ADendroctonusbark engraving (Coleoptera: Scolytidae) from a middle EoceneLarix(Coniferales: Pinaceae): early or delayed colonization?

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Abstract
An engraving made by a scolytid bark beetle, assigned to the genusDendroctonusof the tribe Tomicini, has been identified on a mummified, middle Eocene (45 Ma) specimen ofLarix altoborealiswood from the Canadian High Arctic.Larix altoborealisis the earliest known species ofLarix, a distinctive lineage of pinaceous conifers that is taxonomically identifiable by the middle Eocene and achieved a broad continental distribution in northern North America and Eurasia during the late Cenozoic.Dendroctonuscurrently consists of three highly host‐specific lineages that have pinaceous hosts: a basal monospecific clade on Pinoideae (Pinus) and two sister clades that consist of a speciose clade associated exclusively with Pinoideae and six species that breed overwhelmingly in Piceoideae (Picea) and Laricoideae (PseudotsugaandLarix). The middle Eocene engraving inL. altoborealisrepresents an early member ofDendroctonusthat is ancestral to other congeneric species that colonized a short‐bracted species ofLarix.This fossil occurrence, buttressed by recent data on the phylogeny of Pinaceae subfamilies andDendroctonusspecies, indicates that there was phylogenetically congruent colonization by these bark‐beetle lineages of a Pinoideae + (Piceoideae + Laricoideae) host‐plant sequence. Based on all available evidence, an hypothesis of a geochronologically early invasion during the Early Cretaceous is supported over an alternative view of late Cenozoic cladogenesis by bark beetles onto the Pinaceae. These data also suggest that host‐plant chemistry may be an effective species barrier to colonization by some bark‐beetle taxa over geologically long time scales.
Funding Information
  • National Museum of Natural History (031‐00)