Native mid-gut bacterial community increases resistance to nucleopolyhedrovirus in the cotton leafworm

Nucleopolyhedroviruses (NPVs) are widely used agents for the biological control of Lepidoptera pests. The gut bacterial community of insects plays crucial roles in their biological activities; however, the interaction between NPV and the gut bacterial community in Lepidoptera pests remains largely unexplored. In this study, we found that the diversity and composition of Spodoptera littoralis larvae mid-gut bacteria were significantly altered by a diet containing the antibiotic streptomycin. At all four examined taxonomic levels, the abundance of the dominant native mid-gut bacterial taxa decreased in larvae fed on the streptomycin diet. Biomarker analysis revealed that Enterococcaceae and Enterococcus were significantly enriched in larvae on the control diet. However, Bacteroidetes and Bacteroidales were the differentially abundant taxa in larvae on the streptomycin diet. In the bioassays with 2 × 10⁴, and 1 × 10⁵ NPV OBs/larva, the significantly higher relative dose of NPV was detected in the S. littoralis larvae fed on the streptomycin diet than the ones fed on control diet. Furthermore, subjected to the infection of 1 × 10⁵ NPV OBs/larva, the lifespan of S. littoralis larvae fed on the streptomycin diet (5.78 ± 0.08) were significantly shorten than the ones fed on control diet (6.099 ± 0.08). These findings suggest that the native mid-gut bacterial community of S. littoralis likely plays a role in resistance to NPV, and alterations in its composition may facilitate NPV propagation, increasing NPV susceptibility. Thus, disrupting the native mid-gut bacterial community may represent a novel strategy for controlling S. littoralis using NPV.