phenologically more advanced oak forest. It is very unlikely any obligate scrub oak feeders survived that spring.
Native Lepidoptera are affected by other aspects of outbreaks besides starvation (useful discussion in Sample et al., 1996) but it is very unlikely these impacts would be long term and as those authors suggest such impacts may be within the range of normal fluctuations. As they document and one can easily observe, even in suboutbreak conditions gypsy moth larvae can far outnumber all native caterpillars combined and this might directly affect the latter. Native Lepidoptera may be impacted by induced increases in tannins or other defensive chemicals (Schultz and Baldwin, 1982) in replacement leaves and the next season. Earlier than normal foliation the next spring (Heichel and Turner, 1976) would affect synchrony of egg hatch and weight at maturity of spring feeders such as Xylenini and Alsophila (Schweitzer, 1979; Schneider, 1980). The main effect of foodplant changes will generally be small size and/or reduced fecundity (at least for Xylenini and Catocala, Schweitzer pers. obs.), which is well known for gypsy moth itself. Undersized, but functional adults are commonly observed after defoliation for summer feeding Notodontidae as well. Fecundity reductions are undoubtedly common in natives as well as gypsy moths and Sample et al. (1996) suggest they might occur even without severe defoliation. However there are no such data supporting or refuting this suggestion for natives.
Indeed general moth collecting, for Catocala and Xylenini collecting in particular, are very often excellent immediately after outbreaks and the 1981 New Haven butterfly count (Gall and Schweitzer, 1982) established a record number of 55 species for an eastern US count that held for over a decade, despite severe defoliation and limited effort by the observers. Sargent documents 1971 as a very good Catocala year in southwestern New England as it was in the Poconos of Pennsylvania (Schweitzer). This was also a year of high gypsy moth damage. Probably factors which favor gypsy moth increases (like warm, dry springs) also favor natives. Native species sometimes crash the year following gypsy moth outbreaks but in some cases (such as the 1982 and 1983 New Haven butterfly counts) crashes could be explained by extreme weather events such as torrential spring rains and floods or may have been due to some effect of the widespread defoliation Data on impacts of gypsy moth outbreaks to native species remain few at this time. Those of Sample et al. (1996) are given mainly at the family level--not an ecologically useful OTU for most macromoths other than Notodontidae and Limacodidae.
Undoubtedly starvation can seriously impact some native Lepidoptera at least when defoliation comes early. However, data are minimal. Lepidoptera that often seem to be reduced following gypsy moth outbreaks include Satyrium species, Nemoria bistriaria and some Acronicta species. The mechanism in the last case may not be nutritional. With 20-20 hindsight though it does seem clear that gypsy moth outbreaks do not generally cause extirpations of widespread forest species in the affected areas. To what extent they threaten localized ridgetop species remains undocumented, but past outbreaks probably do explain some current absences of these natives as noted above. It now seems very likely some of the differences between ridgetop and sand plain pine barrens moth faunas reported by Schweitzer and Rawinski (1987) reflect species losses related to past gypsy moth outbreaks. Since then as more sites are collected for moths, most of the so-called sand plain species have turned up on one or more large ridgetop barren.
In terms of non-target impacts chemical biocides have greatest effect on most native biota of the current management strategies. BTK probably reduces native Lepidoptera more than outbreaks themselves overall, but this could not possibly hold consistently at the species level given the great variation in both BTK sensitivity (including lack of any), variable risks for starvation, and other factors. BTK unlike chemical biocides other than perhaps Mimichas little or no impact beyond Lepidoptera. If benign options like pheromone flakes, Gypchek are available, any of these will probably greatly reduce or completely prevent negative impacts associated with gypsy moth with little or no non-target impacts. See the 1995 FEIS for more discussion on the many short-term impacts of gypsy moth outbreaks on other fauna, especially birds and other vertebrates.
Restoration Potential: Except perhaps in Great Britain where it is extirpated, restoration of gypsy moth is obviously not an issue. Restoration of damaged flora and fauna might be. Native fauna that are impacted but not eradicated by either control efforts or gypsy moth itself will usually recover within a few years without intervention unless limiting factors (e.g. Compsilura, loss of foodplant) persist. Native fauna eradicated by control programs may or may not eventually recolonize. For example Pyrgus wyandot has not done so in northern NJ after >40 years and even if this species does not become extinct (as now seems fairly likely) recovery in much of its former range would surely require reintroduction. Isolated populations may have no recovery potential if eradicated. For example, a truly isolated relict bog copper occurrence southward could not be expected to recolonize before the next post-glacial period. More generalized forest species should recolonize within one to three years in most cases. Restoration of Saturniidae, Sphingidae, Datana and others, and native parasitoids, in New England for now seems impossible and will remain so unless Compsilura permanently declines. The recent partial recoveries of many affected species in northern New Jersey (based on 1990s to 2002 records in the collections of Rutgers university, Alnne Barlow and Tony McBride) and very recent observations by Elizabeth Johnson of Eacles near Pottersville does offer some hope that the same might someday happen in New England. No effective control other than lack of host caterpillars is known for Compsilura although possibly some native hyperparasites might be helpful. Release of exotic hyperparasites is not recommended out of concern for already depleted native Tachinidae.
Planting or encouraging affected tree species once the initial invasion has passed could mitigate stand changes in second growth forests. This should be especially feasible where Entomophaga is providing good gypsy moth control and could be considered for restoring populations of state-rare species of oaks in New Jersey for example. However, biodiversity managers should consider that pre-gypsy moth forest composition in many parts of eastern North America was already quite unnatural having been affected by centuries of logging, altered fire regimes, and loss of American chestnut, a former dominant in many stands. The argument is often made that a reduction in oaks is beneficial in reducing the frequency of severe defoliation, and it is also by no means certain that such a reduction makes a forest any less "natural".
Management Requirements: The widely available options include no action, use of a chemical biocide such as Dimilinand use of one or more applications of Bacillus thuringiensis variety kurstaki. All of these have non-target impacts, except non target impacts of no action are minimal if severe defoliation does not occur as a result. Gypchek has no known non-target impacts but is not always available. There are other methods discussed below that do not have non-target impacts but they may not be options. Biodiversity oriented managers must first determine which options are available and decide if any such treatment option will be considered or allowed. This should be done in advance. Decisions and treatments should be made before defoliation is obvious. Defoliation usually is not noticeable until gypsy moth larvae are penultimate or last instar and by then BTK will not be effective. Even Dimilin will not be at all effective with last instar larvae because it cannot kill them until their next molt, which would be at pupation so feeding would be unaffected. Sevin would likely prevent further defoliation and Mimic at least reduce it in such circumstances, but like Dimilin a manager concerned with biodiversity conservation would generally regard the non-target impacts as unacceptable. If defoliation is already occurring a biodiversity oriented manager will usually have no choice but to allow it to run its course and plan monitoring and possible treatment options for next year. See MONITORING section. However in rare situations where serious defoliation is suddenly noticed (usually on west facing ridges) due to extreme number of third or earlier instars BTK will reduce feeding overnight and will kill most of them and might be effective in reducing defoliation depending on how many there were. In such cases risks of starvation to non-target Lepidoptera are probably very high which should be weighed against BTK impacts to them.
If it is determined that gypsy moth control is needed on lands managed for biodiversity, see the rest of this section and also THREATS and IMPACTS sections, for more information on the possible methods some of which have serious non-target impacts. Diflubenzuron (Dimilin or Carbaryl (Sevin are inappropriate except at very small scales (e.g. small campgrounds, high visitations sites, parking areas) if biodiversity conservation is among the management goals. Mimic has not been thoroughly reviewed for this document but would likely have broad impacts within Lepidoptera at least, for an uncertain period of time. BTK should be considered and is appropriate in environmentally sensitive areas that can be reasonably assumed to not have specialized spring feeding Lepidoptera or rare swallowtails. NPV (Gypchek pheromone based mating disruption, trapping of males, sterile male release have very minimal or no negative non-target impacts but may not be available or appropriate--for example if egg mass counts are already very high. USFS staff and sometimes other professionals may be able to offer good up to date information regarding these options.
