Honey bees and other pollinators are key to functioning natural and managed ecosystems. However, their health is threatened by many factors, including pesticides. Spraying fungicides during flowering of fruit trees is widespread even though it directly exposes pollinators to these fungicides. Here, we report a series of experiments designed to understand how the combination of propiconazole and carbendazim, marketed in China as Chunmanchun^®, affects honey bee health. With an acute oral toxicity of 23.8 μg a.i./bee over 24 h in the laboratory, we considered the acute mortality risk from normal Chunmanchun^® applications as relatively low. However, our comprehensive studies revealed other diverse effects: Chunmanchun^® reduced memory after classic conditioning by approximately 25% and altered the activity of protective enzymes and the composition of the honey bees’ gut microbiota. Specifically, the genus Lactobacillus was decreased by ~13%, and Bartonella and Snodgrassella were increased by ~10% and ~7.5%, respectively. The gut metabolome was also disrupted in diverse ways, possibly as a functional consequence of the microbiome changes. Thus, we demonstrated numerous sublethal effects of the combination of propiconazole and carbendazim, which adds to the growing evidence that agrochemicals and fungicides in particular can harm pollinator health in subtle ways that are not captured in simple mortality assays.

The greater wax moth Galleria mellonella (Lepidoptera: Galleriinae) represents a ubiquitous apicultural pest that poses significant threats to global beekeeping industries. The larvae damage honeybee colonies by consuming wax combs and tunneling through brood frames, consequently destroying critical hive infrastructure including brood-rearing areas, honey storage cells, and pollen reserves. Larval feeding behavior is critically dependent on chemosensory input for host recognition and food selection. In this study, we conducted a transcriptome analysis of larval heads and bodies in G. mellonella. We identified a total of 25 chemosensory genes: 9 odorant binding proteins (OBPs), 1 chemosensory protein (CSP), 5 odorant receptors (ORs), 4 gustatory receptors (GRs), 4 ionotropic receptors (IRs) and 2 sensory neuron membrane proteins (SNMPs). TPM normalization was employed to assess differential expression patterns of chemosensory genes between heads and bodies. Nine putative chemosensory genes were detected as differentially expressed, suggesting their potential functional roles. Subsequently, we quantified expression dynamics via reverse transcription quantitative PCR in major chemosensory tissues (larval heads, adult male and female antennae), revealing adult antennal-biased expression for most chemosensory genes in G. mellonella. Notably, two novel candidates (GmelOBP22 and GmelSNMP3) exhibited particularly high expression in larval heads, suggesting their crucial functional roles in larval development and survival. These findings enhance our understanding of the chemosensory mechanisms in G. mellonella larvae and establish a critical foundation for future functional investigations into its olfactory mechanisms.

Smoothened (Smo) is a critical component regulating the Hedgehog signaling pathway. However, whether Smo is associated with the modulation of olfactory recognition capabilities of bees remains unclear. In this study, we amplified Smo from Apis mellifera. The coding sequence of Smo was 2952 bp long, encoded 983 amino acids. Smo was most highly expressed in the antennae. Cyclopamine (200 μg/mL) significantly reduced but purmorphamine (800 μg/mL) significantly increased Smo expression (p < 0.05). OR152 and OR2 expression in the cyclopamine group significantly decreased, whereas OR152 expression in the purmorphamine group significantly increased (p < 0.05). A significant decrease in the relative values of electroantennography was observed in the cyclopamine group exposed to neral. Behavioral tests indicated a significant decrease in the attractive rates of neral, VUAA1, linalool, and methyl heptenone in the cyclopamine group. Conversely, the selection rates of linalool and methyl heptenone in the purmorphamine group significantly increased. Our findings indicate that Smo may play a role in modulating olfactory receptors in bees.

