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The Invasive Gypsy Moth (Lymantria dispar)

Gypsy Moth levels have been monitored since the last serious outbreak in the early 1990’s. Survey results from this past winter indicate that the Moth is once again making a comeback. It is hoped that due to the below minus 15 degrees Celsius gypsy mothtemperatures experienced in the late part of the winter, there may be some egg mortality.

The Gypsy Moth eats the leaves of both deciduous (leafed) and coniferous (needled) trees. If there are repeated annual defoliations on deciduous trees, it is possible the tree will die after a few years. If coniferous trees are defoliated, the tree will die after the first defoliation. It is important to identify the Gypsy Moth in its various stages, particularly the egg stage.

The trees most susceptible are Oak, Basswood, Poplar, Willow and Maple.

Signs and Symptoms of the Gypsy Moth

The four stages in the life cycle, include:
Egg – the Gypsy Moth passes the winter months in the egg stage. Light beige coloured patches 2-3 cm long can be found on branches, trunks, rocks and walls.
gypsy moth caterpillarCaterpillar (Larvae) – The eggs hatch into caterpillars when the trees are starting to bud. As they get larger, the caterpillars feed on the leaves for about 7 weeks, usually only leaving the veins. In the later stages of its development, the caterpillars are charcoal grey in colour with an easily recognizable double row of five blue dots and six red dots on its back, but some variation is known. Initially, small caterpillars hang from threads and let wind carry them to other trees to feed. High populations can defoliate entire trees from mid to late May until mid-July
Pupa – the Moth is now reddish brown, 2-3 cm long and cocoon-like from mid July until the end of July.
Adult – adult moths begin flying in late July or August. Female moths are approximately 30 mm long and are white in colour with zigzag markings on their wings. Females cannot fly; they die about one day after laying their eggs. Males are smaller, brownish in colour, and survive for about one week.

Methods of Control for the Gypsy Moth

Manual Methods:
Scrape off the egg masses in late fall and through the winter months. Soak them in a soapy water solution and dispose of them in the garbage.

In summer, when caterpillars are active, place a band of cloth material around the trunk that is folded over about 15cm (6″) to provide shelter during the heat of the day. Each afternoon, remove the resting caterpillars from underneath the material and soak them in a container of soapy water prior to disposing in the garbage.

Other Methods:
For severe infestations in larger areas of trees, a control agent application may be needed.

Trees that suffer more than 50 per cent leaf loss from this pest for two successive years may have a moderate to high mortality rate. Trees are weakened from trying to produce new foliage, which takes stored energy reserves and makes them more susceptible to other insects or diseases.

For more information about the Gypsy Moth, visit the Natural Resources Canada Website.

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