Observation by Jen Cerullo:
In late September 2020, after a sunset hike up to Mt. Seymour’s Pump Peak, an extremely large population of moths was observed on the drive back down the mountain at dusk. The moths were everywhere, and as they were attracted to the car’s headlights, it seemed as if there was a “snowstorm” of fluttering white insects. This observation was selected for its relevance and impact to the local mountains and trails frequently visited.
Upon further research into the incident on local and provincial websites and through a search for local news stories, the observation seems to have been of an outbreak of Western Hemlock Looper Moths, a native species to the British Columbia that generally appears in ten to twelve-year cycles. According to the municipality of West Vancouver, the current outbreak began in 2019 and generally last three to four years. A CBC article from December 2022 further cites the outbreak and the removal of damaged trees as a result of the damage the herbivorous insects inflict on tree foliage. On a recent drive in early September 2023, an alarming number of dead trees along the Stanley Park Drive in Vancouver’s 1,000 acre Stanley Park was further proof of the recent outbreak. The City of Vancouver cites “recent droughts and hard winters” as making the trees more vulnerable to the moth outbreak, a point reiterated by Vancouver Park Board (2022) in a video addressing public concerns over the browning trees in Stanley Park. The City of Vancouver further notes that consultations with forestry experts are ongoing to determine a mitigation approach to enhance the long-term health of the forest.
The observed moth outbreak in Vancouver is a local phenomenon with similar examples that can be found globally. Similar outbreaks of varying moth and other phytophagous insect species have been observed with increasing regularity. Most notably in Canada, Spongy Moth (Lymantria dispar dispar) or “gypsy moth” outbreaks have been documented over the past thirty or more years in Ontario and Quebec, according to Chung et al. (2021). The article further cites stress from drought conditions as making it harder for trees to cope with infestations of the moth. Cited by Kroschel et al (2012) and Netherer and Schopf (2010), insects cannot regulate their own body temperatures and are therefore subject to the direct effects of warming temperature, and climate-change is therefore a factor to consider in herbaceous insect population changes. Studies by Jepsen et al (2008) and Vanhanen (2007) indicated changes in outbreak patterns and species range of varying moth species during warmer years.
Based on studies of moth populations in other Canadian regions and globally, indications are that the warmer and drier summer conditions are likely to similarly affect populations of Western Hemlock Looper moth outbreaks in the Vancouver region. Although localized effects of climate change vary by region, global trends such as those seen in changing special and temporal patterns of phytophagous insect outbreaks are seen similarly in varying global ecosystems.
This post is in association with a Masters of Environmental Program, Course EECO586 - The Biosphere and Sustainability, at Royal Roads University.
References:
CBC News. (December 19, 2022). Popular North Vancouver park losing trees due to loop moth infestation. Retrieved September 20, 2023 from https://www.cbc.ca/news/canada/british-columbia/looper-moth-infestation-1.6691377
Chung, E., Hopton, A., and Singh, I. (June 28, 2021). Why an invasive moth caterpillar infestation is breaking records in central Canada. CBC News. Retrieved September 20, 2023 from https://www.cbc.ca/news/science/invasive-moths-ldd-canada-infestation-1.6078864
City of Vancouver. (n.d.) Stanley Park Forest Management. Retrieved September 23, 2023 from https://vancouver.ca/parks-recreation-culture/stanley-park-forest-management.aspx.
District of West Vancouver. (n.d.). Hemlock Looper Moths. Retrieved September 20, 2023 from https://westvancouver.ca/environment/plants-insects/hemlock-looper-moths
Jepsen, J. U., Hagen, S. B., Ims, R. A., & Yoccoz, N. G. (2008). Climate change and outbreaks of the geometrids Operophtera brumata and Epirrita autumnata in subarctic birch forest: Evidence of a recent outbreak range expansion. Journal of Animal Ecology, 77(2), 257–264. https://doi.org/10.1111/j.1365-2656.2007.01339.x
Jiang, D., Tan, M., Wu, S., Zheng, L., Wang, Q., Wang, G., & Yan, S. (2021). Defense responses of arbuscular mycorrhizal fungus-colonized poplar seedlings against gypsy moth larvae: A multiomics study. Horticulture Research, 8(1), 245. https://doi.org/10.1038/s41438-021-00671-3
Kroschel, J., Sporleder, M., Tonnang, H. E. Z., Juarez, H., Carhuapoma, P., Gonzales, J. C., & Simon, R. (2013). Predicting climate-change-caused changes in global temperature on potato tuber moth Phthorimaea operculella (Zeller) distribution and abundance using phenology modeling and GIS mapping. Agricultural and Forest Meteorology, 170, 228–241. https://doi.org/10.1016/j.agrformet.2012.06.017
Netherer, S., & Schopf, A. (2010). Potential effects of climate change on insect herbivores in European forests—General aspects and the pine processionary moth as specific example. Forest Ecology and Management, 259(4), 831–838. https://doi.org/10.1016/j.foreco.2009.07.034
Vancouver Park Board. (October 20, 2022). Why Stanley Park’s trees are looking brown. [video]. Youtube. https://www.youtube.com/watch?v=-EowV0dL2dE
Vanhanen, H., Veteli, T., Päivinen, S., Kellomäki, S., & Niemelä, P. (2007). Climate change and range shifts in two insect defoliators: Gypsy moth and nun moth – a model study. Silva Fennica, 41(4). https://doi.org/10.14214/sf.469
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