Unification of symbiotic bacteria during larva-to-adult transition in Culicoides circumscriptus (Diptera:...

Blood-sucking midges such as Leptoconops and Culicoides are of medical importance due to their role in causing skin irritation and potentially transmitting pathogens. Investigating their bacterial communities, including possible endosymbionts, may help clarify ecological adaptations and interactions with hosts. Leptoconops nipponensis Tokunaga (Lnt) and Culicoides circumscriptus (Cc), blood-sucking midges, cause severe itching and inflammation in humans. Cc was collected from a small sample of an outbreak swarm of Lnt in the peninsula area of Yonago City, Tottori Prefecture, Japan. This study compared the bacterial flora of Lnt and Cc, revealing distinct bacterial diversity shifts in these insect species between life stages. We analyzed the bacterial communities of adult and larval females of Cc and Lnt using MiSeq sequencing of the V3-V4 hypervariable region of the 16S rRNA gene. Notably, alpha diversity in Cc adults was significantly reduced to 1.5 (n = 43), indicating that Cc adults were dominated by a single bacterial genus, compared to 14.9 in Cc larvae (n = 19). BLAST (Basic Local Alignment Search Tool) analysis identified this dominant genus in adult Cc as Rickettsia (Candidatus Tisiphisa), which is known for transovarial transmission in arthropod vectors. In contrast, the bacterial diversity of Lnt showed no significant difference between adults (18.1, n = 32) and larvae (n = 15). These findings suggest that the dominance of Rickettsia in Cc (Candidatus Tisiphisa) adults is linked to their emergence, potentially reflecting differences in reproductive biology and ecological adaptations between these two insect species. Further research is needed to elucidate the functional role of Rickettsia in the life cycle and physiology of Cc.