About this Invasive Insect
LDD moths or spongy moths (Lymantria dispar dispar) were originally imported to Boston from Europe as a potential silk producer. Unfortunately, they escaped and have been in Ontario for approximately 60 years.
Unlike the devastation caused by emerald ash borer (EAB), LDD moth outbreaks rarely cause damage to forests on a large scale.
LDD Moth Name
In July 2021 the Entomological Societies of Canada and America (as part of their Better Common Names Project) removed ‘gypsy moth’ from their lists due to its racial connotations. CVC and other organizations have been using the term LDD, short for its Latin name Lymantria dispar dispar, in the meantime.
On March 2, 2022 after consulting with Romani scholars and various insect professionals the Entomological Society of Canada announced ‘spongy moth‘ would be the new official common name for Lymantria dispar dispar. Spongy moth comes from the French term ‘la spongieuse’ which refers to the texture of the egg masses laid by the moth. The name was chosen in part because it highlights a key feature of its lifecycle as the moths spend most of the year as egg masses.
Moving forward, CVC will use both spongy moth and LDD to refer to the moth until use of the new common name becomes more widespread.
Caterpillars start to emerge from egg masses in late-April to early May and will spend about 40 days eating all the leaves or needles that they can consume. Caterpillars prefer to eat oak but will eat many other species such as maple, poplar, cherry, willow, birch and spruce. Each caterpillar will eat about one square metre of leaf material before cocooning for 10 to 14 days.
Adult moths emerge from cocoons in June – July to focus solely on breeding and egg laying. They don’t eat during this stage and live for approximately two weeks.
Females usually lay between 100 to 1,000 eggs. Unlike other caterpilar species such as fall webworm or eastern tent caterpillar, LDD moths do not create ‘tents’.
Frequently Asked Questions
Healthy trees can typically survive three to five years of heavy moth feeding. A healthy tree will usually be able to regrow their leaves later in the season. However, if the trees are stressed due to drought, disease, fungi or other insects, this loss of leaves can deplete the tree’s energy reserves and eventually result in death. Unfortunately, conifer trees (though not the moth’s favourite meal) can die after only one year of very heavy feeding.
Several local species will eat the caterpillars or pupae. Birds such as blue jays and orioles will eat the caterpillars, and chickadees will feed on the egg masses. Mice, chipmunks, skunks, voles and other small mammals will eat the pupae or larvae.
Besides wildlife that eat the LDD, there are some other natural control methods including both a virus and fungus. The nuclear polyhedrosis virus (NPV) infects the caterpillars, causing them to die and continues to spread through contact between 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. Interestingly, when caterpillars die due to the NPV they hang in an upside down “v” shape. The fungus Entomophaga maimaiga overwinters in soil and infects the caterpillars, resulting in their death. It needs cool, wet weather to persist and be effective. These natural controls are part of why the population declines after a few years.
These outbreaks occur every 5 – 10 years and usually last between two and four seasons.
Outbreaks generally collapse due to the combined effects of natural controls: a fungus (Entomophaga maimaiga), a virus (Ld-Nucleopolyhedral virus), and parasitic wasps and flies. The effectiveness of these natural enemies is dependent on weather conditions and the size of LDD moth populations.
Please note: the hairs on LDD moth caterpillars and in egg masses can cause irritation or allergic reactions in some people. Consider using gloves and other protective wear whenever contact is possible.
There are several ways that you can try to help your trees affected by this moth. A combination of these methods works best. You won’t get rid of all the caterpillars, but you can reduce the amount of damage they cause. If there are a few trees on your property that you’re concerned about, you can concentrate your efforts on them. If you have a larger woodlot some damage to a few trees is not likely to have a big effect on the forest in the long term.
If you’re worried about the trees on your property you can try the methods listed below or consult a local tree service company:
- Keeping your tree healthy (year round): This can mean watering in dry periods, adding mulch to the soil around its base and making sure its root zone is clear of heavy objects or things preventing rain from getting into the soil.
- Egg mass scraping (August to late April): Until the tiny caterpillars start emerging in late April, the oval-shaped, tan-coloured egg masses can be scraped off trees and other surfaces into a container. Fill the container with soapy water, and make sure you stir the egg masses and break them up if possible. Let them sit for two days in a sealed container to kill the eggs and then put them in the garbage. Scraping egg masses onto the ground will not kill them. LDD moth egg masses can be found on almost any surface, including the side of your house. Watch the finding and removing LDD moth egg masses video.
