How to control an LDD moth outbreak

Published: June 14, 2021 · Updated: July 15, 2021

gypsy moth LDD moth Photo by Paul Reeves Photography/ Shutterstock

There’s a small critter causing big problems in Ontario. The LDD moth (formerly known as the European gypsy moth) is an invasive species experiencing a boom year in Ontario.

The caterpillars of the LDD moth (Lymantria dispar dispar), which have the same M.O. as the ‘very hungry caterpillar’ of  Eric Carle’s beloved childhood book, have been busy chowing down on the leaves of Ontario’s trees, causing defoliation. The caterpillar’s body hairs can also trigger allergic reactions, leading to a very itchy start to the summer for some Ontario residents.

This isn’t the first time that Ontario has faced a wave of LDD moths. David Dutkiewicz, Entomology Technician with the Invasive Species Centre, says Ontario experienced significant peaks of LDD moth populations in 1985, 1991, 2002, and 2020. He adds that 2020 saw, “the highest outbreak of LDD moths in the history of the moths being in Ontario.”

A perfect storm of environmental conditions can spur an LDD moth outbreak. Warm and dry weather conditions, low predators, and a lack of viruses and fungi attacking the moths can cause a couple of years of perfect growth that will allow the population to shoot up, says Dutkiewicz.

Humans have several natural micro-sized allies in the fight against the LDD moth. One is the nuclear polyhedrosis virus (NPV) is a virus, which is naturally found in populations of LDD moths.

“Us going through the pandemic, we can understand that a virus can go through a population quickly if LDD moths aren’t observing social distancing behaviours,” says Dutkiewicz. The more the population of LDD moths grows, the more the virus can spread and provoke a population collapse.

Another pathogen that takes out the LDD moth is a fungus called Entomophaga maimaiga. But for this fungus to get to work, it needs wet, damp conditions to propagate. “Unfortunately, this spring we didn’t have the wet dampness the fungus requires,” says Dutkiwiz.”

For cottagers and landowners looking to combat LDD moths on their properties, it is essential to first ‘know thine enemy’. “You really have to know your life stages in order to know what is the best method of management,” says Dutkiewicz.

From September to April, he advises hand scraping egg masses off of trees as the best management strategy. When springtime arrives, you go after the caterpillars. This could include using burlap wrap traps at the bottom of trees or applying biopesticides.

Biopesticides are no use once the LDD moth hits the pupae or adults life stage from June to August, because the pesticides must be consumed by the caterpillars to work. If you’re spraying past spring, biopesticides could also affect non-target species like monarch butterflies.

A popular method for trapping LDD moth caterpillars is to apply sticky tape to the trunk of trees, but this strategy poses a risk to other wildlife including birds and reptiles. Dutkiewicz says for people who choose to go the sticky tape route, they must check the traps often, because “if you don’t pay attention to it, you can have these unfortunate mishaps where you’ll be harming a non-target species.”

Photo by Kris Bowes

As for allergic reactions to the caterpillar hairs, it’s still helpful to understand the LDD moth life stages in order to combat the itch factor. Dutkiewicz says that in May to early June, the caterpillars have fine hairs, that they can actually use to float on the wind as a form of dispersal. You’ll want to stick to long sleeves when you’re outside. Dutkiewicz also warns of the possibility of caterpillars hairs making their way into laundry hung out to dry.

Come June into July, the caterpillars are large enough that you have to have physical contact with an individual to experience irritation. Once again, long sleeves can be a form of protection. But, if you’re finding caterpillars crawling all over your deck and home, you can make short work of them with a hose. “If you use an attachment that sprays soap and water, you can actually kill the caterpillars with the soap,” says Dutkiewicz. [Be sure to only use soap well away from the lake.]

If you need help dealing with skin irritation from an LDD moth caterpillar, your best bet is to contact your local pharmacy.

There are a number of resources available for Ontario residents to learn about the LDD moth, its life stages, and best methods of control. Dutkiewicz recommends the species primer on the Ontario government website, as well as checking out local municipality plans to combat the LDD moth.

Read more: 5 invasive species straight out of an alien flick 

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