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Common Insect Species of Northwestern Ontario

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Forest Pests

Gypsy Moth
Lymantria dispar - Order Lepidoptera

Gypsy Moth The gypsy moth has emerged as one of North America's most devastating forest pests and stands to threaten Canada's boreal forest if not unchecked. The species originally evolved in Europe and Asia and has existed there for thousands of years. In the mid-1800s, the gypsy moth was accidentally introduced near Boston, Massachussets. About 10 years after this introduction, the first outbreaks began and the State and U.S. Federal Governments began their attempts to eradicate the species. These attempts ultimately failed and since that time, the range of gypsy moth has continued to spread. Every year, isolated populations are discovered beyond the contiguous range of the gypsy moth but these populations are eradicated or they disappear without intervention. It is inevitable that gypsy moth will continue to expand its range in the future.

The gypsy moth is known to feed on on the foliage of hundreds of species of plants in North America but its most common hosts are oaks and aspen. Gypsy moth hosts are located through most of the U.S. and have spread to southwestern parts of Canada and as far north as the eastern limits of Ontario's boreal forest.

Gypsy moth populations are typically eruptive in North America; in any forest stand densities may fluctuate from near 1 egg mass per ha to over 1,000 per ha. When densities reach very high levels, trees may become completely defoliated. Several successive years of defoliation , along with contributions by other biotic and abiotic stress factors, may ultimately result in tree mortality. In most northeastern forests, less than 20% of the trees in a forest will die but occasionally tree mortality may be very heavy.

Forest Effects
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. A major concern is the potential loss of economically critical and ecologically dominant tree species. 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.

Natural Enemies
A variety of natural agents are known to kill gypsy moths in nature. These agents include over 20 insect parasitoids and predators that were introduced over the last 100 years from Asia and Europe. Small mammals are perhaps the most important gypsy moth predator, especially at low population densities. Birds are also known to prey on gypsy moths but at least in North America this does not substantially affect populations. A nucleopolyhedrosis virus usually causes the collapse of outbreak populations and recently an entomopathogenic fungus species has caused considerable mortality of populations in North America.

Management:
Over the last 20 years, several millions of acres of forest land have been aerially sprayed with pesticides in order to suppress outbreak gypsy moth populations. Though some areas are treated by private companies under contract with land owners, most areas are sprayed under joint programs.

The USDA, State and local governments also jointly participate in programs to locate and eradicate new gypsy moth populations in currently uninfested areas. Most of these projects focus on populations of European origin, but recently several Asian populations have been discovered and eradicated in the U.S. and Canada.


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