Intercontinental diversity of <i>Caballeronia</i> gut symbionts in the conifer pest bug <i>Leptoglossus occidentalis</i>

International audienceMany stinkbugs in the superfamily Coreoidea (Hemiptera: Heteroptera) develop crypts in the posterior midgut, harboringCaballeronia (Burkholderia) symbionts. These symbionts form a monophyletic group in Burkholderia sensu lato, called the“stinkbug-associated beneficial and environmental (SBE)” group, recently reclassified as the new genus Caballeronia. SBEsymbionts are separated into the subclades SBE-α and SBE-β. Previous studies suggested a regional effect on the symbiontinfection pattern; Japanese and American bug species are more likely to be associated with SBE-α, while European bugspecies are almost exclusively associated with SBE-β. However, since only a few insect species have been investigated, itremains unclear whether region-specific infection is general. We herein investigated Caballeronia gut symbionts in diverseJapanese, European, and North American populations of a cosmopolitan species, the Western conifer seed bug Leptoglossusoccidentalis (Coreoidea: Coreidae). A molecular phylogenetic analysis of the 16S rRNA gene demonstrated that SBE-βwas the most dominant in all populations. Notably, SBE-α was rarely detected in any region, while a third clade, the“Coreoidea clade” occupied one fourth of the tested populations. Although aposymbiotic bugs showed high mortality, SBEα- and SBE-β-inoculated insects both showed high survival rates; however, a competition assay demonstrated that SBE-βoutcompeted SBE-α in the midgut crypts of L. occidentalis. These results strongly suggest that symbiont specificity inthe Leptoglossus-Caballeronia symbiotic association is influenced by the host rather than geography, while the geographicdistribution of symbionts may be more important in other bugs