- Spraying Btk (Planning: winter before you want to spray, Spraying: May – June): Btk (Bacillus thuringiensis kurstaki) is a biopesticide that can kill moths in the caterpillar stage when sprayed on the leaves of affected trees. The caterpillar needs to eat the bacteria off the leaf to be killed. Various Btk products are publicly available, however it should be applied by a registered pesticide applicator. This can be done through ground sprays or aerial sprays for larger forested areas. Consult a local tree service company for ground spray options and research for aerial spray options well in advance of the spring season. Note: Pesticides of any kind should only be used with the greatest caution. Always make sure to carefully read the label and follow instructions for the proper timing and dosage of application. Visit Health Canada to read about the safety of Btk. This spraying can be done for individual trees or for large scale infestations.
- Trunk wrapping (May to June): When the caterpillars are present wrap a wide strip of burlap around the trunk, tie it around the middle with string and then fold down the top to create a sort of pocket. Caterpillars will gather there for shelter during the day and they can be routinely caught and disposed of. Watch the LDD burlap banding traps video.
- Hand picking caterpillars and pupa (May to July): Collect caterpillars and pupa from trees or other surfaces into soapy water and make sure the solution is well mixed. And then discard them in the garbage. Wear gloves to ensure your skin is not irritated by the caterpillar hairs.
- Set out pheromone traps (July to August): Pheromone traps can be used to attract and trap adult male LDD moths to stop them from mating with females. Although this is generally used in monitoring LDD moth populations, it can reduce egg mass loading in small areas.
When a population boom occurs, LDD caterpillars often eat all the leaves on their host trees. When this happens they search for more food by crawling around or dropping down on silk lines and the wind blows them onto something else nearby.
When they search for food they are not always successful. This is why they sometimes end up on a house, car and even us. Windy conditions also help blow them out of a tree canopy and onto anything that’s nearby.
This in part is why the trunk wrapping collection method works. Caterpillars climb up trees looking for new leaves to feast on. Caterpillars also climb down the trunk of the tree to seek shelter in the heat of the day.
There is a product TreeAzin which is manufactured by Bioforest that can provide protection for select trees to LDD moth. It’s a systemic insecticide that is injected into a tree. When used for LDD moth, it can severely decrease the amount of defoliation on a treated tree.
Treatments must be done by a qualified professional with special equipment, can be very costly, and require holes to be drilled into the base of each tree. It must be done pre-emptive to the caterpillar outbreak and therefore takes planning to be effective as it targets the first few early life stages of the caterpillar. Learn more information from Bioforest, and see their list of service providers.
In response to the severity of LDD abundance and defoliation impacts in 2021, CVC completed targeted LDD outreach efforts, collaborated with watershed municipalities and formalized our LDD monitoring program.
Outreach and Education
As watershed residents noticed the impacts of LDD throughout the spring and summer of 2021 CVC responded with the following outreach and education actions:
- Responded to LDD-related landowner and media enquiries
- Co-hosted a free webinar (on LDD life cycle, identification and management) with Toronto Region Conservation Authority.
- Released four blogs: Another Year of Invasive Moths, How to be a Good Neighbour, Managing LDD Moths, LDD Moth Update
As part of a larger initiative to create a formalized integrated pest management framework, CVC initiated an LDD egg mass monitoring program in 2021. We completed 29 surveys across 22 conservation areas focusing on vulnerable forest communities characterized by LDD preferred hosts (oak, maple and poplar) throughout the watershed.
Seven survey sites reported egg mass numbers high enough to predict severe defoliation in 2022 however, distribution of those sites was patchy and spread across the upper two-thirds of the watershed. CVC staff have anecdotally reported a decrease in egg mass numbers in 2021 as well as increased presence of parasitic insects, nuclear polyhedrosis virus (NPV) and the fungus Entomophaga maimaiga during the growing season.
2022 Planned Activities
Although we are optimistic that the natural controls are taking effect and LDD populations will begin to decline in 2022, CVC will continue to respond to the LDD outbreak with the following outreach, education, partnership and management actions:
Outreach and Partnerships
We will continue to provide outreach and education to watershed residents and partners including:
- Engaging in social media posts and providing technical information when requested.
- Expanding our LDD webinar partnership to include Toronto Region Conservation Authority, Conservation Halton, Hamilton Conservation Authority and Lake Simcoe Region Conservation Authority. Watch the webinar recording.
- Collaborating with our partnering municipalities and local conservation authorities through working groups, provision of technical knowledge and data sharing.
CVC staff will conduct LDD egg mass surveys at priority vulnerable forest communities in our Conservation Area lands this fall.
Due to the low egg mass numbers found in our urban conservation area plots in Mississauga and the high variability in egg mass numbers across the upper watershed, we will not be conducting aerial sprays for LDD on CVC owned and managed lands in 2022. However, we will be supporting City of Mississauga in their LDD management program as it relates to CVC owned lands.
Additionally, we are investigating the potential for localized control efforts such as tree banding and/or egg mass scraping to protect priority amenity trees in conservation areas where defoliation is predicted to be severe. This will require further field assessments this spring to determine if there are any suitable candidate trees.