A Sting in the Tale

by Dave Goulson

  Of course if we find that commercial bees are established in the wild in Britain, or that they have hybridised with our native bees, there is not much that we can do about it. It may be that the trade in commercial Bombus terrestris has irrevocably muddled the genetics of this species throughout its range, which extends through much of Europe and a chunk of Asia. If it has, then we have lost for ever the local races that once existed. Sad though this might be, I do not think that it is the biggest cause for concern with regard to commercial bumblebees.

  My greatest worry relates to disease. The diseases of honeybees have been studied fairly intensively for many years as they have obvious impacts on beekeeping and honey production. Honeybees are known to suffer from a broad range of viral, bacterial, fungal and protozoan diseases, as well as larger parasites such as mites. In contrast, before the 1990s we knew almost nothing about bumblebee diseases until a Swiss zoologist named Paul Schmid-Hempel turned his attention to them. Paul and his students have been prolific in their findings and much of what we now know about bumblebee diseases comes from them, but as I am sure Paul would admit, we have still only begun to scratch the surface. It has become clear that bumblebees suffer from as broad a range of diseases as do honeybees. Many of them are fairly closely related to the honeybee diseases – for example, honeybees are attacked by the protozoan Nosema apis while bumblebees are attacked by the sister species Nosema bombi. Bumblebee viruses have not yet received serious attention, but it seems that some viruses known from honeybees also turn up in bumblebees. The descriptively named Acute Bee Paralysis Virus and Deformed Wing Virus have both been found in wild bumblebees, and for all we know they may well also infect other bee species and perhaps other insects. At the moment, we know almost nothing about the natural geographic ranges of most of the diseases that infect bumblebees, which bumblebee or other bee species they infect, what harm they do to their hosts, and to what degree there are different strains of diseases in different countries.

  Unfortunately, mass-rearing of bumblebees provides a great environment for the multiplication of disease, no matter how carefully it is done. All diseases spread more quickly when their hosts are packed closely together. Taking bees reared at high density and then shipping them thousands of miles to places where the bees themselves and any diseases they might be carrying do not naturally occur is an incredibly risky strategy. In fact, if one wished to spread bee diseases indiscriminately around the globe it would be hard to come up with a better system. Of course the companies involved do their best to combat disease. Major outbreaks in their factories would be enormously costly; all of the factories I have seen are clean, with protocols in place to reduce the spread of any diseases that appear. Sickly nests are destroyed, and samples of bees are regularly screened. Nonetheless, when scientists examine the nests that leave these factories, they often report them to be infected with a range of diseases. I am currently co-supervising Pete Graystock, a PhD student based at the University of Leeds in the lab of Bill Hughes (himself a former PhD student of mine from my Southampton days). Pete has been using genetic tools to detect the DNA of parasites in commercial bumblebees, which is the most sensitive technique currently available. He has examined nests from the three main companies that supply bumblebees to the UK, and has found Nosema bombi and Apicystis bombi to be common in nests from all three. These are nasty diseases, which can readily kill their hosts. He also found Crithidia bombi in some, and Deformed Wing Virus in others. If Pete’s data are correct, this is pretty damning evidence that, despite the extensive precautions used in the factories, their bumblebees are riddled with diseases.

  If these commercial bees are infected, then just as the bees themselves are certain to escape, so are their diseases. If these escape into a part of the world where they do not naturally occur, they could have a devastating impact on native bees that may lack resistance to them. One of the major reasons for the collapse in populations of Native Americans following the arrival of Europeans was their exposure to European diseases. Influenza, chicken pox, measles and the like, which rarely prove deadly to Europeans, caused devastating loss of life amongst Native American tribes. Interestingly, exactly the same thing might have happened with North American bumblebees. In the 1990s, queens of various North American bumblebees were taken to Europe and reared in factories alongside the European buff-tails. The established nests were then returned to North America. Shortly afterwards, the western bumblebee, yellow-banded bumblebee and rusty-patched bumblebee, all widespread and common species, suddenly disappeared from much of their range. These species are all closely related. Their only other close relative in North America, Franklin’s bumblebee, was always very rare but now seems to have disappeared entirely. Intensive searches for it in sites where it used to occur in northern California and Oregon have failed to find a single one since 2006, so it may have gone globally extinct. An entire group of closely related bumblebees has been devastated across a continent in the space of a few short years. To put this in context for European readers, this would be the equivalent of the disappearance of ubiquitous species such as buff-tailed and white-tailed bumblebees, the everyday bees that make up the majority of those on garden flowers. Many conservationists in North America blame these declines on the accidental introduction of a European bee disease along with the nests that were shipped in from Europe. Nosema bombi is a popular candidate. Or it may be a viral disease that we have yet to identify. In truth we may never know. Almost nothing is known about the bumblebee diseases that were present in North America before the 1990s, although once again this could be examined by looking for their DNA in museum bumblebees. Studying the few survivors is unlikely to be revealing as they are presumably those that didn’t catch the disease, if indeed it was a disease that wiped them out.

