Two sympatric lineages of Australian Cnestus solidus share Ambrosiella symbionts but not Wolbachia.

Sympatric lineages of inbreeding species provide an excellent opportunity to investigate species divergence patterns and processes. Many ambrosia beetle lineages (Curculionidae: Scolytinae) reproduce by predominant inbreeding through sib mating in nests excavated in woody plant parts wherein they cultivate symbiotic ambrosia fungi as their sole source of nutrition. The Xyleborini ambrosia beetle species Cnestus solidus and Cnestus pseudosolidus are sympatrically distributed across eastern Australia and have overlapping morphological variation. Using multilocus sequencing analysis of individuals collected from 19 sites spanning their sympatric distribution, we assessed their phylogenetic relationships, taxonomic status and microbial symbionts. We found no genetic differentiation between individuals morphologically identified as C. solidus and C. pseudosolidus confirming previous suggestions that C. pseudosolidus is synonymous to C. solidus. However, within C. solidus we unexpectedly discovered the sympatric coexistence of two morphologically indistinguishable but genetically distinct lineages with small nuclear yet large mitochondrial divergence. At all sites except one, individuals of both lineages carried the same primary fungal symbiont, a new Ambrosiella species, indicating that fungal symbiont differentiation may not be involved in lineage divergence. One strain of the maternally inherited bacterial endosymbiont Wolbachia was found at high prevalence in individuals of the more common lineage but not in the other, suggesting that it may influence host fitness. Our data suggest that the two Australian Cnestus lineages diverged allopatrically, and one lineage then acquired Wolbachia. Predominant inbreeding and Wolbachia infection may have reinforced reproductive barriers between these two lineages after their secondary contact contributing to their current sympatric distribution.

A review of the distribution and host plant associations of the platypodine ambrosia beetles (Coleoptera: Curculionidae: Platypodinae) of Australia, with an electronic species identification key.

Ambrosia beetles (Platypodinae and some Scolytinae) are ecologically and economically important weevils (Coleoptera: Curculionidae) that develop within the sapwood and heartwood of woody plants, and their larval and adult stages are dependent on fungal symbionts. Platypodinae mostly occur in tropical and subtropical biomes, with a few species occurring in temperate regions. Australia has 44 recorded platypodine species including 13 species which may only have been intercepted at or near ports of entries and are without established populations in Australia. The host tree associations and biogeography of Australian Platypodinae are largely undocumented, and no comprehensive identification key exists. Here, we review species records, host tree associations, biogeographic distributions, and morphological characteristics of Australian Platypodinae. For this, we examined collection specimens, monographs, catalogues, taxonomic inventories, journal articles and online databases, and developed an electronic LUCID identification key for 36 species recorded in Australia. This review and identification key will be a valuable resource for forestry managers and biosecurity officers and will support diagnostics and future research of these beetles, their biology, and ecological interactions.