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City of Mississauga Parks and Forestry - Pest & Disease Management

Gypsy Moth

Gypsy Moth The Gypsy Moth is an insect pest native to Europe that has been introduced to North America. The Gypsy Moth is a species that defoliates or eats the leaves from trees in its caterpillar or larval stage and, in large numbers, can cause trees to be more vulnerable to disease and attack from other insects.

Generally, defoliation stops in early summer and should not have a long-term impact on trees if the trees are healthy and well cared for.

About Gypsy Moths

What is the Gypsy Moth?

The European Gypsy Moth is considered to be a major pest in North America. In the caterpillar or larval stage, the insect eats the leaves of trees making them more susceptible to disease and damage from other insects.

How much damage can the Gypsy Moth cause to trees?

Depending on the level of infestation, damage can range from light to almost complete defoliation or loss of leaves. In some situations, if the tree has been weakened or stressed by other conditions, the tree may die.

What kinds of trees are most affected by the Gypsy Moth caterpillar?

Gypsy Moths prefer oak trees but will eat all kinds of hardwoods including elm, birch, poplar and willow trees. In some rare cases, when the number of Gypsy Moths is extremely high, the caterpillar will feed on evergreens such as pine and spruce. They do not appear to like sycamore, butternut, black walnut, dogwood or balsam fir.

What is the lifecycle of the Gypsy Moth?

The moths are short-lived and seen in mid-summer. Both sexes die after the female lays its eggs on the limbs and trunks of trees, on rocks, buildings or in other sheltered areas. The egg masses remain in place all winter and hatch the following spring from late April to mid-May. Once hatched, the caterpillars begin to feed for approximately seven weeks.

Are there any natural predators to the Gypsy Moth?

Yes. Predators include other insects like wasps, flies, beetles, ants and spiders and animals such as chipmunks, squirrels and raccoons. When caterpillars first hatch, birds such as chickadees, blue jays, robins and nuthatches will prey on them. Gypsy Moth populations are also reduced by diseases caused by bacteria, fungi and viruses.

What is the City doing?

Egg Mass Surveys

The City began surveying trees in 2012 for Gypsy Moth egg masses on City-owned trees along boulevards and in parks and natural areas. Egg mass surveys are an effective way to forecast populations of Gypsy Moth for the following year.

Gypsy Moths have been in the City of Mississauga for many decades. There was a large increase in its numbers in 2006 and 2007. Its numbers returned to lower, normal levels for several years until an increase was observed between 2015 and 2017.

Integrated Pest Management

To help manage future populations, the City will continue to use Integrated Pest Management (IPM) measures. IPM is a sustainable approach to managing pests by combining biological, cultural, physical and chemical tools in a way that minimizes economic, health and environmental risks.

Forestry staff use IPM techniques to determine the Gypsy Moth population. The City installs tree bands and/or burlap to select City-owned Oak trees based on egg mass count and location. In July of each year, pheromone traps are placed in select street trees, park trees and some woodlot locations to catch male moths flying in search of females.

2018 Aerial Spray Program

In response to the large increase in Gypsy Moth and Fall Cankerworm populations, the City conducted an aerial spray treatment in 2018 using Foray 48B Biological Insecticide Aqueous Suspension, containing the active ingredient Bacillus thuringiensis subspecies kurstaki strain ABTS-351 (PCP# 24977) under the Pest Control Products Act (Canada). The goal of the spray program was to lower both the Gypsy Moth and Fall Cankerworm populations.

The City will continue to conduct egg mass searches and use IPM techniques to monitor and manage Gypsy Moth populations.

What can residents do?

The City needs the help of residents to control the Gypsy Moth population in Mississauga. If residents, especially those in neighbourhoods with a high number of oak trees, use IPM techniques on their own trees, working together, we can keep Gypsy Moth numbers at a manageable level.

Learn more about recommended IPM techniques on our IPM webpage.

For more information on Gypsy Moths, email or call 3-1-1 (or 905-615-4311 if outside city limits).

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