Reduced ability of ethanol drinkers for social communication in honeybees (Apis mellifera carnica Poll.)

Physiological and behavioral pharmacology of ethanol in honey bees

Ethanol has been consumed by humans since the dawn of civilization and, over the course of millennia, a wide variety of ethanol-rich drinks have been produced across cultures. Traditionally, it was believed that only humans voluntarily consume ethanol and become inebriated by it. However, a growing amount of evidence is showing that several non-human animal species spontaneously consume ethanol in nature. Among these, there is the honey bee (Apis mellifera), which can find ethanol in decaying fruits and in the fermented nectar of flowers. Importantly, honey bees represent a useful animal model of ethanol consumption as, like humans, they voluntarily consume ethanol, they show acute dose-dependent motor and postural signs of inebriation, they display ethanol-induced disruption of cognitive functions and social behavior, and they develop ethanol dependence. Moreover, they are small, easy to acquire and easy to maintain in the laboratory. Finally, we possess a vast database of information on their natural history, physiology, genetics and behavior, with their ethogram comprising a wide variety of basic to complex behaviors, including the capacity to self-administer large quantities of ethanol. The present article reviews what is currently known about the physiological and behavioral pharmacology of ethanol in honey bees. The topics covered include the effect of ethanol on gene expression, epigenetic changes of DNA, neuronal stress, posture, locomotion, learning (comprising classical and operant conditioning), communication, social feeding (trophallaxis), aggression and foraging-related decision-making in honey bees.

Tolerance and efficient metabolization of extremely high ethanol concentrations by a social wasp

Ethanol, a natural by-product of sugar fermentation, can be found in various fruits and nectar. Although many animals routinely consume ethanol in low concentrations as part of their natural diets, its inherent toxicity can cause severe damage. Even species particularly well adapted to ethanol consumption face detrimental effects when exposed to concentrations above 4%. Here, we investigated the metabolism of ethanol and its impact on survival and behavior in the Oriental hornet (Vespa orientalis), a social wasp that naturally consumes ethanol. We show that chronic ethanol consumption, even at concentrations as high as 80%, had no impact on hornet mortality, construction behavior, or agonistic behavior. Using 13C1 labeled ethanol, we show that hornets efficiently metabolized ingested ethanol and at a much higher rate than honey bees. The presence of multiple copies of the alcohol dehydrogenase (NADP+) gene in the Vespa genera suggests a potential mechanism for ethanol tolerance. These findings support the hypothesis that the mutualistic relationship between ethanol-producing organisms and vespid hosts may be at the origin of their remarkable capacity to utilize and metabolize ethanol.

Occasional and constant exposure to dietary ethanol shortens the lifespan of worker honey bees

Honey bees (Apis mellifera) are one of the most crucial pollinators, providing vital ecosystem services. Their development and functioning depend on essential nutrients and substances found in the environment. While collecting nectar as a vital carbohydrate source, bees routinely encounter low doses of ethanol from yeast fermentation. Yet, the effects of repeated ethanol exposure on bees' survival and physiology remain poorly understood. Here, we investigate the impacts of constant and occasional consumption of food spiked with 1% ethanol on honey bee mortality and alcohol dehydrogenase (ADH) activity. This ethanol concentration might be tentatively judged close to that in natural conditions. We conducted an experiment in which bees were exposed to three types of long-term diets: constant sugar solution (control group that simulated conditions of no access to ethanol), sugar solution spiked with ethanol every third day (that simulated occasional, infrequent exposure to ethanol) and daily ethanol consumption (simulating constant, routine exposure to ethanol). The results revealed that both constant and occasional ethanol consumption increased the mortality of bees, but only after several days. These mortality rates rose with the frequency of ethanol intake. The ADH activity remained similar in bees from all groups. Our findings indicate that exposure of bees to ethanol carries harmful effects that accumulate over time. Further research is needed to pinpoint the exact ethanol doses ingested with food and exposure frequency in bees in natural conditions.

Preliminary Analysis of Genetic Markers for Functional Ethanol Tolerance in Honey Bees (Apis mellifera) Using a Free-Flying Paradigm

Honey bees are a commonly used species for alcohol research due to their genome being fully sequenced, their behavioral changes following consumption, and their preference for alcohol. The purpose of this article is to provide a preliminary examination of the genetic expression of heat shock protein 70 (HSP70) and big potassium ion channel protein (BKP) in honey bees following the consumption of either 0%, 2.5%, 5%, or 10% ethanol (EtOH) solutions. The foraging behaviors of the bees were observed and recorded through their return and drinking times. There were significant differences in the return and drinking times between some of the groups. The bees in the 10% condition took significantly longer to return compared to the other groups. Additionally, the bees in the 5% group spent significantly more time drinking compared to the bees in the control (0%) group. There were no significant differences in HSP70 or BKP between the different ethanol groups. Cumulatively, these findings suggest that, while bees may exhibit behavioral differences, the differences in gene expression may not be observed at the transcriptional level.

