Gypsy Moth

What are they?

Gypsy moth is a non-native insect that is considered a major destructive pest in North America. When populations are high, they can eat all the leaves on a tree in a short amount of time. When leaves are lost in successive years, trees can die.

Based on population surveys conducted in 2017, Oakville faced extreme levels of gypsy moth infestation in 2018 that could have affected 110 hectares (272 acres) of town woodlands and resulted in a significant loss of trees if no action was taken.

In spring 2018, the town conducted an aerial spray in select town woodlands with a safe and naturally occurring insecticide, Bacillus thuringiensis Kurstaki (BtK) to control gypsy moth infestation. The aerial spray was completed successfully in June 2018.

What is the town doing?

The damaging effects of gypsy moth can be controlled with an effective Integrated Pest Management (IPM) plan.

The town continues to track gypsy moth populations and new outbreaks. By the summer months gypsy moth have pupated and laid their eggs. Surveys of egg masses are conducted to predict population levels the following year, and inform management actions that may need to be taken.

Please review our Frequently Asked Questions section for more information. If you have additional questions or concerns regarding gypsy moth, please contact ServiceOakville at 905-845-6601.

What can you do?

Here’s what you can do to protect your trees and help control the spread:

  • In the summer and fall, physically remove gypsy moth egg masses. Use a putty knife or trowel to scrap eggs into a container and destroy the eggs by leaving them in soapy water for several days.
  • In the spring, apply sticky bands or burlap around trees to trap emerging gypsy moth caterpillars. Commercial sticky bands can be found at most home and garden stores.
  • Use gloves to hand-pick caterpillars and crush.
  • Contact a professional tree care service provider to discuss spraying.

For detailed control tips, review the Health Canada Gypsy Moth Pest Control page.

Forestry staff hasbeen monitoring the population of gypsy moth since 2002. In 2005, staff observed an increase in Gypsy Moth population, and undertook a more comprehensive monitoring program.

As a result of a population increase in 2007, Oakville participated in a collaborative spray program in 2008 with neighbouring municipalities to spray 63 hectares (155 acres) of municipally infested woodlands with the insecticide Btk. The aerial spray program was considered a success. The gypsy moth population in the following years was negligible and an integrated pest management approach that did not require aerial spraying was implemented. Forestry staff manually removed egg masses from the trees, where possible, prior to spring emergence.

The 2012 and 2013 egg mass surveys reported a slight increase in population levels High infestation levels were localized and protective injection treatments were implemented in select hot-spot locations from 2013-2017.

In the spring of 2017, the town’s forestry consultant recorded significant increase in the density and population of gypsy moth and cankerworm in town woodlands. In November 2017, Town Council approved the 2018 Gypsy Moth and Cankerworm Mitigation Plan.

What is gypsy moth?

Gypsy moth (Lymantria dispar dispar) is an exotic forest insect pest that is native to Europe and considered to be a serious defoliator of trees and shrubs. After severe or repeated defoliation (loss of leaves), trees can die or become so weakened that they are vulnerable to secondary infestations. All species of oak are susceptible to gypsy moth. This is of particular concern as oaks are high value heritage trees of immense significance to Oakville’s landscape and neighbourhoods.

What is cankerworm?

Gypsy moth caterpillars typically begin to emerge at the end of May. They continue to feed on leaves and grow for about 6 to 8 weeks. They then pupate at the end of June. After turning into moths, they are active for about 2 to 3 weeks, looking for an ideal place to lay an egg mass to start the cycle anew the subsequent year..

How much damage can gypsy moth and cankerworm cause to trees?

According to the town's 2016 iTree Report, gypsy moths, if left untreated, have the potential to impact 409,000 trees in the town of Oakville. This is equal to 23 per cent of the town’s tree canopy. While the moth stage of the gypsy moth does not feed on trees, the caterpillar stage of this insect can potentially devour every leaf of the tree’s canopy. Both gypsy moth and cankerworm are capable of causing a considerable amount of damage to trees during an extreme infestation. The severity of the tree damage depends on the degree of infestation, past defoliations and the current health of the tree. If a tree has been weakened by previous defoliations or stressed by other conditions such as drought and attacks from other insects the defoliation can lead to the death of the tree.

What types of trees are most affected by gypsy moth?

All species of oak are susceptible to gypsy moth. The larva of this insect also feed on poplar, birch, willow, maple, beech, and cherry and if faced with a shortage of deciduous leaves, they will feed on conifers (hemlock,pine and spruce) and ornamental shrubs.

What types of trees are most affected by cankerworm?

The preferred trees of the cankerworm are maple and elm, but it also attacks ash, basswood, bur oak, white birch, and various fruit trees.

Do gypsy moth and cankerworm have any natural enemies?

Yes. At normal population levels, gypsy moth and cankerworm play a crucial role as a food supply for many of the native species of birds that live in Oakville’s urban forest, as well as other woodland animals such as raccoons. Usually, diseases caused by bacteria, fungi or viruses contribute the most to keeping gypsy moth and cankerworm levels low.

Entomophaga maimaigi is a target species specific fungus that infects. It causes mass mortality for populations where established. Infections are more likely to spread in a wet spring, than in any other season.

Nucleopolyhedrosis virus (NPV) is a virus that only affects gypsy moth. NPV occurs only in large populations. The virus severely damages the internal organs of caterpillars, thereby killing them.

How severe is the gypsy moth and cankerworm infestation in Oakville?

In 2018, Oakville faced extreme gypsy moth and cankerworm infestations in a number of areas throughout the town. The infestations in those areas had potential for weakening or wide-spread loss of trees.

How severe is the gypsy moth infestation in Oakville?

In 2018, Oakville faced extreme gypsy moth and cankerworm infestations in a number of areas throughout the town. The infestations in those areas had potential for weakening or wide-spread loss of trees.

What is BtK?

Municipalities across Canada have conducted aerial spray programs in urban settings for decades.

The use of BtK is approved by the Health Canada Pest Management Regulatory Agency and is permitted under Oakville's pesticide-bylaw. It has replaced chemical insecticides in aerial spraying programs worldwide. According to Health Canada, BtK poses no threat to human health through either handling products directly or being exposed to them indirectly during a spray program.

Research shows that BtK used in aerial spray programs has no negative environmental or human health effects. BtK is a bacteria which occurs naturally in soil. The bacteria is poisonous only to a certain group of insects when ingested during their larvae or caterpillar stage.BtK does not affect adult moths or butterflies or other beneficial insects such as honeybees, or pets, birds, fish, or mammals. Learn more about BtK on Health Canada's Btk Fact Sheet (pdf) and on Natural Resources Canada's website.

Will the town spray my private trees?

The town's Urban Forestry section is responsible for the maintenance of town trees only.

What can I do to protect my trees?

There are many ways private tree owners can protect their trees from gypsy moth and cankerworm. Contact a certified tree service provider for information on treatment options or review the What You Can Do section on this page or Health Canada's Gypsy Moth Fact Sheet.

What is the town doing about other insect pests?

Most insects are a nuisance only and under normal circumstances do not require a control program. Visit our Invasive Species page to learn more.