Propolis is a composite substance that worker bees manufacture from plant resins they collect in the field and blend with their own secretions. It seals cracks, reinforces the hive structure, and modulates the microbial environment inside the colony, making it one of the most functionally important products of bee labor. Yet propolis yield varies enormously between colonies, and the biological basis of that variation has remained poorly understood. Because the antennae are the primary sensory organs that detect signals from nectar, pollen, and propolis sources during foraging, the researchers reasoned that resin collection behavior might be tightly linked to olfaction at the colony level, a relationship that had never been directly tested between colony types.

To investigate, the team compared foragers from high propolis-producing colonies with foragers from ordinary colonies of A. mellifera. The first striking result came from morphology: the total length of both the left and right antennae was significantly shorter in high-yield colonies than in ordinary colonies. When the researchers broke the antenna down segment by segment, they found that the lengths of two flagellomeres, FL7 and FL10, were also significantly shorter in the high-yield bees. The flagellum carries the densest array of olfactory sensilla on the bee antenna, so differences in the dimensions of specific flagellomeres suggest that the sensory hardware itself differs between bees that collect resin aggressively and those that do not.

The morphological differences were only the beginning. The researchers sequenced the antennal transcriptomes of the two colony types and analyzed FPKM heatmaps to visualize gene expression patterns across samples. They then comprehensively characterized three gene families central to insect olfaction: the odorant binding proteins, or OBPs; the chemosensory proteins, or CSPs; and the odorant receptors, or ORs. In total, the analysis covered six CSPs, 19 OBPs, and 34 ORs, amounting to 58 genes whose expression could be compared between the high-yield and ordinary colonies.

Characterizing these gene families required more than simple counting. The team mapped the chromosomal locations of each gene and examined their conserved protein domains to confirm family membership, then performed phylogenetic analyses that placed the honeybee genes in evolutionary context with four other species: the eastern honeybee Apis cerana, the parasitoid wasp Chouioia cunea, the jewel wasp Nasonia vitripennis, and bumblebees of the genus Bombus. These comparative trees allow researchers to distinguish genes that have been conserved across social insects from those that have expanded or contracted specifically in the western honeybee lineage, providing clues about which olfactory components might be specialized for resin detection and other colony-level tasks.

The expression results revealed clear differences between the two colony types. Genes from all three families showed differential expression between high propolis-producing and ordinary colonies, indicating that the olfactory gene repertoire is deployed differently in bees whose colonies yield drastically different amounts of resin. This is the first time that differences in antennal morphology and antennal RNA-seq results have been reported between colonies with differential propolis yield, as well as the first report of differences in the expression of these three gene families between the two colony types. The finding implies that the propensity to collect propolis is not merely a matter of opportunity or environment but is associated with measurable molecular differences in the sensory organs of the foragers themselves.

To make sure the sequencing results were robust, the researchers validated the expression patterns of all 58 genes by quantitative real-time PCR, or qRT-PCR. The qRT-PCR expression levels were consistent with the RNA-seq expression patterns across the board, confirming that the transcriptomic differences were not artifacts of library preparation or normalization. This dual-method validation is technically important because antennal transcriptomes can be challenging: the tissue is small, expression levels of individual chemosensory genes are often low, and subtle differences between biological groups can be swamped by noise. Agreement between FPKM-based sequencing quantification and independent qRT-PCR measurement substantially strengthens the conclusion that the two colony types differ in their antennal gene expression.

The study also carries implications for beekeeping practice. Propolis is prized both as a hive product and as a raw material for biomedicine, with documented antimicrobial and anti-inflammatory properties, and colonies that produce more of it are valuable for breeding programs. If the olfactory gene families identified here turn out to be reliable markers of resin collection propensity, they could inform selective breeding of high-yield lines, complementing traditional selection based on colony performance alone. The morphological markers, such as antennal length and the dimensions of specific flagellomeres, might likewise serve as rapid phenotypic indicators that breeders can measure without molecular testing.

From a broader scientific perspective, the results provide a molecular basis for further research into how worker bee antennae function within honeybee colonies. The antennae regulate foraging behavior by detecting signals from nectar, pollen, and propolis sources, and the new data suggest that this regulatory role varies between colonies in ways that correlate with behavioral differentiation. The authors argue that their findings offer new perspectives on the molecular mechanisms underlying the interaction between worker bee behavioral differentiation and the olfactory system, a theme that resonates with long-standing questions in social insect biology about how genetically similar individuals come to perform such different tasks for the same colony.

The research was funded by the China Agriculture Research System under grant CARS-44-SYZ07 and by a Henan Institute of Science and Technology High-level Talent Research Project. The work was conducted by the Bee Products and Biomedicine Research and Development Team at the Henan Institute of Science and Technology, with corresponding authors Dongbiao Lü and Yunchao Kan leading the collaboration. Published open access in BMC Genomics, the study makes its transcriptomic datasets, phylogenetic analyses, and validation data available to the research community, laying the groundwork for functional studies that could pin down exactly which olfactory genes drive the dramatic differences in propolis yield between honeybee colonies.

Subject of Research: Genomics

Article Title: RNA sequencing of antennae and comparative analysis of key gene families in Apis mellifera workers exhibiting drastic differences in propolis yield

Article References: RNA sequencing of antennae and comparative analysis of key gene families in Apis mellifera workers exhibiting drastic differences in propolis yield. (n.d.). https://doi.org/10.1186/s12864-026-13462-8

Image Credits: AI Generated

DOI: 10.1186/s12864-026-13462-8

Keywords: Apis mellifera, propolis, antennal transcriptome, odorant binding proteins, chemosensory proteins, odorant receptors, RNA sequencing, BMC Genomics, sequencing, antennae, comparative, analysis