Bees can suffer serious effects from toxic chemicals in their environment. This includes various synthetic chemicals, such as insecticides and fertilizers, as well as a variety of naturally-occurring chemicals from plants, such as ethanol resulting from the fermentation of organic material. Bee intoxication can result from exposure to ethanol from fermented nectar, ripe fruits, and manmade and natural chemicals in the environment.
The effects of alcohol on bees are sufficiently similar to the effects of alcohol on humans that honey bees have been used as models of human ethanol intoxication. However, the metabolism of bees and humans is sufficiently different that bees can safely collect nectars from plants that contain compounds toxic to humans. The honey produced by bees from these toxic nectars can be poisonous if consumed by humans. Many humans have eaten toxic honey and become quite ill as a result.
Natural processes can also introduce toxic substances into nontoxic honey produced from nontoxic nectar. Microorganisms in honey can convert some of the sugars in honey to the toxic compound ethanol. This process of ethanol fermentation is intentionally harnessed to produce the alcoholic beverage called mead from fermented honey.
The introduction of certain chemical substances—such as ethanol or pesticides or defensive toxic biochemicals produced by plants—to a bee's environment can cause the bee to display abnormal or unusual behavior and disorientation. In sufficient quantities, such chemicals can poison and even kill the bee.
The effects of alcohol on bees have long been recognized. For example, John Cumming described the effect in an 1864 publication on beekeeping.
When bees become intoxicated from ethanol consumption or poisoned with other chemicals, their balance is affected, and they are wobbly when they walk. Charles Abramson's group at Oklahoma State University has put inebriated bees on running wheels, where they exhibit locomotion difficulties. They also put honey bees in shuttle-boxes that used a stimulus to encourage the bees to move, and found that they were less mobile as they became more intoxicated.
A temulent bee is more likely to stick out its tongue, or proboscis. Inebriated bees spend less time flying. If a bee is sufficiently intoxicated, it will just lie on its back and wiggle its legs. Inebriated bees typically have many more flying accidents as well. Some bees that consume ethanol become too inebriated to find their way back to the hive, and will die as a result. Bozic et al (2006) found that alcohol consumption by honeybees disrupts foraging and social behaviors, and has some similar effects to poisoning with insecticides. Some bees become more aggressive after consuming alcohol.
Some honey bees like to consume fermented nectars containing ethanol more than others, and become notorious chronic inebriates around the hives. Bee colonies station guard bees outside the hives, and these reject the strangely-acting intoxicated bees, forcing them to stay out of the hive until they sober up. If a bee is a repeat offender and returns in an inebriated state to the hive too often, the "bee bouncers" will chew the offending bee's legs off.
Exposure to alcohol can have a prolonged effect on bees, lasting as long as 48 hours. This phenomenon is also observed in fruit flies and is connected to the neurotransmitter octopamine in fruit flies, which is also present in bees.
"Advances over the past three decades in our understanding of nervous systems are impressive and come from a multifaceted approach to the study of both vertebrate and invertebrate animals. An almost unexpected by-product of the parallel investigation of vertebrate and invertebrate nervous systems that is explored in this article is the emergent view of an intricate web of evolutionary homology and convergence exhibited in the structure and function of the nervous systems of these two large, paraphyletic groups of animals.
The behavior of honey bees intoxicated by ethanol is being studied by scientists at The Ohio State University, University of Oklahoma, University of Ljubljana in Slovenia, and other sites as a potential model of the effects of alcohol on humans. At the Oklahoma State University, for example, Abramson's research found significant correlations between the reactions of bees and other vertebrates to ethanol exposure.
"The purpose of this experiment was to test the feasibility of creating an animal model of ethanol consumption using social insects.... The experiments on consumption, locomotion, and learning suggest that exposure to ethanol influences behavior of honey bees similar to that observed in experiments with analogous vertebrates."
It has thus been found that "the honey bee nervous system is similar to that of vertebrates". These similarities are pronounced enough to even make it possible to derive information on the functioning of human brains from how bees react to certain chemicals. Julie Mustard, a researcher at Ohio State, explained that:
"On the molecular level, the brains of honey bees and humans work the same. Knowing how chronic alcohol use affects genes and proteins in the honey bee brain may help us eventually understand how alcoholism affects memory and behavior in humans, as well as the molecular basis of addiction."
The evaluation of a bee model for ethanol inebration of vertebrates has just begun, but appears to be promising. The bees are fed ethanol solutions and their behavior observed. Researchers place the bees in tiny harnesses, and feed them varying concentrations of alcohol introduced into sugar solutions. Tests of locomotion, foraging, social interaction and aggressiveness are performed. Mustard has noted that "Alcohol affects bees and humans in similar ways—it impairs motor functioning along with learning and memory processing."
