Abstract
Plants can have fundamental roles in shaping bacterial communities associated with insect herbivores. For larval lepidopterans (caterpillars), diet has been shown to be a driving force shaping gut microbial communities, where the gut microbiome of insects feeding on different plant species and genotypes can vary in composition and diversity. In this study, we aimed to better understand the roles of plant genotypes, sources of microbiota, and the host gut environment in structuring bacterial communities. We used multiple maize genotypes and fall armyworm (Spodoptera frugiperda) larvae as models to parse these drivers. We performed a series of experiments using axenic larvae that received a mixed microbial community prepared from frass from larvae that consumed field-grown maize. The new larval recipients were then provided different maize genotypes that were gamma-irradiated to minimize bacteria coming from the plant during feeding. For field-collected maize, there were no differences in community structure, but we did observe differences in gut community membership. In the controlled experiment, the microbial inoculation source, plant genotype, and their interactions impacted the membership and structure of gut bacterial communities. Compared to axenic larvae, fall armyworm larvae that received frass inoculum experienced reduced growth. Our results document the role of microbial sources and plant genotypes in contributing to variation in gut bacterial communities in herbivorous larvae. While more research is needed to shed light on the mechanisms driving this variation, these results provide a method for incorporating greater gut bacterial community complexity into laboratory-reared larvae.
Highlights
Insect herbivores commonly harbor diverse microbial assemblages in their gut tissues[1,2,3]
Permutation MANOVA analyses supported these trends in that different plant genotypes did not influence the structure as a whole (F2,15 = 0.72; p = 0.60)
Alpha diversity estimates were not influenced by different plant genotypes in the fall armyworm guts of larvae fed field-collected leaves (Supplemental Table 1)
Summary
Insect herbivores commonly harbor diverse microbial assemblages in their gut tissues[1,2,3]. Plant diets can contribute substantially to gut microbial community taxonomic and functional composition[4,5,6] This is especially the case for lepidopteran herbivores, where variable patterns of bacterial gut colonization have been observed in response to different host plant species, genotypes, and o ntogeny[7,8,9,10,11,12,13,14,15]. The community membership and composition that resides in lepidopteran gut tissues can be affected by several factors related to the host insect ecology and gut biochemistry, the phytochemistry of ingested plant foliage, and the source of bacteria that seed the gut bacterial community These complex, multipartite interactions are generally not-well elucidated for larval lepidopterans, and whether there are overarching effects of any one of these processes on components of gut microbial communities is unclear. Some bacterial taxa have been observed to suppress plant defenses[33], while other isolates can exacerbate the deleterious effects of plant defenses on c aterpillars[16]
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