Fossil lepidopteran scales found in lake sediments are a new proxy for reconstructing population outbreaks of important forest moth pests such as spruce budworm (Choristoneura fumiferana Clemens), hemlock looper (Lambdina fiscellaria Guenée), and forest tent caterpillar (Malacosoma disstria Hübner). We introduce a new method to distinguish these pests and two others, eastern blackheaded budworm (Acleris variana Fernie) and jack pine budworm (Choristoneura pinus Freeman), by traits on their wingscale ultrastructure as seen using scanning electron microscopy. We made qualitative and quantitative comparisons of morphological traits at the ultrastructural level and found that hemlock looper and eastern blackheaded budworm scales could be categorically separated from each other and from the three other species. The remaining three species were not as easily distinguished, especially when trying to identify unknown fossil scales. Using this new proxy, we produced a high-resolution record of fossil lepidopteran scales using a 173-cm sediment core collected from Killarney Lake, in central New Brunswick, Canada. Our results show that fossil scales were abundant and well preserved over a 1620-year period. A total of 29 scale peaks were detected for an average periodicity of 55.8 years.
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