Evolution of host-use among the Scolytini (Coleoptera: Curculionidae: Scolytinae)

The bark and ambrosia beetle tribe Scolytini (Curculionidae: Scolytinae) contains four genera and approximately 225 species distributed in the Neotropical and Holarctic regions. The Scolytini are primarily composed of two distinct ecological feeding groups: true bark beetles and ambrosia beetles. True bark beetles(Cnemonyx, Scolytus, Scolytopsis) feed on phloem and cambium of moribund or living trees. Ambrosia beetles (Camptocerus) tunnel into the xylem of a dead host tree and cultivate a symbiotic fungus. All genera feed on angiosperms except Scolytus, which includes species that feed exclusively on conifers in the Holarctic. Feeding on plants is an important factor in the diversification of beetle species. Plant structural and chemical barriers deter beetle feeding. Once these barriers are overcome through natural selection, subsequent generations tend to feed on a specific plant species. Detailed knowledge of host-plant preferences and species-level phylogenies will provide the foundation for testing of hypotheses related to evolution of host-use and host preference. In this study, we examine Scolytini and host tree coevolution in a phylogenetic context. We include 61 taxa in Bayesian analysis using 2340 nucleotides from mitochondrial (COI) and nuclear genomes (28S, ArgK, CAD). Several trends in host-use evolution are apparent including: a single derivation of fungus-feeding among Camptocerus from a lineage of angiosperm-feeders; angiosperm host-use among South American Scolytus spp. is conserved but it is plastic among Holarctic Scolytus spp.; a single derivation of conifer-feeding among Scolytus spp. from angiosperm feeding and conservation of host-genera among the Nearctic conifer-feeders.