Intracellular symbiosis is widespread in the insect world where it plays an important role in evolution and adaptation. The weevil family Dryophthoridae (Curculionoidea) is of particular interest in intracellular symbiosis evolution with regard to the great economical and ecological features of these invasive insects, and the potential for comparative studies across a wide range of host plants and environments. Here, we have analyzed the intracellular symbiotic bacteria of 19 Dryophthoridae species collected worldwide, representing a wide range of plant species and tissues. All except one ( Sitophilus linearis ) harbor symbiotic bacteria within specialized cells (the bacteriocytes) assembled as an organ, the bacteriome. Phylogenetic analysis of the 16S rDNA gene sequence of the Dryophthoridae endosymbionts revealed three endosymbiotic clades belonging to 3-Proteobacteria and characterized by different GC contents and evolutionary rate. The genus name Candidatus Nardonella was proposed for the ancestral clade infesting Dryophthoridae 100 MYA and represented by five of nine bacterial genera studied. For this clade showing low GC content (40.5 GC) and high evolutionary rate (0.128 substitutions/site per 100 Myr), a single infection and subsequent cospeciation of the host and the endosymbionts was observed. In the two other insect lineage endosymbionts, with relatively high GC content (53.4 and 53.8 GC), competition with ancestral pathogenic bacteria might have occurred, leading to endosymbiont replacement in present-day last insects.

Herbivorous insects and other small consumers are often specialized both in use of particular host taxa and in use of particular host tissues. Such consumers also often seem to show consistent differences in the rates of evolution of these two dimensions of host use, implying common processes, but this has been little studied. Here we quantify these rates of change in host use evolution in a major radiation of herbivorous insects, the Chrysomeloidea, whose diversity has been attributed to their use of flowering plants. We find a significant difference in the rates of evolutionary change in these two dimensions of host use, with host taxon associations most labile. There are apparently similar differences in rates of host use evolution in other parasite groups, suggesting the generality of this pattern. Divergences in parasite form associated with use of different host tissues may facilitate resource partitioning among successive adaptive radiations on particular host taxa.