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

## TL;DR

Oligosaccharides in Camellia flowers harm the health of Apis cerana bees and disrupt their gut microbes, explaining their reluctance to pollinate these plants.

## Contribution

This study reveals how oligosaccharides affect bee survival and gut microbiota, providing a molecular explanation for pollination reluctance.

## Key findings

- Oligosaccharides significantly reduced the survival rate and sucrose consumption of Apis cerana.
- Gut microbial communities, especially Gilliamella, were disrupted by oligosaccharide treatments.
- Metabolomic changes suggest oligosaccharides alter key metabolic pathways in bees.

## Abstract

Pollinating insects play a crucial role in maintaining global biodiversity and enhancing crop yield and quality. As a native bee species in China, studying the health of the Apis cerana is of significant value. The study elucidates the detrimental effects of oligosaccharides (stachyose and raffinose) on the physiology, gut integrity, and microbial homeostasis of Apis cerana, offering a mechanistic explanation for the species’ reluctance to pollinate Camellia reticulata. These results advance the understanding of host-diet-microbiota (especially Gilliamella) interactions in pollinators and underscore the ecological risks associated with specific floral metabolites. The research provides a theoretical foundation for developing oligosaccharide-adapted bee diets and for optimizing pollination management strategies for C. reticulata and related crops, ultimately promoting sustainable apiculture and crop production.

Honeybees are vital pollinators that contribute substantially to global ecosystem stability and agricultural productivity. Camellia reticulata, a cross-pollinated crop species, depends on honeybees for successful reproduction. Apis cerana shows reluctance to pollinate C. reticulata, yet the molecular mechanisms underlying this phenomenon remain unexplored. In this study, we performed controlled feeding experiments in which adult worker A. cerana 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 A. cerana. Both mixed and single-oligosaccharide treatments caused pronounced intestinal cell damage and disrupted the gut microbial community structure. Among the gut microbes, Gilliamella 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 A. cerana mortality associated with C. reticulata 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 A. cerana for C. reticulata pollination and the development of oligosaccharide-adapted bee diets.