June 2015 in Australia ccThehh senseeory mmiissttrryy world of bees

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ALSO IN THIS ISSUE: • One X-ray technique better than two • Haber’s rule and toxicity • Madeira wines worth the wait The tale in the Working and sensory lives DAVE SAMMUT g sBY tin of bees

18 | Chemistry in Australia June 2015 Bees have a well-earned reputation for pollination and honey-making, but their lesser known skills in electrocommunication are just as impressive.

ccording to the United Nations, ‘of Once the worker bee’s honey stomach is the 100 crop species that provide full, it returns to the hive and regurgitates the 90 per cent of the world’s food, partially modified nectar for a hive bee. The A over 70 are pollinated by bees’ hive bee ingests this material to continue the (bit.ly/1DpiRYF). It’s little wonder, then, that conversion process, then again regurgitates it bees continue to be a subject of study around into a cell of the honeycomb. During these the world. More surprising, perhaps, is that so processes, the bees also absorb water, which much remains to be learned. dehydrates the mixture. Bee-keeping (apiculture) is believed to Hive bees then beat their wings to fan the have started as far back as about 4500 years regurgitated material. As the water evaporates ago; sculptures in ancient Egypt show workers (to as little as around 10% moisture), the blowing smoke into hives as they remove sugars thicken into honey – a supersaturated honeycomb. In ancient Greece, Aristotle either hygroscopic solution of carbohydrates (plus kept and studied bees in his own hives or oils, minerals and other impurities). examined the observations passed to him by Some researchers think that the hive bees beekeepers. In doing so, he made some astute inject a venom into each comb, giving the conclusions; for example, that there are three honey its antibacterial properties; others classes of bees, one of which is sterile. Along dismiss this idea, saying that the high with his better observations, he thought concentration of sugars means that incorrectly that bees do not make honey and fermentation cannot happen. Either way, there instead that it is distilled from dew. seems to be general agreement that the acidic In reality, the manufacture of honey by bees nature of the honey is hostile to bacteria, is both complex and elegant. Honey varies in mould and fungi. composition depending on many factors (such In its entire lifetime (approximately seven as the different species of flower from which weeks, as compared to Aristotle’s estimate of the inital nectar is collected), but in general seven years), an average bee will produce less terms it is dominated by two key simple than a gram of honey. sugars: dextrose (glucose isomer) and But how does the worker bee select its levulose (fructose isomer), constituting over flowers in the first place? In 2013, Professor 70% by mass. It also contains aromatic volatile Daniel Robert and his team at the University of oils (giving it rich flavour), mineral elements, Bristol made a fascinating discovery ( Science ,

iStockphoto/ursusarctos some proteins, enzymes, vitamins and doi: 10.1126/science.1230883). colouring matter. It was already well known that bees generate Worker bees collect nectar from selected a positive charge as they move, and most flowers. Containing about 80% water, together particularly as they fly. It was also known that with complex sugars, this nectar is stored in a flowers generate a weak negative charge over special stomach (the ‘honey stomach’) where time. Using a Faraday pail (a sort of electrically the invertase enzyme secreted by the bee’s shielded bucket, similar to the wire cage in a salivary glands begins the process of breaking microwave oven), Robert and his team v

o down the sucrose in the nectar into simple measured this positive charge on individual l y a h glucose and fructose. Some of the glucose bees. They went on to demonstrate that when k i M n reacts with a second enzyme, glucose oxidase, the bee lands on a flower, this charge is a v I /

o to form gluconic acid and hydrogen peroxide, temporarily passed to the flower, and that for a t o h p creating conditions of low pH (3.2–4.5). period of minutes after the visit the flower will k c o t sucrose + O fructose + glucose have a measurably more positive charge. S

i 2

June 2015 Chemistry in Australia | 19 Sensational species The multiple senses that humans and their nerves, while fish also generate This electroception is caused by a animals possess beyond the ‘standard fields from the ion pumps associated multitude of biological mechanisms. five’ are fascinating. In humans, this with osmoregulation at the gill Sharks use field sensors called the includes mechanical senses for balance membrane. Some predators use this to ampullae of Lorezini: electroreceptor (‘equilibrioception’) or for locomotion detect their prey (sharks have been cells connected to seawater by pores in (‘propioception’), and many more. shown to attack any source of an their snout and head. Monotremes Electroreception is the biological electric field, which was a problem for (particularly the platypus, but also two ability to perceive electrical stimuli. In early telegraph cables), while others use species of echidna) use free nerve some species of the animal kingdom, the sense to avoid predators. endings located in the mucous these senses are highly developed – This has led to an ‘arms race’, for membranes of the snout. particularly in aquatic or wet terrestrial example in the evolution among some In species with ‘active environments where charge is carried fish species towards more complex or electrolocation’, the animal generates its better. As an example, some species of higher frequency electrical fields that own electrical field using a specialised shark can detect DC fields as low as are harder for their predators to detect. organ of modified muscle or nerves, and n a

k 5 nV/cm. Conversely, some species of fish then modifies the frequency and s o d a

l The most common usage is in communicate by modulating the waveform in a manner that might be v / o t electrolocation in predation. Living waveform of their electrical field, for unique to the species or even the o h p

k organisms generate small electrical fields mating and territorial displays. individual. c o t S i in the movement of their muscles and in

