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.

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.

Chemicals used within managed pollinator systems can become developmental stressors for non-target organisms, yet their effects on reproductively specialized individuals remain insufficiently understood. Here, we examined the developmental ecotoxicity of the in-hive acaricide amitraz in honey bee (Apis mellifera) queens by exposing fourth-instar larvae to amitraz in acute-toxicity and sublethal-exposure assays and assessing responses from organismal to metabolic levels. The 72-h LD₅₀ of amitraz was 4.428 μg/queen. Residue-informed sub-LD₅₀ exposure (0.01-1 μg/queen) impaired queen development, as shown by reduced capping and emergence rates, prolonged developmental duration, and decreased body and abdomen weights. Notably, ovary mass was reduced in a dose-dependent manner even at 0.01 μg/queen, indicating high sensitivity of reproductive development to larval amitraz exposure. These phenotypic effects were accompanied by elevated catalase, superoxide dismutase, and glutathione S-transferase activities, together with increased malondialdehyde content, indicating redox disturbance and lipid peroxidation. Amitraz exposure also altered the expression of antimicrobial peptide genes, including Abaecin, Defensin1, Defensin2, Hymenoptaecin, and Apidaecin, suggesting disruption of immune homeostasis. Untargeted hemolymph metabolomics identified 502 differentially abundant metabolite annotations. Upregulated features were mainly associated with glycerophospholipid and alpha-linolenic acid metabolism, whereas downregulated features were associated with tryptophan and porphyrin metabolism. Collectively, these findings demonstrate that larval amitraz exposure compromises queen development and reproductive quality through oxidative, immune, and metabolic perturbations. This study highlights the need to incorporate developmentally sensitive measures in the environmental safety assessment of in-hive acaricides.