Comparative study of the gut microbial community structure of Spodoptera frugiperda and Spodoptera literal (Lepidoptera)

Abstract

Background: Spodoptera frugiperda, the fall armyworm is a destructive invasive pest, and S. litura the tobacco cutworm, is a native species closely related to S. frugiperda. The gut microbiota plays a vital role in insect growth, development, metabolism and immune system. Research on the competition between invasive species and closely related native species has focused on differences in the adaptability of insects to the environment. Little is known about gut symbiotic microbe composition and its role in influencing competitive differences between these two insects.

Methods: We used a culture-independent approach targeting the 16S rRNA gene of gut bacteria of 5th instar larvae of S. frugiperda and S. litura. Larvae were reared continuously on maize leaves for five generations. We analyzed the composition, abundance, diversity, and metabolic function of gut microbiomes of S. frugiperda and S. litura larvae.

Results: Firmicutes, Proteobacteria, and Bacteroidetes were the dominant bacterial phyla in both species. Enterococcus, ZOR0006, Escherichia, Bacteroides, and Lactobacillus were the genera with the highest abundance in S. frugiperda. Enterococcus, Erysipelatoclostridium, ZOR0006, Enterobacter, and Bacteroides had the highest abundance in S. litura. According to α-diversity analysis, the gut bacterial diversity of S. frugiperda was significantly higher than that of S. litura. KEGG analysis showed 15 significant differences in metabolic pathways between S. frugiperda and S. litura gut bacteria, including transcription, cell growth and death, excretory system and circulatory system pathways.

Conclusion: In the same habitat, the larvae of S. frugiperda and S. litura showed significant differences in gut bacterial diversity and community composition. Regarding the composition and function of gut bacteria, the invasive species S. frugiperda may have a competitive advantage over S. litura. This study provides a foundation for developing control strategies for S. frugiperda and S. litura.

Keywords: 16S rRNA; Competition; Gut bacterial community; S. frugiperda; S. litura.

Figure 1. Comparison of gut microbial diversity and differences between S. frugiperda and S. litura.

(A) Columnar scatter plot of the number of OTUs. (B) Exponential dilution curve. (C–F) Bacterial Alpha diversity index of different samples. (G, H) Unifrac principal coordinate analysis (PCoA) and nonmetric multidimensional scaling (NMDS) of different samples.

Figure 2. Gut bacterial composition of S. frugiperda and S. litura.

(A, B) Relative abundance at phylum level in S. frugiperda (A) and S. litura (B). (C, D) Relative abundance at genus level in S. frugiperda (C) and S. litura (D).

Figure 3. Gut microbiome biomarkers of S. frugiperda (left) and S. litura (right).

(A) All the bar charts show those taxa that were significantly differentially abundant between comparison groups. All the taxa are ranked by effect size, and only taxa meeting an LDA significance threshold of >2.0 are shown. (B) The taxonomic cladograms obtained from LEfSe analysis of 16S rDNA sequences are shown. Small circles highlighted in different colors (red and green) in the diagram represent the taxa that were significantly elevated in the respective group. Yellow circles indicate taxa that were not significantly differentially represented (P > 0.05).

Figure 4. Functional predictions and differences in the gut flora of S. frugiperda and S. litura.

(A) Clusters of Orthologous Group (COG) function classification. (B) Kyoto Encyclopedia of Genes and Genomes (KEGG) function classification. (C) Principal component analysis (PCA) of KEGG.