Thousands of Spongy moth caterpillars (Lymantria dispar dispar)

Observation by Jessica Koudys:

Nearly every spring in Fenwick, Ontario, from 2001 to 2011, I found enormous amounts (estimating in the hundreds of thousands) of Lymantria dispar dispar (European Gypsy moths or Spongy moths) covering the trunks of the trees and eating their foliage. The effects of these caterpillars eating the leaves for the first few years was noticeably destructive to the hardwood trees and the tree canopy. Most of the leaves were completely defoliated and several trees began dying after a few years of this. I followed this species through its entire life cycle from small larvae on webs, the formation of large beige nests all over the tree bark, to eventually turning into moths in the summer months.

To protect our forests and the local fruit farms, the neighborhood agreed to share the cost of a conservationist to perform an aerial spray of the area using a bacterial compound. We found this method to be extremely effective at decreasing this species and repeated it for eight years. Although the abundance of spongy moths was lessened by the aerial sprays, they continued to persist. According to Ontario's Ministry of Natural Resources and Forestry (2023), spongy moths are considered an invasive species and remain abundant in southern Ontario, causing severe defoliation to forests in Aylmer and Guelph.

Reference: Ministry of Natural Resources and Forestry. (2023). Spongy moth. Ontario. https://www.ontario.ca/page/spongy-moth

Comment from LEO.ai:

The repeated defoliation caused by Lymantria dispar dispar, commonly known as the Spongy moth, can lead to significant stress on hardwood trees, potentially resulting in tree mortality and reduced forest health. The use of bacterial compounds, such as Bacillus thuringiensis var. kurstaki (Btk), for aerial spraying is a common biological control method that targets the larval stage of the moth without harming most other insects, birds, or mammals. This method has been widely used due to its specificity and relatively low environmental impact compared to chemical pesticides. However, the persistence of the Spongy moth despite repeated treatments highlights the challenges in managing invasive species and the importance of integrated pest management strategies that may include a combination of biological control, habitat management, and public education. Continued monitoring and adaptive management are crucial to mitigate the impact of this invasive species on forest ecosystems and local agriculture.

Reference: Minnesota Department of Natural Resources. (n.d.). Gypsy moth in Minnesota. Retrieved from https://www.dnr.state.mn.us/invasives/terrestrialanimals/gypsymoth/index.html