Localization of symbiotic bacteria in embryogenesis of the lesser grain borer Rhyzopertha dominica and the African powderpost beetle Lyctus africanus (Coleoptera: Bostrichidae)

Embryogenesis of two pest beetles of the family Bostrichidae, the lesser grain borer Rhyzopertha dominica (Fabricius) and the African powderpost beetle Lyctus africanus Lesne, was investigated, in which the developmental process of the bacteriome formation was particularly focused on using whole-mount fluorescence in situ hybridization targeting 16S rRNA of the bacterial symbiont ‘Candidatus Shikimatogenerans bostrichidophilus’. In R. dominica, we described the following embryonic developmental stages: the superficial cleavage stage, with symbiont cells scattered in the surface region; the germband formation stage, with symbiont cells migrating into the yolk and gathering around the germband; the germband extension stage, with symbiont cells remaining around the germband; the germband retraction stage, with symbiont cells infecting the germband; and the bacteriome formation stage, with paired bacteriomes formed in parallel with dorsal closure. In L. africanus, similar stages of the embryonic development were identified. These results lay the foundation for future studies on the developmental and evolutionary biology of the microbial symbiosis in the Bostrichidae.