Chemical biocides have been very widely used to combat gypsy moth and as recently as the 1985 FEIS very minimal consideration was given to non-target species. Millions of acres were sprayed with DDT and/or Carbaryl (see Doane and McManus, 1981) with a peak of about 8,000,000 acres in 1958 sprayed with DDT. However in the 1990s concern for non-target impacts increased greatly and the US Forest Service funded or conducted substantial research on the topic. Diflubenzuron (trade name Dimilin promoted as an "insect growth regulator" thus avoiding terms like pesticide, is the only chemical treatment currently widely used in Cooperative Suppression Programs and there has been a marked shift toward BTK in most states and by the US Forest Service. Mimic has recently had some use against gypsy moth and is also promoted as a "growth regulator". It is said to be specific to caterpillars and kills by inducing a prmature lethal molt. Carbaryl (Sevin is still used in some private operations. It is acutely toxic, especially by ingestion, to most Arthropods and very destructive in aquatic systems and severely impacts pollinators, including native species and honeybees. However it does not persist for months or longer on foliage, leaf litter, bark etc. like Diflubenzuron can, so Carbaryl probably does not impact canopy herbivores as severely. Unlike Diflubenzuron, Carbaryl kills adult as well as immature Arthropods quickly. Carbaryl is not discussed further in this document.
Literature on Diflubenzuron (Dimilin is too extensive to cover fully here (see 1995 FEIS). Diflubenzuron disrupts chitin formation in insect and other Arthropods (broad sense) that produce it by similar processes, such as a great diversity of Insecta and Crustacea. Death is at the next molt. Therefore it cannot kill adult insects. It is potentially lethal to immature Arthropods that ingests it, often at doses of a few parts per million and for some aquatics at doses of a few parts per billion. It also impacts fungi that produce chitin. It is also considered a contact insecticide but most research suggests this is not a major source of non-target mortality in applications aimed at gypsy moth and that ingestion is clearly the major source of mortality to most terrestrial organisms and to aquatic leaf shredders. It can kill eggs upon contact or affect fecundity of exposed adult females of some insects and even at least one Nematode. It is apparently not clear how widespread impacts to eggs are. See 1995 FEIS, Appendix G for an extensive list of affected organisms.
Some published studies, in some cases aimed mainly at assessing immediate impacts to vertebrate food supplies, show only modest impact to moths overall especially the same summer. Most moths in same summer samples come from unexposed overwintered pupae and/or come from habitats other than local forests. Larval sampling in areas treated with Diflubenzuron underestimates mortality (FEIS, 1995), probably greatly, because generally no attempt is made attempt to rear "survivors" to adults. Undoubtedly most would die at subsequent molts, especially considering that they would continue to ingest Diflubenzuron at subsequent feedings. Nevertheless, field studies show major reductions of Lepidoptera in treated areas, which remain significant at least through the second summer. In general mortality to non-target spring feeding Lepidoptera and probably other immature leaf chewing Arthropods should be similar to that of gypsy moth larvae. Mortality might be lower but is substantial to summer feeding caterpillars (FEIS, 1995), and probably few mobile larvae escape lethal exposure even in mid or late summer. Sedentary species occasionally might. Good data on actual mortality levels for summer leaf eaters were not found and the FEIS estimates probably are too low since caterpillars typically move around and will likely eventually eat a lethal dose.
See Appendix G of the 1995 FEIS for discussion of the fate of Diflubenzuron in the environment. Much Diflubenzuron washes off foliage in the first major rainfall, but a a substantial amount adheres to leaf surfaces for weeks to months. Typically 20 to 80% of the original amount applied remains two to three weeks after treatment, but thereafter its decline in the canopy is slow for the rest of the season and 5% to 50% will remain until leaf fall. There is some effective dilution via leaf expansion but not likely enough to reduce mortality to leaf chewers. At least usually potentially lethal doses remain on foliage for the rest of the growing season. Diflubenzuron probably can remain lethal on broadleaf evergreens for more than a year. However on pine needles the FEIS (citing Mutanen et al., 1988) states that by 61 days levels were undetectable on two samples and 10 and 25% of the original on two others. Other studies show traces of Diflubenzuron or its metabolites on foliage or leaf litter were still present at 319 days. Longer persistence has been presented at conferences but is not reported in the FEIS. Citing data from Mary Wimmer, the FEIS states that residues in leaf litter were over 1000 ppb soon after application, dropping due to microbial activity to 15 to 200 ppb just before leaf fall and then rising again with leaf fall. Residues remained stable over winter and declined to 100 to 400 ppb by the end of the second summer. Obviously leaf litter will remain highly toxic to litter feeding Lepidoptera and many other detritivores through at least two seasons (noted in FEIS, Appendix G) and probably to some extent into the third season or beyond. It is also well-known that residues adhered to falling leaves kill leaf shredders in streams for at least several months.
Diflubenzuron breaks down within a few days from microbial action in some soils and eutrophic pond mud but this can vary with microbial action and other factors. Usually half-life is a few days in eutrophic ponds. However significant amounts commonly do remain in the water column for several days to two weeks (FEIS, 1995, Appendix G, page 7-6). One study showed 98% degradation within four weeks and another showed 50% degradation within two days in soil in field situations. A half-life of 3.5 to 7 days may be typical in soil but persistence is longer in soils with low microbial activity or at low temperature. Without microbial action in sterile soils degradation is reported at 6% in four weeks in one study and negligible in one year in another. Diflubenzuron does not biomagnify up the food chain like DDT.
Impact to narrowly endemic cave fauna in Appalachia is a serious conservation concern. Diflubenzuron is not expected to reach groundwater because it rarely penetrates far into soil. Therefore there should not be an impact if a cave is fed solely by ground water. However if there is a surface stream involved lethal levels could easily occur since Diflubenzuron is somewhat soluble in water, is often suspended in the water column, and can readily enter caves adhered to leaf litter and other particulate matter. Short-term exposure to Diflubenzuron causes very high mortality to immatures of crustaceans (including true crabs and horseshoe crabs as well as small fresh water types), and diverse insect orders. The expected impact of a lethal dose (which could be as low as 10 ppb or slightly less) in a cave system would be death at next molt for most to all immatures of aquatic cave Arthropods (broad sense) and possibly sterilization of adult females. Extinction of endemic species would be a very real possibility. Exactly what species are at risk would depend in part whether exposure was from dissolved or suspended Diflubenzuron or via contaminated leaf remains and depends in part on the feeding habitats of the organisms. Potential impacts to endemic Carabidae are particularly hard to assess. High mortality to terrestrial cave Arthropods from Diflubenzuron seems unlikely unless they would actually ingest it but this is uncertain. They might be exposed via predation or scavenging.
In general Lepidoptera larvae, other chewing herbivores, and leaf shredders in streams are the most severely impacted non-target groups from Diflubenzuron. Insects that do not ingest Diflubenzurin, including sucking insects in the canopy, bees, wasps, ants, and many others are usually not reported to be greatly reduced in field studies, although species level data are few. Some studies indicate reductions of spiders. However sucking insects might in fact be impacted since Kim et al. (1992) document major fecundity reductions in the lab. Reductions in canopy and subcanopy Arthropods are substantial enough overall that Whitemore et al. (1993) were able to demonstrate significant reductions in fat accumulation in seven species of Neotropical migrant bird species. Bird species that depend heavily on caterpillars would be most likely to be affected. See the 1995 FEIS and references therein for details.
