Chronic oral exposure to Amistar fungicide does not significantly affect colour discrimination but may impact memory retention in bumblebees

Background Intensive agriculture, including pesticides, is one of the many reasons for pollinator decline. The EU legislation on plant protection products (hereon pesticides) demands that the risks of active substances and their use in pesticide products are assessed for bees. However, the risk assessment is not always sufficient as shown, for example, in the case of the fungicide Amistar. The fungicide has been shown to cause lethal and sublethal effects on bumblebees at levels that, according to the EU risk assessment, do not require risk mitigation measures to protect bees. In order to understand the effects of chronic Amistar exposure on bumblebees, we studied whether 5 days of oral exposure to 0.015 µl Amistar (3.75 µg azoxystrobin/day) impairs bumblebees’ learning and memory performance in the 10-colour discrimination task. Results Chronic Amistar treatment did not impair the learning of the bees, but a statistically non-significant negative trend was observed in memory retention between the final learning bout and the subsequent memory test. Conclusions The results of our study suggest that chronic sublethal exposure to Amistar fungicide did not significantly impair the learning ability of bumblebees. However, there was a trend towards impaired memory retention, although this was not statistically significant. These findings provide further support for the hypothesis that Amistar may have a negative effect on bee cognitive performance. It is important to continue studying the effects of widely used pesticides on pollinators, as their decline is a complex issue with multiple contributing factors. Understanding the effects of different pesticide residue levels on bumblebees can inform policymakers in making more sustainable pesticide legislation and help protect pollinators.