Gypsy Moth epidemic said to threaten Renfrew Forests

Editor’s note: The following letter was recently received from a reader who suggests that the Gypsy Moth is no less destructive to trees than the Coronavirus is to humans.

Dear Editor,

The summer of 2021 is predicted to go down in Renfrew’s history as one of the worst for the defoliation of its forests by the Gypsy Moth. This defoliator has moved north and eastward since the last major epidemic in 1981 which cost the government and landowners millions of dollars in damages.

The summer of 2020 witnessed swarms of moths and caterpillars whose droppings covered homeowners’ patios, decks and driveways. This set the stage for next summer’s approaching pestilence. Without a major extended cold snap this winter of at least -23C the epidemic almost seems inevitable.

Ubiquitous beige egg masses now cover everything from lawn furniture, outbuildings and farm equipment to the caterpillar’s preferred host trees of oak, birch and poplar. But when populations get high this introduced pest is not averse to eating most deciduous, conifer and even agricultural crops with little provocation.

Healthy deciduous trees can re-leaf after caterpillars have defoliated their limbs providing the epidemic is a singular rather than serial event. Epidemics normally run three to five years. But the accumulative effects of dry weather, human disturbance and other forest pests have continued to dramatically compromise our forests’ resiliency over the past decade .

The scientific literature emphasizes the importance of leaving woodlots and rural properties in a natural state. Outbreaks peak during dry springs and where forests have been opened up by logging or by the cosmetic clearing of undergrowth by property owners. During the early larval stage newly hatched caterpillars take advantage of these forest openings to extend their range by being carried on silken fibres using the elevated wind draughts.

Drought conditions over the past few summers have also exacerbated the problem by reducing the incidence of an introduced fungi which can help limit Gypsy Moth egg survival. Not only does clearing vegetation, seedlings and undergrowth extenuate these hot dry conditions, it removes the habitat for the few predators which feed on the Gypsy Moth eggs, larva, and pupae. Collectively these predators — which include mice, shrews, beetles, spiders, carpenter ants and several bird species — can drop the number of gypsy moth by 50 percent. Furthermore, caterpillars prefer to attack mature trees. If the larger host trees die from defoliation a cleared understory equates to no future forest. As the trees thin out, the surviving individuals are more prone to wind-throw.

Eastern Ontario’s exploding deer population with its voracious appetite functions similarly by opening up the understory to arid conditions and eliminating regrowth which would otherwise replace mature trees lost to repeated defoliation. The eggs masses are also transported by the movement of infected firewood and contaminated vehicles such as farm equipment and ATVs.

The most effective defence remains areal spraying with Bacillus thuringiensis ( B.t.); a product made from naturally occurring bacteria which only targets the butterfly and moth family ( lepidopterous ). All other insects and animals are unaffected.

This requires a proactive and collaborative effort by property and woodlot owners to share costs to hire a private aviation company to spray their neighbourhoods.

Ironically, the MNRF has to date taken no initiative to spray public forests, despite the anticipated epidemic.

In the interim property owners can help control the Gypsy Moth spread by:

  • Crushing or scraping off egg masses, preferably into a container of soapy water.
  • Manually spraying egg masses on trees with a 50 percent mixture of vegetable oil and water using a used Windex bottle or equivalent.
  • Wrapping and folding a burlap strip on tree trunks at chest height where caterpillars will congregate during the day and can be captured and killed.
  • Tightly applying a 4” band of duct tape around the tree trunk and smearing the outside with Vaseline to prevent caterpillars from climbing up into the canopy each night to feed.
  • Maintaining vegetation, “downed woody debris” and leaves under trees which is a necessity in providing habitat conditions for Gypsy Moth predators, such as spiders, mites, beetles, harvestmen (“daddy longlegs”), and shrews.
  • Encourage birds such as chickadees, blue jays, tanagers, vireos and grosbeaks to nest by retaining thickets and dense undergrowth on your property.
  • Avoid unnecessary openings and disturbance with heavy equipment during forestry operations.
  • Inspect equipment and recreational vehicles for egg masses, to prevent the spread into new areas.


Ian Huggett


photos MNRF

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  1. Pingback: May 3 2021 | Madawaska Valley Current

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