Studies such as Martinat et al. (1988) that use very broad operational taxonomic units (OTUs) and do not follow immature insects to the adult stage underestimate Diflubenzuron effects, probably severely so for Lepidoptera. See above and also comments in the 1995 FEIS. Such field studies may however provide good data relevant to birds and other predators for whom viability of prey is not directly important. Abagrotis alternata was noted as apparently unaffected by a Diflubezuron treatment by Butler et al. (1997), but that species would be present overwhelmingly as last instars at spray time (e.g. Peacock et al., 1998) and only late instars are easily sampled under burlap bands. There is no known mechanism by which last instars could be affected by Diflubenzuron prior to pupation when most or all treated larvae probably died unobserved underground. No caterpillars of gypsy moth, Lithophane hemina, Orthosia rubescens, "Polia" latex, the four most common species collected under burlap bands, were found post-spray in the treated plots that year (Butler et al., 1997, Table 3). These three native noctuids are collected by this method as late instars, solely as last instars for L. hemina and O. rubescens whose penultimate and younger larvae are green and stay among foliage. L. hemina would be mostly mid instars at spray time (e.g. see data on congenerics, especially L. petulca, in Peacock et al., 1998), O. rubescens would probably be mostly antepenultimates and penultimates (this species runs slightly later than the two congenerics in Peacock et al., 1998), and few or no eggs of "P". latex would have been laid yet (Wood and Butler, 1989; Schweitzer, pers. obs.). The data for these three plus gypsy moth indicate virtual eradication of spring Macrolepidoptera larvae by the last instar, including "P". latex which not yet even present as larvae at spray time. As would be expected, the difference was not as great for caterpillars collected off foliage, which would include various instars of questionable viability which was not assessed. It has not been demonstrated, and is not expected, that substantial numbers of immature leaf chewers, such as caterpillars, katydids or tree crickets, survive to the adult stage after eating Diflubenzuron. Also caterpillars alive on sample dates would likely ingest additional Diflubenzuron. A reasonable assumption is that mortality to native spring and early summer feeding caterpillars and probably other leaf chewers from this biocide will be comparable to that for gypsy moth.
Dale Schweitzer examined a number of moth samples from summer 1989 for Delaware Natural Heritage Program. The samples noted here were from more or less wooded habitat sprayed with Diflubenzuron in May. Nearby fields, thickets and tidal marsh were not sprayed. These were not paired controlled studies, but the interpretation is obvious to anyone who has ever run a blacklight in an eastern forest on a summer night and has a basic understainding of moth phenology. Marsh, thicket, old field, and lawn species were well represented, but there were almost no forest species except for some that came from previous years' pupae. There were no litter feeding Herminiinae (normally an abundant and diverse group) in most of these samples. The total number of tree feeders that could have been larvae in May to July that year was five moths of four species in a blacklight sample on 6 August at Pike Creek "Natural Area". Two of these were Hypsoropha hormos a persimmon feeder and so probably from an insprayed old field or thicket. There were six individuals of three forest species in a 2 September trap sample out of about 33 moths, mainly weedy Pyralidae. Four of the six were Semiothisa granitata, which suggests residues on pines were no longer lethal by about late July, which is consistent with the 1995 FEIS, Appendix G (see above). The other two could easily have come off wild cherries in old fields or thickets but were larvae since June. A July 12 sample contained a mere 47 macromoths at Ted Harvey Wildlife Refuge. Two oak feeding Catocala and one Abagrotis alternata were probably the only individuals that would have been larvae in forest trees that year. One Anavitrinella could have come from the forest but probably came from another habitat. Old field and thicket species such as the Prunus feeding Catocala ultronia (3) and dogbane feeders (3 of two species) seemed normal and there were three of the persimmon feeding H. hormos. Forest tree feeders from previous years' pupae were better represented with 12 individuals of at least four species of Notodontidae in that sample which probably came mostly from oaks or maples. Overall one would conclude a modest reduction (perhaps 70-80%) of moths comparable to some published studies, but these samples strongly suggest forest species were virtually eradicated as larvae at least into July. Identical traps in comparable, except more light-polluted, New Jersey forests a few dozen kilometers to the east generally take 100-600 forest moths per night at those seasons (Schweitzer 1999-2001 data), suggesting about a 95-100% reduction of forest species.
Because of its severe impact to several major non-target groups in forest canopy and aquatic systems, its persistence on foliage, leaf litter and other surfaces, and the availability of more benign alternatives, Diflubenzuron is inappropriate for large-scale use on lands where biodiversity preservation is among the management goals. Natural Heritage Programs should re-rank tracked Lepidoptera, Orthoptera and certain aquatic insect occurrences to historic if most habitat is treated with Diflubenzuron unless the species is known to have multiple overwintering as pupae. Diflubenzuron, Carbaryl, or DDT applications, even decades previously, should also be considered a negative factor in evaluating "natural community" occurrences if community is assumed to include more than flora, since eradication of specialized Arthropods may have occurred. Data on persistence and non-target impacts from the apparently caterpillar-specific Mimichave not been evaluated for this document. Mimicis not now used in Cooperative Suppression Programs. While BTK or chemical spraying will generally prevent defoliation they do not provide long-term control.
Dichlorvos, the organic phosphate neurotoxin in no-pest strips (see FEIS, 1995, Appendix G) is is placed in small pheromone baited traps. Disparlureis a synthetic gypsy moth pheromone often used this way. Grids of such traps are used for detection or quatitative survey work and are not now used for control purposes . Males are attracted and killed inside the trap. Dichlorovos will likely kill other invertebrates that wander inside the traps or outside them if the traps are destroyed and knocked to the ground. It is very unlikely the dosage would be harmful to any organism any meaningful distance from the traps in normal use. Significant non-target effects are not expected and not reported in the FEIS or elsewhere. The only likely objection to this methodology by preserve managers would be on philosophical grounds. An alternative may be traps with a sticky coating (such as Tangelfootinside but these might kill a few small mammals should they fall to the ground.
Gypchek the commercial product of the NPV virus is available through the US Forest Service (contact Richard Reardon, Morgantown WVA office) but only for government (federal, state, county etc.) sponsored suppression or eradication programs. It can be used on private lands as part of suppression efforts. Gypchek does affect some native Lymantriidae at least in the laboratory (R. Reardon, pers. comm., March 2003) but otherwise there are no suspected negative impacts to non-target species. See Reardon and Podgwaite (1992) and Reardon et al. (1996) for details.
Synthetic gypsy moth pheromones can disrupt mating and can give good control or even local eradication when used against low-density populations. While traps are used for monitoring, when used for control pheromone is broadcast on tiny flakes over substantial areas. This technology has no known harmful impacts. For now pheromone based suppression will not be technically feasible for most managers unless as part of a larger USFS sponsored program in the area. Since the gypsy moth has no native close relatives, disruption of other species seems unlikely in North America and notably there have been no reports of males of other species being lured to traps baited with gypsy moth pheromone. Sterile male release (see Reardon and Castro, 1993) is also without negative impacts but is usually not an option.
Various Microsporidia have been investigated as biological controls of gypsy moth larvae. Some are reported to be significant in gypsy moth populations in Europe (McManus et al., 1989) and some have the advantage that they are passed on to offspring via eggs. According to Richard Reardon (pers. comm., 2003) they are more likely to cause chronic sub-lethal infection than high mortality. At least two have been "experimentally" introduced in Maryland and one is probably established. The literature reviewed contained little on non-target impacts, if there would be any. Impacts to native caterpillars have been investigated in the 1990s, and some species can host these pathogens at least in the lab. Results have not been reviewed for this document, and it is unknown if these biocontrols would have significant negative impacts on native species. Nothing on these organisms appears in Appendix G of the 1995 FEIS.