The Effects of Ethanol and Acetic acid on Behaviour of Extranidal Workers of the Narrow-Headed Ant Formica exsecta (Hymenoptera, Formicidae) during a Field Experiment

Ethanol addiction belongs to the most important problems encountered in the domain of human mental health. The research on the behavioural effects of exposure to/consumption of ethanol are investigated largely with the help of animal models that also include insects, mainly fruit flies and honeybees. The effects of ethanol on ant behaviour remain, however, little known. In the present field study, we investigated the behaviour of workers of the narrow-headed ant (Formica exsecta) displayed in the vicinity of cotton pads soaked in water or in water solutions of ethanol or acetic acid during 5 min tests (n = 30 tests in each group). Both ethanol and acetic acid induced significant modifications of ant locomotion, exploratory behaviour, self-grooming behaviour, and aggressive social behaviour. We confirmed that acetic acid is aversive for the ants, but ethanol enhances their exploratory behaviour. We also found out that field studies may document more types of responses to experimental compounds than laboratory ones, as the tested animals may also escape from aversive substances. Our findings documented a wide spectrum of behavioural effects of exposure to ethanol and acetic acid in a highly social animal species and broadened the general knowledge about behavioural responses to these compounds encountered in animals.

Drug effect and addiction research with insects - From Drosophila to collective reward in honeybees

Animals and humans share similar reactions to the effects of addictive substances, including those of their brain networks to drugs. Our review focuses on simple invertebrate models, particularly the honeybee (Apis mellifera), and on the effects of drugs on bee behaviour and brain functions. The drug effects in bees are very similar to those described in humans. Furthermore, the honeybee community is a superorganism in which many collective functions outperform the simple sum of individual functions. The distribution of reward functions in this superorganism is unique - although sublimated at the individual level, community reward functions are of higher quality. This phenomenon of collective reward may be extrapolated to other animal species living in close and strictly organised societies, i.e. humans. The relationship between sociality and reward, based on use of similar parts of the neural network (social decision-making network in mammals, mushroom body in bees), suggests a functional continuum of reward and sociality in animals.

Discontinued alcohol consumption elicits withdrawal symptoms in honeybees

The honeybee continues to be developed as a model species in many research areas, including studies related to the effects of alcohol. Here, we investigate whether workers display one of the key features of alcoholism, namely withdrawal symptoms. We show that workers fed for a prolonged time on food spiked with ethanol, after discontinuation of access to such food, exhibited a marked increase in the consumption of ethanol and a slight increase in mortality. We additionally show that withdrawal symptoms do not include an increase in appetitiveness of ethanol diluted in water. Our results demonstrate that workers can develop alcohol dependence, which might be especially important in the natural setting of repeated exposure to ethanol in floral nectar and for their potential as a model of alcohol addiction.

Honey Bees (Apis mellifera) Show a Preference for the Consumption of Ethanol

BACKGROUND

Alcohol abuse and alcoholism are significant global issues. Honey bees are excellent models for learning and other complex behaviors; furthermore, they share many behavioral responses to ethanol (EtOH) with humans and animal models. We develop a 2-feeder choice assay to determine whether honey bees will self-administer and preferentially consume solutions containing EtOH.

METHODS

Gustatory responsiveness to EtOH is determined using the proboscis extension reflex and consumption assays. A 2-feeder choice assay is used to examine preference for the consumption of EtOH. Survival assays assess the metabolic and toxic effects of EtOH consumption.

RESULTS

Honey bees find the taste of EtOH to be aversive when in water, but addition of sucrose masks the aversive taste. Even though the taste of EtOH is not appetitive, honey bees preferentially consume sucrose solutions containing 1.25 to 2.5% EtOH in a dose-dependent manner. Based on survival assays, honey bees may not be able to derive caloric value from EtOH, and EtOH concentrations of 2.5% or higher lead to significant increases in mortality.

CONCLUSIONS

Honey bees will self-administer EtOH and show a preference for consuming solutions containing EtOH. Bees may not be able to efficiently utilize EtOH as an energy source, but EtOH-dependent increases in mortality complicate separating the effects of caloric value and toxicity.

