LDD Moth or Spongy Moth

The LDD moth (Lymantria dispar dispar) is a non-native moth species that can cause defoliation of trees in Ontario and Eastern North America.

The caterpillars will eat the leaves of more than 400 species of plants. They prefer oak, but will also eat other hardwood trees such as sugar maple, spruce, elm, birch and poplar.

They also feed on garden shrubs, flowering plants, and coniferous trees.

IMAGES: LDD moth larval caterpillar stage; adult male (Photo by Ryan Hodnett – Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=50965794); and adult female (Photo courtesy of City of London)

LDD moth outbreaks in Ontario are cyclical, occurring every five to ten years.

During severe population outbreaks, caterpillars can devastate trees and forests. A single LDD moth caterpillar can consume one square meter of leaves in a season.

Several years of defoliation can cause tree mortality, especially when it occurs alongside other stressors such as droughts, forest tent caterpillar (Malacosoma disstria) outbreaks, and fungal pathogens, although most hardwood trees are able to survive up to three years of defoliation.

LDD moths do not typically eat the leaves (or needles) of coniferous trees such as white spruce unless they have run out of other leaves to eat. Unfortunately, coniferous trees may not survive a single bad year of LDD moth infestation.

In addition to ecological impacts, such as compromised health of trees and changes to forest composition over time, there are also economic and social impacts of an outbreak, including the temporary loss of beautiful forest canopies and the cost of removing and replacing dead trees from areas and parks. Some people even have allergies to LDD moth caterpillar hair.

TRCA is taking an Integrated Pest Management approach. This means that we are monitoring certain areas and evaluating management options, which may involve using a combination of techniques.

Given that LDD moths are behaving like a native pest, and many other invasive species require management, TRCA is unlikely to undertake widespread management.

Instead, management actions will focus on the protection of important individual trees or groups of trees (such as shade trees within a manicured area of a conservation park).

TRCA will support its neighbours through information and education about management techniques, as described below. Please note that TRCA will not visit private properties to assess or treat pest infestations. Property owners should contact tree service companies for assessment and other control options.

If you have a property at least 2 acres in size, you may qualify for subsidized tree planting under TRCA’s Private Land Planting Program, or if you have a forest at least 4 hectares in size, you may qualify for Forestry and MFTIP planning services. If you have a rural property you may qualify for the Rural Clean Water Program.

Contact us for more information: trees@trca.ca.

MANAGEMENT OPTIONS FOR HOMEOWNERS*

*These techniques are for protecting individual trees, and are not intended for large-scale management.

1. How to Identify the LDD Moth

• The LDD moth has four life stages: egg, caterpillar, pupa, and moth.
• Caterpillars start off very small (about 2mm) and molt three to four times, growing larger each time. By the time they reach their last molt, caterpillars can be 5-6cm long. They are dark and hairy, with five blue and red dot pairs on the back.
• As adults, female moths are white with dark markings and cannot fly.
• Adult male moths are brown with dark markings and large feathery antennae, and can fly.
• Egg masses (shown below) are tan in colour, between the size of a dime and toonie and can be found on tree trunks, under bark, the outsides of buildings and cars, on patio furniture, on tents and trailers, etc.

IMAGES: LDD moth egg masses (TRCA photos)

2. LDD Moth Life Cycle

• Egg masses hatch into caterpillars in the spring just as tree leaves begin to flush out. The caterpillars are tiny at this time and may not even be noticed. They can be carried by the wind for distances of up to 1km.
• Caterpillars are most active in May and June and their appetite grows as they get larger. Caterpillars typically eat at night and seek shelter during the heat of the day.
• Caterpillars become pupae in late June-early July and remain in this stage for 1-2 weeks.
• Adult moths emerge from the end of June through to August and live for about 2 weeks. They exist solely to reproduce; they do not eat. Only male moths can fly and during this time they pursue females by following the pheromone scent females produce.
• Females produce only one egg mass in their lifetime which can contain 100-1,000 eggs.
• Egg masses persist through the winter and ones that are buried by snow typically have higher survival as the snow protects them from temperature extremes.

Select life cycle image below to view a full-sized version of the chart.

3. What Makes This Invasive Species More Like a Native Pest?

The LDD moth arrived in North America as a result of a misguided attempt to create a domestic silk industry. Its presence was met with alarm as the impact of defoliation became apparent.

