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Pine sawflies (Hymenoptera: Diprionidae) are eruptive herbivores found throughout eastern North America. The Diprionidae family, which contains at least 140 species, constitutes the most persistent threat to conifers as population outbreaks can cause widespread defoliation. Because some species are more prone to large, destructive outbreaks than others, species identification is critical to effective management. Although existing taxonomic keys are primarily based on internal adult morphology, substantial variation among species in larval color traits, geographic location, overwintering strategy, host plant, and egg patterns can be diagnostic at the species level. Here, we focus on the Pinaceae-feeding subfamily Diprioninae, of which there are 25 species in eastern North America. We describe the general biology, life cycle, and host-use ecology of Diprioninae, with an emphasis on the variation among these traits within this subfamily. In addition, we provide tools for species identification, including a taxonomic key that utilizes external diagnostic characteristics. Finally, we discuss available management strategies.

 

Abstract Biological introductions are unintended “natural experiments” that provide unique insights into evolutionary processes. Invasive phytophagous insects are of particular interest to evolutionary biologists studying adaptation, as introductions often require rapid adaptation to novel host plants. However, adaptive potential of invasive populations may be limited by reduced genetic diversity—a problem known as the “genetic paradox of invasions”. One potential solution to this paradox is if there are multiple invasive waves that bolster genetic variation in invasive populations. Evaluating this hypothesis requires characterizing genetic variation and population structure in the invaded range. To this end, we assemble a reference genome and describe patterns of genetic variation in the introduced white pine sawfly, Diprion similis. This species was introduced to North America in 1914, where it has rapidly colonized the thin-needled eastern white pine (Pinus strobus), making it an ideal invasion system for studying adaptation to novel environments. To evaluate evidence of multiple introductions, we generated whole-genome resequencing data for 64 D. similis females sampled across the North American range. Both model-based and model-free clustering analyses supported a single population for North American D. similis. Within this population, we found evidence of isolation-by-distance and a pattern of declining heterozygosity with distance from the hypothesized introduction site. Together, these results support a single-introduction event. We consider implications of these findings for the genetic paradox of invasion and discuss priorities for future research in D. similis, a promising model system for invasion biology.