Update from the Gypsy Moth Team

Subdivisions from Grand Bend to Port Franks are working separately and together to address the current gypsy moth infestation. Everyone is concerned about the wellbeing of our rare and fragile oak savanna, and what it means to local tourism, our enjoyment of our neighbourhoods and outdoor spaces, and our property values. Groups in each area are informing their communities and coordinating with the municipality to find the best course of action.

A ten-minute presentation was made to Lambton Shores Council on July 14 by Romayne Smith Fullerton of Port Franks. It provides an excellent overview of the situation and the need for coordinated action. You can view it here: https://www.youtube.com/watch?v=IwbEUEd3xM4The relevant section is from 11:45 to 22:00

Attached are some “Questions and Answers” that will give you a basic understanding of the gypsy moth situation and the measures you can take to help deal with the infestation.

The next step for the team is to gather information from companies about the processes and costs of aerial spraying, whether it is done by individual property owners, as a community or by the municipality. We will keep you informed.

Why should I worry about gypsy moths?

Gypsy moths are an invasive species that, when in the larval (caterpillar) stage, can cause extensive damage to the tree canopy and have a huge impact on the quality of life of the residents living in the area affected.

During moderate infestations, they will strip trees of their foliage, leaving them vulnerable to disease and other pests, particularly if they are weak, or if there are other environmental stress factors like drought. It is possible for most healthy trees to withstand a year or two of being defoliated.

During a severe infestation, after they have eaten foliage on hardwood trees, the caterpillars will move on to understory plants and shrubs.  Each mated female can produce as many as 1,000 caterpillars the following spring.

Caterpillars are messy eaters. They create a large amount of frass (excrement – the black pellets the size of large grains of rice), half-eaten pieces of leaves, and other debris as they shed their skin. Some people get a rash when they come into contact with them. The caterpillars make it difficult for those of us living in a forested area to enjoy our outdoor space in the summer months. Severe infestations can result in conditions that are the stuff of horror films, as those who were here during our last major infestation in 1994 can attest: outdoor surfaces, including doors and windows, are covered in caterpillars; umbrellas are necessary when stepping outside, and windshield wipers to see when driving.

Major infestations occur every seven to ten years and peak over a two-to-three-year period. Oak trees’ survival is threatened if the infestation persists. The severity of these major infestations can vary. Last year Port Franks was experiencing what we are seeing this summer. This year they are experiencing a much worse infestation.

What can I do about gypsy moths?

Many places that experience a severe invasion of gypsy moths use an Integrated Pest Management (IPM) approach – employing as many means as possible at their disposal to control and eradicate the pest. This includes burlap skirting, hand-picking pupae, moth traps, destroying egg masses and aerial spraying of a biological insecticide.

Most of these measures are implemented by property owners themselves at specific times from May through August, with the removal of egg masses happening in the winter. (For more detailed information about how to carry out these control measures, visit: http://www.london.ca/residents/Environment/Trees-Forests/Pages/Gypsy-Moth.aspx

Keep your trees healthy and well watered if they are vulnerable or stripped of foliage.

Aerial spraying of a biological insecticide is an option chosen by municipalities, property owners, or groups of property owners when an infestation is severe. Spraying occurs during the caterpillar stage (usually May) and is done by hiring a licensed helicopter or plane spraying service. This involves the coordination of participants months in advance to ensure the necessary permissions are acquired, to reserve a slot in the spraying window, and to guarantee the biological pesticide will be available.

What is the biological pesticide and is it safe?

Foray 48B is a BTk (Bacillus thuringiensis var. kurstaki) biological pesticide (as opposed to a contact chemical pesticide) which has been commonly used to target gypsy moths, tent caterpillars, and other pests across North America and around the world for the past 30 years. It is a bacterium that naturally occurs in the soil and was found to be effective in killing 90% of gypsy moth caterpillars if applied at the appropriate time in appropriate conditions. It is cultured and fermented, and the resulting solution is sprayed onto foliage – about 1.6 litres per acre – in two applications a few days apart. A protein in BTk destroys the caterpillar’s gut, causing the insect to stop feeding. It only impacts other moth and butterfly caterpillars that are in the same larvae stage, but most, including monarchs and swallowtails, are not affected, as they are not in the larval stage at the same time as gypsy moth caterpillars. BTk breaks down in sunlight within a few days.

It is considered safe for humans, animals, birds, other insects, and aquatic life by Health Canada. It is used to treat pests by certified organic produce farmers. No special precautions are required for residents in the spray zone, although anyone who wants to avoid exposure is advised to remain indoors during and immediately after the spraying.

What will happen if we do nothing?

When no measures are taken to control a gypsy moth infestation, it usually peaks over two to three years. Natural controls, such as fungi, bacteria and, viruses, reduce the levels of gypsy moths to a normal range two to three years after the peak of the infestation. The E. maimaiga fungus may kill gypsy moth caterpillars even when populations are low, but only if it is moist and humid enough during May and June for the spores to germinate. The abnormally dry conditions this year mean this fungus may not have the chance to develop as it would during wetter weather cycles, and it makes it harder for defoliated trees to survive. Also, warmer temperatures mean fewer eggs are killed off during the winter.

The gypsy moth nucleopolyhedrosis virus is seldom prevalent until gypsy moth populations reach very high levels. It is often referred to as “wilt” because dead caterpillars hang in an inverted “V” from tree trunks or foliage.

The full extent of this year’s infestation will not be known until later this fall when egg mass surveys can be conducted to determine the degree of infestation expected next year. Surveys can be conducted in the spring, also, to see if the egg masses have remained viable over the winter. If we were to get a particularly harsh winter with prolonged periods of weather below -20 degrees, it could decrease the numbers next year. If property owners are not confident carrying out these surveys, an arborist can be hired to do them. (The City of Toronto Forestry Department uses 10 to 15 egg masses per tree as a threshold to carry out an aerial spraying program the following spring.)

The gypsy moth has natural predators that help reduce the population: wasps, flies, beetles, ants and spiders; and chickadees, blue jays, robins and nuthatches. Chipmunks, squirrels and raccoons also prey on the caterpillar.

Gypsy Moth Life Cycle and What You Can Do When

Defoliation Comparison between 2017 and 2019








2 thoughts on “Update from the Gypsy Moth Team

  1. Thank you Angela for sharing this information with the community. Your hard work is greatly appreciated.

  2. Thanks Marg
    The credit for writing this post goes to Anne Thornton. She did a lot of research, writing and editing to boil down the large amount of information available. We’re glad you found it helpful!

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