Honeybees show adaptive reactions to ethanol exposure

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.

Prior social experience affects the behavioral and neural responses to acute alcohol in juvenile crayfish

The effects of alcohol on society can be devastating, both as an immediate consequence of acute intoxication and as a powerful drug of abuse. However, the neurocellular mechanisms of alcohol intoxication are still elusive, partly because of the complex interactions between alcohol and nervous system function. We found that juvenile crayfish are behaviorally sensitive to acute alcohol exposure and progress through stages that are strikingly similar to those of most other intoxicated organisms. Most surprisingly, we found that the social history of the animals significantly modified the acute effects of alcohol. Crayfish taken from a rich social environment became intoxicated more rapidly than animals that were socially isolated before alcohol exposure. In addition, we found that the modulation of intoxicated behaviors by prior social experience was paralleled on the level of individual neurons. These results significantly improve our understanding of the mechanisms underlying the interplay between social experience, alcohol intoxication and nervous system function.

Quality versus quantity: Foraging decisions in the honeybee (Apis mellifera scutellata) feeding on wildflower nectar and fruit juice

Foraging animals must often decide among resources which vary in quality and quantity. Nectar is a resource that exists along a continuum of quality in terms of sugar concentration and is the primary energy source for bees. Alternative sugar sources exist, including fruit juice, which generally has lower energetic value than nectar. We observed many honeybees (Apis mellifera scutellata) foraging on juice from fallen guava (Psidium guajava) fruit near others foraging on nectar. To investigate whether fruit and nectar offered contrasting benefits of quality and quantity, we compared honeybee foraging performance on P. guajava fruit versus two wildflowers growing within 50 m, Richardia brasiliensis and Tridax procumbens. Bees gained weight significantly faster on fruit, 2.72 mg/min, than on either flower (0.17 and 0.12 mg/min, respectively). However, the crop sugar concentration of fruit foragers was significantly lower than for either flower (12.4% vs. 37.0% and 22.7%, respectively). Fruit foragers also spent the most time handling and the least time flying, suggesting that fruit juice was energetically inexpensive to collect. We interpret honeybee foraging decisions in the context of existing foraging models and consider how nest-patch distance may be a key factor for central place foragers choosing between resources of contrasting quality and quantity. We also discuss how dilute solutions, such as fruit juice, can help maintain colony sugar-water balance. These results show the benefits of feeding on resources with contrasting quality and quantity and that even low-quality resources have value.

Ethanol-induced effects on sting extension response and punishment learning in the western honey bee (Apis mellifera)

Acute ethanol administration is associated with sedation and analgesia as well as behavioral disinhibition and memory loss but the mechanisms underlying these effects remain to be elucidated. During the past decade, insects have emerged as important model systems to understand the neural and genetic bases of alcohol effects. However, novel assays to assess ethanol's effects on complex behaviors in social or isolated contexts are necessary. Here we used the honey bee as an especially relevant model system since bees are typically exposed to ethanol in nature when collecting standing nectar crop of flowers, and there is recent evidence for independent biological significance of this exposure for social behavior. Bee's inhibitory control of the sting extension response (SER) and a conditioned-place aversion assay were used to study ethanol effects on analgesia, behavioral disinhibition, and associative learning. Our findings indicate that although ethanol, in a dose-dependent manner, increases SER thresholds (analgesic effects), it disrupts the ability of honey bees to inhibit SER and to associate aversive stimuli with their environment. These results suggest that ethanol's effects on analgesia, behavioral disinhibition and associative learning are common across vertebrates and invertebrates. These results add to the use of honey bees as an ethanol model to understand ethanol's effects on complex, socially relevant behaviors.

Invertebrate models in addiction research

While drug addiction is a uniquely human problem, most research examining the biological mechanisms of the transition from substance use to addiction is conducted with vertebrate animal models. Many other fields of neuroscience have greatly benefitted from contributions from simple and manipulable invertebrate model systems. However, the potential of invertebrate research has yet to be fully capitalised on in the field of addiction neuroscience. This may be because of the complexity of addiction and the clinical imperative of addiction research. We argue that the homocentric diagnostic criteria of addiction are no more a hindrance to the use of invertebrate models than they are to vertebrate models. We highlight the strengths of the diversity of different invertebrate model systems in terms of neuroanatomy and molecular machinery, and stress that working with a range of different models will aid in understanding addiction and not be a disadvantage. Finally, we discuss the specific advantages of utilising invertebrate animals for addiction research and highlight key areas in which invertebrates are suited for making unique and meaningful contributions to this field.