  Whether or not a European disease is the cause of these terrible declines, the principle remains. Shipping bees around is inherently risky unless they can be guaranteed to be free of disease. Oddly, despite the commercial trade in bumblebees now being well over twenty years old, there is very little regulation. Honeybees cannot be transported between most countries unless they have been certified free of an agreed list of their major diseases, but no such regulations have been applied to bumblebees. In the UK, there are no independent checks whatsoever on the bumblebees that are shipped in, despite Defra being well aware of the situation – they paid me to provide them with a report on the issue in 2009.

  All of this is of relevance not just to bumblebee conservationists and those who supply and use bumblebees for pollination. There is a bigger issue here. Honeybees have also suffered from major health problems in recent years, both in North America and Europe. One of the most significant of these is caused by the parasitic mite, Varroa. First discovered in Asia, this unpleasant creature sucks the blood of honeybees and their brood, and in doing so rapidly spreads viral disease within colonies. Unlike their Asian cousins, European honeybees – which are also the bees kept in North America – have very little resistance to Varroa, and it can rapidly destroy their colonies. It was accidentally introduced from Asia to Eastern Europe in the 1960s, and has since spread steadily and relentlessly westwards, arriving in the UK in 1992. It also turned up in North America in 1987 and New Zealand in 2000. The only country that it has yet to conquer is Australia. Beekeepers have been battling with Varroa ever since.

  In 2007, a new honeybee plague struck North America. During the winters of 2007 and 2008, commercial beekeepers in the USA lost between 30 and 90 per cent of their honeybee colonies. The symptoms were rather peculiar: there were no corpses. The adult bees had simply disappeared, leaving behind tens of thousands of empty honeybee hives. Various terms were coined for this phenomenon, my favourite being Marie Celeste Syndrome, but these days it is generally known by the clumsy name of Colony Collapse Disorder, or CCD for short. Beekeepers in Europe heard about the catastrophe in the USA, and when rumours of heavy colony losses in the UK surfaced in 2008 there was something approaching hysteria at
the prospect that CCD had crossed the Atlantic. There was wild speculation as to the causes – disease, pesticides, intensive farming, GM crops, even mobile phones were variously blamed, and the media had a field day. In fact the rumours of colony losses in Europe were rather exaggerated; and often when colonies did die it was due to obvious causes and not CCD. It is unclear whether CCD affected honeybees in Europe at all, not least because we still have little idea what CCD actually is. In the USA scientists have been frantically searching for the cause, but five years later we are not much wiser, and the heavy colony losses seem to have ceased, or at least declined. Most experts think that there isn’t a single cause – that it probably involves one or more diseases, perhaps viruses, but that some other factors such as exposure to pesticides may trigger outbreaks.

  To provide a bit of perspective on CCD, it is worth noting that it is normal for perhaps 10 to 25 per cent of honeybee colonies to die every winter, due to a variety of causes. Also, CCD is probably not new. There are records from 1869 of outbreaks of ‘disappearing disease’, which certainly sounds very similar, making the mobile phone theory look rather flimsy.

