LTVCA Watershed – We are listening to many watershed residents reporting their concerns about the effects of the invasive European Gypsy Moth (scientific name:  Lymantria dispar dispar) on Lower Thames Valley Conservation Authority (LTVCA) forests, and woodlands and individual trees growing on private lands.

Unfortunately, our LTVCA conservation areas are experiencing the defoliation (eating) of leaves on trees.  These tree species in our watershed are hosts (favorites) of this caterpillar including: oak, birch, aspen, sugar maple, American beech, and eastern white pine.  Populations of the gypsy moth are now established across southern Ontario, based on the moth’s preferred food supply.  Spraying was not an option in our conservation areas.

Gypsy moth outbreaks occur every 7 to 10 years. The eggs of the gypsy moth overwinter on the bark of trees.  In the spring, eggs hatch and the larvae move up the trees to feed into July on the new leaves.  Then, spongy egg masses can be seen on tree trunks and branches, followed by pupae and adult moths in July and August.

Natural predators and pathogens are the main reason the gypsy moth outbreak in North America is collapsing, including the effects from viral infections and fungi known to kill the larvae. Birds, mammals, other insects and parasites also prey on the gypsy moth.  Extreme cold winters reduce gypsy moth egg survival.

According to an Ontario government webpage about gypsy moths https://www.ontario.ca/page/gypsy-moth, there are some control options that can be tried at various stages of its life cycle:

August to mid-April remove the egg masses and discard

Mid-April to mid-May apply biological pesticide to the early stage caterpillars

Mid-May to June attach burlap bands on tree trunks and discard the late stage caterpillars

June to mid-July remove by hand and discard the pupae

By now, spraying will have a minimal effect on the larva and could kill beneficial pollinators like butterflies and moths. It is anticipated that after 2 years of large populations, the gypsy moth numbers may begin to decrease as they have in the past.

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For further information contact:

Randall Van Wagner – LTVCA Manager of Conservation Lands and Services

Randall.VanWagner@ltvca.ca