Influence of Diet, Sex, and Viral Infections on the Gut Microbiota Composition of Spodoptera exigua Caterpillars

Abstract

The gut microbiota plays essential roles in processes related with metabolism, physiology, and immunity in all organisms, including insects. In the present work, we performed a broad analysis of the Spodoptera exigua gut microbiota, a major agricultural pest. We analyzed the influence of multiple parameters such as diet, geographic location, sex, or viral infections on S. exigua caterpillar gut microbiota composition. Our study revealed a high variability in bacterial composition among individuals, and a major influence of environmental bacteria (including those acquired through diet) on the gut microbiota composition, supporting previous studies that claim resident microbiota are lacking in caterpillars. Previous studies with laboratory-reared insects showed that changes in caterpillar gut bacterial composition affect the insecticidal properties of entomopathogenic viruses and bacteria. Our study revealed different microbiota composition in field insects carrying a natural viral infection with Spodoptera exigua nucleopolyhedrovirus (SeMNPV) and/or Spodoptera exigua iflavirus 1 (SeIV1). Few taxa can be specifically associated with the infection, suggesting microbiota influence the infective process of these natural pathogens, and providing new strategies for insect pest management.

Keywords: 16S rRNA; Spodoptera exigua; lepidoptera; microbiota; viral infection.

FIGURE 1

Bacterial phyla distribution in the gut of S. exigua. Pie charts represent the relative abundance in percentages of the main phyla found in the gut of S. exigua larvae collected on the field from pepper greenhouses and the laboratory colony fed with different diets (AD: artificial diet; A: Ailsa variety; MM: Money Maker variety).

FIGURE 2

Microbiota of S. exigua larvae according the diet. Canonical correspondence analysis (CCA) (A), estimation of the Shannon index diversity (B), the Chao1 index of richness (C) and the relative abundance of the 20 most abundant genera in S. exigua larvae from the laboratory colony fed with different diets (D) at a genus level.

FIGURE 3

Microbiota composition of S. exigua according the location. Relative abundance of the 20 most abundant genera in S. exigua larvae from field. The codes of numbers and letters refer to the different greenhouses in which larvae were collected.

FIGURE 4

Influence of sex on the microbiota of S. exigua. Sex determination of the S. exigua larvae from field by quantification of the kettin gene copy number (A). Canonical correspondence analysis (B), the estimation of the Shannon index diversity (C) and the Chao1 index for richness (D) at a genus level according the sex of the collected larvae.

FIGURE 5

Microbiota analysis of S. exigua larvae according their viral infection status. Canonical correspondence analysis (A), the estimation of the Shannon index diversity (B) and the Chao1 richness index (C) at a genus level in field S. exigua larvae naturally infected and non-infected with viruses. Calculation of the total bacterial load of S. exigua larvae from viral-infected and viral-free field samples (D) and their relationship with diversity (E) and richness (F). The best-fit lines, the Spearman r correlations and the p-values of the regression are shown for each analysis.