Lymantria dispar (LDD), also called Spongy moth or Gypsy moths

In the summers of 2019/2020 these pesky moths inundated Mazinaw from the beginning of July until almost the end of August. The woods looked bare in many areas and you could see the rocks along the shoreline that would normally be covered by tree canopy.  The moths flitted around you and sometimes were so bothersome they’d drive you inside.

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The gypsy moth is not native to North America. They are very destructive with an insatiable appetite.  They have the ability to completely defoliate large amounts of trees. Gypsy moth infestations are cyclical, coming in waves every 7 to 10 years or so, with most infestations lasting approximately three years. 
 

Recognizing them:
 

There are four developmental life stages of the gypsy moth: egg, larva (caterpillar), pupa and adult and it’s important to know how to recognize them to take action.

 

When there are a few dry seasons, a massive number of moths can lay their eggs resulting in millions of caterpillars hatching in the spring.

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Locating egg masses is very important in the eradication of the gypsy moth. There could be up to 1000 eggs within each mass.  Look for them on tree trunks outdoor furniture, tents, sides of buildings and outhouses – just about anywhere!  This is the time to take action.  Scrape off the egg masses with a knife and burn them.  Do not bother to knock eggs and nests to the ground, because from there they can still hatch. The nests have to be destroyed.

 

Caterpillars and pupae slither up the trees to get to the juicy leaves so wrapping the tree with a 45 cm (roughly 18 inch) wide strip of burlap around the tree trunk at chest height helps prevent them from making their way. Cover this with duct tape, sticky side out. Or, tie a string around the centre of the burlap and fold the upper portion down to form a skirt, with the string acting as a belt. The caterpillars will crawl under the burlap to escape the sun and become trapped. Later in the day, lift the burlap. Pick off the caterpillars and dispose of them. 

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If they make it to adult moths, it’s time to trap them in a timely fashion to knock down the population by preventing males from mating with females and decreasing the number of eggs for next year’s hatch.  You can make a homemade trap but you need the pheromone strip to put in the trap, to lure the male moths.  

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Home-made traps:

 

Yogurt Container Trap. Trials have shown this style of trap works 10X better than a bottle trap. There are lots of YouTube videos. Pheromone strips can be bought online.  

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There are two natural enemies that help to squash the moth population.

1. is a virus and is usually the most important factor in the collapse of gypsy moth outbreaks. Typically, 1 to 2 years after an outbreak begins, the NPV virus causes a major die-off of caterpillars.

   • The virus is always present in a gypsy moth population but it spreads naturally through the gypsy moth population, especially when caterpillars are abundant. During a gypsy moth outbreak, caterpillars become more susceptible to this virus disease because they are stressed from competing with one another for food and space. 

1. is a fungus. Fungal spores that overwinter in the soil will infect young caterpillars early in the summer. When the young caterpillars die, their bodies produce windblown spores that can spread and infect older caterpillars. Large caterpillars killed by the fungus will hang head down from the tree trunk, and the bodies of the dead caterpillars appear dry, stiff and brittle. Within several days, the cadavers fall to the soil and disintegrate, releasing the spores that will overwinter back into the soil.  We have definitely seen this at Mazinaw and it is a weird thing to witness.
    

The good news is the forest has proven to be remarkably resilient. Some, minor, thinning of the interior canopy has occurred, but even the very young trees have held their own overall. The defoliation feels pretty traumatic. It is shocking to see the leaves disappear. It’s even weird to see little caterpillar poop in abundance on your deck!  Yes, that’s a thing.  Healthy trees can hold out through a few years of caterpillar loading.  Since evergreens generally hold needles for 2 to 5 years before naturally dropping them, they will take about three years to look like their old selves. 

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References:  https://en.wikipedia.org/wiki/Lymantria_dispar