Gut microbial communities associated with phenotypically divergent populations of the striped stem borer Chilo suppressalis (Walker, 1863)

Heavy metal exposure reduces larval gut microbiota diversity of the rice striped stem borer, Chilo suppressalis

Cadmium (Cd), a widely distributed environmental pollutant in agroecosystems, causes negative effects on crops and herbivores through bottom-up processes. The gut microbial community of an insect can play a critical role in response to metal stress. To understand how microbiota affect the stress responses of organisms to heavy metals in agroecosystems, we initially used 16S rRNA sequencing to characterize the larval gut microbiota of Chilo suppressalis, an important agricultural pest, exposed to a diet containing Cd. The species richness, diversity, and composition of the gut microbial community was then analyzed. Results revealed that while the richness (Chao1 and ACE) of gut microbiota in larvae exposed to Cd was not significantly affected, diversity (Shannon and Simpson) was reduced due to changes in species distribution and relative abundance. Overall, the most abundant genus was Enterococcus, while the abundance of the genera Micrococcaceae and Faecalibaculum in the control significantly superior to that in Cd-exposed pests. Phylogenetic investigation of microbial communities by the reconstruction of unobserved states (PICRUSt) showed that the intestinal microorganisms appear to participate in 34 pathways, especially those used in environmental information processing and the metabolism of the organism. This study suggests that the gut microbiota of C. suppressalis are significantly impacted by Cd exposure and highlights the importance of the gut microbiome in host stress responses and negative effects of Cd pollution in agroecosystems.

Antibiotic feeding changes the bacterial community of Chilo suppressalis and thereby affects its pesticide tolerance

BACKGROUND

Owing to the widespread use of chemical pesticides to control agricultural pests, pesticide tolerance has become a serious problem. In recent years, it has been found that symbiotic bacteria are related to pesticides tolerance. To investigate the potential role of microorganisms in the pesticide tolerance of Chilo suppressalis, this study was conducted.

RESULTS

The insect was fed with tetracycline and cefixime as the treatment group (TET and CFM, respectively), and did not add antibiotics in the control groups (CK). The 16S rDNA sequencing results showed that antibiotics reduced the diversity of C. suppressalis symbiotic microorganisms but did not affect their growth and development. In bioassays of the three C. suppressalis groups (TET, CFM, and CK), a 72 h LC50 fitting curve was calculated to determine whether long-term antibiotic feeding leads to a decrease in pesticide resistance. The CK group of C. suppressalis was used to determine the direct effect of antibiotics on pesticide tolerance using a mixture of antibiotics and pesticides. Indirect evidence suggests that antibiotics themselves did not affect the pesticide tolerance of C. suppressalis. The results confirmed that feeding C. suppressalis cefixime led to a decrease in the expression of potential tolerance genes to chlorantraniliprole.

CONCLUSIONS

This study reveals the impact of antibiotic induced changes in symbiotic microorganisms on the pesticide tolerance of C. suppressalis, laying the foundation for studying the interaction between C. suppressalis and microorganisms, and also providing new ideas for the prevention and control of C. suppressalis and the creation of new pesticides.

Rice Defense Responses Orchestrated by Oral Bacteria of the Rice Striped Stem Borer, Chilo suppressalis

Plant defenses in response to chewing insects are generally regulated by jasmonic acid (JA) signaling pathway, whereas salicylic acid (SA) signaling is mainly involved in plant defense against biotrophic pathogens and piercing-sucking insects. Previous studies showed that both JA- and SA-related defenses in rice plants were triggered by the infestation of the rice striped stem borer (SSB, Chilo suppressalis), a destructive pest causing severe damage to rice production. Herbivore-associated microbes play an important role in modulating plant-insect interaction, and thus we speculate that the SSB symbiotic microbes acting as a hidden player may cause this anomalous result. The antibiotics (AB) treatment significantly depressed the performance of field-collected SSB larvae on rice plants, and reduced the quantities of bacteria around the wounds of rice stems compared to non-AB treatment. In response to mechanical wounding and oral secretions (OS) collected from non-AB treated larvae, rice plants exhibited lower levels of JA-regulated defenses, but higher levels of SA-regulated defenses compared to the treatment of OS from AB-treated larvae determined by using a combination of biochemical and molecular methods. Among seven culturable bacteria isolated from the OS of SSB larvae, Enterobacter and Acinetobacter contributed to the suppression of JA signaling-related defenses in rice plants, and axenic larvae reinoculated with these two strains displayed better performance on rice plants. Our findings demonstrate that SSB larvae exploit oral secreted bacteria to interfere with plant anti-herbivore defense and avoid fully activating the JA-regulated antiherbivore defenses of rice plants.