Intercontinental Diversity of Caballeronia Gut Symbionts in the Conifer Pest Bug Leptoglossus occidentalis

Many stinkbugs in the superfamily Coreoidea (Hemiptera: Heteroptera) develop crypts in the posterior midgut, harboring Caballeronia (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. SBE symbionts are separated into the subclades SBE-alpha and SBE-beta. Previous studies suggested a regional effect on the symbiont infection pattern; Japanese and American bug species are more likely to be associated with SBE-alpha, while European bug species are almost exclusively associated with SBE-beta. However, since only a few insect species have been investigated, it remains unclear whether region-specific infection is general. We herein investigated Caballeronia gut symbionts in diverse Japanese, European, and North American populations of a cosmopolitan species, the Western conifer seed bug Leptoglossus occidentalis (Coreoidea: Coreidae). A molecular phylogenetic analysis of the 16S rRNA gene demonstrated that SBE-beta was the most dominant in all populations. Notably, SBE-alpha 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, SBE-alpha- and SBE-beta-inoculated insects both showed high survival rates; however, a competition assay demonstrated that SBE-beta outcompeted SBE-alpha in the midgut crypts of L. occidentalis. These results strongly suggest that symbiont specificity in the Leptoglossus-Caballeronia symbiotic association is influenced by the host rather than geography, while the geographic distribution of symbionts may be more important in other bugs.

Automated summary

This study investigated the gut symbionts of the Western conifer seed bug and found that the specificity of the symbionts is influenced by the host rather than geography.