Canadian Forest Service Publications
Bottom-up factors contribute to large-scale synchrony in spruce budworm populations. 2018. Bouchard, M.; Régnière, J.; Therrien, P. Can. J. For. Res. 48 : 277-284.
Issued by: Laurentian Forestry Centre
Catalog ID: 38364
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Understanding the mechanisms that cause large-scale synchrony in insect population dynamics might yield key insights for predicting potential outbreak occurrence. Here, we evaluated which environmental factors best explain synchronous population fluctuations in the spruce budworm (Choristoneura fumiferana Clem.) (SBW), a major defoliator of coniferous forests in North America. SBW population levels were assessed with pheromone traps during the 1986–2014 period across a 625 000 km2 territory located in the province of Québec (Canada). The populations were characterized by abundance fluctuations that were often synchronized across the whole study area. Interannual population fluctuations were correlated with host tree cone production (a source of food) and high May temperatures, suggesting that synchrony was influenced by food availability and phenological mismatch during shoot development. Cone production was itself correlated with low precipitation during the previous summer. This study indicates that bottom-up trophic factors can drive spatiotemporal synchrony in insect populations and contribute to explain important and sustained population increases during some years. We also suggest that several biological processes, all influenced by weather, are likely to interact to explain population synchrony during the different phases of the approximately 35 year SBW outbreak cycle, complicating the prediction of climate change effects on this insect.
Plain Language Summary
This study indicates that for the spruce budworm (SBW), synchronized increases (annual changes) in population are largely correlated with annual variations in the production of male cones, which constitute a favourite food source of young larvae in the spring.
The main goal of this study was to assess the effects of environmental variations on the spatial synchronization of annual fluctuations in SBW populations.
These results support the theory that the large-scale synchronization of this insect’s endemic populations, under the direct (survival) and indirect (food source) influence of climate, has a role to play in the triggering of SBW outbreaks.