2020 proved to be a big year in the Kawarthas for the destructive European gypsy moth (Lymantria dispar dispar), an invasive species that feeds mostly on oak trees but is also found on other hardwoods, such as maple, birch, poplar and willow, and – during particularly bad years – white pines. Its population is known to surge every six or seven years, and during these outbreak years, the caterpillars – or larvae – are seen everywhere, and have been known to completely defoliate trees, weakening them and making them more susceptible to disease and other insects. 

For some effective natural solutions to these pests, scroll down the page. For detailed information about the most common biological insecticide, Btk, including a review of scientific literature on the treatment, read the blue section, below.

Fo more general information click here.



The Science of Gypsy Moth and Btk Spray

Summary by Ed Paleczny 

For the full report by Lake Guardian Coordinator Madeline Tregenza click here.

The Gypsy moth infestation seemed to have peaked last summer (2020) with severe defoliation of many oak and white pine around Stoney, Clear and White Lakes. This caused a lot of anxiety for many who want to protect healthy forest ecosystems. We have received many questions about what can be done to control the outbreak of Gypsy moth and whether the aerial spray of Btk is effective and safe for the environment. To ensure that we are providing sound advice, we asked Madeline Tregenza, Lake Guardian Coordinator, to complete a science literature review of the impacts of Btk in the environment and sought expert advice from Dr. David Beresford, Trent University Professor.

Based on the literature review, there is evidence of impacts of Btk on non-target species in the environment and a lack of sufficient studies to understand the impacts, including:

1)  Potential human uptake and unknown immunological response by humans.

2)  Persistence in the environment

3)  Impacts to non-target invertebrate species.

4)  Impacts to the micro biota of the soil and soil health.

5)  Impacts to honey bee health and viability.

6)  Impacts to non-targeted Lepidopterans (butterflies and moths).

7)  Potential impacts to bird species in subsequent years.

8)  Aquatic impacts (not well known and not studied).

Dr. David Beresford, an integrated pest management expert, an insect conservation specialist and a professor at Trent University, concurs with the findings in the literature review. In his professional opinion, “While there is scientific evidence that Btk does kill other pollinators, moths and butterflies, the sheer numbers of these insects will buffer impacts to their overall population. Gypsy moths pose no threat to the forest, but do pose a threat to individual trees that might be vulnerable because of old age or poor nutrition. Some gypsy moths will die when sprayed with Btk, however, it is unlikely that aerial spray of Btk will control numbers since the natural cycles are controlled by natural enemies like the Gypsy moth virus.” He also cautioned that “Widespread Btk application may interrupt or delay this natural control cycle, and actually prolong the outbreak. Lots of times pesticide applications do prolong outbreaks.”

We have seen signs of the Gypsy moth virus in caterpillars (hanging in an upside-down V) last summer, which is a sign that Gypsy moth populations will decline. There are also natural control methods that can be applied by landowners to protect trees on their property, such as scraping egg masses in the fall, winter and spring, applying burlap wraps to trap caterpillars moving up tree trunks in the spring, and watering stressed trees to keep them healthy in the summer.

A summary of “Gypsy Moth Control Options and Impacts - Questions and Answers" (click here to read) consolidates our understanding of current information on the effectiveness of Btk spray, the potential impacts of Btk in the environment and alternative natural control methods that we encourage you to use on your property to reduce any risk of impact to the environment.



The gypsy moth has four developmental stages: egg, larva, pupa (see image), and adult (moth). Gypsy moth eggs hatch between late April and mid-May. The larvae feed on the leaves of a variety of trees, most notably oak trees, for approximately seven weeks from late May to early or mid-July. Then they enter the one to two week pupa phase during which they appear dormant though inside their cocoon great changes are taking place. Adult moths emerge in mid- to late July and into August. Adult gypsy moths don't feed. They live only for a couple of weeks and for the sole purpose of reproducing. Males may mate multiple times, but females produce just one silky egg sack filled with between 600 and 1,000 eggs. They deposit these on sides of buildings, in eaves, and under flaps of bark. This is the time to destroy them, if possible.

To watch a video demonstrating the removal of egg sacks, click here.

Photo by Tina Warren



Rid your trees of gypsy moths with these natural, simple remedies

spray bottle - lighted while spraying on


There are several recipes combining soap, oil and water that EC members have been using to good effect. But here's one that incorporates essential oils that scientists have been testing specifically for use against gypsy moths:

2 cups of water

1 cup castile soap (Dr. Bronner's makes a good one)

15 drops EACH of nutmeg, thyme and rosemary essential oils

These oils are toxic to the GMs and will kill them shortly after contact.


Using burlap or any kind of fabric (our EC vice chair John has been using old sheets on his trees effectively) wrap your tree, using a piece of twine at the middle of the wrap. Then fold the top half of the wrap down over the twine to create a cool, dark place for the GMs to gather. Once the GMs have collected, remove the band and drop it into a bucket of soapy water. This will kill the GMs. Rinse. Repeat. Click here to watch a demonstration of tree wrapping.

This method is effective during the caterpillar/larva stage and also the adult moth stage. The female moths don't fly so you can trap and dispose of them in soapy water before they lay their eggs.

Firefighters spray water during isolate.


Here's a solution with a dual benefit: using a high-powered hose, such as a pressure washer or a fire hose, to spray the GMs out of the trees and then do away with them once they hit the ground. Yes, we're talking squishing them. Not only will you be destroying the GMs you'll be giving your trees a much-needed drink at the same time.


©2020 by Environment Council for Clear, Ston(e)y and White Lakes.