Gypsy Moths One of the most notorious pestsof hardwood trees in the eastern United States
Scientific Classification Kingdom: AnimaliaPhylum: ArthropodaClass: InsectaOrder: LepidopteraFamily: LymantriidaeTribe: LymantriniGenus: LymantriaSpecies: Lymantria dispar
History of the Invasion • Etienne Leopold Trouvelot (December 26, 1827 – April 22, 1895) • He fled from France during a coup d’etat in 1852, and settled in what is now Medford, Massachusetts • He made a living as an artist, however he was also an amateur in entomology (the study of insects) • Trouvelot wanted to do something about the growing taxes on imported silks from France and Italy since there was a disease running through their silkworm populations Etienne Leopold Trouvelot
Trouvelot went to France in the 1860s and on his return trip, he brought some gypsy moth egg masses with him to see if they could be used for silk production in America • While he was culturing the moths in his backyard, the larva somehow escaped • Trouvelot tried to take action when he discovered that they were gone by notifying local entomologists • However, no responsetook place • Trouvelot turned to the field of astronomy soon after, losing interest in entomology Early attempt at gypsy moth eradication… obviously unsuccessful as have been all other methods.
Egg Stage • Longest stage, typically July through April. • Eggs laid in large egg masses, containing 500-1000 eggs • Eggs need to be kept warm and dry, and the female covers the masses with velvety hairs from their bodies • Eggs placed in sheltered areas to survive the potentially harsh overwintering stage
Larvae Stage • Caterpillar stage, early spring to mid May. • Larvae go through 5 to 6 larval stages (instars). Males have 5 and females 6 due to size. Between stages they molt by shedding their skin. • High growth period where defoliation occurs • Dark-colored and covered with setae (hair-like bristles), with five pairs of blue dots followed by six pairs of red dots lining the back. • Since females are flightless, how do they get around?
Natural Dispersal • Occurs as soon as the newly hatched larva emerge because they can be found on the host trees hanging from a silken thread. Once the wind picks up, it will carry the larva about a mile in distance (ballooning)
Artificial Dispersal • Occurs when people transport the larva miles from the infected areas by car, in or onhousehold goods, or on wood products such as whole tree timber or firewood • Humans are a major problem in controlling the spread of the moth. • If the public becomes more educated, will that stop every occurrence, or will there still be occasions where the moth is still dispersed?
Pupae Stage • Late June through July, 10-14 days. • Gypsy moth pupae are covered with brown, tear-drop shaped protective shells about 1 to 2 inches long. • Caterpillars seek hidden spots in which to pupate. This is important because once they have pupated, they are quite vulnerable to attack by predators and parasites.
Adult Stage • Adult gypsy moths emerge in mid July. • Males are dark brown to grey, are good fliers, and have feathery antennae. • Females are cream colored, larger and flightless.
Adult stage, contd. • Adults live for 7-10 days, and do not feed on leaves. • Newly emerged adult females release a sex pheromone (a strong scent) that attracts males. • Males can detect female pheromones from a mile away. After mating, females begin to lay eggs. • Females usually deposit their eggs just a few inches from where they emerged from their pupal stage. • Egg laying completes the life cycle, and the adults die.
Gypsy moth egg masses on the trunk and branch of a tree Gypsy moth larvae emerging from egg mass (first instar) Older gypsy moth larvae showing five pairs of raised blue spots and six pairs of raised brick-red spots
Gypsy moth pupae after all instars are completed Male gypsy moths will emerge first Female gypsy moth laying eggs after mating occurs
European and Asiatic Hybrid • First identified in North America late in 1991 near the Port of Vancouver in British Columbia, Canada. Moths were discovered in Washington, Oregon, and British Columbia shortly after. • Ships infested with egg masses from ports in eastern Russia probably introduced the pest to North America while visiting ports on the West Coast. Scientists believe that while the ships were docked, larvae hatched from the eggs and were blown ashore.
