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University
of Rhode Island GreenShare Factsheets
Gypsy
Moth
The gypsy moth,
a native of Europe, Asia and North Africa, was introduced into Massachusetts
in 1869 by a French naturalist who was experimenting with silkworms.
It is now found throughout all northeastern states and bordering
areas of eastern Canada. Spot infestations have been found in the
Midwest. Gypsy moths prefer oaks (white, chestnut, red), apple,
basswood, gray birch, hawthorn, poplar, beech and willow, but may
attack hardwoods and conifers as well. Older larvae will feed on
conifers. In outbreaks, gypsy moths will feed on almost anything
including many ornamentals, vegetables and even houseplants. The heavy,
flightless, 50 mm (2 inch) long female moth is white with a yellow
to buff abdomen and irregular blackish bands on the forewings. The
male moth is active during the day, searching for females. The male
is smaller than the female and mottled brown and black. The eggs are
deposited in 20 to 40 mm (3/4 to 1 1/2 inch) masses of 100 to 700
eggs, covered with bright yellow to buff velvety scales from the
female's abdomen. Older egg masses become bleached as they weather.
Fully-grown
gypsy moth caterpillars are 40 to 65 mm (1 1/2 to 2 1/2 inch) long,
hairy, and vary from slate-gray to a sooty or dusky color. The caterpillars
have five pairs of blue spots followed by six pairs of red spots
along the back, which distinguish the gypsy moth caterpillar from
other defoliating caterpillars. The head capsule is black and gold.
The female
lays her eggs on trees, stones or fences, under loose bark, and
in other protected places in mid- to late summer. The eggs overwinter
and hatch in early May, when Amelanchier spp. (serviceberry,
shadbush) blooms. The newly-hatched caterpillars spin silken threads
on which they may be wind-borne for long distances. In mid-summer
(six to seven weeks), mature caterpillars spin a few strands of
silk and pupate within a dark brown pupal case. The moths emerge
in one to three weeks (males first). There is one generation a year.
Vigorous hardwoods
can usually survive one complete defoliation, but a similar attack
may be fatal to conifers. Repeated defoliation of hardwoods, however,
will reduce tree vigor to a point where other factors or pests may
cause death. Tree losses have been noted after one to two years
of complete defoliation during drought periods, particularly on
poor sites. The aesthetic, recreational and watershed values of
forest, park and ornamental trees can be seriously threatened by
the gypsy moth. The hairs of the young larvae often cause a skin
rash on humans. A fungal disease
caused by Entomophaga maimaga has controlled the gypsy moth
in recent years throughout most of its range in the United States
and further controls have been unnecessary. Natural:
Gypsy moth infestations are regulated by many factors, most
important of which is stand composition (hosts). Gray birch and
chestnut/white oak stands are favored for initial buildup, whereas
maples are not. Persistently low winter temperatures (-20 degrees
F/ -29 degrees C) may cause egg mortality in unprotected situations.
Populations may be reduced by birds and mammals. There are also
a number of parasitic or predatory insects which attack gypsy moths,
including Calosoma beetles, and some species of parasitic wasps
and flies. Cultural
Control: Stressed trees are more vulnerable to damage from defoliation.
Keep trees in good health and vigor. Maintain good soil nutrient
and moisture relationships by mulching, watering, judicious green
wood pruning, and fertilizing when needed. Replace susceptible species
of low commercial or aesthetic value with resistant species. Create
mixed plantings with species not generally fed upon. Quarantine:
It is very important that gypsy moths not be spread to areas
outside of the northeastern states. Gypsy moths are commonly transported
in the egg or pupal stage on home and yard objects, mobile homes,
trailers, etc. There is a USDA-APHIS regulation prohibiting the
transportation of gypsy moth-infested items. Chemical:
Chemical control is not presently warranted against this insect.
Adapted
from G.R. Nielson, University of Vermont Extension, 1999
Pesticides
are poisonous! Read and follow all safety precautions on labels.
Handle carefully and store in original containers out of reach
of children, pets or livestock. Dispose of empty containers
immediately, in a safe manner and place. Pesticides should never
be stored with foods or in areas where people eat.
When trade names are used for identification, no product endorsement
is implied, nor is discrimination intended against similar materials.
Be sure that the pesticide you intend to use is registered for
the state of use.
The user of this information assumes all risk for personal injury
or property damage.
For more
information, call the URI CE Gardening and Food Safety Hotline
at 1-800-448-1011 or (401)874-2929 from outside Rhode Island;
Monday-Thursday between 9 am and 2 pm.
University
of Rhode Island Cooperative Extension provides equal program
opportunities.
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