The composition of the gut bacteria in Spodoptera frugiperda (Lepidoptera: Noctuidae) larvae as influenced by ingestion of dicot plant diets

The gut bacteria of insects influence the physiology of their host positively, although the mechanism is not yet understood. This study characterized the gut bacterial biota of fall armyworm (FAW), Spodoptera frugiperda larvae fed on two groups of dicot plant diets; fruit/root dicot diets (R) and leafy dicots diets (L) by sequencing V3-V4 hypervariable region of the16S rRNA gene. The results revealed that the gut bacterial composition varied among larvae samples fed on different plant diet groups. Kruskal- Wallis test revealed significant differences (p < 0.05) on the number of OTUs among larvae samples fed with the different plant diets. Alpha diversity indices (observed species richness, ACE and Chao1) of gut bacterial diversity of FAW were highly significant (p < 0.001) among the various larvae samples. Analysis of molecular variance (AMOVA) and Analysis of similarity (ANOSIM) also revealed that the bacterial communities were significantly different (p < 0.05) among individual members of FAW larvae fed with various plant diets. Three bacteria phyla; Firmicutes, Proteobacteria and Cyanobacteria were prevalent across the larvae samples and Firmicutes (47.0%) was the most dominant. Redundancy Analysis (RDA) revealed that chemical components of various plant diets significantly (p < 0.001) influenced the gut bacteria community distribution of FAW larva fed with the two diet groups (R and L). Functional Annotation of Prokaryotic Taxa (FAPROTAX) analysis predicted 66 putative functions and chemoheterotrophy was the most dominant putative function. Network analysis also showed that the topological properties varied among different diet groups. Our study has shown that diets are among the major drivers shaping FAW gut microbiota.