Bacterial communities and their predicted function change with the life stages of invasive C-strain Spodoptera frugiperda (J. E. Smith, 1797) (Lepidoptera: Noctuidae)

Spodoptera frugiperda is known as a highly polyphagous and invasive insect pest of maize and many other important agricultural crops. Spodoptera frugiperda is categorized into two host-adapted strains, namely 'R' (rice) and 'C' (corn). Bacterial communities that inhabit the insect body play various physiological as well as biological roles. To design effective and environmentally safe management strategies, an understanding of the diversity and functions of microbiota harbored across the development stages is essential, specifically strain-specific. The assessment of the diversity of development-associated bacteria and their predicted functions was conducted in C-strain of S. frugiperda using 16S rRNA amplicon sequencing obtained by the Illumina MiSeq technology. The results showed that the unique number of operational taxonomic units (OTUs) was higher in the pupal stage (145 OTUs) and lowest in the third instar larval stage (76 OTUs). Species richness progressively increased with metamorphosis and was significantly higher in adult females. Firmicutes and Proteobacteria were dominant phyla across all developmental stages. Firmicutes were dominant in egg (53.47%) and larval stages (52.38%), and Proteobacteria were dominant in pupa (41.26%) and adult male and female stages (54.69% and 46.49%, respectively). Enterococcus (46.74% and 12.54% in larva and pupa, respectively) was the most dominant genera at the genus level. Clostridium, Enterobacteriaceae, and Erwinia were the dominant genera in the egg and adult stages. The principle coordinate analysis (PCoA) and linear discriminant effect size (LEfSe) results showed significant differences in developmental stages. PICRUSt analysis showed that microbial communities involved in membrane transport were significantly high in third-instar larvae than in the other stages of development. Amino acid metabolism-associated microbial communities were predicted to be highest in eggs and lowest in third-instar larvae. Similarly, microbiota involved in energy metabolism was predicted to be highest in eggs and least in third-instar larvae. Additionally, the replication and repair processes associated with microbial communities were predicted highest in eggs and least in pupae. The current study provides documentation and information on symbiotic bacteria and how they work with strain-specific S. frugiperda. This will also lead to the creation of novel biological management strategies.