An invasive forest defoliating insect found in Ontario that is now naturalized. Recent observations and surveys in the Ottawa area indicate its populations are increasing. The City of Ottawa is carefully monitoring the situation but does expect some defoliation to occur within the outbreak areas. The outbreak is expected to last two to three years.
Characteristics and Life Cycle
The European Gypsy moth is an invasive insect native to Europe. It is currently established in much of eastern Canada. The caterpillar stage of this insect feeds on the leaves and foliage of a large number of hardwood and softwood trees and can feed on over 300 plant species including landscape and garden plants.
Oak (Quercus) is the preferred species of the Gypsy moth with other hosts ranging from birch (Betula) and aspen (Populus), to various hardwoods such as sugar maple (Acer saccharum), American beech (Fagus grandifolia) and softwoods such as eastern white pine (Pinus strobus) and Colorado blue spruce (Picea pungens).
The Gypsy moth:
- Overwinters in the egg stage often on the bark of trees.
- In spring, eggs hatch and larvae ascend the trees to feed on the new foliage.
- Feeding occurs during the day, but as the caterpillars mature feeding occurs mainly at night — often this can delay the detection of infestations.
- Mature larvae are 50 mm long, dark coloured, hairy, with a double row of five pairs blue spots, followed by a double row of six pairs red spots, down the back.
- Feeding is completed in July-August.
- Male moths are light brown and slender-bodied, while females are white and heavy-bodied.
Tree impacts (signs/symptoms)
- Gypsy moth outbreaks can occur every seven to ten years.
- Larvae chew holes in leaves or devour entire leaves.
- In late July, spongy egg masses can be observed on the trunks and branches of infected trees and on items such as outdoor equipment, trailers and vehicles.
- During severe outbreaks, trees and shrubs are completely defoliated over large areas; despite the trees’ ability to produce a new crop of leaves over the summer, the damage causes significant growth loss.
- Understory shrubs and plants may also be affected.
What is the City doing about it?
The City of Ottawa is conducting Gypsy moth surveys which started in February 2021 throughout the urban and rural area to determine the extent of the outbreak. We have communicated with other partners such as the Ontario Ministry of Natural Resources and Forestry and they report to be monitoring the issue with increased populations of this insect in other areas of the province. City staff continue to monitor this issue and will communicate to residents about gypsy moth status in Ottawa and about best practices for residents to consider for control.
What might residents notice?
Residents may see large groups of caterpillars on tree trunks and branches and some loss of leaves (defoliation) on trees this spring as a result of this insect. Healthy trees are able to sustain loss of leaves and some trees will produce a second flush of leaves in the same season following leaf loss. It is only repeated years of caterpillar feeding that cause concern with tree health.
What residents can do?
On their properties, residents can consider the following to reduce tree damage:
- During spring and summer, inspect outdoor equipment, trailers, vehicles and firewood on a regular basis for egg masses and caterpillars.
- In spring, remove egg masses or larvae by scraping. Then destroy them immediately by crushing the eggs or by submerging the eggs into a bucket filled with water and household bleach or soap for at least two days. After two days, discard the solution and egg mixture.
- Between May and early June, Btk (Bacillus thuringiensis kurstaki) can be purchased at a local hardware store and applied. Always consult with knowledgeable professionals about pesticide use.
- In June and July, burlap can be attached to the trunk of trees using a string in a band around the trunk and folded in half. Often caterpillars will congregate in the burlap and this can be disposed of daily in compost etc. Caution: the caterpillars have long hairs that can cause skin irritation, so it is recommended to wear gloves.
For quick tips for insect removal or more information about this insect and where the above information was obtained, please visit the following links: