Buzzed but not elated? Effect of ethanol on cognitive judgement bias in honeybees

Ethanol is a neuroactive compound known to alter cognition, behavior, and physiology in a diverse range of vertebrate and invertebrate animals. It is also naturally present in many environments and might exert ecology-shaping influence on various organisms, such as honeybees feeding on fermenting nectar. In this study, we tested whether exposure of honeybees to low ethanol concentrations (1%) induces ‘pessimistic’ or ‘optimistic’ cognitive judgment bias (CJB), an information processing pattern thought to be related to affective processes. Bees were trained in a classical olfactory conditioning paradigm and then presented with conditioned stimuli and ambiguous odor mixtures to assess changes in decision-making under uncertainty. We additionally measured locomotor performance and ethanol absorption via spectrophotometric analysis of hemolymph. Ethanol levels peaked rapidly and remained elevated throughout the testing period. Despite this, ethanol had no detectable effect on choices in the CJB assay or locomotor behavior. These findings suggest that acute exposure to low-dose ethanol does not induce affect-like changes in honeybees. Our study represents the first test of pharmacologically induced judgment bias in an invertebrate and contributes to understanding the resilience of insect cognition to natural neuroactive compounds. The results highlight the limits and potential of CJB paradigms for probing affect-like states across taxa and support the honeybee as a valuable model in comparative cognition and the behavioral ecology of neuroactive substance exposure.