The Gypsy Moth...
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The gypsy moth is
a native insect of Europe, North Africa, and Asia. There are two varieties
of gypsy moth (Lepidoptera:Lymantriidae), the European and the Asian.
The European variety is established in the northeastern and midwestern
United States, having expanded from the original introduction near Boston.
European moths are smaller than the Asian variety; however, they are both
members of the same species. Unlike the flightless European females, Asian
female moths can fly long distances to lay their eggs. The caterpillars
feed on several hundred species of trees and shrubs. Preferred hosts include
oak, apple, alder, aspen, basswood, willow, birch, cottonwood, and plum;
coniferous species such as Douglas fir, pine, and western hemlock are
suitable hosts as well.
In 1868, scientist
Leopold Trouvelot brought European gypsy moths from France to Massachusetts
to breed a silk-producing caterpillars or "silkworms." The experiment
failed and some of his caterpillars escaped. They found the environment
here in the United States conducive with their feeding requirements, with
abundant food and few natural enemies.
Gypsy moth spread naturally by "ballooning". Newly hatched larvae
hang from long silken threads from the end of branches. Wind breaks the
threads and carries the larvae on air currents. Distance traveled is usually
short, often to the next tree. The majority are moved less than a kilometer.
Long distance spread is assisted by man through the artificial transport
of life stages. Typically this is by the movement of outdoor household
The gypsy moth goes through four life stages: egg, larva (caterpillar),
pupa, and adult.
Eggs hatch around the time of oak bud break. Early stage larvae will tend
to stay in the lower forest canopy, but under high populations, larvae
will move higher in the crown to disperse through ballooning. Larvae or
caterpillars go through 5 stages or instars for males and 6 for females.
Each caterpillar is capable of eating a square meter of foliage, before
spinning a resting area and pupating. Moths emerge in early summer. Females
release scent or pheromone to attract a mate. This pheromone has been
synthesized for used in detection traps as well as for control.
In early summer, females lay eggs on trees as well as a variety of outdoor
items. Each egg mass can have several hundred eggs. Gypsy moths overwinter
in the egg stage, and hatch in April or May. The young caterpillars are
black and hairy, later becoming mottled gray with tufts of bristlelike
hairs, and blue and red spots on the back. There is one generation per
year. Adults differ in appearance, males being brown with a fine, darker
brown pattern on the wings. Females are nearly white, with a few dark
markings on the wings. European females do not fly. Caterpillars climb
trees and feed mostly at night. They are capable of reaping foliage from
trees, and this activity will kill many trees if repeated over a few years.
Trees also become weakened and more susceptible to diseases and wood boring
Like those of other
defoliators, gypsy moth outbreaks usually last two years. In oak-dominated
stands, gypsy moth outbreaks usually persist two or three years, before
collapsing. Populations can remain low for up to ten years before rebounding
Effects of gypsy moth defoliation are usually most severe during the initial
outbreak in a newly infested area. If more than 60 percent of the tree's
canopy is consumed by gypsy moth caterpillars, trees typically refoliate,
producing a second set of leaves later in summer. Low rates of diameter
growth are common during years of heavy defoliation and often for one
or more years after defoliation ceases.
The amount of tree mortality and topkill sustained during a gypsy moth
outbreak depends on the severity and frequency of defoliation, as well
as tree health. Defoliated trees often become more susceptible to attack
by other insects and disease.
Outbreak populations naturally decline due viral disease, fungi, natural
enemies, and starvation. Low gypsy moth populations may be held in check
by birds, insect predators, and small mammals for several years, before
the next outbreak occurs.
of gypsy moth requires an integrated approach that includes several strategies.
When population densities are high or in outbreak situations, the most
effective approach for preventing widespread defoliation and reduction
of the population is aerial applications of a biologically derived compound
known as Bacillus thuringiensis kurstaki, or Btk. Bt sprays are only effective
during the caterpillar life stage, and otherwise harmless to other animals,
including birds, humans, and fish.
A fungal disease of gypsy moth called Entomophaga maimaiga is a promising
control of gypsy moth. The fungus was probably imported from Japan to
areas near Boston, Massachusetts around 1910. This attempt to establish
the fungus seemed to fail since extensive surveys did not reveal the pathogen.
E. maimaiga was not observed in North America again until June, 1989 when
dead caterpillars found clinging to trees in the northeastern U.S. revealed
Mating disruption (MD) is used primarily in the Slow-the-Spread Zone.
MD involves broadcasting pheromone flakes over a specific treatment area.
Pheromones are chemicals produced by insects to communicate. To control
gypsy moths, the pheromone is incorporated into plastic laminated flakes
that are mixed with a sticking agent and released from the air. The sticking
agent is not strong, but will ensure the pheromone is distributed at all
levels in the forest canopy where gypsy moths may live.
Once the flakes are released, they saturate the air in the treated area
with the pheromone for two to three months, disrupting the communication
between the female and male gypsy moth. The pheromone flake release in
early to mid-June is timed to correspond with the male gypsy moth's flight,
preventing the male from finding the flightless female and mating.
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