Gypsy Moth

By: John Degroot

July 19 2008

            Let summer of 2008 be the summer of caterpillars.  Lambton County has been plagued by caterpillars this year, and they show no signs of slowing down.

            Mugho Pines were attacked in mid early June by Pine Sawfly, a hardly visible moth that eats older needles of Pine, causing the centre of the shrub to look like a skeleton.  Pine Sawfly eats for only a few weeks then pupates for a few weeks before turning into an adult which dutifully lays eggs ensuring more damage next year.

            Army Worm has hit wheat in June of this year.  Army Worm is not foreign to Lambton County, but such large infestations are unprecedented in our corner of the world.

            By early August we will see Fall Webworm attacking trees.  Eggs that were laid last fall by the adult moth have begun to hatch this week, and in short order we will see hundreds of tents dotted in trees throughout Lambton County.  These smart caterpillars spin silken web tents to protect themselves from predators. 

            This year’s nastiest caterpillar pest is the Gypsy Moth, a voracious pest that has practically been non-existent till this year.  Residents in northeast Sarnia are suddenly quite familiar with Gypsy Moth.  They love feeding on Oaks, but will also feed on Poplar, Maple, Ash, Birch, and even evergreens. Gypsy Moths are so abundant that they can be found on decks, patios, cars, picnic tables and more.  I have heard some reports from folks who claim they can actually hear the caterpillars eating.  Just as quickly as they eat, Gypsy Moth leaves behind excrement which resembles clumps of black peppercorns. 

            We can thank a gentleman named Leopold Trouvelot for today’s Gypsy Moth.  Back in 1869, Leopold brought Gypsy Moth from Europe to Massachusetts, with the hopes of breeding the insect for silk production.  A few insects escaped his backyard laboratory, and within a few decades the caterpillars became a major pest of forested areas. 

            Gypsy Moth has one generation with 4 stages per year: egg, caterpillar, pupal and adult stages.  Female moths lay masses of eggs on limbs, houses, structures and even cars.  The eggs remain viable through winter, and hatch in spring as soon as temperatures remain consistently over 17 degrees celcius.  Young recently hatched caterpillars begin eating immediately.  They eat anytime of day or night and are not fussy about their host plant.  As the caterpillar gets older they eat less, preferring to seek shelter through the day and feeding at night.  Mature caterpillars pupate in late July, depending on the weather. 

            The pupae stage of Gypsy Moths lasts for about two weeks, after which they transform into adults.  The adult is rather short lived and after a week the female adult busies herself depositing egg masses in carefully chosen sights where her young can easily find food.

            All caterpillars have similar growth cycles, differing only in timing of cycles.    The only stage in life where they eat and cause damage is the caterpillar stage.  The moth or adult stage lasts only a few weeks, and will hardly be noticed.

Thankfully, all trees are equipped with two sets of leaves and a healthy tree can recuperate from defoliation by producing a second set of leaves.  Usually a tree can survive one year of damage, but two or more consecutive years of severe defoliation may be fatal. 

It is premature for us in Lambton County to hit the panic button.  We have only had one season of heavily caterpillar infestation, and we know that insects are cyclical.  The City of Mississauga was hit two years ago with such an abundance of Gypsy Moths that several residents reported skin rashes and upper respiratory tract irritation.  In the interests of protecting their trees, The City of Mississuaga undertook an aggressive aerial spray program coupled with an education plan for their residents and it appears as if Gypsy Moth in that area is now manageable. 

            Let’s hope natural factors and our weather in the next 6 to 8 months will keep Gypsy Moth and other caterpillars in check.