Bacteriomes, cryptic forms and evolution of a common wireworm pest species, <i>Hypnoidus bicolor</i>

Like other insects, coleopterans harbour dynamic bacteriomes that shape core aspects of their life history. The bacteriomes of several wireworm species (Coleoptera: Elateridae) have been described; however, little research has been undertaken to determine the factors that influence their structure and composition. These soil-dwelling larvae of click beetles are significant agricultural pests in the Canadian Prairies, with the most ubiquitous species, Hypnoidus bicolor, delineated into two genetically distinct clades and both sexual and parthenogenetic populations. In this study, we collected 69 H. bicolor adults and larvae from nine populations spanning three Prairie provinces and subjected them to Sanger and 16S rRNA gene sequencing to determine their clade and characterize their bacteriome, respectively. Combined with long-term surveillance, we provide compelling evidence that the parthenogenetic and sexual populations are associated with different clades. Development, sampling location and host genetics all contributed to the plasticity of H. bicolor bacteriomes. These differences are largely attributed to gut bacterial community composition of larvae, whereas, in adults, they appear driven by overall community structure as well as differences in the presence/absence of taxa and within-clade/population variance. Several notable genera emerged from our study, including Alphaproteobacteria and Rickettsiella endosymbionts that predominated in the parthenogenetic clade. Incorporation of this research into integrative pest management and reclassification of H. bicolor into a cryptic species complex is also discussed. Overall, this study advances our understanding of Elateridae bacteriomes, including factors that contribute to their richness and community composition.