Gilliamella and Snodgrassella, members of core gut microbiota in corbiculate bees, have high species diversity and adaptability to a wide range of hosts. In this study, we performed species taxonomy and phylogenetic analysis for Gilliamella and Snodgrassella strains that we isolated in our laboratory, in combination with published whole-genome. Functional effects of accessory and unique genes were investigated by KEGG category and pathway annotation in pan-genome analysis. Consequently, in Gilliamella, we inferred the importance of carbohydrate metabolism, amino acid metabolism, membrane transport, energy metabolism, and metabolism of cofactors and vitamins in accessory or unique genes. The pathway mentioned above, plus infectious disease, lipid metabolism, nucleotide metabolism as well as replication and repair exert a pivotal role in accessory or unique genes of Snodgrassella. Further analysis revealed the existence of functional differentiation of accessory and unique genes among Apis-derived genomes and Bombus-derived genomes. We also identified eight and four biosynthetic gene clusters in all Gilliamella and Snodgrassella genomes, respectively. Our study provides a good insight to better understand how host heterogeneity influences the bacterial speciation and affects the versatility of the genome of the gut bacteria.

Glyphosate (GY) is the most widely used herbicide in agriculture worldwide. Lead is a common heavy metal in the natural environment. Honeybees, as pollinators, are exposed to these pollutants. So far, few reports have evaluated the toxic effects of GY mixed with heavy metals on honeybees (Apis cerana cerana). This study found that the acute toxicity of lead (LC50 = 1083 mg/L) is much greater than that of GY (LC50 = 4764 mg/L) at 96 h. The acute toxicities of the mixed substances were as follows: LC50 = 621 mg/L of lead and LC50 = 946 mg/L of GY. The combination of lead and GY was more toxic than either of the individual substances alone. Compared to the individual toxicity, combined treatment significantly affected the bees’ learning and cognitive abilities and changed the relative expression of genes related to immune defense and detoxification metabolism in A. c. cerana. The combination of lead and GY seriously affected the behavior and physiology of the studied honeybees. This study provides basic data for further research on the combined effects of GY and heavy metals on bee health. It also serves as a reference for effective colony protection.

Pesticides such as neonicotinoids frequently harm beneficial insect pollinators and affect their survival, social behavior, digestive system, and metabolism. Investigating the mechanisms behind these impairments is crucial for enhancing pesticide risk assessments. Apis cerana, a native honeybee species in Asia, has received limited research attention regarding the toxicological mechanisms of thiamethoxam (TMX) exposure. We exposed newly emerged worker bees of A. cerana to a field-relevant dose of TMX (400 ng/g) under laboratory conditions to examine whether TMX exposure triggers similar or distinct effects in different biological processes and tissues. Our results demonstrate that TMX damages the gut cell structure and significantly increases mortality. Gut transcriptomic analysis revealed that the activation of signaling pathways such as glycosphingolipid biosynthesis, Notch signaling, and Wnt signaling likely contributed to structural damage in gut cells. Head transcriptomic results indicated that the activation of pathways including pyruvate metabolism, glycolysis/gluconeogenesis, thiamine metabolism, and riboflavin metabolism might negatively affect the stability of the neural system in A. cerana. The metabolic dysfunction of glycine, serine, threonine, as well as glycerophospholipids potentially impairs the neural system, leading to behavioral abnormalities and mortality. In summary, field-level TMX damages the gut cell structure, destabilizes the neural system, and increases the mortality rate of A. cerana. These findings demonstrate that TMX exposure induces complex, tissue-specific effects. This study provides a comprehensive understanding of the molecular and physiological impacts of TMX on A. cerana, offering valuable insights for the conservation and protection of this important pollinator species.

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.

The size of comb cells is a key factor influencing the body size of honey bee workers. Comb cells and the body size of Chinese honey bee workers are smaller than those of Italian honey bee workers. To increase the size of Chinese honey bee workers, this study used newly built combs from Chinese honey bee colonies (control group) and Italian honey bee colonies (treatment group). These combs were provided to Chinese honey bee colonies for queens to lay fertilized eggs with the aim of rearing larger workers. Workers emerging from the control and treatment combs were designated as control and treatment workers, respectively. We compared 13 external morphological traits, including right forewing length and width; linear length of veins a, b, c, and d; proboscis length; right hind femur length; tibia length; metatarsal length and width; and the longitudinal diameters of the third and fourth tergites between the two groups. The results identified six types of cell contents in the combs, excluding empty cells: capped honey (most abundant), followed by capped brood, uncapped honey, and smaller amounts of pollen, larvae, and eggs. Additionally, the average body weights of 6-day-old worker bee larvae, white-eyed pupae, adult worker bees, and honey stomachs containing sucrose solution were significantly higher in the treatment group than in the control group. Except for proboscis length, the average size of 12 out of 13 traits in the treatment group was significantly larger than in the control group, indicating that increasing cell size can produce larger Chinese honey bee workers. In the control group, only the left forewing was significantly shorter than the right, with no significant side-to-side differences in the other morphological traits. In the treatment group, the left forewing width, hind leg femur length, tibia length, and hind leg metatarsus width were significantly smaller than their right-side counterparts, while the other six traits showed no significant side-to-side differences. These findings provide a basis for using Italian honey bee combs to rear larger workers in Chinese honey bee colonies, offering beekeepers a strategy to enhance foraging capacity and improve honey production.

Honey bees provide essential pollination services in natural and agricultural ecosystems, yet little is known about honey bee-associated pathogens in Cambodia and Laos. Here, we screened 53 colonies from 10 sites, including Apis cerana (n = 28), A. mellifera (n = 18), A. dorsata (n = 4), and A. florea (n = 3), for common honey bee viruses and the microsporidian Nosema ceranae using PCR and RT-PCR assays. Six viruses—acute bee paralysis virus, black queen cell virus, deformed wing virus type A, Israeli acute paralysis virus, Kashmir bee virus, and Lake Sinai virus—and N. ceranae were detected in A. cerana and A. mellifera, with overall low detection frequencies across sites. No targets were detected in A. dorsata or A. florea; however, the limited sample sizes for these species restrict interpretation of absence. Partial gene fragment sequences showed similarity to previously reported Asian isolates, indicating consistency with known regional viral diversity. These findings provide baseline detection data for honey bee-associated pathogens in Cambodia and Laos and support the need for expanded sampling across host species and seasons to better characterize pathogen occurrence in the region.