Past and present outbreaks of the balsam fir sawfly in western Newfoundland: An analytical review

Historical data of defoliation and population density were examined to determine whether a sustained outbreak of balsam fir sawfly (Neodiprion abietis Harris) in western Newfoundland, Canada is unprecedented in severity and duration. Results indicate that the current outbreak departs substantially from historical trends, covering a surface area twice the sum of all infestations occurring in the preceding 50 years. The current outbreak is also of longer duration due to a northward expansion of the range usually subjected to severe defoliation by this insect. Time-series analysis indicates that balsam fir sawfly dynamics have a strong second-order component, providing testable hypotheses for future studies investigating the factors responsible for population fluctuations.