Ethanol self-administration in free-flying honeybees (Apis mellifera L.) in an operant conditioning protocol

BACKGROUND

This study examines the effect of ethanol (EtOH) on continuous reinforcement schedules in the free-flying honeybee (Apis mellifera L.). As fermented nectars may be encountered naturally in the environment, we designed an experiment combining the tools of laboratory research with minimal disturbance to the natural life of honeybees.

METHODS

Twenty-five honeybees were trained to fly from their colonies to a fully automated operant chamber with head poking as the operant response. Load size, intervisit interval, and interresponse times (IRTs) served as the dependent variables and were monitored over the course of a daily training session consisting of many visits. Experimental bees were tested using an ABA design in which sucrose only was administered during condition A and a 5% EtOH sucrose solution was administered during condition B. Control bees received sucrose solution only.

RESULTS

Most bees continued to forage after EtOH introduction. EtOH significantly reduced the load size and the intervisit interval with no significant effect on IRTs. However, a look on individual data shows large individual differences suggesting the existence of different kinds of behavioral phenotypes linked to EtOH consumption and effects.

CONCLUSIONS

Our results contribute to the study of EtOH consumption as a normal phenomenon in an ecological context and open the door to schedule-controlled drug self-administration studies in honeybees.

Physiological state influences the social interactions of two honeybee nest mates

Physiological state profoundly influences the expression of the behaviour of individuals and can affect social interactions between animals. How physiological state influences food sharing and social behaviour in social insects is poorly understood. Here, we examined the social interactions and food sharing behaviour of honeybees with the aim of developing the honeybee as a model for understanding how an individual's state influences its social interactions. The state of individual honeybees was manipulated by either starving donor bees or feeding them sucrose or low doses of ethanol to examine how a change in hunger or inebriation state affected the social behaviours exhibited by two closely-related nestmates. Using a lab-based assay for measuring individual motor behaviour and social behaviour, we found that behaviours such as antennation, willingness to engage in trophallaxis, and mandible opening were affected by both hunger and ethanol intoxication. Inebriated bees were more likely to exhibit mandible opening, which may represent a form of aggression, than bees fed sucrose alone. However, intoxicated bees were as willing to engage in trophallaxis as the sucrose-fed bees. The effects of ethanol on social behaviors were dose-dependent, with higher doses of ethanol producing larger effects on behaviour. Hungry donor bees, on the other hand, were more likely to engage in begging for food and less likely to antennate and to display mandible opening. We also found that when nestmates received food from donors previously fed ethanol, they began to display evidence of inebriation, indicating that ethanol can be retained in the crop for several hours and that it can be transferred between honeybee nestmates during trophallaxis.

The behavior and social communication of honey bees (Apis mellifera carnica Poll.) under the influence of alcohol

In this study, the effects of ethanol on honey bee social communication and behavior within the hive were studied to further investigate the usefulness of honey bees as an ethanol-abuse model. Control (1.5 M sucrose) and experimental (1.5 M sucrose, 2.5% w/v ethanol) solutions were directly administered to individual forager bees via proboscis contact with glass capillary tubes. The duration, frequency, and proportion of time spent performing social and nonsocial behaviors were the dependent variables of interest. No differences in the relative frequency or proportion of time spent performing the target behaviors were observed. However, ethanol consumption significantly decreased bouts of walking, resting, and the duration of trophallactic (i.e., food-exchange) encounters. The results of this study suggest that a low dose of ethanol is sufficient to disrupt both social and nonsocial behaviors in honey bees. In view of these results, future behavioral-genetic investigations of honey bee social behavior are encouraged.

Ethanol increases HSP70 concentrations in honeybee (Apis mellifera L.) brain tissue

