• Invasive – native to Europe.
  • This European defoliator feeds on a variety of trees.
  • The first detection of LDD moth in Ontario occurred in 1969; however, widespread defoliation did not occur until 1981.
  • Established populations exist south of a line from Sault Ste. Marie east to North Bay and Mattawa; a separate infestation exists in New Liskeard.
  • The Ontario distribution coincides with the range of the insect’s preferred hosts of oak; however, no known populations of LDD moth exist in northern parts of the range of bur oak north of New Liskeard in the northeast region, and west of Thunder Bay to Lake of the Woods in the northwest region.

“Invasive” refers to a species that has moved outside of its native habitat and threatens the new environment, economy or society by disrupting local ecosystems.

"Defoliator" refers to species that eat leaves.

Host species

Hosts range from oak (Quercus), birch (Betula) and aspen (Populus) in the north, to various hardwoods such as sugar maple (Acer saccharum), American beech (Fagus grandifolia) and softwoods such as eastern white pine (Pinus strobus), balsam fir (Abies balsamea) and Colorado blue spruce (Picea pungens) in Southern Ontario.

Characteristics and life cycle

  • 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.
  • Initially, 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 of blue spots, followed by a double row of six pairs of red spots, down the back.
  • Feeding is completed in July.
  • Male moths are light brown and slender-bodied, while females are white and heavy-bodied.

Two dark, hairy caterpillars with blue spots at the front and red spots at the back eating a leaf.

Gypsy moth adults laying eggs

Symptoms and damage

  • LDD moth outbreaks occur every 7 to 10 years.
  • Larvae chew holes in leaves or devour entire leaves.
  • In late July, LDD egg masses can be observed on the trunks and branches of infected trees.
  • Understory shrubs and plants may also be affected.
  • 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 substantial growth loss.
  • Defoliation makes trees more susceptible to secondary pests, drought, and poor growing conditions.

Gypsy moth defoliation

Control measures

You can take a localized approach to manage LDD moths on your property. Control options depend on the LDD moth life stage and the time of year.

Learn how to protect trees on your property.

LDD moth life stage and control options

Image of the LDD moth life stage and control options

TimingLife stageControl options
August to mid-AprilEgg massesRemove egg masses and discard
Mid-April to mid-MayEarly stage caterpillarApply biological pesticide
Mid-May to JuneLate stage caterpillarAttach burlap bands and discard larvae
June to mid-JulyPupaeRemove by hand and discard
July to AugustAdult mothShort-lived; focus on other stages

Natural controls

Natural predators and pathogens are the main reason the LDD moth outbreak in North America is collapsing.

Nuclear polyhedrosis virus (NPV)

  • NPV is a viral infection known to kill LDD moth larvae once the virus builds up in a population.
  • It can spread quickly from infected larvae to non-infected larvae, killing them.
  • Dead larvae hanging on a tree in an upside-down “V” show the virus is at work in the population.

Entomophaga maimaiga

  • A fungus known to cause LDD moth populations to collapse.
  • Cool, wet conditions provide an ideal environment for its spread.
  • Dead larvae hanging vertically along tree trunks that appear brittle and desiccated show that this fungus is active.

Predation and parasitism

  • Birds, mammals and other insects are known to prey on LDD moth.
  • A species of wasp called Ooencyrtus kuvanae is known to parasitize LDD moth eggs and can reduce populations.

Cold weather

  • Extended days of extreme cold (−20 degrees Celsius) may kill overwintering larvae in exposed egg masses.

Regulation and monitoring

  • LDD moth is a regulated pest by the Canadian Food Inspection Agency (CFIA). The CFIA is responsible for establishing and maintaining standards to prevent the introduction and spread of plant pests in Canada.
  • Forest health is monitored every year by the ministry. We conduct ground and aerial surveys to map major forest health disturbances on the landscape. When pest populations reach outbreak level, we may complete pest specific forecast surveys to help predict defoliation for future years.

State of LDD moth in 2021

We began aerial forest health surveys in early July. We based flight lines on:

  • public reports of potentially infested areas
  • 2020 survey data
  • knowledge of previously infested areas

After the aerial surveys, we did ground verification surveys. This included collecting LDD moth specimen samples to confirm species identification in the laboratory.

Areas affected by LDD moth defoliation in 2021

Defoliation caused by LDD moth in Ontario increased from 586,385 hectares in 2020 to almost 1.8 million hectares in 2021.

