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ISSUE 6  JUNE 10, 1999


TREES - Gypsy Moth

    More than 350 gypsy moth traps were placed around North Dakota over the last
few weeks. These traps contain a pheromone to detect the presence of male gypsy moths
in the state. The green, triangularly-shaped traps are placed in larger communities and
forested areas where damage is expected to first occur when a gypsy moth enters North
Dakota. It’s important to control infestations before they become established populations
and early detection is essential for a successful eradication program.

    Gypsy moths are nonnative insects that were introduced into the United States in
1869 by a naturalist who was attempting to breed a hardy, disease-resistant silk worm.
The insects escaped into the Massachusetts forests and have been spreading westward
ever since. Fifteen states are now infested, including states in the Northeast and the
Midwest. Gypsy moth caterpillars are capable of defoliating more than 300 different
tree and shrub species. Repeated defoliation can weaken trees, ultimately killing many of them.

    The two life stages which are most often seen entering non-infested areas are larvae
and egg masses. Larvae cause damage to trees by consuming entire leaves except
midribs. Gypsy moth caterpillars can be distinguished by a double row of five pairs of
blue dots followed by a double row of six pairs of red dots on their backs. Egg masses may
contain 75 to 800 eggs and are covered with tan to light brown hairs.

    Since the female moths do not fly, the advancement of gypsy moth depends on caterpillars
moving from tree to tree under their own power, or on caterpillars being blown by wind.
Humans have increased the rate that this insect spreads through movement of various life
stages, especially egg masses and caterpillars. The female gypsy moths will deposit egg
masses on automobiles, trailers, campers, lawn furniture, firewood, nursery stock, and other
surfaces. As people transport these items and relocate from infested states to non-infested
states, gypsy moths may catch a ride and enter new areas.

    Gypsy moths have been found in North Dakota on nursery stock shipped in from
infested states and in campgrounds frequented by out-of-state visitors. However, no
established populations of these destructive insects are known to occur in North Dakota.
Field studies conducted with sterile gypsy moth egg masses revealed that gypsy moths
can successfully overwinter in North Dakota.

    Feeding studies and observations where gypsy moths are already abundant suggest
that the destructive insects have many potential hosts in North Dakota. Favored hosts
include: apple, aspen, basswood, birch, boxelder, hawthorn, oak, poplar, sumac, and
willow. Less favored hosts include: buckeye, chokecherry, elm, hackberry, larch,
maple, pine, and spruce. Woody plants which are generally avoided by gypsy moths
include: arborvitae, ash, black walnut, catalpa, dogwood, honey-locust, juniper, and

    If you suspect that you have found a gypsy moth life stage, or would like additional
information about gypsy moths in North Dakota, please contact Marcus Jackson
(701-231-8478), Phil Mason (701-239-7295), or the USDA Animal and Plant Health
Inspection Service (701-250-4473).

Coauthored by Phil Mason, NDDA Plant Protection Specialist

Marcus Jackson, Extension Forester


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