Evidence From the Fossil Record About the Evolution of Insect Adaptations to Wood Boring

ABSTRACT Several groups of insects, including termites and species of roaches, beetles, wasps, moths, and flies, bore into and feed on woody remains (xylophagy), either as larvae or throughout their life cycle. Wood is a plant mechanical defense against herbivores, and so, wood‐boring insects utilize numerous adaptations to mechanically and chemically process wood material and often associate with mutualistic fungi to break down plant tissue. Here, we review the literature on the evolutionary history of wood‐boring insects, including the trace fossil record of borings in fossil wood, the fossil record of insects with physical adaptations to wood‐boring, and phylogenetic estimates of when wood‐boring lineages originated, to develop a picture of when different insect groups developed adaptations to overcome wood. The oldest lineages of borers include the Blattodea (roaches), which may have carried out wood boring as early as the Carboniferous, and evolved obligate xylophagous lineages (termites and wood‐roaches), with tough mandibles to chew wood and physiological adaptations to digest wood, during the Jurassic, leaving boring traces in plant fossils from the Cretaceous and Cenozoic. The dominant wood‐borers across the entire fossil record, however, are the Coleoptera (beetles), which diversified quickly following their Permian origin and provide the most extensive trace fossil record of insect borers from the Permian through the Cenozoic. Initially, coleopteran borings are primarily associated with dead wood, suggesting early beetles only had physical adaptations to break down wood. Living wood‐associated beetle borings are known from the late Permian, suggesting physiological adaptations to digest wood followed shortly thereafter. Other insects within, for example, the Diptera, Hymenoptera, and Lepidoptera are known today to have wood‐boring lifestyles as larvae, but their fossil record is limited.