The fungus Entomophaga maimaiga has sometimes been directly introduced into gypsy moth outbreak areas but from at least West Virginia and New Jersey northward it is now well established naturally and it is spreading. At this time its application as an insecticide is not legal under EPA regulations. This fungus was introduced to New England from Japan in 1909 and considered a failure. Whether from this introduction or some other undocumented event, in 1989 Entomophaga collapsed a huge incipient outbreak in Connecticut and most of that state has not had severe defoliation since 1981 or 1982. This event got a lot of press coverage including articles in the New York Times, Science News and Discover magazine. The USFS Gypsy Moth News volume for April 1993 was appropriately titled "Maimaiga Mania" and is still a useful practical reference, for example if one wants to determine if virus or fungus is killing gypsy moth larvae on a site (see also Reardon et al., 1996). Spectacular collapses of gypsy moth populations continued south through New Jersey and into at least West Virginia. This fungus is now clearly established and likely to be a permanent major factor in regional forest ecology, although it is unlikely it will completely prevent all outbreaks. As discussed previously nontarget impacts range trivial to minor (some native Lymantriidae only) and this fungus this is safe for application on virtually any preserve. Caution would be suggested only if a rare native Lymantriid were present--perhaps possible on the outer coastal plain with Orgyia detrita but based on congeners impacts should be minor. Reported impacts to Dasychira species suggest little cause for concern assuming impacts to the rarer species would be comparable to commmon ones.
For biodiversity-oriented managers if Gypchek and pheromone flakes are not available, very often the only options are no action or aerial application of Bacillus thuringiensis variety kurstaki (=BTK) formulations. BTK occurs naturally in some soils, but not on foliage. Like chemical biocides, BTK is used for short-term control, but unlike Diflubenzuron the lethal crystal exotoxins are non-persistent and are nearly specific to some caterpillars. However the spores are much more persistent. Generally lethal effects from BTK persist a week or less after application (e.g. 1985 and 1995 FEIS; Sample et al., 1996; many others), but. Johnson et al. (1995) shows lethal effects persist for at least a month with swallowtails. High susceptibility to spores alone probably explains such lethal residual effects (Richard Reardon, pers. comm., August 2002). Most studies do not find persistent effects implying that most native Lepidoptera are not highly susceptible to the spores alone. Miller (1990a,b) demonstrates that even from two or three applications impacts disappear before August. Wagner et al. (1996) found differences between plots once treated once in May and untreated plots disappeared in June. Wagner's results strongly imply impacts for only about a week or less since the sampled caterpillars required several weeks of growth. The data in Butler et al. (1995) suggest BTK applied in May had little or no impact on a wide array of summer caterpillars. Schweitzer noted large numbers of large nests of Hyphantria cunea and defoliation by the catalpa sphinx (Ceratomia catalpae) less than two months after BTK spraying in Port Norris, New Jersey in the 1990s, implying little impact to hatchlings of either species by late May or early June. Still while very many or most Lepidoptera are not greatly impacted by spores months after applications, the possiblity of persistent lethal effects such as reported for swallowtails exists for other species. More information on impacts to caterpillars such as Saturniidae from the persistent spores is needed.
BTK will generally prevent defoliation or high numbers of gypsy moth caterpillars when properly applied. Like chemical biocides it will not aid in long term control. A single application should result in about 60 to 90% reduction of gypsy moth larvae (R. Reardon, pers. comm., 2003) which is usually sufficient to provide adequate foliage protection. A second application is often used in eradication projects or against unusually dense larval populations. Mortality from two or three applications is generally at least 80 to 90% and this strategy is commonly used in USFS eradication projects, often for two seasons. Biodiversity managers should carefully consider BTK and balance its impacts against those of defoliation. Since gypsy moth outbreaks and BTK have different negative impacts, from a biodiversity perspective a case can often be made for partial treatment of outbreak areas especially in large forested tracts.
BTK has two modes of action. Toxic protein crystals formed by the bacteria damage the gut and enter the body, and/or the caterpillar may succumb to a massive sepsis upon ingesting the spores. For some species both the spores and the crystal must be ingested for high mortality to occur (R. Reardon, pers. com., 2003). Sublethal effects also commonly occur (Peacock et al., 1998 and numerous other studies). All strains of BT must be ingested to kill. In terrestrial systems, non-target impacts from BTK will be limited or very nearly so to Lepidoptera larvae. Appendix G of the 1995 FEIS reviews investigations of BTK impacts to other organisms. It can kill some aquatic insects, primarily midges and blackflies, which is not surprising since another BT strain is often used to kill these. Less expected was mortality to some species of stoneflies (FEIS, Table 5-1). Biodiversity managers should consider buffers to minimize BTK in ponds and streams. Some other strains of BT kill leaf chewing larval or adult beetles, but apparently this impact has not been reported with BTK. It apparently does not affect Orthoptera and definitely does not kill at least most sawfly larvae. Concern for adult butterflies such as monarchs appear groundless. Data (see FEIS) are clearly adequate to conclude that most terrestrial, aquatic, estuarine and marine Arthropoda (broad sense) are unaffected by BTK, still with so many species and so much variation within Lepidoptera (even within families and genera) and variable effects among stoneflies, it is impossible to be sure there are no potential impacts. There is some chance a few additional Arthropods will prove sensitive to BTK. Note though mortality in sensitive species is not always high enough to be of conservation concern, even among Lepidoptera (Peacock et al., 1998; Wagner et al., 1996). For example (FEIS, 1995, Table 5-1) mortality to one of the stoneflies was only 30%. There are (same reference) some other studies showing low field mortality or mortality at high concentrations in artificial diets for other non-Lepidopterous insects. Some field reductions may be from indirect effects. While some of the references cited in the FEIS were not reviewed in preparation of the present document, it appears that significant direct impacts from BTK to terrestrial non-targets other than caterpillars are at worst quite rare.
Within the Lepidoptera impacts of various BT strains including BTK are widespread (Krieg and Langenbruch, 1981; Peacock et al., 1998). Field studies including Miller (1990a, 1990b), Sample et al. (1996), Wagner et al. (1996) and others show reductions (often about 30-70%) in Lepidoptera abundance, and sometimes species richness, following BTK applications. However most field studies do not examine species level effects so findings are invariably cumulative impacts to species that were unaffected, moderately affected, severely affected, or even eradicated. While the study was not optimally designed, the results of the sampling associated with the Highlands North Carolina Eradication Project (Schweitzer, 2000; Adams, 2001) indicate remarkably little impact to a very diverse macromoth fauna containing more than 758 species. See the discussion in Wagner et al. (1996) for a realistic assessment of the technical difficulty of sampling caterpillars, which would be the ideal way to assess BTK impacts. That study contains some useful species level data and Butler et al. (1995) also present useful species level data as do the Schweitzer and Adams Highlands reports. The Peacock et al. (1998) lab assays are the most useful source of species level information for the species included. In contrast to Diflubezuron studies some BTK field studies did include rearing out larvae to determine viability (or verify identity) and the data and discussion in Peacock et al. (1998) and Wagner et al. (1996) address this issue. Many to most, but definitely not all, larvae alive a week after BTK applications are viable (see below).
Within Lepidoptera, species level impacts of BTK vary enormously. Peacock et al. (1998) assayed native non-target species in instars actually present at the time of gypsy moth suppression applications. Effects under ideal laboratory conditions impacts ranged from none through slight developmental delay to 100% mortality in under five days. Mortality was significant for 27 of the 42 species (64%) assayed with Foray 48B, but 14 of these 27 produced viable adults and for some more than a third survived. Thirteen of the 42 species (31%) were considered highly sensitive. Such species would be at some risk of eradication from sprayed areas. Foray 48B and Dipel results were similar. Sensitivity was highly variable within Geometridae, Noctuidae, and Lymantriidae (see also Wagner et al., 1996) and varied greatly within genera Catocala and Lithophane in our data, and also within Orthosia and Dasychira if compared with Wagner et al. (1996). The fact that even for sensitive species a few to many individuals recover from BTK effects is an important difference from Diflubenzuron, and furthermore they will usually have little or no further exposure at least to the crystals. Note however Peacock et al. (1998) report delayed mortality in a few species including some that did not have significant mortality at 5-7 days. One butterfly had significant (100%) mortality only at or after pupation. So reliable claims of insensitivity to BTK really should ideally be based on survival to the adult stage and such claims should be rejected if not based at least on survival to pupation (see Peacock et al. 1998). No Microlepidoptera were included in these lab assays. Most micros gain some protection by feeding within shelters. Wagner et al. (1996) report 16 of the 17 most abundant micros were more frequent in treated plots, but species level results were not significant. Sample et al. (1996) report modest reductions of micros in their adult but not larval samples. However Miller (1990b) reports successful control of spruce budworm (a Tortricid) with BTK. Krieg and Langenbruch (1981) report numerous micros as affected by BT varieties.
