Seasonal Dynamics Without Reset: Core Microbiota Stability Across Development in a Gall-Dwelling Weevil.

Coccotorus beijingensis is a typical gall-inducing insect whose larvae complete their development within enclosed galls, providing a unique model for investigating host-microbe symbiosis. This study aimed to characterize the dynamic succession of the symbiotic microbiota in C. beijingensis across the larval stage (April-August) and pupal stage (September). Using high-throughput 16S rRNA gene sequencing, we performed a systematic analysis of monthly collected samples spanning the larval and pupal stages. The results revealed significant temporal variation in the structure of the larval microbial community. Bacillota and Bacteroidota were the dominant bacterial phyla throughout development. Although non-core bacterial groups, such as Pseudomonadota, showed pronounced seasonal fluctuations, no clear microbial reset was observed during metamorphosis. Exploratory PICRUSt2-based functional prediction suggested that the predicted metabolic potential of the microbiota may vary across development, with pathways related to carbohydrate metabolism, amino acid metabolism, and energy metabolism showing higher predicted representation during the middle larval stages. Overall, this study demonstrates that, within the confined gall microhabitat, larval development and seasonal dynamics jointly drive the temporal restructuring and functional adaptation of the microbial community. These findings provide new insights into the symbiotic mechanisms of holometabolous insects and their associated microbiota.