Effects of UV-B radiation on honey bee (apis mellifera L.) behaviour and physiology

Changes in stratospheric ozone dynamics associated with global climate change can alter the intensity and distribution of ultraviolet (UV) radiation reaching the Earth's surface. According to climate modelling results, it is stated that the UV index could increase by approximately 3–8 per cent by the end of the 21st century, including in mid-latitudes. The visual spectrum of honeybees also encompasses ultraviolet (UV) wavelengths, and bees use UV signals in fundamental behaviours such as distinguishing the UV patterns of flowers, contrast perception, and orientation; therefore, it has been hypothesised that potential increases in environmental UV could affect bees' sensory inputs and associated behavioural/physiological responses. The UV spectrum is classified as UVA (315–400 nm), UV-B (280–320 nm) and UVC (100–280 nm); the UV-B band was selected as a variable in this study due to its higher energy structure, which can cause photochemical damage to DNA and is associated with oxidative stress responses. This study evaluated the behavioural, biochemical, and molecular responses of forager worker bees returning to the hive following UV-B exposure. Worker bees were captured at the hive entrance in August 2024 and acclimatised under controlled laboratory conditions. Behavioural effects were assessed using a phototaxis test conducted in a linear arena under dark and light conditions, with control and two UV-B intensities (400 and 800 µW/cm²); the positions of individuals and their residence times in the arena were quantified using camera recording and image processing-based analyses (3 replicates × 11 bees; n=33). For physiological and molecular responses, TAS and TOS were measured from thoracic tissue in groups exposed to 0/400/800 µW/cm² UV-B for 120 minutes under dark conditions; expression of the Msh2 and Msh6 genes was analysed via RT-qPCR using RNA isolated from head tissue. The findings indicate that the duration of exposure to the UV-B region was increased in the UV-B-treated groups compared to the control groups, and that UV-B induced a positive phototaxis response in worker bees; however, no statistically significant dose-dependent differentiation was observed between the 400 and 800 µW/cm² intensities. In contrast, no statistically significant differences were detected between groups in TAS, TOS, and Msh2/Msh6 expression levels. These results suggest that UV-B can induce attraction at the behavioural level under the applied conditions; however, it does not produce a significant stress response in the measured biochemical and molecular markers.