Recent evidence, however, indicates that LDD moths are behaving more like a native pest than an invasive species. This is due, in part, to the presence of several natural factors that help to regulate the population:

• The fungus Entomophaga maimaiga overwinters in soil and infects LDD moths, resulting in their death. It needs cool, wet weather to persist and be effective.
• The nuclear polyhedrosis virus (NPV) infects caterpillars, causing them to climb to the top of the tree and die. The dead larvae become liquified, helping the virus to spread and infect other caterpillars. (It can also be spread through the feces of birds that eat dead or dying caterpillars.) The effectiveness of the virus is dependent on high caterpillar density — the more caterpillars there are per tree, the more likely that NPV can spread and effectively control populations.
• Prolonged extreme cold (below negative 26 degrees Celsius) coupled with a lack of snow can kill LDD moth eggs.
• Natural predators including other insects, spiders, and several birds will eat LDD moths in their various life stages — although this factor alone is unlikely to have significant population effects.
• Parasitoids (species that use others as hosts for their young) kill LDD moths by feeding on their tissue. These species may play an important role in population control; however, this is not yet well understood.
• Host tree natural defences: as host trees are eaten by LDD moths, they respond by growing tougher, less nutritious leaves making it more difficult for caterpillars to be successful.
• Competition between LDD moths and ultimately starvation due to a lack of food will cause a collapse of LDD moth populations, which is reflected by their typical cyclical outbreaks.

LDD Moth (Lymantria dispar dispar) Management:
Frequently Asked Questions

LDD moth or spongy moth (formerly known as European gypsy moth) is a non-native insect that defoliates trees in North America. Outbreaks occur every five to 10 years.

The LDD moth behaves like a native pest, with natural controls present. Therefore TRCA is not overly concerned about its long-term effects on our forests.

What is Integrated Pest Management (IPM)?
TRCA is currently taking an Integrated Pest Management (IPM) approach to the LDD moth outbreak. IPM focuses on the long-term prevention and mitigation of pests or their damage through techniques such as monitoring, biological control, and manual control.

A major component of this program consists of egg mass surveys in the fall and winter to predict defoliation levels for the following year. Following that, prescription and implementation of various control strategies can be undertaken.

Given that the LDD moth is behaving like a native pest, and that many other invasive species also require management, TRCA will not undertake widespread management. Instead, management actions will focus on the strategic protection of individual trees in high public use areas where required.

What is TRCA doing about LDD in 2022?
The 2021 LDD infestation was the largest documented in Ontario’s history. However, the infestation was highly variable across the province and locally. Some areas experienced complete defoliation, while other areas were barely touched. Defoliated trees had largely re-grown their leaves by early July

TRCA undertook targeted egg mass surveys in our conservation parks in Peel Region in late 2021, which indicate that the infestation level in 2022 will be light to moderate. Egg mass surveys undertaken by York Region indicate variable levels of infestation from light to severe.

Additionally, many egg masses appear to be parasitized or predated, and are smaller than they were in 2020, which indicates that the LDD population is contracting.

Because of this, as well as the cold temperatures we experienced this winter (resulting in increased egg mass mortality) and the presence of natural controls such as NPV and the fungus Entomophaga maimaiga (resulting in increased caterpillar mortality), TRCA is not overly concerned about the health of our forests and will not be undertaking any Btk application in 2022.

TRCA may choose to apply tree bands to trees in certain areas of our conservation parks to trap caterpillars and reduce the impact on individual trees.

TRCA is focusing its 2022 efforts on increased communication about LDD so that land managers and the public are better informed and can take action to protect their trees. Efforts will include a free public webinar, a printable management fact sheet, and social media posts.

Can the LDD moth affect my health directly?
Extreme LDD moth outbreaks have been associated with skin rashes and upper respiratory tract irritation in some people exposed to airborne LDD hairs, silken threads, or shed skins.

There is a potential for some people to develop minor skin irritations or rashes when they come in contact with these insects. If this is a concern, it is recommended that you try and avoid contact whenever possible.

What measures can I take to help keep the LDD moth population in check on my property?
Residents can help in the following ways:

• Remove egg masses from trees and other hard surfaces. Soak them in soapy water for 48 hours and put them in the garbage.
• Install burlap skirts around tree trunks at beginning of June to act as caterpillar traps. Caterpillars will find shelter under the burlap, making it easy to collect and dispose of them in the garbage.
• Destroy pupae/cocoons.
• Do not move firewood around without first scraping off egg masses to destroy them.
• Consult with a private arborist when larger trees require attention for control of the LDD moth.

Though effective, these control options are time-sensitive: they must be implemented at the appropriate time to be effective. TRCA recommends these IPM techniques:

• September to beginning of May: Scrape LDD moth egg masses from trees and other hard surfaces such as tree trunks, branches, and vehicles. Soak them in soapy water for 48 hours to destroy them.
• May to mid-August: Burlapping — install burlap wraps or tree bands around tree trunks to trap the caterpillars, and then collect and destroy the caterpillars, pupae, adults, and egg masses.
• End of June to mid-August: Collect, crush, or otherwise destroy pupae/cocoons when you see them.
• Beginning of May to mid-June: Consider chemical treatments such as Btk-based products or TreeAzin; be aware, however, that the effectiveness of these treatments at controlling the LDD moth is extremely time-sensitive. It is highly recommended that you consult with a private arborist by early March if you are looking at having your trees treated/sprayed, to allow the arborist time to properly schedule the work. Once the caterpillars grow too large (approximately mid-June is the cut-off point for treatment), pesticides are no longer effective at controlling the LDD moth. Some private companies will conduct egg mass removal for your trees during the winter months. The earlier you can consult with an arborist, the better.