Integrated Ultrastructural and Transcriptomic Analysis of the Proboscis in Apis cerana cerana Under Different Foraging Conditions

The proboscis of Apis cerana cerana is primarily regarded as a feeding organ, whereas its potential structural and molecular characteristics associated with chemosensory processes remain poorly understood. This study integrated ultrastructural and transcriptomic analyses to investigate the morphological characteristics and chemosensory-associated molecular features of the proboscis under different pollen-load conditions. Scanning electron microscopy revealed a highly organized glossal architecture characterized by longitudinal ridge–groove structures and densely distributed hair-like structures on the distal glossa and flabellum, indicating regional structural specialization of the proboscis surface. Transcriptomic analyses identified 1549 and 1652 differentially expressed genes (DEGs) in workers carrying pear pollen loads and rapeseed pollen loads, respectively, compared with workers without visible pollen loads, whereas only 89 DEGs were detected between the two pollen-load groups. These results indicate that pollen-load status was associated with greater transcriptional differences than the comparison between the two floral sources under the present experimental conditions. Functional enrichment analyses showed that DEGs were mainly associated with cellular processes, signal transduction, and metabolic regulation pathways. Additionally, six candidate OR-like transcripts, including several odorant receptor-like genes, were identified from the proboscis transcriptome, and their expression patterns were validated by quantitative real-time PCR. Phylogenetic analyses revealed both conserved orthologs and lineage-specific divergence. Collectively, these structural and molecular findings suggest that the honey bee proboscis may possess chemosensory-related characteristics, providing a basis for future studies investigating their functional significance.