Dynamics of symbiotic bacterial community in whole life stage of Harmonia axyridis (Coleoptera: Coccinellidae)

Abstract

Introduction: Bacteria play critical roles in the reproduction, metabolism, physiology, and detoxification of their insect hosts. The ladybird beetle (Harmonia axyridis) harbors a myriad of endosymbiotic microbes. However, to date, little is known about how the microbial composition of H. axyridis varies throughout its life cycle.

Methods: In this study, 16S rRNA amplicon sequencing and quantitative PCR were employed to investigate the diversity and dynamics of bacterial symbionts across the egg, larval, pupae, and adults stages of H. axyridis.

Results: Higher bacterial community richness and diversity were observed in eggs, followed by those in adults and pupae. The community richness index differed significantly between second-instar larvae and other developmental stages. Proteobacteria, Firmicutes, and Actinobacteria were the dominant phyla. Staphylococcus, Enterobacter, Glutamicibacter, and Acinetobacter were the dominant bacteria genera; however, their relative abundances fluctuated across host developmental stages. Interestingly, the larval stage harbored high proportions of Firmicutes, whereas the adult microbial community largely consisted of Proteobacteria.

Discussion: This study is the first to determine the symbiotic bacterial composition across key life stages of H. axyridis. These outcomes can foster the development of environmental risk assessments and novel biological control strategies.

Keywords: Harmonia axyridis; high-throughput sequencing; life stages; quantitative PCR; symbiotic bacteria.

Figure 1

Overview of development stages of the Harmonia axyridis.

Figure 2

Non-metric Multidimensional Scaling (NMDS) ordination based on (A), weighted and (B), unweighted UniFrac distances of bacterial communities of Harmonia axyridis.

Figure 3

Bacterial community composition at the level of (A), phyla (>0.01), (B), family (>0.01) and (C), genus (>0.01). *denotes unclassified operational taxonomic units (OTU) reported at higher taxonomic levels. Refer to Figure 1 for sample abbreviations.

Figure 4

Linear discriminant analysis effect size (LEfSe) analysis of microbial abundance across all life stages of Harmonia axyridis. Linear discriminant analysis (LDA) score identified the size of differentiation across all life stages of H. axyridis with a threshold value of 4.0.

Figure 5

Inferred functions of bacterial communities associated with Harmonia axyridis. All of the predicted Kyoto Encyclopedia of Genes and Genomes (KEGG) metabolic pathways are shown at the second hierarchical level and grouped by major functional categories.