BTK sensitivity is a species and/or instar level trait and based on the Peacock et al. (1998) data there appears to be little basis for predicting sensitivity of third and later instars of macromoths even on the basis of data for congenerics. Still some generalizations are justified regarding BTK impacts to caterpillars. In the absence of data to the contrary, first and second instar larvae can be presumed sensitive. All of 18 species assayed by Peacock et al. (1998) as first to third instars had significant mortality, which was 95-100% for 8 (42%) of them. For some species sensitivity was clearly reduced in the third instar. For 25 species evaluated as fourth to last instar, 10 had significant mortality, which exceeded 95% in five species (20%). While some species are highly sensitive in all instars, consecutive instars of other species differed substantially. By the third instar the only generalization apparently justified by the lab assay data is that Xylenini other than some Lithophane species are insensitive or only moderately sensitive.
The claim by Wagner and Miller (1995) that Saturniidae are highly sensitive to BTK is neither justified nor refutable based on the data in Peacock et al. (1998) because of high control mortality for two of the three species, in contrast to other assays in which the median control mortality at day seven was zero. Kaya (1974) found that 13% of fourth and fifth instar but virtually no early instars of another Saturniid, Anisota senatoria, survived BT var. alesti applications. Except for Hemileuca maia (which is highly sensitive to BTK), no other eastern US forest Saturniidae would have high exposure within a week (or often even a month) of typical single gypsy moth suppression applications. Assuming they are not at risk from lingering residual spores a month or more later, most Saturniidae and other summer feeding moths such as most Acronicta, Notodontidae, Limacodidae, actually should benefit from gypsy moth suppression applications of BTK. Treated areas will probably not be defoliated and thus their larvae will have normal food resources and lower generalist parasitoid levels in summer. Furthermore reduction of gypsy moth larval numbers might reduce impacts later in the season to native summer species from Compsilura.
Herminiine Noctuidae whose larvae feed in leaf litter (Hohn and Wagner, 2000) have been suggested as a potentially severely impacted group--especially if BTK spores were to persist and germinate in the litter possibly contaminating their food supply for several years. Unpublished laboratory data (D.Wagner and L. Butler, pers. comm.to Schweitzer in 2002) show several Herminiinae to be BTK sensitive and it is even possible species in some genera are consistently so contrary to the findings of Peacock et al. (1998) for other genera. Field samples of adults in the Highlands North Carolina Eradication project reports (Schweitzer, 2000; Adams 2001; and some additional interpretation herein) are highly consistent with sensitivity for many of the genera and species despite some sampling design issues. Idia species appeared unaffected but Renia species were rather uniformly represented at all sites early in the first season but for adults from larvae present at treatment time, frequencies per sample averaged 5.0 for the untreated samples and 0.5 at both treated sites. Polypogon (aka Zanclognatha) also appeared affected. Numbers of Renia and Polypogon were lowest the year of treatment suggesting there probably is not a large lingering impact from BTK spores in the litter or active bacteria in the soil. Actually the data in the final report (Adams. 2001) seem very definitive on that important issue. Herminiinae numbers clearly did not continue to decline further in 2000 and 2001 from the 1999 spraying, which is inconsistent with a severe lingering impact due to BTK persistence or reproduction seriously affecting the larval food supply of Herminiinae for several years. More data are desirable for Herminiinae but current results suggest variable sensitivity the first season with recovery starting the next season, in other words impacts comparable to other Noctuidae. There does not appear to be a basis for concern over severe long-term impacts to Herminiinae other than rare or highly localized species. However it should be stressed Herminiinae were almost unique among macromoths in showing any apparent impacts in these Highlands samples. Since potentially lethal Dimilinresidues do remain on leaf litter at least into the second summer and possibly longer, Herminiinae are likely to be much less impacted by BTK than by Dimilin.
Many species of butterflies, possibly all species, are highly sensitive to BTK. The published literature documents very high (often 100%) mortality to species in the Pieridae, Papilionidae, Lycaenidae and Nymphalidae (Peacock et al., 1998; Wagner et al., 1996; Krieg and Langenbruch, 1981; Herms et al., 1997; Johnson et al., 1995; Wagner and Miller, 1995). Drift from a single application of BTK apparently eradicated the population of Speyeria idalia at Gettysburg National Battlefield in the early 1980s. According to the USFWS Candidate Evaluation forms several populations of the imperiled Euphydryas editha taylori were eradicated by BTK applications aimed at Asian Gypsy Moth. No treated larvae of Speyeria diana, Papilio glaucus, Asterocampa clyton, Limenitis arthemis astyanax produced adults in the Peacock et al. (1998) assays. Eradication of local populations may have occurred with certain Lycaenidae in a Utah gypsy moth eradication effort (data not reviewed). Unpublished reports of high butterfly larval mortality exist for example to Lycaenidae even for substantial distances downwind in that project. No reports of insensitivity or moderate sensitivity to BTK were found for any butterfly, but Krieg and Langenbruch's tabulation suggests only moderate sensitivity for "Vanessa" io exposed to another BT strain. This could be misleading though since most or all BT mortality is delayed until pupation for two other Nymphalidae: Vanessa cardui (Morris, 1969) and Limenitis arthemis (Peacock et al., 1998). Wagner and Miller (1995) referring to the Peacock et al. data reported that the "spring azure" (actual species not stated because only NABA sanctioned common names were allowed) is highly sensitive. The species was Celastrina lucia. Significant differences in larval survival between treatment replicates precluded formal analysis or inclusion in the published results (Schweitzer, pers. obs.). Also few control pupae and no treateds eclosed probably due to inappropriate pupal storage. The sensitivity of this species is unclear other than that some treated larvae did pupate. Concern is clearly justified concerning eradication of localized populations of butterflies with spring feeding larvae such as Asterocampa, regionally localized Polygonia and relatives, azures, elfins, many hairstreaks, and the spring forest Pieridae.
Taken together field studies show that BTK significantly reduces but does not come close to eliminating native Lepidoptera as a whole (e.g. Wagner et al., 1996; Sample et al., 1996; Butler et al., 1995; Miller, 1990a,b). In general effects do not persist on summer foliage, so summer feeding species undoubtedly often benefit from BTK applications if these prevent severe defoliation or even high numbers of gypsy moth caterpillars. A few widely cited studies document that reductions of caterpillars cause emigration or decreased reproduction by vertebrates, including birds (Rodenhouse and Holmes, 1992) and shrews (Bellocq et al., 1992) in BTK treated areas. Some studies such as Holmes (1998) do not show such effects. See the 1995 FEIS for more studies. Such effects are also well known from chemical biocides applied against gypsy moth. Generally though BTK impacts to vertebrate food supplies are much less than those from Diflubenzuron and it is possible that in some cases they are less than those from gypsy moth defoliation, although data are not adequate regarding the last point.
The field studies cited cannot adequately address the issue of impacts to highly localized species (e.g. almost all species tracked by Natural Heritage Programs or ranked as globally rare by NatureServe), although there is discussion in Peacock et al. (1998) and Wagner et al. (1996). A few of these rare species (with varying sensitivities) are covered by the lab assays. Risks to such rare species must be assessed species by species at least for macro-moths. In the absence of actual data, the most prudent suggestions seems to be that managers should assume BTK is lethal to caterpillars of rare species, other than most Xylenini, feeding within a week of application, highly lethal if they are first or second instar. A reasonable working assumption when faced with lack of data for a given species that would be present as larvae, would be that impact to it will be comparable to those to the targeted gypsy moth. First to third instar gypsy moth larvae do appear to be more sensitive to BTK than most native species assayed by Peacock et al. (1998), and some in various field studies, but some caterpillars are more sensitive than gyspy moth larvae.
