Gypsy Moth (Lymantria dispar dispar)
Gypsy 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.
Caterpillars start to emerge from egg masses in mid-to-late 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 at all during this stage and live for approximately two weeks.
Females usually lay between 100 to 1,000 eggs.
They don’t create ‘tents’ like some other species such as fall webworm or eastern tent caterpillar.
Unlike the devastation caused by emerald ash borer (EAB), gypsy moth outbreaks rarely cause damage to forests on a large scale.
Will gypsy moths kill my trees?
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.
Does anything eat the gypsy moth?
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.
How long will a heavy infestation last?
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 gypsy moth populations.
What can I do on my property?
Please note: the hairs on gypsy 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 a tree affected by this moth. Usually 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 run.
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: 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: Until the tiny caterpillars start emerging in May, 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 let them sit for two days to kill the eggs and then put them in the garbage. Scraping egg masses onto the ground will not kill them.
Trunk wrapping: When the caterpillars are present (May to July) various forms of wrap can be used on the trunks of trees to catch and dispose of caterpillars. Double-sided sticky tape can catch caterpillars as they walk across it. There are some products available at garden centres which are specifically designed for this purpose. You can also 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 (scrape the caterpillars into a bucket of soapy water to kill them).
Set out pheromone traps: Pheromone traps can be used July-August to attract and trap adult male gypsy moths to stop them from mating with females. Although this is generally used in monitoring gypsy moth populations, it can reduce egg mass loading in small areas.
Spraying Btk: (Bacillus thuringiensis kurstaki). Btk 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.
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.
What is CVC doing?
There are many invasive species in our watershed and we’re currently focusing our efforts on the ones that have the potential to cause the most damage to our ecosystems. For this and other reasons we’re not actively managing gypsy moth on our properties at this time.
However, we are doing the following:
- Developing an Integrated Pest Management framework based on the latest research which will include a gypsy moth monitoring program for our properties.
- Working with our partners to increase collaboration and formalization of watershed initiatives.
CVC is happy to provide information and education about management techniques, as described above. If you have questions, please contact us at email@example.com
For further information on Gypsy Moth, visit the Invasive Species Centre.