The European Gypsy Moth (EGM) is an invasive insect species, meaning it has moved outside of its native habitat and threatens the new environment, economy and society by disrupting local ecosystems. The EGM is unfortunately considered a well-established regional pest in southern Ontario. Learn what you can do to help prevent the spread of the EGM this year

About the European Gypsy Moth

European Gypsy Moth

The first detection of the EGM in Ontario occurred in 1969 and has quickly spread across southern Ontario since the 1980’s. The EGM is classified as a defoliating insect, meaning it damages trees by eating leaves or needles. This destroys the photosynthetic tissue that is critical for plant maintenance and growth. A tree that has lost a significant amount of leaves or needles will display signs of growth loss, and increased susceptibility to attack by other insects and pathogens. Repeated defoliation stresses trees and can lead to tree mortality, especially in urban or drought-stricken areas. This also impacts seed production and root sprouting which weakens tree regeneration. 

The EGM is most destructive in its larval stage. A single EGM caterpillar can eat an average of one square metre of leaves! The EGM has over 300 known host plant species, and 150 of which are preferred hosts. In Ontario, the EGM is most often found in tree species, primarily oak (Quercus), maple (Acer), poplar (Populus), and willow (Salix) trees.

Impact on Southwestern Ontario

EGM outbreaks occur every 7 to 10 years. During severe outbreaks, trees and shrubs are completely defoliated over large areas. Defoliation caused by the EGM in Ontario increased from 47,203 hectares in 2019 to 586,385 hectares in 2020. In Southwestern Ontario, the area affected totaled 99,387 hectares in the Guelph and Aylmer districts, an increase from 37,551 hectares in 2019

In 2020, the Ministry of Natural Resources and Forestry conducted surveys to forecast anticipated gypsy moth populations in 2021 based on fall egg mass density, which is the number of egg masses on trees in a given area. This data was then used to help predict defoliation, which can be seen in the map of projected 2021 gypsy moth defoliation: 

Map of Moth Defoliation

In London, the City is taking an Integrated Pest Management (IPM) approach. This means different management techniques are being used to address the pest population starting with the least harmful to the environment. Over the winter, the Upper Thames River Conservation Authority (UTRCA) has been hard at work removing over 8,000 egg masses from Environmentally Significant Areas (ESAs) in London. The UTRCA manages the ESAs under contract for the City of London.

Additionally, The City of London recently launched the one-year pilot Veteran Tree Incentive Program to help Londoners maintain their large veteran trees for longer and protect against EGM. This program will offer financial assistance to Londoners who are actively caring for their veteran trees, helping to maintain them for longer and provide alternatives to removal. A percentage of eligible costs may be claimed by households up to a maximum of $1,000 per tree. 

What you can do

The EGM will continue to infest various tree species across our city, and we need help from Londoners to reduce the spread!. There are various methods that can be used to trap this species throughout its lifecycle. 

  • November to late April (egg stage)- This is the easiest method of EGM removal. Simply remove and destroy egg masses by gently scraping them off the tree bark into soapy water. The City of London has a video to teach Londoners how to remove gypsy moth egg masses. Click here to view the video!
  • May to July- within this time frame the EGM will go through the early caterpillar stage, the large caterpillar stage, and the pupa stage, respectively. Burlap banding, biological pesticide, and hand picking work best during these stages. 
  • July to August- within this time frame the EGM will enter the moth stage. Burlap wrapping works best to trap female moths, who are unable to fly. Male moths can be trapped by hanging non-toxic pheromone baited traps (available at hardware and nature stores) in trees to attract male moths. 

The earlier and more often the pest’s life cycle can be interrupted, the more successful we will be in managing the pest. To learn more about these methods, click here.

In addition to EGM trapping throughout the lifecycle and the City’s Veteran Tree Incentive Program, you can help tackle gypsy moths in London by:

  • Spreading the word to your friends, family, neighbours, and colleagues. As more Londoners become aware of the EGM infestation, the more equipped we will be to reduce it. 
  • Follow the Community Moth-Up project (hosted by the London Environmental Network) to hear about upcoming EGM clean-ups in high-priority neighbourhoods. While the first moth-up was cancelled due to the recent lockdown, we hope to run more community clean-ups throughout the summer and fall!
  • Learn about the urban trees in London by listening to The Forest City podcast episode, the first in our London, ON: One of Canada’s Greenest Cities? podcast series.