Influence of dietary aconitine and nicotine on the gut microbiota of two lepidopteran herbivores.

The gut microbiota plays an important role in pheromone production, pesticide degradation, vitamin synthesis, and pathogen prevention in the host animal. Therefore, similar to gut morphology and digestive enzyme activity, the gut microbiota may also get altered under plant defensive compound-induced stress. To test this hypothesis, Dendrolimus superans larvae were fed either aconitine- or nicotine-treated fresh leaves of Larix gmelinii, and Lymantria dispar larvae were fed either aconitine- or nicotine-treated fresh leaves of Salix matsudana. Subsequently, the larvae were sampled 72hr after diet administration and DNA extracted from larval enteric canals were employed for gut microbial 16S ribosomal RNA gene sequencing (338 F and 806 R primers). The sequence analysis revealed that dietary nicotine and aconitine influenced the dominant bacteria in the larval gut and determined their abundance. Moreover, the effect of either aconitine or nicotine on D. superans and L. dispar larvae had a greater dependence on insect species than on secondary plant metabolites. These findings further our understanding of the interaction between herbivores and host plants and the coevolution of plants and insects.

Variation in the pH of experimental diets affects the performance of Lymantria dispar asiatica larvae and its gut microbiota.

To study dietary pH effects on Lymantria dispar asiatica larvae and provide a theoretical basis for its control in different forests, phosphate buffers (PBs) of pH 6, 7, and 8 were used to prepare experimental diets. The diet prepared with pH 6 PB was named as DPB6, with pH 8 PB as DPB8, and with pH 7 PB as DPB7 (control). The dietary pH was 5.00 in DPB6, 6.05 in control, and 6.50 in DPB8. After feeding on the diets with different pH values for 84 hr, fourth-instar caterpillars were randomly collected. Growth and various physiological traits were determined and 16S recombinant DNA sequencing was performed using the intestinal microflora of surviving larvae. Results showed that the mortality was 30% in DPB6, and 10% in DPB8, while no mortality was observed in control. The partial least squares discriminant analyses suggested that diets prepared with PB of different pH resulted in different food intake, amount of produced feces, weight gain, digestive enzyme activities, and antioxidant enzyme activities in larvae. Interestingly, both the highest weight gain and the lowest total antioxidant capacities were seen in control larvae. Results also showed that the larval gut microbiota community structure was significantly affected by dietary pH. Moreover, linear discriminant analysis effect size suggested that the family Acetobacteraceae in control, genus Prevotella in DPB8, and genus Lactococcus, family Flavobacteriaceae, family Mitochondria, and family Burkholderiaceae in DPB6 contributed to the diversity of the larval gut microbial community.

Diel pattern in the structure and function of the gut microbial community in Lymantria dispar asiatica (Lepidoptera: Lymantriidae) larvae.

In the present study, diel pattern in gut microbial communities in insects were evaluated. Lymantria dispar asiatica fourth instar larvae (72 ± 2 hr after molting) at noon (LdD) and midnight (LdN) were used for a comparative analysis of the gut microbial community. Ten bacterial operational taxonomic units (OTUs) were shared between LdD and LdN samples. One bacterial OTU was specific to LdD. The dominant gut microbes were OTU72 in LdD and OTU75 in LdN. A linear discriminant analysis effect size cladogram suggested that ten bacterial OTUs maintain significant differences in relative abundances between LdD and LdN. These results agreed with the discrete ellipses between LdD and LdN in principal coordinates analysis plots. Additionally, using phylogenetic investigation of communities by reconstruction of unobserved states, the gut microbial community was assigned to 23 functional terms, among which 22 exhibited significant differences between LdD and LdN. To conclude, the present study documented a diel pattern in the gut microbial community of L. dispar asiatica larvae.

Avermectin stress varied structure and function of gut microbial community in Lymantria dispar asiatica (Lepidoptera: Lymantriidae) larvae.

Lymantria dispar asiatica is a globally distributed herbivorous pest. Avermectin is a highly effective, broad-spectrum insecticide. In this study, fourth instar L. dispar asiatica larvae were exposed to a LC30 dose of avermectin. The structure and function of larval gut microbial community was analyzed to examine how gut microbiota in L. dispar asiatica larvae responded to avermectin stress. Results showed that the structure and function of gut microbial community in L. dispar asiatica larvae were varied by avermectin stress. To be precise, more than half quantity of the observed Optical Taxonomic Units (OTUs) showed significantly different abundances under avermectin stress. Linear discriminant analysis effect size (LEfSe) suggested nine bacterial genera and 12 fungal genera contributed to the different gut microbial community structure in L. dispar asiatica larvae. Gut microbial function classification (PICRUSt and FUNGuild) suggested that three bacterial function categories and a fungal function guild were significantly increased, and two fungal function guilds were significantly decreased by avermectin stress. This study furthers our understanding of the physiology of L. dispar asiatica larvae under avermectin stress, and is an essential step towards future development of potential pesticide targets.