Periodicity and synchronism of spruce budworm outbreaks in Quebec

A time series analysis was performed on 32 dendrochronological chronologies using Dutilleul's multi-frequential periodogram. Our aim was to estimate the periodicities of spruce budworm (Choristoneura fumiferana (Clem.)) outbreaks in the province of Quebec. Our analysis estimated a signal of 25-38 years corresponding to spruce budworm, outbreaks. Analyses conducted in the 20th century indicated the existence of true periodicities in half of the series suggesting local population dynamics. These periodicities were estimated to be 29-34 years. For the other series, outbreaks were explained by the addition of a second periodic component to the fundamental periodicity. These combined periodicities (pseudoperiodicities or complex periodicities) described most of the 130-year series analysed. The lack of several outbreaks explained part of the combined periodicity. The results suggest a migration effect and complex local population dynamics. A third periodic component explains the double epidemic waves. These estimated periodicities are often similar and in phase. We believe that a common regional effect (the Moran effect) acts on the minor fluctuations of the insect populations and helps synchronize the outbreaks. This research shows that different types of outbreak dynamics can be found within a same insect species.