European Gypsy Moth Infestation Research

Paul Harpley, article and photographs

The European gypsy moth (Lymantria dispar dispar) is an invasive insect that has become naturalized throughout southern Ontario, including South Lake Simcoe. It comes from Europe and was first confirmed in the province in the late 1960’s.

The moth larvae feed on hardwood trees like maple, oak, birch and elm. Egg sacks are the first evidence of them on your property, being easy to see on tree trunks in the winter. On our property we (Debra and I) found the egg sacks on most all tree species, even commonly on Eastern White cedar trees, as in two of the photographs accompanying this article.

Over the winter we scrapped off the egg sacks from trees using a hunting knife or stick. It is recommended wearing gloves and a having a bag to collect them, then soaking them in soapy water later for a few days, to destroy them before putting in the garbage. We visually found over 200 egg masses in roughly 5 areas of forest. We were casually finding them while skiing/walking. Even now egg masses are still apparent in May. So, if you look on the trees on your property you still have time to collect the eggs before they hatch into the destructive caterpillars.

Gypsy moth egg sack on cedar tree. P.H.

The caterpillars eat the leaves from a range of tree species such as oak, birch and maple, causing the trees to lose some of their leaves. The canopy of forest areas can be broken depending on the severity of the infestation. Sometimes foliage can recover in the season, sometimes not, from our past experience. Last year we had egg masses on Butternut trees that we purged of egg masses/caterpillars in May and June. About 15% of the foliage was affected. All signs and reports by others University researchers, conservation authorities and others that suggest this year will have a much higher infestation in our area.

The eggs in the egg masses are able to survive in our winter forest habitats through cold, windy and harsh weather. P/H

Pupae from caterpillars to the emerging moths last year on a maple tree, photographed this spring. P.H.

Broken egg mass and eggs in spring in lab. P.H.

The moth caterpillars are dark and hairy in appearance and not very large. They are distinguished by having a row of blue and red spots along their back. The caterpillars on the trunks and branches of trees can be trapped by wrapping cloth or burlap around the tree trunk. Think of it as giving the tree a skirt. If the fabric is 3’ wide, tie with string at the 1.5’ mark and let the fabric fold in half, opening towards the ground. As the caterpillars come down the trees in hot summer days to cooler shaded forest, they pass the cloth or burlap but later in the day get trapped as they climb, and that is when you can collect them.      

It should be noted that it is important for everyone to find and purge trees of this invasive species wherever possible, especially on private lands if we are to protect our forests. Municipalities, Regions and the province are undertaking various control measures on public lands.