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Combined Forest Pest
Home and Garden Bulletin
The Gypsy Moth:
An Illustrated Biography
by Michael L. McManus1 and
Roger T. Zerillo2
In 1974 the U.S. Department of I
Agriculture initiated the Combined
Forest Pest Research and
Development Program, an
interagency effort that
concentrated on the Douglas-fir
tussock moth in the West, on the
southern pine beetle in the South,
and on the gypsy moth in the
Northeast. The work reported in
this publication was funded in
whole or in part by the program.
This manual is one in a series on
the gypsy moth.
The gypsy moth is probably the
most important defoliating insect of
hardwoods-especially oak-in the
Northeastern United States (fig. 1).
Much effort and money have been
spent to control this pest, yet it
continues to spread south through
Pennsylvania and west to Ohio.
This booklet details the insect's life
cycle and, through photographs,
provides identification of each life
stage, from egg to adult moth.
Figure 1.--Gypsy moth larva
Research coordinator, Expanded Gypsy Moth
Piogi.im. Hamden, Conn.
2 Biological laboratory technician, Forest
Service, Hamden, Conn.
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The female gypsy moth lays one egg
mass in June or July and then dies
shortly after. The eggs are deposited
in a well-formed egg mass on trees
as well as on rocks, stumps, ground
foliage, houses, yard equipment,
wood piles, stone walls, and
camping trailers (figs. 2 and 3). The
eggs do not hatch until the following
Figure 2.-Many egg masses laid
on the undersides of branches of an
Figure 3.-Freshly deposited egg
masses on a stone.
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Figure 4.-Female moth depositing
Figure 5.-Weathered egg masses
showing characteristic emergence
holes of the egg parasite,
Figure 6.-Adult 0. kvianae
resting on egg mass.
The egg masses are buff colored
when first laid (fig. 4) but may
bleach out over the winter months
when exposed to direct sunlight and
weathering (fig. 5). Small pinholes
evident on egg masses are
emergence holes of a parasite (fig.
6) that can destroy up to 40 percent
of the eggs within a mass.
Egg masses contain from 75 to 1,000
eggs. Each egg is encased in a
secretion produced by the female
moth, along with scales and hairs
from the underside of her body (fig.
7). The mixture provides the eggs
excellent protection from
desiccation and from winter
temperatures as low as -200 F
In late April or early May, first-stage
larvae (caterpillars) emerge from
individual egg masses in 3 to 5 days.
Egg hatching may continue over a
period of 2 to 3 weeks in any one
locality, depending on the placement
of egg masses and exposure to
sunlight. Newly hatched larvae are
buff colored but turn black within 4
hours after hatching (fig. 8). They
may rest on or around the egg mass
for hours if temperatures are below
400 F (40 C). If it is raining, larvae
may remain in this position for 24 to
Figure 7.-Scales and hairs from
the underside of female gypsy
Figure 8.-Newly hatched larvae
(buff colored) and older larvae on
surface of egg mass.
When conditions are favorable,
larvae climb trees in response to
light and trail silk continually as
they move (fig. 9). When they reach
the outer branches or tops of the
trees, they drop on silken threads
(fig. 10), reclimbing the strands until
carried by the wind to a new
location. Both the silk and long
lateral hairs provide buoyancy to
the windborne caterpillars (fig. 11).
Larvae begin feeding on acceptable
host plants (of which there are
many) and usually chew small holes
within the perimeter of the leaf (fig.
12). In later stages. larvae usually
feed on the leaf margins. There are
two or three feeding periods during
the day. First-stage larvae usually
produce a mat of silk on the
underside of the leaf where they rest
when not feeding.
Figure 9.-Larvae trailing silk on
Figure 10.-Larva reclimbing silk
after dropping from foliage.
Figure 11.-Newly hatched larva
showing long hairs that aid
Figure 12.-Leaf damage caused
by feeding of early-stage gypsy
Figure 13.-Third-stage larva.
Figure 14.-Newly emerged
moltedd) fourth-stage larva.
Figure 15.-Fifth-stage larva.
Male larvae molt (shed their outer
skin) through five stages, females
through six (figs. 13-15). The
number of days spent in each stage
varies from 4 to 10 days, depending
on the stage and temperature.
Second- and third-stage larvae
characteristically stay in the tree
crowns but may migrate to the
undersides of branches and twigs.
Figure 16.-Late-stage larvae
beginning to aggregate on
undersides of branches.
Figure 17.-Bark crevice and
sign, ideal protective sites for
Figure 18.-Larvae resting in leaf
litter at base of tree.
Figure 19.-White-footed mice
feeding upon late-stage larvae.
When larvae molt to the fourth
stage, their behavior changes
dramatically. They feed during the
night then descend the trees at dawn
(fig. 16) in search of protective
locations, where they rest for the
remainder of the day. At dusk,
larvae climb the trees again to feed.
The movement up and down the
tree is triggered by low light. Larvae
prefer to rest under bark flaps or
other structures on the tree (fig. 17).
If none is present, the insects will
descend to the ground and rest
beneath leaf litter or other nearby
objects (fig. 18), where they are
susceptible to attack by small
vertebrate predators such as mice
and shrews (fig. 19).
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Larvae usually complete their
development in late June or early
July and begin to pupate (transform
into the adult, or moth, stage),
usually in the same location where
they rested as fifth- or sixth-stage
larvae. During this process the
larvae attach themselves to the
surface with strands of silk and
eventually transform into
mahogany-colored pupae (fig. 20).
The pupae, which are immobile and
defenseless, are vulnerable to
predators such as the ground beetle
(fig. 21) and parasites like the a,,p
in figure 22.
Figure 20.-Larvae attached by
strands of silk beginning to
transform into pupae similar to
those on the left.
Figure 21.-Ground beetle
((Caloomna sp.). predator of both
larvae and pupae.
Female pupae (fig. 23, right) are
characteristically much larger than
male pupae because they pass
through an additional larval stage.
The pupal stage of both sexes
usually lasts about 2 weeks. Male
moths usually emerge first because
they pass through one less life stage
and usually pupate earlier than the
Figure 22.-Adult parasite
(Bruchymeria intermedia) stinging
and ovipositing an egg in gypsy
Figure 23.-Male (left) and female
Figure 24.-Male moth.
Male moths (fig. 24) are strong fliers 2 25
and are usually most active during
the daytime within the forest
canopy. They fly in zigzag patterns
and can be seen searching up and
down tree trunks for female moths.
The female has well-developed
wings but does not fly (fig. 25). She
compensates for this by releasing a
strong sex attractant that lures male
moths from the surrounding area. .
Mating occurs and shortly thereafter
the female deposits her egg mass.
If you spot a gypsy moth infestation ,
in your area, contact one of the
following for information about
* County extension agent
* State forestry organization
* State agriculture department Figure 25.-Female moth.
* Forest service or Animal and
Plant Health Inspection Service,
U.S. Department of Agriculture.
Issued December 1978
Available from the Superintendent
U.S. Government Printing Office
Washington, D.C. 20402
Stock No. 001-000-03850-8
* U.S. GOVERNMENT PRINTING OFFICE: 1978 0-273-084
UNIVERSITY OF FLORIDA
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