Abstract: 【Aim】Orthosia songi is a monophagous pest damaging Eucommia ulmoides leaves. The objective of this research is to explore the characteristics of the gut bacterial communities of O. songi larvae at different instars.【Methods】 Illumina HiSeq high-throughput sequencing was employed to investigate the composition and diversity of the gut bacteria of the 1st, 3rd and 6th instar larvae of O. songi from Lüeyang, Shaanxi Province and Lingbao, Henan Province. 【Results】 At the phylum level, the gut bacterial communities of O. songi larvae from the two regions were dominated by Pseudomonadota, Cyanobacteriota, Actinomycetota, Bacillota and Bacteroidota, and the abundance of various phyla differed between samples of larvae at different instars. Notably, the abundance of Pseudomonadota decreased and that of Bacillota increased gradually with the increase of the larval instars of O. songi. At the genus level, Acinetobacter was the dominant bacterium, and its abundance also decreased with the increase of the larval instars of O. songi. Diversity analysis result showed that there were no significant differences in the gut bacterial alpha diversity indexes (Shannon index, Simpson index, ACE index and Chao index) among samples of O. songi larvae at different instars, while the beta diversity of the gut bacterial diversity among samples of O. songi larvae at different instars showed significant difference. 【Conclusion】 The results of this study suggest that the gut bacterial community composition of O. songi larvae collected from Lüeyang, Shaanxi Province and Lingbao, Henan Province is similar, but there is significant difference in the gut bacterial community composition among different larval instars, suggesting that the gut microbiota of O. songi larvae is influenced by their growth and developmental stages.

Key words: Orthosia songi; Eucommia ulmoides, monophagy, gut bacteria, larval instar