Most importantly, using artificial learn both the constant and the of non-human communications for flowers with a controlled electrical modulated electric field components learning, and it won von Frisch the charge, the Bristol team was able to in the context of appetitive proboscis 1973 Nobel Prize in Physiology or show that the bees could sense the extension response conditioning.’ Medicine. And now we know that electrical charge on the flowers, and (Proc. R. Soc. B , doi: 10.1098/ electrical fields also play their part in that they could be trained to use that rspb.2013.0528) this communication. charge to guide their activities. This The ‘waggle dance’ is itself a However, the waggle dance is not was a breakthrough – the first time that remarkable note in the journals of without controversy. Some experts electroreception had been science. Much like the Rosetta Stone argue that the waggle dance cannot documented in an invertebrate unlocking the secrets of hieroglyphics, give guidance on a nectar source, and species (see Sensational species box). the seminal work of zoologist Karl von that floral odour is actually the It now seems that bees also use Frisch unlocked in the mid-20th dominant method of recruiting bees to electrocommunication. In a paper to century the secrets of the movement of the source. For most of us, this is a the Royal Society in 2013, Greggers et successful foragers returning to the matter of nuance. It would seem that al. note that ‘the electric fields emitted hive. He correlated the dance to most scientists would agree that both by dancing bees consist of both low- directions on flower patches via mechanisms contribute, and that it is and high-frequency components. Both relative position of the sun and the only the relative weighting that is in components induce passive antennal distance from the hive, with different contention. For the antagonists, it is movements in stationary bees dances particular to different bee often a matter of polarised principle, according to Coulomb’s law. Bees species. It was the first demonstration even outright hostility.

20 | Chemistry in Australia June 2015 The honeybee can see only Investigating bee decline four basic colours, compared Bee populations, both wild and commercialised, are in to the 60 distinct colour decline globally. Current research is largely focused on trying to identify the causes of decline (called colony combinations collapse disorder in the US). The main areas under v o l y

a investigation are bee parasites (most particularly the h

from the three k i

M varroa destructor mite), use of pesticides and the build-up n a v I of toxins in the foraging environment, loss of biodiversity primary colour / o t o

h and foraging rich environments, spread of the Africanised p photoreceptors k c

o honey bee (in the US), and extremes of weather t S in humans. i associated with changing climates. Work is being done in gene manipulation of honey bees to protect them from mites, as well as research into alternative pollinators that can be used should bee populations fail catastrophically. Electroreception in bees is associated with a collection of Some recent good news in Australia is an innovative sensory cells in the second segment of the antennae called beehive design using a slight flexing of a plastic the Johnston’s organ, which detects motion in the flagellum framework to allow honey to flow directly out of the hive (the final antennal segment). As with other animals, the sense (literally honey on tap) for collection. This could have is mechanical, but it represents yet another mechanism for implications in the fight to strengthen bee colonies, by electroreception. It is a truly wondrous demonstration of the allowing more user-friendly beekeeping set-ups for the ability of evolution to take up every advantage available in the rapidly expanding urban apiarist markets. No smoking or physical world. And because the presence of the Johnston’s bee suits required! organ is a defining characteristic that separates the class Chantelle Craig insect from other hexapods, it opens the possibility of yet undiscovered behavioural triggers in invertebrates. Returning to the Bristol study, the researchers found that the electrical charge stimulus worked best in combination with colour triggers, and this brings me to another remarkable aspect of bees and the animal kingdom more generally. The honeybee can see only four basic colours, compared a i to the 60 distinct colour combinations from the three primary d e M

colour photoreceptors in humans. Their visible spectrum w o l F

stretches from about 300 to 650 nm, and they are red-blind. Yet a i d e

with their vision in the UV portion of the spectrum, bees can M

w o see a quite remarkable amount of detail in flowers that we l F cannot, which is obviously an evolutionary response between the two organisms. Indeed, the extensive publications of The cells of the honeycomb fracture during this new type of Professor Lars Chittka of Queen Mary University of London process, allowing the honey to flow down, but they don’t actually break. suggests that the photoreceptor abilities of ancestral bees pre-dated the existence of flowers by more than 100 million years, and that the colouration of flowers evolved in response to the bees’ ability, rather than the other way around. That there is a topic so thoroughly researched over such a long period, and with so many insights yet to offer, is simply delightful. Given the importance of bees to our global food supply, these advances in our understanding are of more than mere esoteric interest. They might one day become critical to our existence.

Dave Sammut FRACI CChem is principal of DCS Technical, a boutique scientific consultancy, providing services to the Australian and international minerals, waste recycling and general scientific industries. Honeybees on the plastic beehive framework.

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