Hybrid, contd. Hybrids may be resistant to particular means of controls. They also: Feed more readily on conifers Have better flight capabilities (females capable of flight) Have a broader host range Norfolk Island Pine Araucaria heterophylla
Asian gypsy moth survey 2005-08 http://pest.ceris.purdue.edu/searchmap.php?selectName=ITAXQBA
Hosts White OakQuercus alba • Gypsy moths are known to feed on more than 500 species of plants, principally broad-leafed trees and shrubs. In the eastern U.S., the gypsy moth’s favorite trees include apple, speckled alder, basswood, gray and river birch, hawthorn, oak (many species but preferentially white oak), poplar, and willow • The gypsy moth tends to avoid ash trees, tulip trees, American sycamores, butternut, and black walnut trees
Effects of Defoliation • Effects depend on many factors, including: time of year, consecutive defoliations, soil moisture, and sp. • If less than 50 percent of their crown is defoliated, most hardwoods will experience only a slight reduction (or loss) in radial growth • If more than 50 percent of their crown is defoliated, most hardwoods will refoliate or produce a second flush of foliage by midsummer • Trees weakened by consecutive defoliations are also vulnerable to attack by disease organisms and other insects
Rate of Spread • Maps show that the moth has spread south and west at a rate of up to 20.9 km/year in some areas • Gypsy moths have even been found in eastern Canada and Michigan • Scientists believe that the gypsy moths arrived in Michigan and Ontario as a result of an accidental introduction in the early 1960s (though they are not really sure) and there were failed attempts to eradicate it there
European Gypsy Moth Survey 2005-08 http://pest.ceris.purdue.edu/searchmap.php?selectName=ITAXAIA
General range of the gypsy moth as of 2003. Photo courtesy of Sandy Liebhold.
The USDA Forest Service is currently working on a national project in order to slow down the spread of the gypsy moths • This is based upon the grids of pheromone traps along the expanding front in order to detect isolated colonies • These colonies are then eradicated or suppressed in hopes of preventing them from coalescing, and this would decrease the rate of spread
Why is this a problem? • Gypsy moths make their homes in many of the hardwood trees here in the U.S., mainly in oaks and aspen trees • Highest concentration of gypsy moth colonies can be found in the southern Appalachian Mountains, and within the northern lake states • Gypsy moth populations can fluctuate within the forest stand depending on the breakout; densities could be 1 egg mass per ha to over 1,000 per ha • Whenever the densities reach over 1,000 per had or higher trees could become completely defoliated
Major changes will begin to appear in the vegetation since the gypsy moths will eat almost anything in sight One of the biggest and major concerns is that there will be a potential loss of the economically critical and ecologically dominant on the oak species Most studies are showing that forest compositional changes with the gypsy moth defoliation indicate that less susceptible species (in the near future) will dominate; which in turn will present the forest with problems Forest Effects?
Cluster of trees killed following gypsy moth defoliation, central PA. Defoliations like shown can significantly alter the habitat by removing high canopy species and promoting increases in shrub species like the Eastern Towhee (Pipilo erythrophthalmus)
Biological Controls Peromyscus maniculatus • Deer Mice (Peromyscus) • considered the most important predator of low-density gypsy moth populations and their abundance may be critical in determining whether populations go into an outbreak mode • abundance is strongly affected by the amount of mast (e.g., acorns) in the previous year
Biological Controls, contd. • Tachnid Flies (family Tachinidae) • Parasitize gypsy moth populations. While they may become quite abundant during a gypsy moth outbreak, they apparently have little effect on the population dynamics Parasitoid wasps (family Braconidae) • Parasitize moths as well, but has little effect on population dynamics.