The interaction of bees with antabuse (disulfiram, a common medication administered as a treatment for alcoholism) has been tested as well.
This problem has been the object of growing concern. For example, researchers at the University of Hohenheim are studying how bees can be poisoned by exposure to seed disinfectants. In France, the Ministry of Agriculture commissioned an expert group, the Scientific and Technical Committee for the Multifactorial Study on Bees (CST), to study the intoxicating and sometimes fatal effects of chemicals used in agriculture on bees. Researchers at the Bee Research Institute and the Department of Food Chemistry and Analysis in the Czech Republic have pondered the intoxicating effects of various chemicals used to treat winter rapeseed crops. Romania suffered a severe case of widespread bee intoxication and extensive bee mortality from deltamethrin in 2002. The United States Environmental Protection Agency (EPA) even has published standards for testing chemicals for bee intoxication.
Detzel and Wink (1993) published an extensive review of 63 types of plant allelochemicals (alkaloids, terpenes, glycosides, etc.) and their effects on bees when consumed. It was found that 39 chemical compounds repelled bees (primarily alkaloids, coumarins and saponins) and 3 terpene compounds attracted bees. They report that 17 out of 29 allelochemicals are toxic at some levels (especially alkaloids, saponins, cardiac glycosides and cyanogenic glycosides).
Various plants are known to have pollen which is toxic to honey bees, in some cases killing the adults (e.g., Zigadenus), in other cases only a problem when passed to the brood (e.g., Heliconia). Others plants which have toxic pollen are Spathodea campanulata and Ochroma lagopus. Both the pollen and nectar of the California Buckeye (Aesculus californica) are toxic to honeybees, and it is thought that other members of the Buckeye family are also.
However, the flower is constructed in such a way as to make the surface almost impossible to cling to, with smooth, downward-pointing hairs; the bees commonly slip and fall into the fluid in the bucket, and the only navigable route out is a narrow, constricting passage that either glues a "pollinium" (a pollen sack) on their body (if the flower has not yet been visited) or removes any pollinium that is there (if the flower has already been visited). The passageway constricts after a bee has entered, and holds it there for a few minutes, allowing the glue to dry and securing the pollinium. It has been suggested that this process involves "inebriation" of the bees, but this effect has never been confirmed.
In this way, the bucket orchid passes its pollen from flower to flower. This mechanism is almost but not quite species specific, as it is possible for a few closely-related bees to pollinate any given species of orchid, as long as the bees are similar in size and are attracted by the same compounds.
The Gongora horichiana orchid was suspected by Lanau (1992) of producing pheromones like a female euglossine bee and even somewhat resembles a female euglossine bee shape, using these characteristics to spread its pollen:
"A hapless male bee, blind drunk with the flower's overpowering pheromones, might well mistake a toadstool for a suitable mate, but the flower has made at least a modest attempt at recreating a beelike gestalt.
However, this seems unlikely, given that no one has ever documented that female euglossines produce pheromones; male euglossines produce pheromones using the chemicals they collect from orchids, and these pheromones attract females, rather than the converse, as Cullina (2004) suggests.
There have been famous episodes of inebriation of humans from consuming toxic honey throughout history. For example, honey produced from nectar of Rhododendron ponticum (also known as Azalea pontica) contains alkaloids that are poisonous to humans but do not harm bees. Xenophon, Aristotle, Strabo, Pliny the Elder and Columella all document the results of eating this "maddening" honey. Honey from these plants poisoned Roman troops in the first century BCE under Pompey the Great when they were attacking the Heptakometes in Turkey. The soldiers were delirious and vomiting after eating the toxic honey. The Romans were easily defeated.
Honey produced from the nectar of Andromeda flowers contains grayanotoxins which can paralyze the limbs, and eventually the diaphragm and result in death. Honey obtained from Kalmia latifolia, the calico bush, mountain laurel or spoon-wood of the northern United States, and allied species such as sheep laurel (Kalmia angustifolia) can produce sickness or even death. The nectar of the "wharangi bush", Melicope ternata, in New Zealand also produces toxic honey, and this has been fatal. The dangers of toxic honey were also well-known among the Pre-Columbian residents of the Yucutan Peninsula, though this was honey produced by stingless bees, not by honey bees, which are not native to the Americas. Bee nectar collection from Datura plants in Mexico and Hungary, belladonna flowers, henbane (Hyoscamus niger) plants from Hungary, Serjania lethalis from Brazil and Gelsemium sempervirens from the American Southwest can all result in toxic honey.