Dietary ethanol produces endpoint-specific dose responses in honeybees

Ethanol is naturally present in nectar, but we still know little about how pollinators cope with long-term exposure to it at low concentrations. We exposed adult worker honeybees (Apis mellifera carnica Poll.) for eight days to diets containing 0, 0.1, 0.5, 1, 2, or 10% ethanol and measured survival, estimated intake, open-field locomotion, sting extension, whole-body trehalose, and hemolymph ethanol. Hemolymph ethanol was correlated with dietary concentration, attesting to internal exposure. Survival differed among diets, an effect which was driven by the difference between the 10% ethanol treatment and the control. Food intake was lowest at the 10% ethanol diet. There was also a modest increase in intake under the 0.1% ethanol treatment. In terms of locomotor features, bees moved less, moved more slowly, explored less space, covered shorter distances, and followed more tortuous paths after the 10% ethanol treatment. Neither sting extension nor trehalose were affected by dietary ethanol. The results showed no beneficial stimulation at lower concentrations. Instead, performance was endpoint-specific: at 0.1-2% ethanol in the diet, performance remained relatively stable across most parameters, whilst clear impairment was evident at 10%. These findings highlight resilience to repeated ethanol exposure in honeybees.