The data in Butler et al. (1995) suggest various families of sucking insects (Homoptera) benefit from BTK as compared to moderate defoliation. They probably benefit drastically when defoliation is near 100%. While there are no data it would seem very likely total defoliation obliterates these insects. Schweitzer strongly suspects drastic declines of aphids, Membracyids etc. might explain why sometimes (e.g. very late June and July 1981 around New Haven, Connecticut) sugar baiting for moths can be spectacularly good just after near total defoliation. Honeydew from these sucking insects is an adult noctuid food source, possibly an important one. One would expect some other insect herbivores such as katydids, tree crickets, Cynipidae and sawflies to benefit from BTK applications when the alternative would be severe defoliation.
In eradication projects the US Forest Service generally uses two or three BTK applications to a large portion of the treatment area for one or two seasons. It is well known that later treatments kills most gypsy moth larvae that survive the first one. Impacts to non-targets from these projects undoubtedly vary. Miller (1990) is an often-cited study from Oregon that showed substantial impacts, but without species level data little can really be concluded. Schweitzer (2000) and Adams (2001) concluded that the 1999 Highlands, North Carolina eradication project had very little impact on most native moths even in thrice sprayed areas. Impacts based on adult sampling were clearly minor or less for most species, including some that were sensitive in the lab assays. One has to wonder if larval mortality to BTK might have been offset by relaxation of some other density dependent mortality agent in this instance. Exceptions were major reductions of certain Herminiinae and probably Feralia jocosa. In particular there was no hint of any impacts to summer feeding species which is consistent with published studies. The Highlands studies did not look at butterflies.
Dale Schweitzer and Jane Carter at the USFS facility used by them previously (Peacock et al., 1998) and illustrated by Wagner and Miller (1995) assayed six species using two applications of 36 BIU equivalent ten days apart. These results are unpublished. For the geometrid Prochoerodes transversata the second treatment did kill all survivors of the first. For five noctuids the second treatment produced zero or insignificant additional mortality, including Eupsilia vinulenta, Chaetaglaea sericea, and Sericaglaea signata which are essentially insensitive to BTK, but also Egira alternans and Lithophane grotei which had significant first treatment mortality and were sensitive in the published assays.
Management Research Needs: More research on the impacts, or lack thereof, of gypsy moth outbreaks on native spring and summer feeding Lepidoptera and comparison to BTK treatment effects seems like a high priority. However field studies present some extreme difficulties (See Wagner et al., 1996; Sample et al., 1996). Observations of sleeved larvae of native spring species to quantify maturation dates relative to defoliation would give a better idea of which species are vulnerable to the most severe impact--outright starvation. Native summer species could be sleeved at low density to assay relative suitability of regrowth foliage after defoliation versus normal foliage. One could sample adult Xylenini and some other moths in defoliated and BTK treated areas and compare fecundity directly or indirectly using weights. However treatment areas would have to be at least thousands of acres since these moths are dispersive.
Research seems warranted to determine if there is any possibility of effective control of the parasitoid Compsilura concinnata. This could potentially benefit dozens of summer species which have been greatly reduced in New England and elsewhere and lead to re-establishment of now absent large native moths. Such research might include investigation of indirect impacts of BTK applications on this fly. Native parasitoids might also benefit.
A more general topic for which data seem inconsistent is persistence of lethal BTK residue on foliage. For most species lethal period is clearly only a few days but for a few such as Papilio glaucus it is reportedly much longer. Species that are unusually sensitive to the spores alone could probably be killed to some extent for the rest of the summer. Direct assays using larvae of known sensitive species sleeved in field treatment areas perhaps at ten-day intervals would answer questions about lethal residual impacts to groups like Saturniidae about which concerns have been raised. The USFS also maintains an excellent facility for bioassays with caterpillars at Ansonia, Connecticut. It is critical that any such experiments be designed such that control mortality approaches zero (the median in Peacock et al., 1998). High control mortality (except if with hatchlings which fail to establish in the rearing sleeve) generally raises the possibility of other major stresses to larvae besides BTK. The best way to achieve such low mortality is to sleeve larvae on growing plants as soon as practical.
Some miscellaneous topics follow:
- Better understanding of mortality as a function of dosage would be useful in protecting very sensitive non-targets such as some butterflies from BTK drift.
- A definitive answer to questions regarding sensitivity of native Lymantriidae (Orgyia, Dasychira) to NPV.
- Research aimed at predicting sensitivity of native Lepidoptera to BTK and a basis for predicting species level effects without actually doing assays.
- Research into the possibility of use of BTK as part of a strategy to reduce Compsilura impacts to larger summer moths.
- Documentation on the current status of native parasitoids, especially Tachinidae in areas heavily infested by Compsilura.
- Some effort to establish baseline data and monitor Saturniidae, Sphingidae, Datana and perhaps others as Compsilura continues to expand and increase, including where this fly was introduced in the western USA.
Relevance to Humans and Ecosystems
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.
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.
Negative Impacts: crop pest
Gypsy moth defoliation can benefit humans by opening up forest canopies and by reducing overcrowding of trees on homeowner's properties.
Stewardship Overview: Despite recently increased control from Entomophaga, gypsy moth will probably be a factor in North American forest ecology for the foreseeable future and it can certainly be expected to continue to expand its range by natural dispersal and to be moved to more distant areas by human transport. If gypsy moth populations reach release phase an outbreak will usually develop (but not as certainly as pre-1989 due to Entomophaga) and managers must decide whether to control them or let outbreaks run their course. On preserves such as those of The Nature Conservancy, or state "natural areas" which are actually managed as such, only biodiversity related issues (including possible tree mortality) need consideration. In some other contexts such as state parks, scenic and recreational areas, and residential areas nuisance factors may also be important. Risks associated with standard management tactics are discussed elsewhere. BTK, Gypchekand the several chemical biocides currently used are generally effective at suppressing defoliation. Dimilinoften provides somewhat greater reduction of gypsy moth larvae (and has much greater impact on non-target caterpillars etc.) than BTK or Gypchekbut the results are not immediate because it does not kill until the next naturally occurring molt and larvae feed normally until then. The newer Mimicwould likely kill faster since it induces a premature molt. Carbaryl (Sevinand BTK typically affect larvae at their next feeding, with death within hours from the former, and thus defoliation is greatly reduced byt either treatment within a day or two. Gypcheckcauses a viral disease which takes several days to two weeks to kill, but when applications are timed properly against young larvae it is quite effective at suppressing noticeable defoliation without killing non-targets. Data in Reardon et al. (1996) suggest about an 85% reduction of larvae and about a 50% reduction in defoliation--which is normally enough to prevent significant damage to trees even where heavy defoliation would otherwise be expected. BTK at least as a single application, may not be adequate to prevent significant defoliation in truly extreme situations with thousands of egg masses per acre and the same is probably true of GypchekIt should be stressed that both BTK, which impacts some non-target Lepidoptera, and Gypchekwhich apparently has minimal or no non-target impacts, are normally quite adequate for foliage protection. In such extreme cases where these alternatives would not be adequate, consider the high probability that the outbreak will collapse after the upcoming defoliation without treatment. In some cases it is virtually impossible to assess whether BTK or no action is the preferred alternative in terms of impacts to native biota. Any review of options should always strongly consider no action as a possible alternative.
