Lymantria dispar dispar (LDD) Outbreak
Photo credit: Jon Hayes
The Ministry of Natural Resources and Forestry (MNRF) and Simcoe County's prediction that 2021 was going to be an outbreak year for Lymantria dispar dispar (LDD) (formerly European Gypsy Moth) have already been proven to be correct. NVCA residents are likely already seeing the first instars emerging from their over wintering egg masses as warmer temperatures set in.
“LDD are seeing a peak in population this year and likely for the next couple of years, until we will see a natural crash in their population," noted Rick Grillmayer, NVCA's Manager of Forestry. “I have seen caterpillars traveling across large fields in search of suitable foraging areas. When populations of LDD are as high as they are anticipated for this year, there really isn't much landowners can do to control the infestation, other than to patiently wait it out."
LDD populations are cyclical, peaking after 7-10 years then crashing from parasites or fungus. Although they are not harmful to people, high concentrations of the caterpillars will defoliate trees. A healthy tree will likely survive, however young, newly planted or trees that were already stressed may not bounce back as easily from the defoliation.
LDD caterpillars prefer deciduous trees, including oaks, poplars and birches, but will also consume conifers, if there are no alternatives available. LDD will overwinter in pale brown egg masses on the bark of trees, emerging in April-June as first instars (caterpillars) feeding heavily during this period before developing into moths during their reproductive phase in late summer.
Urban landowners may be able to control a localized infestation on individual trees, if they can find supplies. Products such as burlap and tanglefoot may be in short supply with many landowners trying to deal with their own infestations.
Rural landowners with larger properties may just have to wait until the population naturally collapse.
This population explosion isn't all bad news. “During our spring bird monitoring surveys, we've seen a noticeable increase in bird species that specialize in eating caterpillars like LDD" says Dave Featherstone, Senior Ecologist at NVCA. “We are more frequently coming across avian species like the Black and Yellow-Billed Cuckoos and Rufous-sided Towhees. We also saw Black-capped Chickadees eating egg masses during the winter."