Canadian Forest Service Publications

Derivation of Pheromone-Based Larval Thresholds in Spruce Budworm Accounting for Distance to Defoliated Forest Stands. 2021. Rhainds, M.; DeMerchant, I.; Therrien, P. Journal of Economic Entomology 114 (2): 769-775

Year: 2021

Issued by: Atlantic Forestry Centre

Catalog ID: 40594

Language: English

Availability: PDF (request by e-mail)

Available from the Journal's Web site.
DOI: 10.1093/jee/toaa275

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Mark record


Spruce budworm, Choristoneura fumiferana Clem. (Lepidoptera: Tortricidae), is the most severe defoliator of Pinaceae in Nearctic boreal forests. Three tools widely used to guide large-scale management decisions (year-to-year defoliation maps; density of overwintering second instars [L2]; number of males at pheromone traps) were integrated to derive pheromone-based thresholds corresponding to specific intergenerational transitions in larval densities (L2i → L2i+1), taking into account the novel finding that threshold estimates decline with distance to defoliated forest stands (DIST). Estimates of thresholds were highly variable between years, both numerically and in terms of interactive effects of L2i and DIST, which limit their heuristic value. In the context of early intervention strategy (L2i+1 > 6.5 individuals per branch), however, thresholds fluctuated within relatively narrow intervals across wide ranges of L2i and DIST, and values of 40–200 males per trap may thus be used as general guideline.

Plain Language Summary

Pheromone-based thresholds aimed at predicting larval density in year i (L2i) were derived on a per year basis for spruce budworm in the province of QC between 2012 and 2017, taking into account past L2 density (L2i+1) and distance to defoliation (Di-1). Pheromone thresholds (number of males per trap) were highly variable between years, which limit their value as a monitoring tool; the noise between years is such that pheromone trapping has been discontinued in QC in 2020. That said, pheromone threshold corresponding to EIS threshold (6.5 L2 / branch) varied within a relatively narrow range of 40 to 200 males across a broad range of distance to defoliation and larval density in parental generations.

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