Concern about defoliation itself is not usually a major issue for managers of biodiversity oriented preserves, but tree mortality sometimes is. Old growth forests should be protected from at least repeated severe defoliation. Gypchekis always acceptable and in most cases BTK should be considered preferable to repeated defoliation in old growth. Old growth forests are not likely to contain Lepidoptera not found in similar adjacent second growth forest and risks to other terrestrial organisms is minimal at worst. For example once surviving specimens at rutgers University were examined and misidentifications such as Heterocampa "varia" and a large majority of the Papaipema were corrected, the moth list for old growth Hutcheson Memorial Forest, New Jersey compiled by Moulding and Madenjian (1979) contains no globally rare species among the 410 species encountered in a five year light trapping study. Oligia crytora (2), Cycnia inopinatus (1), Tornos scolopacinarius (1), if correctly identified, are the only possibly state-rare species but the last two are not forest species and C. inopinatus was probably a misidentification for the common C. tenera. One might expect litter feeding Herminiinae to contain unusual species in old growth areas, but there are only common ones in the Moulding and Madenjian list and among the specimens examined and there is no evidence any rare Herminiinae are particularly associated with old growth. There is no reason to believe these findings are highly atypical, so there should be no long-term negative impact from BTK in most old growth areas especially if there are unsprayed similar second growth stands nearby. The Lepidoptera species most likely to be of concern in the context of old growth forests is Diana fritillary but its optimal Appalachian habitats usually are not susceptible to heavy defoliation. It is highly sensitive to BTK (Peacock et al., 1998).
Globally rare plants are almost never a direct management issue in dealing with gypsy moth. Few globally rare plants are vulnerable to defoliation, in large part because gypsy moth larvae seldom eat herbaceous species. A more important concern with globally rare plants might be protecting their habitat if they are especially sensitive to decreased canopy cover caused by tree mortality. Information on susceptibility of new growth of box huckleberry would be useful but other species in that genus are disfavored as foods. Betula uber would seem to be at minimal risk based on its habitat. State-rare species of trees and shrubs could be an issue. For example two state-uncommon peripheral oaks, Quercus nigra and Q. michauxii, were substantially reduced by persistent initial outbreaks in Cumberland County, NJ. The latter may have been eliminated from Bear Swamp West preserve (Stevens Heckscher, pers. comm., 1990) but seems to have been little impacted in adjacent Bear Swamp East where overall tree mortality was lower. Most of the few mature Q. nigra were killed by the multiple defoliations (see above).
Some globally significant natural communities might be at risk of unacceptable levels of alteration from repeated defoliations, especially with initial invasions. Substantial stand changes are most likely in mixed hardwood stands with substantial oaks but not oak dominance. Such stands usually are on moderately acid or near neutral mesic soils. See 1995 FEIS Appendix G for more information and references. Mortality of scrub oak (Quecrus ilicifolia) from gypsy moth defoliation appears to be unreported and seems very unlikely. This shrub is an important component of several rare natural communities and a foodplant for many rare Lepidoptera. Foodplant mortality is not likely to be a significant impact to barrens Lepidoptera.
Generally protection of native fauna from outbreaks will not be a concern since impacts are usually only short-term (see 1995 FEIS Appendix G). Special cases could occur, most likely involving localized occurrences of rare Lepidoptera, perhaps rare salamanders. A tentative decision was made to use partial treatment with BTK to protect disjunct occurrences of Heterocampa varia and Acronicta albarufa on Nature Conservancy lands at Manumuskin, NJ in the 1990s. Both are summer oak feeders. However, while surrounding xeric and mesic forests were mostly 80-100% defoliated once or twice, the ultraxeric oak woodlands these species prefer locally had neither detectable defoliation nor high numbers of gypsy moth larvae so no treatment was needed. Probably delayed phenology of the oaks minimized gypsy moth hatchling establishment.
In some cases a BTK treatment might even be considered to protect occurrences of spring feeding moths id severe defoliation is anticipated and Gypchekis not an option. Or a manager may wish to consider the relative impacts of BTK versus expected defoliation. For spring feeding butterflies BTK impacts will probably exceed defoliation impacts except perhaps if defoliation would lead to virtually 100% starvation. If severe defoliation is likely to occur unusually early posing a risk (or certainty) of mass starvation, moderately BTK-sensitive or insensitive (Peacock et al., 1998) spring feeding and nearly all summer feeding native caterpillars should benefit from BTK treatment as opposed to no action. Beneficiaries probably include a majority of forest moths, but some of the others and most breeding butterflies could be severely reduced or even eradicated. If defoliation occurs at more normal time (e.g. mid or late June for Connecticut) spring species are likely to be less impacted by severe defoliation than by BTK. The benefits from BTK would probably outweigh the risk to a species with lab assay BTK mortality under 80% and good recovery of survivors. Field mortality will probably be lower. The practical problem though is that it is generally impossible to know the sensitivity of the species of concern (see Peacock et al., 1998), unless the actual species (not its family or even genus) is included in published or otherwise available data.
Determining whether or not a particular Lepidoptera species is at risk from BTK is difficult. To be sure, a manager needs to know the phenology of the species and its sensitivity to BTK, but the latter is unknown and unpredictable for many moths. See discussion elsewhere in this document. For now at least it appears butterfly larvae generally are highly sensitive. For other Macrolepidoptera the Peacock et al. (1998) assay data indicate nearly all species will incur significant mortality from BTK applications if they are first or second instars and for half of these species nearly all larvae could be killed. See Peacock et al. Tables 2, 3, 4 to roughly estimate instar present for the genus. Local Lepidopterists might be able to help land stewards determine the precise phenology of species of concern. Dale Schweitzer can be contacted for rare species. The NatureServe website may also be helpful. In some cases published literature would suffice. However consider the ecology of the species: even 100% mortality of larvae present on application day may not be cause for concern if large numbers of eggs will be hatching a week or more later. At this time of year no macromoth eggs can normally develop to hatching in less than 10 days and many need twice that, so sensitive species such as Actias luna, Antheraea polyphemus, spring Zale, Eutrapela clemataria, Lambdina "fervidara" still flying as adults should not be at risk unless they are unusually sensitive to residue for several weeks. Likewise hatchling mortality may not be of much concern if mid instars are less sensitive (which is by no means a safe assumption except with most Xylenini) and are already present. On the other hand species such as Hemileuca maia, Ennomos magnarius, some Catocala would be 100% at risk as first or second instars from eggs laid the previous fall and the first two and some Catocala were highly sensitive in the lab assays. Early spring species that finished oviposition within two weeks before application would also have very high exposure as first or second instars, likely examples include Pyrgus wyandot, Euchloe olympia, Callophrys henrici.
If the species of concern is a xylenine noctuid (=Lithophanini, Antitypini of Forbes, 1954) of a genus other than Lithophane and present in third or later instar, impacts of BTK will very likely be trivial or at least not worse than from severe defoliation. This is based on Peacock et al. (1998) results consistently showing low or no BTK-sensitivity for species of Chaetaglaea, Sericaglaea, Metaxaglaea, Sunira, Eupsilia, Xylotype, and moderate for Xystopeplus. The four species of Lithophane were more variable, with L. grotei extremely sensitive in a mid instar. On the other hand more than half of treated second instars of the globally rare L. lemmeri produced normal adults making it possibly the least sensitive species assayed as first or second instars. Catocala is another group with multiple state-rare species in the eastern USA that occasionally are at risk of severe mortality in gypsy moth outbreaks (Gall, 1984). The species assayed varied greatly in sensitivity to BTK. However impact to this genus appeared unexpectedly minimal from the Highlands, North Carolina gypsy moth eradication project (Schweitzer, 2000), although the data were not extensive.
Protection of native Lepidoptera or other organisms from impacts of established biocontrols is essentially impossible. A land steward might decide to decline releases of future biological control species on a preserve. However if the organism establishes elsewhere in the area it will soon be present anyway. Serious impacts to native species are known or strongly suspected only from Compsilura concinnata among the parasitoids and pathogens now established, but impacts from the pupal parasitoid Coccygomimus pedalis (Hymenoptera: Ichneumonidae) may also be a concern. No effective action to maintain or restore populations of species affected by exotic parasitoids is possible since the problem extends far beyond any preserve boundaries. It sometimes happens that Compsilura reaches high levels in outbreaking gypsy moth populations. In this case impacts from both species might be reduced with BTK, or even with a quickly lethal non-persistent chemical biocide, which should greatly benefit vulnerable summer caterpillars, although to the detriment of spring species. Gypcheckprobably would not kill quickly enough to prevent maturation of Compsilura. Such use of BTK could backfire and lead to unusually high parasitism of native spring caterpillars since Compsilura females would not be killed by BTK but would be deprived of gypsy moth larvae. Data are not available on this issue. Furthermore sublethal effects on native spring caterpillars could leave them more vulnerable than usual to parasitism (FEIS, 1995, Appendix G). In reality though a manager will probably not know that Compsilura numbers are excessive in time to consider acting.
