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Roper, Teryl R. (ed.) / Wisconsin Cranberry School 1994 proceedings

Mahr, Daniel L.
Gypsy moth: a future Wisconsin cranberry pest?,   pp. 44-47

Page 44

Daniel L. Mahr Department of Entomology 
University of Wisconsin - Madison 
  The gypsy moth, Lymantria dispar, which is native to Europe and Asia, was
purposefully brought into Massachusetts in 1869 by a Frenchman who wanted
to cross it 
with the silkworm to improve the fledgling U.S. silk industry. Not only was
this a foolish 
and impossible venture, the gypsy moths escaped and became established. It
has since 
spread throughout the northeastern United States and adjacent Canada, where
it has 
become a serious pest. In recent years, significant numbers have been found
in eastern 
  Gypsy moth is normally considered to be a pest of trees, especially deciduous
Areas most vulnerable to gypsy moth attack are forests, parks, recreational
areas, and urban 
forests (street and home yard trees). The gypsy moth larvae are known to
feed on over 300 
types of trees and shrubs, including nursery stock and fruit crops. In Massachusetts
New Jersey, gypsy moth is an occasional pest of cranberry, and has the potential
of causing 
significant injury, especially in those years during an outbreak period,
when growers must 
routinely monitor for activity in the beds and be prepared to apply appropriate
This paper summarizes the biology of gypsy moth, its status in Wisconsin,
and its potential 
threat to the cranberry industry. 
The gypsy moth is a relatively large insect. The male is dark brown, with
a wingspan of 
about 1.5 inches. The female has white wings with thin, wiggly dark stripes;
her wingspan 
is about 2 inches. Although she has fully developed wings, the female is
flightless, but 
males are strong fliers. Adults occur in July and August. The female produces
a sex 
pheromone for luring the male. Immediately after mating she begins to lay
a single large 
egg mass that may contain up to 1,000 eggs. The egg mass is covered with
hairs from the female's body. Because the female doesn't fly, the eggs are
laid wherever she 
happens to be. This is usually on the trunk or branches of a tree, but may
also be on rocks, 
walls of buildings, vehicles, or any other surface. The insect remains in
the egg stage 
through the remainder of the summer, fall, and winter. Hatching occurs in
May about the 
time oak leaves start to develop. Gypsy moth larvae are densely hairy caterpillars
that grow 
to about 2-3 inches long. Down the back of the caterpillar there is a double
row of 5 blue 
spots followed by a double row of six brick-red spots.  Several other large,
caterpillars are confused with the gypsy moth. Most frequently, eastern tent
which makes dense silken webbing, is thought to be gypsy moth, but gypsy
moth does not 
produce webbing. Larvae feed until mid to late July, and then pupate in protected
areas on 
or at the base of trees.  Adults emerge about two weeks later, completing
the one 
generation per year. 

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