Oligosaccharides Reduce the Survival of Apis cerana and Disrupt the Gut Symbiont Gilliamella

Honeybees are vital pollinators that contribute substantially to global ecosystem stability and agricultural productivity. <i>Camellia reticulata</i>, a cross-pollinated crop species, depends on honeybees for successful reproduction. <i>Apis cerana</i> shows reluctance to pollinate <i>C. reticulata</i>, yet the molecular mechanisms underlying this phenomenon remain unexplored. In this study, we performed controlled feeding experiments in which adult worker <i>A. cerana</i> were supplied with stachyose, raffinose, and their combination. We assessed physiological traits including survival rate, sucrose solution consumption, and body weight gain, alongside histological changes in intestinal cell structures. We conducted RNA-seq of gut tissues as well as 16S rRNA sequencing and metabolomic profiling. Our findings revealed that the mixed oligosaccharide treatment significantly reduced the survival rate of workers, and three oligosaccharide treatments significantly reduced sucrose consumption in <i>A. cerana</i>. Both mixed and single-oligosaccharide treatments caused pronounced intestinal cell damage and disrupted the gut microbial community structure. Among the gut microbes, <i>Gilliamella</i> exhibited the most substantial decline in the stachyose group. Metabolomic analysis further demonstrated that oligosaccharide feeding significantly altered amino acid and galactose metabolism pathways, which may play critical roles in oligosaccharide utilization and directly influence honeybee survival. In summary, this study provides new insights into the molecular mechanisms underlying <i>A. cerana</i> mortality associated with <i>C. reticulata</i> pollination. These findings not only enhance our understanding of host-diet-microbiota interactions in honey bees but also offer a theoretical basis for the integrated management of <i>A. cerana</i> for <i>C. reticulata</i> pollination and the development of oligosaccharide-adapted bee diets.