Species Impact: Public nuisance factors during gypsy moth outbreaks can be severe (see Goebl, in Fosbroke and Hicks, 1987; FEIS, 1995) but are not dealt with here. Defoliation is obviously aesthetically unpleasing and can have direct economic impacts. The extreme number of larvae are sometimes also a legitimate nuisance, even ignoring irrational entomophobia. A few people are allergic to the larval hairs, but neither current control practices nor gypsy moth pose serious human health risks (see FEIS, 1995). Generally biodiversity managers need to consider three possible impacts: tree mortality, impacts of control measures, and sometimes impacts of outbreaks themselves, including defoliation per se on native species. See Threats Section for this topic.
The most obvious long-term ecological impact of outbreaks is tree mortality, which is very variable. Rarely are the affected trees rare species themselves so low or moderate tree mortality might not necessarily concern biodiversity managers. Oaks are most likely to be killed (Nichols, 1980 and many others) followed by conifers, but hickories and others also may be killed. For initial outbreaks 10% to 30% mortality to oaks and other highly susceptible hardwoods is likely if two or more severe defoliations occur, with generally lower mortality in subsequent outbreaks. Mortality is often zero to 10% (Gansner and Herrick, 1979), but in worst case scenarios (e.g. sites selected for the Quimby, 1985 study) can run about 50% of the stand. A useful review is Hicks and Fosbroke (in Fosbroke and Hicks, 1987), but USFS staff can probably suggest more current works. Trees on poor sites such as ridgetops or in poor condition or stressed by low soil moisture are most likely to die. Defoliation insufficient to force oaks to refoliate causes virtually no mortality to hardwoods. Heavy tree mortality may alter future stand composition especially if edaphic conditions are good for less favored species. Healthy hardwoods normally recover from one complete defoliation but hemlocks and some other conifers generally die, although white pines often recover (Stephens, 1984). With the loss of hemlocks to adelgids, white pine is now the most likely conifer to be defoliated in much of the US range of gypsy moth. Pines in extensive pine barrens and pine forests are not at risk of defoliation from the established gypsy moth strain.
Besides tree mortality, other changes such as altered competitive interactions, reduced seed production, changes in herbaceous flora which might affect germination of tree and shrub seeds and others changes can in some situations alter future forest composition, as can deliberate silvicultural manipulations. See Musika (1993) for a useful introduction to the many possible ecological factors besides tree mortality. As he points out composition changes are possible but also vary greatly with site conditions and location. Probably an even more over-riding impact now in many areas such as many National Parks, and places like Connecticut and northern New Jersey where hunting is minimal is extreme herbivory by deer, often leading to drastic reduction or total elimination of tree reproduction. Deer and invasive exotic plants are likely to interact with direct gypsy moth impacts in affecting future forest composition and the relative importance of gypsy moth will vary. Stand composition is a complex issue which is not addressed in detail in this document and review of post FEIS literature on the topic was minimal. In some places poor acid soils prevent replacement of oaks with other species as long as deer and other factors do not severely suppress oak reproduction.
Other impacts of defoliation are numerous but mostly short term (FEIS, 1995, Appendix G), but in certain circumstances localized populations of Lepidoptera and other herbivores could be eradicated if defoliation is severe (see threats section above), especially on west facing xeric ridges where defoliation may occur earlier. In general the conclusion of the FEIS Appendix G that impacts of gypsy moth outbreaks to native Lepidoptera are mostly short term is certainly correct (see also Sample at al., 1996) but the possibility exists for long term impacts.
Soil and litter fauna including salamanders are affected by increased insolation and temperature for several weeks while the canopy refoliates. However, apparently mortality is not generally high since most can move deeper into the humus or find shelter. It is worth remembering that some forests defoliated by gypsy moth are also subject to occasional defoliation by native caterpillars. A temporary rise in water temperature of streams and ponds may be a concern but long term biotic changes are not the norm. Nesting success of birds may or may not be affected positively or negatively by outbreaks. Fee the 1995 FEIS and references in it for more details regarding birds. Gray squirrels are among the most heavily impacted vertebrates due to the loss for several years of hard mast production, especially acorns. Many native and exotic understory plant species are temporarily favored by the increased light during outbreaks (e.g. Musika, 1993), e.g. the globally rare orchid Isotria medeoloides (Brackley, 1985) and Asclepias tuberosa (Schweitzer). Probably the greatest concern for rare and even common native understory plants and their native herbivores if tree mortality occurs is increased invasion of exotic plants or aggressive natives like Smilax rotundifolia with increased light.
The Gypsy Moth (Lymantria dispar) are moths in the family Erebidae. Lymantria dispar covers many subspecies, subspecies identification such as L. d. dispar or L. d. japonica leaves no ambiguity in identification. Lymantria dispar subspecies have a range which covers in Europe, Africa, Asia, North America and South America.
|Common name||Subspecies||Distribution||Identifying characteristics|
|North American Gypsy Moth||Lymantria dispar dispar||Eastern North America:6||Females winged but flightless:6|
|European Gypsy Moth||Lymantria dispar dispar||Europe, western Asia and north Africa:6||Females winged but flightless:6|
|Asian Gypsy Moth||Lymantria dispar asiatica||Eastern Asia,:6 western North America||Flying females; attracted to lights:6|
|Japanese Gypsy Moth||Lymantria dispar japonica||All of Japan:6||Large males, very dark brown color:6|
The Asian Gypsy Moth (Lymantria dispar asiatica) is native to southern Europe, northern Africa, Asia and Pacific. It is spreading to northern Europe (Germany, and other countries), where it hybridized with the European Gypsy Moth. A colony had been reported from Great Britain in 1995.
This moth is an important defoliator on broad-leaf and conifer trees.
The order Lepidoptera contains moths and butterflies characterized by having a complete metamorphosis; larvae transform to pupae and then metamorphosing into adult moths or butterflies.:9 The family is Lymantriidae.:9 Lymantriid larvae are commonly called tussock moths because of the tufts of hair on larvae.:9
The meaning of the name Lymantria dispar is composed of two Latin-derived words. Lymantria means 'destroyer'. The word dispar is derived from the Latin word that means 'to separate' and it depicts the differing characteristics between the sexes.:9
The North American gypsy moth and the European gypsy moth are of the same species, often listed as Lymantria dispar dispar.:6 Confusion over the species and subspecies, for classification still exists. The U. S. Department of Agriculture defines the Asian gypsy moth as "any biotype of Lymantria dispar possessing female flight capability",:5 despite Lymantria dispar asiatica not being the only classified subspecies that is capable of flight.:6 Traditionally, Lymantria dispar has been referred to as "gypsy moths" even when referring to Japanese, Indian and Asiatic gypsy moths.:5
- Pogue, Michael. "A review of selected species of Lymantria Huber ". Forest Health Technology Enterprise Team. Retrieved September 14, 2012.
- "Asian Gypsy Moth Lymantria dispar asiatica". Pest Tracker National Agricultural Pest Information System. Retrieved September 14, 2012.
- FAO - Profiles of selected forest pests
- The Gypsy Moth: Research Toward Integrated Pest Management, United States Department of Agriculture, 1981
- Free Dictionary for Lymantria
Names and Taxonomy
Comments: This is the familiar gypsy moth and it has a massive synonymy. Some authors recognize subspecies in which case the American one is still basically the typical European L. dispar dispar but other strains will probably get mixed in and the Asian one perhaps already has. Other generic names have been used in older literature, such as Porthetria
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