High gypsy moth populations in Dundas

By: Elizabeth Ivanecky

Hamilton Conservation Authority staff have noted that the Dundas and Ancaster regions in Hamilton are expected to experience a high degree of defoliation this summer due to the high levels of the European gypsy moth populations.

Noticeable defoliation will occur in the Dundas Valley Conservation Area east of the Hermitage Parking lot and south of the Hydro cut where HCA staff recorded 275 to 4580 egg masses of the gypsy moth. Comparable to the last spike in the gypsy moth population in 2008, when staff recorded 2600 to 10 000 egg masses.

The DVCA south of Little John Road is expected to bear the brunt of the defoliation with a count of approximately 7150 egg masses of the gypsy moth. In 2008, staff recorded 26 000 to 40 000 egg masses.

Other areas such as Spencer Gorge, Iroquoia Heights and other locations in the DVCA have been monitored for 25 to 600 egg masses per HA comparing to 500 to 15,000 that staff counted in 2008.

Originally introduced into the United States in 1869 as an attempt to begin a silk industry, the gypsy moth spread into Canada in Quebec in 1924 and gradually expanded into Ontario, New Brunswick, Nova Scotia and British Columbia. It is considered the most significant tree defoliator in North America.

Gypsy moth larvae chew holes in or consume leaves thereby hindering a tree’s ability to produce new crop of leaves over the summer.

In their caterpillar stage, gypsy moths produce a large amount of caterpillar frass, or fecal matter, which becomes a bother to clean up on property owners’ driveways, patios, picnic tables and homes.

Lesley McDonell, a terrestrial ecologist for the HCA, prepared an update of the Gypsy Moth surveys in the Dundas and Ancaster regions to the Conservation Authority Board alongside Mike Stone, a member of the Canadian Institute of Planners and registered professional planner, which included proposed solutions to the defoliation issue.

HCA staff veer away from an aerial spray of the biological insecticide Btk since it kills more organisms than simply the gypsy moths. In 2008, the Dundas and Ancaster tree regions experienced a much more severe level of defoliation due to the Gypsy moth as compared to this year and were treated with an aerial spray.

“Gypsy moths develop in the same way a lot of our moths and butterfly species do, [with] the same sets of stages at the same time, so Btk kills every moth and butterfly at the same stage of development as the gypsy moths,” said McDonell

Instead, McDonell and staff advocate for an organic solution rather than a chemical one. She said gypsy moth populations can be kept in check with the fungus Entomophaga maimaiga and Nuclear Polyhedrosis Virus among other things.

The Entomophaga maimaiga fungus is most successful in wet weather during the spring showing a stark decline in gypsy moth caterpillars than in drier springs. Caterpillars killed by this fungus appear withered and hang in a vertical position.

A strain of NPV that enters a gypsy moth produces and reproduces in the nucleus of cells causing the host to become visibly swollen with fluid of the virus — thereby contributing to its decay.

Human mediation is also possible by scraping egg masses and placing sticky bands around infected tree trunks to catch and kill the moths in their caterpillar life stage.

HCA staff have already employed sticky tape to catch hatching gypsy moths before they begin to defoliate trees and began scraping trees for egg masses.

Staff also considered the use of pheromone traps which lure adult male gypsy moths in a lethal trap through the guise of sex pheromones.

The moderately high level of gypsy moth populations in the Dundas and Ancaster regions especially concerns HCA staff about tree health and mortality since the Fall Canker worm defoliation that occurred last spring, the summer drought which followed and the possibility of a second defoliation looming this summer. Staff remark that this will further stress the trees within these regions’ forests.

“The trees are stressed, so we will be watching some of these severe areas closely to see how they react and then to see how the gypsy moth population levels change over time,” McDonell claims.

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