Honeybees show adaptive reactions to ethanol exposure

Abstract

The honeybee is being developed as a simple invertebrate model for alcohol-related studies. To date, several effects of ethanol consumption have been demonstrated in honeybees, but the tolerance effect, one of the hallmarks of alcohol overuse, has never been shown. Here, we confirm our hypothesis that the response to ethanol (in terms of motor impairment) is lower in bees that have previously experienced intoxication than in bees encountering ethanol for the first time, indicating that the chronic tolerance effect occurs in honeybees. Furthermore, we investigated the basis of this effect and found that it likely results from conditioned compensatory responses to cues associated with ethanol delivery. Our findings significantly improve our understanding of the suitability of honeybees as models for alcoholism-related research and underline the first and foremost function of all conditioned reactions – their adaptive value.

Alcohol intoxication resistance and alcohol dehydrogenase levels differ between the honeybee castes

“…On the other hand, consuming ethanol-corrupted sugar may disrupt homing ability of foragers and cause them to lose their way to the hive (Abramson et al 2000(Abramson et al , 2004a(Abramson et al , 2005Maze et al 2006;Sokolowski et al 2012). Of particular importance, in this context, is the development of tolerance in workers (Miler et al 2018), which may act to reduce the magnitude of any detrimental effects.…”

“…Other studies have gone as far as blocking proneness to consume ethanol in bees using Antabuse®, a drug developed to treat human alcoholics (Abramson et al 2003). Also, the tolerance effect to ethanol, a hallmark of alcoholism, was recently demonstrated in the honeybee, in the form of a drop in the impairing effect of ethanol on locomotion after repeated exposure to the drug (Miler et al 2018). However, even in light of these studies, our knowledge of the natural history of the honeybee with regard to ethanol exposure remains rudimentary and hinders the development of the honeybee as a model in research devoted to alcoholism.…”

“…Therefore, in nurses, ethanol exposure is passive and likely rare, whereas in foragers it is more active and likely frequent. Using this assumption and taking into account the finding that workers display a tolerance effect to ethanol when they encounter it repeatedly (Miler et al 2018), we hypothesised that foragers would show higher intoxication resistance to ethanol than nurses. However, there is an issue connected to the proper testing of this hypothesis, namely that the division of labour which occurs in the honeybee is heavily age-dependent.…”

Diel rhythmicity of alcohol‐induced intoxication in the honeybee workers

“…The intoxication resistance, that is, the latency to full sedation, was measured for each bee. Full sedation was observed shortly after full‐length proboscis extension and at the time of loss of righting reflex (Ammons & Hunt, 2008; Miler et al ., 2018). Afterwards, each individual was transferred into a 1.5 mL Eppendorph tube and frozen at −20°C for later wing wear analysis, a proxy for age of workers and means of morphologically differentiating younger and older bees (Mueller & Wolf‐Mueller, 1993).…”

“…For that purpose, we used an already established methodology of exposing bees to alcohol vapour (Ammons & Hunt, 2008; Miler et al ., 2018) with sedation latency as a measure of the intoxication resistance. The main advantage of this method of alcohol delivery lies in bypassing the metabolic side effects of alcohol ingestion; in it alcohol is absorbed through the tracheal respiratory system rather than the digestive system (Ammons & Hunt, 2008; Miler et al ., 2018). Notably, such side effects might differ in magnitude in different types of workers (e.g.…”