Natural disturbances have a major impact on boreal forest landscape dynamics, and although fire history is well documented at the Holocene scale, spruce budworm (Choristoneura fumiferana (Clemens)) (SBW) dynamics have only been known for the last three centuries. This is likely due to the difficulty in using and interpreting existing indicators (cephalic head capsules and feces). In this methodological study, we present an original approach using lepidopteran wing scales to reconstruct insect abundance. We analyzed two sediment cores from the boreal forest in central Quebec and extracted wing scales at every stratigraphic level. The required quantity of sediment for paleoecological analysis is relatively small given the large quantity of wing scales produced by Lepidoptera and their small size. Scales are well preserved due to their chitinous structure and their great variety of shapes offer a high potential for taxonomic identification. A statistical model based on the shape of scales of the three major epidemic lepidopterans in Quebec discriminated 68% of SBW scales. This indicator allows a more efficient and more precise reconstruction of SBW history with respect to the use of cephalic head capsules or feces.

At a multi-millennial scale, various disturbances shape boreal forest stand mosaics and the distribution of species. Despite the importance of such disturbances, there is a lack of studies focused on the long-term dynamics of spruce budworm (Choristoneura fumiferana (Clem.)) (SBW) outbreaks and the interaction of insect outbreaks and fire. Here, we combine macrocharcoal and plant macrofossils with a new proxy—lepidopteran scales—to describe the Holocene ecology around a boreal lake. Lepidopteran scales turned out to be a more robust proxy of insect outbreaks than the traditional proxies such as cephalic head capsules and feces. We identified 87 significant peaks in scale abundance over the last 10 000 years. These results indicate that SBW outbreaks were more frequent over the Holocene than suggested by previous studies. Charcoal accumulation rates match the established fire history in eastern Canada: a more fire-prone early and late Holocene and reduced fire frequency during the mid-Holocene. Although on occasion, both fire and insect outbreaks were coeval, our results show a generally inverse relationship between fire frequency and insect outbreaks over the Holocene.