Metabolism, digestion, and horizontal transfer: potential roles and interaction of symbiotic bacteria in the ladybird beetle Novius pumilus and their prey Icerya aegyptiaca .

In this study, we first time sequenced and analyzed the 16S rRNA gene data of predator ladybird beetles Novius pumilus and globally distributed invasive pest Icerya aegyptiaca at different stages, and combined data with bacterial genome sequences in N. pumilus to explored the taxonomic distribution, alpha and beta diversity, differentially abundant bacteria, co-occurrence network, and putative functions of their microbial community. Our finding revealed that Candidatus Walczuchella, which exhibited a higher abundance in I. aegyptiaca , possessed several genes in essential amino acid biosynthesis and seemed to perform roles in providing nutrients to the host, similar to other obligate symbionts in scale insects. Lactococcus , Serratia , and Pseudomonas , more abundant in N. pumilus , were predicted to have genes related to hydrocarbon, fatty acids, and chitin degradation, which may assist their hosts in digesting the wax shell covering the scale insects. Notably, our result showed that Lactococcus had relatively higher abundances in adults and eggs compared to other stages in N. pumilus , indicating potential vertical transmission. Additionally, we found that Arsenophonus , known to influence sex ratios in whitefly and wasp, may also function in I. aegyptiaca , probably by influencing nutrient metabolism as it similarly had many genes corresponding to vitamin B and essential amino acid biosynthesis. Also, we observed a potential horizontal transfer of Arsenophonus between the scale insect and its predator, with a relatively high abundance in the ladybirds compared to other bacteria from the scale insects.IMPORTANCEThe composition and dynamic changes of microbiome in different developmental stages of ladybird beetles Novius pumilus with its prey Icerya aegyptiaca were detected. We found that Candidatus Walczuchella, abundant in I. aegyptiaca, probably provide nutrients to their host based on their amino acid biosynthesis-related genes. Abundant symbionts in N. pumilus , including Lactococcus , Serratia , and Pseudophonus , may help the host digest the scale insects with their hydrocarbon, fatty acid, and chitin degrading-related genes. A key endosymbiont Arsenophonus may play potential roles in the nutrient metabolisms and sex determination in I. aegyptiaca , and is possibly transferred from the scale insect to the predator.
Competing Interests: The authors declare no conflict of interest.