Fungicides play a critical role in crop protection, yet their potential threats to pollinator remain a concern. This study investigated the sublethal effects of a commercial fungicide, Chunmanchun^® (a suspension-emulsion of 7% propiconazole and 28% carbendazim), on cognitive functions of the honey bee (Apis mellifera). Using the proboscis extension reflex (PER) assay, we evaluated sucrose sensitivity and olfactory learning and memory in workers exposed to the recommended field concentration (PC), along with sublethal (LD₁₀) and semi-lethal (LD₅₀) concentrations. Fungicide exposure significantly reduced sucrose sensitivity across all concentrations tested (0.1%, 1%, and 3%), with the strongest reductions occurring at the LD₁₀ and LD₅₀ levels. While olfactory associative learning was not significantly impaired, memory retention was adversely affected. Bees in the LD₅₀ group showed significantly reduced PER rates at both1 h and 6 h post-training, and LD₁₀ and LD₅₀ groups exhibited significant memory deficits by 1 h and 6 h relative to the control. These results demonstrate that Chunmanchun^® impairs both sucrose responsiveness and olfactory memory in honey bees, which may impair foraging efficiency and ultimately affect colony performance. This study highlights a potential ecological risk posed by this fungicide to pollinators in agricultural environments.

To systematically investigate how the olfactory system of Bombus terrestris adapts to its social division of labor and reproductive strategies, this study integrated the micromorphology of antennal sensilla and the expression profiles of olfactory receptor (OR) genes from the heads of its three castes (workers, drones, and queens) for a multi-level analysis. Scanning electron microscopy (SEM) revealed that drones possess significantly longer chaetic sensilla (Sch), sensilla trichodea (Str A/B), and sensilla basiconica (Sba A), as well as larger-diameter sensilla coeloconica (Sco) compared to workers and queens, indicating structural and functional specialization for sensitive detection of single key signals (e.g., queen pheromones). In contrast, workers and queens exhibited a more complete composition of sensilla types and a higher sensilla distribution density, suggesting the construction of a perceptual system capable of processing multiple chemical signals simultaneously. RNA-seq combined with qRT-PCR confirmed the significant upregulation of seven OR genes (e.g., BterOR3, BterOR4) in drones, while workers showed upregulation of BterOR3/5/7 accompanied by enrichment of P450 detoxification pathways. Phylogenetic analysis suggested that BterOR5 serves as a conserved co-receptor, and some OR genes may originate from recent duplication events. In summary, distinct differences were observed in the morphological structure and molecular expression of the olfactory system among B. terrestris castes. Drones exhibited structural and gene expression features consistent with specialization in queen pheromone detection, while workers and queens demonstrated sensilla diversity and olfactory receptor expression patterns indicative of a broader response capacity to diverse chemical signals. These findings support the view that the olfactory system has undergone multi-level adaptive evolution driven by social division of labor and reproductive roles.

Objectives: This study presents a comprehensive molecular investigation of Apis cerana cerana populations inhabiting the Lüliang Mountain region, aiming to evaluate their genetic diversity and population structure using polymorphic microsatellite and mitochondrial DNA (mtDNA) markers. Methods: A total of 23 microsatellite loci and three mtDNA fragments (COI–COII, COI, Cytb) were successfully amplified, of which 21 loci were polymorphic and used for subsequent genetic analyses. Measures of genetic variability, population differentiation, and molecular variance were computed to assess intra- and interpopulation diversity. Results: High levels of genetic variation were detected (mean PIC = 0.349), with observed heterozygosity (Ho = 0.827) exceeding expected heterozygosity (He = 0.608). Analysis of molecular variance (AMOVA) revealed that 95.28% of total genetic variation occurred within populations, while 4.72% was attributed to among-population differences. Mitochondrial analyses identified 20 polymorphic sites forming 19 haplotypes, with high haplotype (Hd = 0.884) and nucleotide diversity (π = 0.00157). Conclusions: These results indicate substantial gene flow and interpopulation connectivity among A. c. cerana populations in the Lüliang region. Collectively, the findings provide critical molecular evidence supporting the conservation and sustainable management of A. c. cerana genetic resources in this area.