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Gypsy Moth

​​​​​​​​​​European Gypsy Moth (Lymantria dispar) is a non – native invasive insect from Europe that was brought to North America in the 1860's. First established in Massachusetts, it had spread to Ontario by 1969.

The gypsy moth larvae (caterpillar) feed on the leaves of many deciduous tree species, including red oak, white oak, poplar and white birch and a few conifer species such as white pine. The caterpillars can consume a significant amount of leaves when populations are high resulting in noticeable defoliation. 

Populations of this species are cyclical with population surges approximately every 7-10 years. When populations rapidly rise, they are historically followed by a crash.  This population crash is due to competition or mortality from a host specific virus or fungus.   

An increase in European Gypsy Moth feeding within the County of Simcoe was observed in 2019 and populations continued to expand in 2020.  In 2019 parts of the following local municipalities were being impacted:

  • Midland
  • Penetanguishene
  • Tiny Township
  • Adjala-Tosorontio Township

See link​ for a map of 2019 impacted areas​.

Simcoe County completed egg mass sampling in fall 2019 to assess the population level of this insect. Monitoring of this species will continue in 2020 and will provide updated mapping of impacted areas.

History has shown that no major or long lasting impacts to forest or tree health occur from European Gypsy Moth, and as a result no large scale control efforts are warranted. Although defoliation is understandably concerning, healthy trees survive high populations of European Gypsy Moth. Defoliation levels of 50% or greater and repeated annual defoliation are normally required to cause mortality of healthy trees. This current outbreak will invariably follow the historic pattern of a surge followed by a population crash. 

If residents or landowners are concerned and want to manage European Gypsy Moth,  several resources are available below or it is recommended to contact an arborist or professional forester.

Maintaining healthy trees and forests is an important defense against Gypsy Moth.

Gypsy Moth Population Chart.png 

(Source: MNRF, https://files.ontario.ca/mnrf-foresthealthconditionsontario2018.pdf)

For further information, please visit:

Homeowners Management Guide to European Gypsy Moth

Landowners Management Guide to European Gypsy Moth 

Ministry of Natural Resources and Forestry - European Gypsy Moth

To contact a Certified Arborist or Professional Forster, please visit: