Concordance in evolutionary history of threatened plant and insect populations warrant unified conservation management approaches

© 2016 Elsevier Ltd. Threatened organisms may act as host to a suite of dependent organisms, which are potentially cothreatened, yet management is rarely coordinated between host and dependent species. Here, we test the congruency of patterns of genetic structure between two critically endangered interacting taxa; the feather-leaf banksia (Banksia brownii R.Br.), and its host-specific herbivorous plant-louse Trioza barrettae Taylor & Moir, to establish whether conservation actions should be implemented jointly for both species. We also examine the role of host population size and fire history on the density of psyllids on host plants. We show that the patterns of mtDNA variation in T. barrettae and microsatellite variation in both species support the presence of at least two conservation units across each species, with the microsatellites also showing a high evolutionary congruency between plant and insect populations. The extinction of divergent B. brownii populations, therefore, is likely to have resulted in the extinction of divergent plant-louse populations. Larger populations of host plant (>. 150) and more recent fire history (