Gypsy
moth (Lymantria dispar
(Linnaeus))
DESCRIPTION: There are two
varieties of gypsy moth found in the United States,
the European and the Asian. European moths are smaller but more widespread
than the Asian variety; however, they are both members of the same species.
The gypsy moth goes through four life stages: egg, larva (caterpillar),
pupa, and adult. Female Asian moths can fly long distances to lay their
egg masses, unlike the flightless European females. The caterpillars
feed on several hundred species of trees and shrubs. Preferred broad-leaved
hosts include oak, apple, alder, aspen, filbert, willow, birch, madrone,
cottonwood, and plum; coniferous species such as Douglas fir, pine,
and western hemlock are suitable hosts as well. Tree species not favored
by the gypsy moth include ash, balsam, fir, catalpa, cedar, dogwood,
sycamore, rhododendron, and tulip tree. (13)
INTRODUCTION
HISTORY AND DISTRIBUTION:
European gypsy moth caterpillars escaped from a “silk experiment” by
Ettiene Leopold Trouvelot in Medford, MA, in 1868. The first widespread
outbreak of tree defoliation damage occurred in that area in 1882.
The local government’s first attempt at controlling the moths was in
1890, but by then it was already too late—this invasive pest had escaped
into the American landscape. (14) The gypsy moth is a native
insect of Europe and North
Africa,
and it occurs across Asia to Japan.
The European race is established in the northeastern and Midwestern
United States, having expanded from the original
introduction at Medford. During the 1970s
and 1980s, it was found in numbers sufficient to cause concern in the
western states of California, Utah, Oregon and Washington.
These occurrences were caused by the transportation of egg-laden materials
from eastern sources. In 1991, federal inspectors found egg masses
of the Asian race on Russian ships at Vancouver
waiting to load with grain; male moths were subsequently trapped on
shore. Canada
therefore now faces the threat of gypsy moth introductions from sources
to the east, south and west. (15) Gypsy moths spread locally
as young larvae ballooning on air currents and artificially as egg masses
on objects moved by people. (13)
IMPACTS
ON ECOSYSTEM: One
of the most notorious pests of hardwood trees in the Eastern United States, the gypsy moth is known to feed on
the foliage of hundreds of species of plants in North America but
its most common hosts are oaks and aspen.
A major
concern is the potential loss of economically critical and ecologically
dominant oak species (Quercus, spp.). (14) Despite over 100
years of presence in North America,
researchers are still at a loss to explain and predict the extent of
the changes in forest vegetation likely to take place through gypsy
moth disturbance. Most studies of forest compositional changes with
gypsy moth defoliation indicate that less susceptible species will dominate
the forest, so in effect, forests may have fewer gypsy moth problems
in the future.
The mortality
associated with gypsy moth outbreaks can profoundly affect forest successional
trends. In formerly oak-dominated forests, oak accounts for barely
10% of all regeneration. Naturally, the composition will change slightly
over time, but it is obvious that gypsy moth acts as a mechanism to
temporally disengage succession as exploitive species like red maple
dominate the landscape. (14)
Gypsy
moths have a tremendous capacity to increase in numbers and feed on
a wide range of trees and shrubs. Populations can rapidly build to
large infestations causing widespread defoliation, weakening or sometimes
killing trees. Defoliated forests are susceptible to disease, fire,
erosion, and may provide a poor habitat for other forms of plant and
animal life. Defoliation reduces the aesthetic, recreational and economic
value of forests, parks, and homeowner properties. (13) Since
1980, the gypsy moth has defoliated close to a million or more forested
acres each year. In 1981, a record 12.9 million acres were defoliated.
This is an area larger than Rhode Island, Massachusetts, and Connecticut combined. (16)
CONTROL
EFFORTS: The
United States
now spends over half a million dollars annually on aerial pesticide
spraying to control gypsy moths. Over
100 species have been imported to US in attempt to control gypsy moths,
many of which are likely to adversely affect native butterfly and moth
species and in effect become invasives themselves (7).
