Differential Effects of Tebucur® 250 EW (a.i. tebuconazole) on Learning and Memory in Bombus terrestris L. Following Single Exposure

The effects of fungicides on pollinators remain relatively understudied despite their widespread use and high likelihood of environmental exposure. We assessed the effects of a single exposure to the commercial formulation Tebucur® 250 EW (containing tebuconazole as the active ingredient) on learning and memory in Bombus terrestris workers. Using the Free-Moving Proboscis Extension Response (FMPER) paradigm, bees were exposed to two concentrations: 9.4 µg of tebuconazole per mL (group T 1/100) and 94 ng of tebuconazole per mL (group T/10,000) of tebuconazole through either pure sucrose (Method 1) or Tebucur® 250 EW-supplemented sucrose (Method 2) during conditioning. No significant differences between groups were detected during the learning phase (all p > 0.05). In contrast, significant differences emerged during the memory test at the earliest time point (5 min). In Method 1, bees exposed to the higher concentration (treatment group T 1/100) showed significantly lower performance compared to the control group (p < 0.05). In Method 2, the lowest performance was observed in the group exposed to the lower concentration (treatment group T 1/10,000; p < 0.01). No significant differences were detected at later time points (10 and 30 min). These results indicate that a single exposure to Tebucur® 250 EW (active ingredient: tebuconazole, 250 g/L) can affect short-term memory in bumblebees without impairing initial learning performance. Although the observed effects were subtle and time-limited, they may have important implications for foraging efficiency and pollination under natural conditions.