LDD Moth Update

Ontario has once again been hit hard by the invasive LDD moth (gypsy moth). They’ve been nearly impossible to ignore in most areas of southern Ontario as large numbers of invasive caterpillars have been seen crawling over almost everything. As forecasted by the Ministry of Natural Resources and Forestry (MNRF) earlier this year, many areas have experienced severe defoliation on a variety of trees and shrubs.

Status of the Outbreak

By now most of the caterpillars are in their last stage of development before their transition into moths. We see mostly large caterpillars and in some areas the caterpillars are already pupating (forming a cocoon). They’ll remain in the pupa stage for 10-14 days before emerging as a moth.

LDD moth caterpillar
Large LDD caterpillar seen in Caledon on June 30.

In late July, we can expect to see fewer caterpillars and more moths. This is a good thing for our trees as the moths focus their attention on breeding and egg laying, not feeding. As we reach this point it gives most healthy deciduous trees a chance to send out new leaves before they’re fully depleted of energy and resources. Unfortunately, if caterpillars have moved from your deciduous trees to the conifers, there is less of a chance that the conifers will survive a severe defoliation as they do not produce more needles this time of year.

LDD moth larvae
LDD pupa with old egg mass beneath.

The good news is that we’re starting to see the effects of natural control methods including the nuclear polyhedrosis virus (NPV), which is harmless to people but lethal to LDD moths, spreads through contact between infected caterpillars. It can also be spread through the feces of birds that eat dead or dying caterpillars. The virus is more effective at spreading when there is a high density of caterpillars. The fungusEntomophaga maimaiga, also harmless to people and lethal to LDD moths, overwinters in soil and infects the caterpillars. It needs cool, wet weather to persist and be effective.

Dead caterpillar due to NPV in a V shape.
Dead caterpillar due to the fungus.

What can you do?

As the transition from caterpillar to pupa to moth happens, we can help limit future outbreaks on a local scale and reduce the chance of another year of severe defoliation.

Collect and dispose of pupa and egg masses in the coming weeks. Once the moths emerge, they start to lay egg masses about the size of a toonie that can hold up to 1,000 eggs. To remove them, use a strong edge to scrape the pupa and egg masses into a container of soapy water. A butter knife, coin or drywall trowel works great. Then let them sit for 48 hours in the solution before disposing of them. Make sure you use a lid to stop any escapees and stir the mixture well so that the soap doesn’t settle out.

Female LDD moth laying egg mass.

Learn more about the LDD moth, what CVC is doing and read answers to frequently asked questions on our LDD page.

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