Avian Predators Coccyzus americanus • Cuckoos (family Cuculidae) have been known to prey on caterpillars. • Chickadees (family Paridae) will peck at egg masses. • In general, birds do not have a strong effect on gypsy moth population dynamics. Poecile atricapillus
Nucleopolyhedrosis Virus (Gypcheck) • Viral disease, sometimes also known as “wilt” is naturally occurring in all gypsy moth populations • It is caused by a nucleopolyhedrosis virus (NPV), and is derived by the existence of a matrix of polyhedral proteins that are surrounded by the viral DNA • Infection occurs when caterpillars eat foliage contaminated with this viral oclusion bodies • At low populations not much happens, though when there is a high population level the virus works more effectively Virus killed gypsy moth larva
Entomophagamaimaiga Gypsy moth remains after E. maimaiga • Fungal biological control (family Entomophthorales) • Presence of E. maimaiga may be determined by late instar gypsy moth larvae which, when infected with this fungus, die hanging vertically from tree trunks with prolegs extended laterally. The cadavers subsequently fall to the bases of trees • Quite family-specific to gypsy moth, but highly variable and unpredictable as a control
DDT • Dichloro-Diphenyl-Trichloroethane, a synthetic pesticide • Became available after World War II • Banned in 1972, due to concerns over environmental contamination, and its effect on the thinning of avian egg shells
Sevin (Carbaryl) • Controversial insecticide initially used with DDT. • Known effects include: Can wipe out bee colonies. Causes birth defects in mammals, especially dogs. Worsens the condition of people with hypertension and people on anti-depressant drugs. Impairs the function of the pituitary gland, the thyroid gland, and the reproductive system. Causes hyperactivity and learning disabilities in mammals. Could increase the chance of heart attack in people with weak hearts. The main break-down product, nitrosocarbaryl, which is easily created in the human gut, is a potent cancer-causing agent. It causes irreversible chromosomal damage to human DNA • Illegal in some countries, including the U.K.
Dimlin • Insect growth regulator that interferes with the synthesis of chitin, essential to arthropod exoskeletons. • Toxic to a wide spectrum of arthropods, and persists for a long period of time in canopy and leaf litter. • Still used fairly regularly due to cost and results.
Bt (Bacillus thuringiensis) • World’s most widely used organic insecticide • The bacterium produces a crystal protein toxin that kills the cells lining the insect gut. When ingested, the bacterial cell wall is digested which releases this toxin. Since insects have guts that are only one cell layer thick, this toxin literally "eats" a hole in the gut, causing an infection in the body cavity (only particular insects affected). • An article by Broderick 2006 showed that Bt only kills gypsy moths when other native bacteria are present in the insect's intestines.
What are local agencies doing to fix this problem? • Many local agencies are working on ways to stop the spread of the gypsy moth; many states have already lost millions of acres due to this invader • States like Pennsylvania and West Virginia are trying to make the general public aware of the growing problem at hand • Many areas that are infected badly are holding work shops to help educate the public in what to do if they spot the moths on their trees
In West Virginia, gypsy moths appeared in 1972, and has spread across the eastern panhandle and northern counties of the state • The local Division of Forestry department has five essentials steps in which would minimize the impact that the gypsy moth, and these are: • Identify stands where the severe impacts are likely • Determine when defoliating populations are present • Spray to prevent heavy defoliation • Use silviculture to minimize impacts • Salvage dead trees within two years • Gypsy moth regulatory program
Other states like Wisconsin are changing their silvicultural techniques to help control the problem Selection and spacing of the hardwoods trees could help reduce the speed in which the gypsy moths move Also, the type of trees that are planted could also affect how many will die after a breakout Woodlots also need to be stocked with trees and thinned to proper densities in order to control the spread The variety of trees that are found within a woodlot could also help slow down an outbreak by providing less suitable hosts for the moth
Over the past 20 years, several millions of acres of forest land have been aerially sprayed with pesticides to control the outbreaks There are areas in the infected areas that are treated by private companies, or by joint programs of state governments and the USDA Forest Service In 1992, the USDA Forest Service began a pilot program in order to test the feasibility of slowing the spread of the gypsy moth These STS pilot programs are currently being done in North Carolina, Virginia, West Virginia, and also in Michigan Management and Research
Funding • So far, intensive studies have been done over the 100 years in North America to figure out how to either control or stop this growing problemAll work is being funded by the USDA Forest Service, the USDA Agricultural Research Service, the USDA Cooperative State Research Service, the USDA Animal and Plant Health and Inspection Service and state and private universities