Vetnuus | May 2025 13 Bee cognition and health Balzani et al. (2022) evaluated the effects of acute and chronic ingestion of polyethylene (PE) microplastics on the health and cognition of A. mellifera. Individuals were analyzed for survival, food intake, response, and habituation to sucrose and appetitive olfactory learning, as well as memory capacity. They showed that the worker bees are not entirely affected by the acute and prolonged ingestion of PE. However, a significant effect was observed; a high mortality of individuals exposed to the highest concentration (50 mg L−1). It was also observed that bees exposed to low concentrations (0.5 and 5 mg L −1) of PE consumed much more food (1 day: PE bees 31.8%, controls: 8.8%; 7 days: PE bees 19.3%, controls 10.9%) than those in the control group. On the behavioural and cognitive analyses, the researchers observed that high concentrations of PE affect the ability to respond consistently to sucrose. However, it does not affect sensitivity and habituation to it, nor does it affect learning and memory skills—such results also were observed for prolonged exposures). Even so, Balzani et al. (2022) warn that it is necessary to be very careful when discarding the possibility that PE particles are not harmful to honeybees, mainly due to the lack of knowledge about the concentrations of these particles in the natural environment. They also suggest that the potentially harmful effects of other types of microplastics as well as their combination must be studied, to verify whether such compounds reduce the integrity of the colony and fitness. Pasquini et al. (2024) analyzed the effects of oral exposure to spherical particulate matters (MPs) on cognitive capacity and brain accumulation in Apis mellifera bees. Acute exposure was assessed after 48 h of exposure to polystyrene (PS, 4.8–5.8 µm), polymethyl methacrylate (PMMA, 1–40 µm), and their combination (MIX) at concentrations of 0.5, 5, and 50 mg/L. The study evaluated responsiveness, appetitive olfactory learning, and memory capacity. Additionally, fluorescent thermoset amino formaldehyde microspheres (1–5 µm) were used to determine whether microspheres of this diameter can penetrate the blood-brain barrier of bees, utilizing two-photon fluorescence microscopy (TPFM) in combination with the DISCO clearing technique. The results indicated that PS caused a decrease in sucrose responsiveness at a concentration of 50 mg/L. The authors emphasize that this behavioural aspect is crucial for bees, as it reflects their ability to detect and respond to nectar sources. Consequently, PS can significantly impair the foraging behaviour of workers, even though the effects observed in the experiment were relatively mild. PMMA did not show a significant effect, while MIX demonstrated a strong negative impact on sucrose responsiveness at concentrations of 5 mg/L and 50 mg/L, suggesting that the combination of these substances can have synergistic effects on the cognitive function of workers. All three treatments impaired learning capacity and memory, with PS causing the most severe effects. The 3D brain imaging analysis revealed that MPs measuring 1 to 5 µm penetrated and accumulated in the brain after just 3 days of oral exposure, predominantly in the optic lobes, where particle aggregation occurred at varying depths within the tissue. The authors emphasize that these findings raise concerns about the potential mechanical, cellular, and biochemical damage these contaminants could inflict on the central nervous system. They suggest that a deeper understanding of the risks posed by MPs to bees can be achieved through complementary studies focused on the accumulation and persistence of these particles in the brain, and their effects on sensory systems, cognitive mechanisms, and behaviour patterns. Bee’s microbiota, immune system, and susceptibility to infections Wang et al. (2021) carried out experiments that proved the role of the intestinal microbiota of A. mellifera in protecting against the risks of polystyrene microplastics (PS) exposure. It was observed that after 14 days of exposure, the effects on bee mortality were relatively low (up to 1.6%), and no changes were observed in terms of mass body gain compared to control groups. However, significant reductions in the α diversity of the intestinal microbiota of exposed individuals were observed, followed by changes in the expression of antioxidant enzymes (CAT, CypQ1, and GstS3) and genes associated with the immune system (Domeless, Hopscotch, and Symplekin). After dissection, it was found that PS microplastics were accumulated and degraded within the hindgut of the bees so that they interacted with the local microbiota. Consequently, it was observed that the combination of microplastics-PS with tetracycline drastically increased the lethality of these particles, proving the protective role of the intestinal microbiota of bees against xenobiotics. These experiments were performed using bees outside the hive; thus, it is crucial to verify if this pattern also occurs within the hive. Another study by Wang et al. (2022) sought to assess the possible influences of polystyrene (PS) particles of different sizes (micro and nano-plastic) on A. mellifera, evaluating changes in the total body weight, as well as the accumulation of microplastics and intestinal development. Nano-plastics (NPs) alterations in the intestinal microbiota, gene transcription, and consequently alterations in the resistance of honeybees to pathogenic bacteria were also analyzed. As for body weight, it was observed that weight increased in the first 9 days of treatment, followed, after the 10th day, by a slight decrease in the exposed groups; in the control group, this decrease in body weight occurred only after the 12th day. The histological analyses showed that the epithelial cells of the intestine of the bees in the control group had normal nuclei with high staining capacity, intact cell boundaries, and homogeneous cytoplasm, while in the exposed group’s adverse effects were observed, such as basement membrane disruption and vacuolated cytoplasm. After dissection, it was observed that the group exposed to PS-100 nm had a thinner intestinal wall when compared to the control group; the crypt depth/thickness ratio was also significantly higher than in the control group and in the group exposed to PS-1 µm. It showed the intestines of individuals in the 100 nm group were atrophied. Concerning the displacement and storage of particles after ingestion, the authors indicate an accumulation of microplastics in the rectum because the rectum harbours an abundant microbiota. Leading Article
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