This area included both light and moderate to severe defoliation mapped mainly in the southern region but also north to Sault Ste. Marie, Sudbury, North Bay and Temiskaming Shores.

All affected districts reported an increase in area defoliated from 2020. Visit ministry regional and district offices to see a map of our districts.

Defoliation caused by LDD moth was most severe in forest stands containing species of:

  • oak
  • maple
  • poplar
  • willow
  • other broadleaf trees

In some areas, LDD moth defoliated conifer species including eastern white pine and spruce species.

Southern region

In the southern region, we recorded most of the moderate to severe defoliation in the eastern districts including Peterborough, Bancroft and Kemptville.

The Peterborough District had the largest area of moderate to severe defoliation of 374,268 hectares, an increase from 159,578 hectares in 2020.

This concentrated area of defoliation extended north to Pembroke District, where we mapped smaller areas of defoliation.

Southwestern Ontario

In Southwestern Ontario, areas of moderate to severe defoliation were more fragmented. Defoliation in the Aylmer District totaled 119,586 hectares and Guelph District totaled 113,877 hectares; both increased from 2020.

We also recorded increased areas of defoliation in the Midhurst and Aurora districts (176,264 and 97,164 hectares, respectively) that extended to the Parry Sound District where we mapped 75,349 hectares.

Northeast region

In the northeast region, the Sudbury District had the largest area of moderate to severe defoliation of 68,874 hectares.

In the North Bay and Sault Ste. Marie districts, we recorded smaller areas of moderate to severe defoliation, but in both cases the total area was higher than in 2020.

A small area of defoliation, totaling 52 hectares, was recorded in the Kirkland Lake District. This was a record high for this area.

Map of areas defoliated by LDD moth in 2021 across Ontario

Map of Northeast and Southern Ontario, showing LDD moth defoliation areas northwest of Sudbury, along the north shore of Lake Huron, and across much of Southern Ontario.
Enlarge Map

LDD moth populations in 2022

In 2021, we conducted surveys to forecast anticipated LDD moth populations in 2022. The forecast is based on fall egg mass density, which is the number of egg masses on trees in a given area. We use this data to help forecast defoliation. Survey locations were selected to:

  • support operational surveys in 2022
  • confirm the state of the current outbreak

Although the LDD moth is considered an invasive species regulated by federal quarantine legislation, it has evolved to a state of naturalization. This means the LDD moth population may have periodic outbreaks, which is what occurred in 2020 and 2021. As part of the quarantine legislation, you are not allowed to move firewood from regulated areas where LDD moth has been found.

2021 egg mass survey results

Based on egg mass surveys conducted in late fall in six districts across the Southern Region, defoliation is forecast to be:

  • severe in areas of Aylmer, Guelph, Parry Sound, Bancroft and Pembroke districts
  • moderate in areas of Guelph, Parry Sound, Bancroft and Pembroke districts
  • light in areas of Midhurst District

During the survey, we observed egg mass predation (attacks) by birds and small mammals. At some egg mass sample sites, we also found evidence of parasitism. For example, small pinholes in egg masses indicated the presence of the tiny parasitic wasp, Ooencyrtus kuvanae.

These predators and parasites can help to reduce LDD moth populations, but we won’t know their effects until the LDD moth larvae emerge in the spring.

Map of projected 2022 LDD moth defoliation

This map shows:

  • LDD moth damage in 2021, represented by shaded areas
  • the defoliation forecast for 2022 (represented by dots, which are egg mass survey locations)
Map of southern Ontario showing distribution of projected 2022 LDD moth defoliation
Enlarge map

Forecasting defoliation: Egg mass survey protocol

To predict LDD moth defoliation, we use a Modified Kaladar Plot (MKP) protocol at select locations across the defoliated area. This protocol considers:

  • egg mass location in the stand
  • the proportion of new egg masses relative to old ones

The total number of egg masses per hectare is used to forecast LDD moth defoliation for the following year:

  • severe defoliation (more than 75% of forest stand) is projected in areas with more than 6,175 egg masses per hectare
  • moderate defoliation (40% to 75% of forest stand) is projected in areas with 1,236 to 6,175 egg masses per hectare
  • light defoliation (1% to 40% of forest stand) is projected in areas with 1 to 1,235 egg masses per hectare

Complete an egg mass survey

To complete your own egg mass survey on your property, you can request the Modified Kaladar Plot (MKP) protocols from us by emailing info.mnrfscience@ontario.ca.

Contact us

Visit our forest health conditions page to read our annual report summaries.

For more information, email us at info.mnrfscience@ontario.ca.