Gypsy moth impacts

What happens when gypsy moth becomes established?

Once gypsy moths become permanently established, it may take several more years for moth populations to build before residents see any noticeable defoliation. The first outbreak may last three to 15 years depending on weather patterns, local site conditions, and the presence of natural enemies. Typically, the first outbreak is by far the most severe because there are abundant host trees and very few natural enemies present. The first outbreak is when most environmental, social, and economic impacts will occur as a result of repeated defoliation and associated tree mortality.

Competition for food, increasing disease, and natural enemies eventually cause gypsy moth populations to collapse. After the first outbreak, gypsy moth populations behave more like those of native insects, with cyclic outbreaks every eight to 12 years.

 

Gypsy moth defoliation.
Gypsy moth defoliation

What happens to the trees?

Gypsy moths do not kill trees directly they defoliate them. Severe defoliation can add to other stresses such as weather extremes or human activities. This cumulative stress can leave trees vulnerable to disease or other pest infestation that can cause death. For example, stressed oak trees are susceptible to two-lined chestnut borer and the fungus that causes Armillaria root rot, both of which can lead to oak tree death. The trees most at risk of dying as a result of gypsy moth defoliation are those that are already under stress. Most trees die following a gypsy moth outbreak in:

  • urban areas, where trees are under constant pressure from air pollution, road salts, construction damage, or other forms of disturbance
  • areas under acute drought stress
  • areas where preferred host species are being grown where they are not well suited
  • suppressed understory areas where trees compete for limited resources.

 

What do they eat?

  Gypsy moth host preferences (Gottschalk, K.W. 1993)

Category Overstory species Understory species
Preferred: Species readily eaten by all caterpillar stages all oak
bigtooth and quaking aspen
basswood
paper and river birch
larch
mountain-ash
tamarack
willow
red alder
apple
hawthorn
hazelnut
hophornbeam
hornbeam
serviceberry
witch-hazel
Less preferred: Species fed upon when preferred species are unavailable and by older caterpillar stages yellow birch
box elder
butternut
black walnut
sweet and black cherry
eastern cottonwood
American, Siberian, and Chinese elm
hackberry
hickory
Norway, red, and sugar maples
all pine
all spruce
buckeye
pear
blueberries
pin cherry
chokecherry
sweet fern
Avoided: Species that are rarely fed upon all ash
eastern red cedar
balsam fir
silver maple
slippery elm
northern catalpa
Kentucky coffeetree
horse chestnut
sycamore
black and honey locusts
red mulberry
dogwood
elderberry
grape
greenbrier
juniper
mountain and striped maple
raspberry
viburnum
buckthorn

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