Previous research on the honeybee ethanol model established how acute ethanol exposure altered function at different levels of organization: behavior and learning, ecology, and physiology. The purpose of this study was to evaluate whether ethanol doses that affect honeybee behavior also induce a significant stress response, measured by heat shock protein 70 (HSP70) concentrations, in honeybee brain tissues. Experiment 1 examined how pretreatment handling influenced brain HSP70 concentrations in three pretreatment groups of bees; immediately after being collected, after being harnessed and fed, and after 22-24h in a harness. HSP70 concentrations did not differ among pretreatment groups within replicates, although we observed significantly different HSP70 concentrations between the two replicates. Experiment 2 investigated the relationship between ethanol dose and brain HSP70 concentrations. Bees were placed in seven experimental groups, the three pretreatment groups as in Experiment 1 and four ethanol-fed groups. Bees in ethanol treatments were fed 1.5M sucrose (control) and 1.5M sucrose-ethanol solutions containing 2.5, 5, and 10% ethanol, allowed to sit for 4h, and dissected brains were assayed for HSP70. We observed ethanol-induced increases in honeybee brain HSP70 concentrations from the control group through the 5% ethanol group. Only bees in the 5% ethanol group had HSP70 concentrations significantly higher than the control group. The inverted U-shaped ethanol dose-HSP70 concentration response curve indicated that ingestion of 2.5% ethanol and 5% ethanol stimulated the stress response, whereas ingestion of 10% ethanol inhibited the stress response. Doses that show maximum HSP70 concentration (5% ethanol) or HSP70 inhibition (10% ethanol) correspond to those (> or =5% ethanol) that also impaired honeybees in previous studies. We conclude that acute ethanol intoxication by solutions containing > or =5% ethanol causes significant ethanol-induced stress in brain tissue that impairs honeybee behavior and associative learning.

Identification of Quantitative Trait Loci and candidate genes influencing ethanol sensitivity in honey bees

Invertebrate models have greatly furthered our understanding of ethanol sensitivity and alcohol addiction. The honey bee (Apis mellifera), a widely used behavioral model, is valuable for comparative studies. A quantitative trait locus (QTL) mapping experiment was designed to identify QTL and genes influencing ethanol vapor sensitivity. A backcross mating between ethanol-sensitive and resistant lines resulted in worker offspring that were tested for sensitivity to the sedative effects of alcohol. A linkage map was constructed with over 500 amplified fragment length polymorphism (AFLP) and sequence-tagged site (STS) markers. Four QTL were identified from three linkage groups with log of odds ratio (LOD) scores of 2.28, 2.26, 2.23, and 2.02. DNA from markers within and near QTL were cloned and sequenced, and this data was utilized to integrate our map with the physical honey bee genome. Many candidate genes were identified that influence synaptic transmission, neuronal growth, and detoxification. Others affect lipid synthesis, apoptosis, alcohol metabolism, cAMP signaling, and electron transport. These results are relevant because they present the first search for QTL that affect resistance to acute ethanol exposure in an invertebrate, could be useful for comparative genomic purposes, and lend credence to the use of honey bees as biomedical models of alcohol metabolism and sensitivity.

Characterization of honey bee sensitivity to ethanol vapor and its correlation with aggression

Several candidate genes identified from quantitative trait loci (QTL) for defensive behavior in honey bees (Apis mellifera L.) are homologous to genes known to influence ethanol sensitivity in other organisms. To investigate this possible link between aggression/defense and ethanol sensitivity, assays were developed to evaluate ethanol vapor responses in worker bees from a low-defensive (gentle) colony and a high-defensive colony. Defensive workers exhibited characteristic signs of ethanol-induced sedation significantly faster than gentle workers upon exposure to ethanol vapor. Backcross workers displayed ethanol sensitivity intermediate to the parental defensive and gentle lines, suggesting a genetic basis for the trait. Workers were screened with sequence-tagged site markers linked to three defensive-behavior QTL and their genotypes were tested for associations with ethanol sensitivity. There were no significant associations, indicating that the defensive QTL were not having a pleiotropic effect on ethanol sensitivity. It is possible that gentle-source alleles at these QTL are dominant with respect to sensitivity, one or more of these QTL were not segregating in the backcross family, or unidentified QTL are influencing alcohol sensitivity.

Ethanol levels in honeybee hemolymph resulting from alcohol ingestion

Our previous work on a social insect model of ethanol-induced behavior focused on behavioral studies of honeybees (Apis mellifera L.). We now investigate the dependence of honeybee blood ethanol concentration on both the amount of ethanol consumed and time elapsed since ingestion. Blood ethanol level was determined using gas chromatograph using hemolymph taken from harnessed bees. Significantly increased levels of ethanol in honeybee hemolymph were detected within 15 min of feeding bees alcohol. Within 30 min, ethanol concentration increased 2.7 times. The concentration of ethanol ingested also had a significant effect on blood ethanol level. However, postfeeding times greater than 30 min did not significantly increase ethanol concentration in bee hemolymph. This study integrates with our behavioral data on the effect of ethanol on honeybees. Our laboratory and field experiments show a correlation between the time frame for behavioral changes and significant increases of blood ethanol levels shown in this study.