New from the Canadian Journal of Forest Research:
by Mathieu Bouchard, Jacques Regniere, & Pierre Therrien
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 (SBW). SBW population levels were assessed with pheromone traps during the 1986-2014 period across a 625,000 km<sup>2</sup> 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 (mast years) 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 ca. 35 years SBW outbreak cycle, complicating the prediction of climate change effects on this insect.