Gut microbial changes in a specialist blister beetle larvae and their nutritional metabolic characteristics.

Insect gut microbiota and their metabolites play a significant role in the shaping of hosts' diets and feeding habits. We conducted 16S rDNA amplicon sequencing on the gut microbiota of specialist blister beetle larvae that feed on locust eggs and artificial food at different instars, to explore the relationship between gut microbiota and the specialized feeding habit of the blister beetle larvae. There is no significant difference in the gut microbial structure among the second to the fourth instar larvae under the same rearing conditions, but the gut microbial structure of the first instar larvae was significantly different from the second to the fourth instar larvae fed by different diets. Bacteria associated with polysaccharide utilization are relatively barren in first instar larvae. Compared to the carbohydrate content between the artificial diet and locust eggs, we speculate that an excessive amount of polysaccharides in the artificial diet may be detrimental to the growth and development of first instar larvae. Gut microbiota of the second to the fourth instar larvae fed with different diets significantly differ in microbial community structure. The different bacteria, especially the metabolism-related intestinal bacteria in locust eggs-fed larvae, may help the hosts adapt to the environment and contribute to the production of active ingredients. The relative abundance of polysaccharide utilization-related bacteria was significantly higher in the artificial diet-fed larvae compared to the locust eggs-fed larvae, which showed the same result when compared to the first instar larvae. Changes in gut microbes of blister beetle larvae and their metabolic inferences could enrich our understanding of the nutritional requirements of the specialist and help optimize the artificial diet of medicinal cantharides.