Tree-ring evidence for endemicity of the larch sawfly in North America

We present a 300-year tree-ring series (1682–1989) from eastern larch (Larixlaricina (Du Roi) K. Koch) that shows 10 distinct periods of major growth suppression attributable to larch sawfly (Pristiphoraerichsonii (Htg.)) infestations. The dendroecological record and histological data bring new evidence for endemicity of this forest insect in North America, leading to the conclusion that the larch sawfly was probably present as early as 1744 in the study site, i.e., more than a century before its presumed accidental introduction to North America from Europe around 1880. Rather than supporting the theory of a recent introduction, our results indicate that the disturbance regime associated with larch sawfly activity in northeastern North America shifted at the end of the 19th century.