European Gypsy Moth - Lymantria Dispar Dispar (LDD Moth)

What does LDD moth look like?

The LDD moth has four distinct developmental stages in its life cycle similar to other butterflies and moths.

1. Egg (Late August to early May)
   • Dormant stage (easiest to manage)
   • Egg masses range in size from 2-8cm long and can contain between 100-1000 eggs
   • Egg masses are usually oval shaped and beige/light brown in colour
   • Often found on tree trunks and the underside of larger branches
2. Caterpillar (Early May to mid-July)
   • Tree damaging stage
   • Newly hatched caterpillars are about half a centimetre long and dark in colour. As they grow, they change colour becoming dark coloured and 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
   • Caterpillars can be found feeding on the leaves of trees since this is their main food source
3. Cocoon (Mid July to early August)
   • Stage lasts for 10 to 14 days
   • Once the adult moth emerges, it leaves the empty cocoon behind which can be seen on infested trees
4. Moth (Late July to late August)
   • Stage lasts 10 days
   • An adult LDD moth’s only function is to reproduce and not eat anything, unlike other moth and butterfly species
   • Female is larger, white and cannot fly
   • Male is smaller, brown and is attracted to pheromones produced by female moths

What does an LDD moth infestation look like?

• From late August to late April, spongy, light-brown or beige egg masses can be observed on the trunks and branches of infected trees.
• From May to August, once the eggs have hatched, caterpillars chew holes in or devour entire leaves. During severe outbreaks, trees and shrubs have significant leaf canopy loss. Healthy trees can regrow their canopy as the season progresses.

Infestation levels in Richmond Hill have been low since the early 1990s however, recent observations have identified a re-emergence in 2020/2021.

Richmond Hill is using a number of different methods to minimize damage to trees on City property and help reduce the spread of LDD moth in our community. This includes egg mass removal, selective pesticide treatment, watering and monitoring. 

The City also consults with York Region on how to manage this insect. Level of action and priority areas are largely determined from surveys York Region conducts within the City, which identify areas of high population or importance. These surveys can have a high impact on predicting and managing the numbers in the following year.

2021 LDD moth management activities

Street and park trees that exhibit LDD moth infestations are targeted throughout the winter and early spring when the moth is most manageable. During the winter/early spring, LDD moth populations are present as egg masses found along the trunks and underside of larger branches of trees.

• Egg mass removal - City staff are removing egg masses on small to medium sized trees using a specialized portable vacuum and through manual scraping to reduce the number of hatched caterpillars in the spring. To date, 65,281 egg masses have been removed.
• TreeAzin treatment - In late April, select trees will be treated with pesticide (TreeAzin™) which is injected into the trunk of the tree to help minimize damage caused by LDD moth.
• Watering will occur in the hotter summer months if necessary. In addition, during the active feeding months in the summer, caterpillars are sprayed with high pressured water which reduces their survivability.

The City will not be spraying pesticide

• Spraying pesticide is costly, time sensitive and not feasible for a large spread out area such as a city
• It is non-selective, which means it will kill all caterpillars, not just LDD moth. This also has negative impacts on birds that feed on caterpillars.
• Caterpillars still need to ingest the leaves in order for the pesticide to work, so trees will still suffer defoliation and there will still be caterpillars around for some time as it is not 100 % effective.

What you should do if you have an LDD moth infestation on your private property

Trees on private property are the responsibility of the property owner. You are encouraged to monitor the trees on your property to identify any signs of infection and take action to remove LDD moth egg masses and/or caterpillars as often as possible.

There are a number of actions you can take to help reduce LDD moth populations. Control methods are closely linked to the LDD moth’s life cycle stage and time of year. To help prevent infestation, water your tree regularly to promote tree health, especially during the hottest days of summer.

In the event that managing populations becomes unfeasible through the methods described, seek a professional tree care company for assistance.

Trees that have lost their leaves should be watered regularly to promote leaf growth. Extensive watering should occur in the mornings and evenings during the hot summer months when natural precipitation is low, trees are stressed and most caterpillars are in their cocoon stage.