  Whatever the truth behind CCD, there is no denying that honeybee keepers the world over are having a tough time, and that diseases of one sort or another are a major part of their problems. How does this relate to the commercial trade in bumblebees? To rear bumblebee colonies, you need pollen – lots of it. To rear hundreds of thousands of bumblebee colonies, you need lorry-loads of pollen. One million nests – a conservative estimate of the European trade – probably requires in the region of 500 metric tonnes of pollen each year. Unfortunately, there is only one way to get hold of these sorts of quantities of pollen – from honeybees. Pollen can be collected from honeybee hives by fitting a metal grille to the entrance. The grille has holes that are just large enough for honeybees to squeeze through, but small enough so that the balls of pollen on the legs of returning foragers get knocked off into a collecting tray beneath. It seems a little cruel as the poor bees spend all day foraging only to have the fruits of their labour repeatedly snatched away just as they get home, but it doesn’t do them any real harm. Of course you can’t attach one of these grilles to a honeybee hive for too long or the colony would run out of pollen and the brood would begin to starve. To obtain the quantities of pollen required, the factories must buy it from beekeepers all over Europe. Are the honeybee hives from which the pollen is obtained all free of disease? This seems highly unlikely, perhaps impossible, since almost all honeybee hives have some viral and fungal diseases. Hence tonnes of pollen, almost inevitably contaminated with a range of bee diseases, are shipped into the factories, and there it is fed to bumblebees, which are then despatched all over the world. We know that bee viruses such as Deformed Wing Virus will readily infect both bumblebees and honeybees, so it is no surprise that Pete Graystock found it in commercial bumblebee nests. Honeybee diseases to which bumblebees are immune may also be spread, simply because the bumblebee nests are shipped out with a supply of pollen inside them, and as soon as the bumblebees are deployed at their destination the workers will fly out and start visiting flowers, perhaps carrying contaminated pollen on their bodies.

  A lot of time and money is spent on trying to control and manage the spread of honeybee parasites and diseases; many countries including the UK employ bee inspectors to keep an eye on the health of honeybees in their area. At the same time, almost no attention is being paid to the mass transport of bumblebees. It is quite likely that the bumblebee trade has led to the wholesale redistribution of bee diseases around the globe, including those that infect honeybees. It may have had something to do with CCD in honeybees. Parasitic mites from Europe have been accidentally spread to Japan with commercial bumblebees, and they now attack native Japanese bumblebees. In Chile and Argentina there is a strong suspicion that non-native diseases that arrived with imported bumblebees are responsible for rapid declines of the giant native Bombus dahlbomii, the only bumblebee that is native to southern South America. Crithidia bombi and Apicystis bombi may not be native to South America, but they are rapidly spreading with introduced buff-tails from Europe and ruderal bumblebees from the UK, along with who knows what else. Buff-tails could easily spread through much of South America, using the cool temperatures found at altitude in the Andes to spread northwards towards the equator, and if other native South American species respond in the way that Bombus dahlbomii has, then it is conceivable that many of them could be wiped out.

  I don’t want to paint a picture of the commercial bumblebee breeders as irresponsible cowboys. Of course they are in the business of making money, but it is not in their interests to spread bee diseases, or to have non-native bumblebees escape into new environments. Most of these companies also supply biological control agents, and actively promote them as alternatives to chemical pesticides. Many of the staff involved in bee-rearing are passionate about bumblebees, and mortified at the suggestion that they might be doing harm. Two of the bigger companies recently started rearing native buff-tails (Bombus terrestris audax) for the UK market, following criticism that they were shipping in non-native bees. Nonetheless, there is mounting evidence that current practices are threatening the health of wild bees the world over. It is high time that strict hygiene regulations were imposed on the bumblebee trade, before any more disasters occur. It would be better still if local, native bees were reared in factories in the country where they are to be used, negating the need for long-distance transport. The native buff-tails being reared for use in the UK are currently bred in factories in mainland Europe and shipped in. Some countries, such as Canada, New Zealand and Turkey, have banned importation of bumblebees. This has forced companies to set up local factories producing local bees, something they are not keen to do since it is cheaper to have just one large factory and distribute bee nests from there. Unfortunately, the UK government seems loath to go down this route, despite the environmental benefits and the opportunity to create jobs.

  Is there an alternative to using commercial bumblebees to pollinate crops? For tomatoes in glasshouses, the answer is probably no. Farmers would certainly not want to return to using teams of labourers with vibrating wands. However, commercial bumblebees are increasingly being used to pollinate outdoor crops such as strawberries, blueberries and apples. Farmers used to rely upon wild bees to visit such crops, but are increasingly of the opinion that there are not enough wild bees to go around. In the pear orchards of Sechuan in China, intensive farming has all but eradicated wild bees, and the farmers now pay locals to clamber amongst the trees each spring armed with a paintbrush and a jar of pollen, with which they hand-pollinate every flower. This is just about viable in China, where labour is plentiful and very cheap, but it is not an option for most farmers elsewhere. In Canada, intensive blueberry farming over vast areas has also led to low populations of native bumblebees, for there are few wild flowers for them to feed on when the blueberries themselves are not in flower, and there are also few places for them to nest. Just as in China, widespread pesticide use no doubt exacerbates the problem. Many blueberry farmers now buy in commercial nests of the native common eastern bumblebee, Bombus impatiens, to pollinate their crop. On the soft-fruit farms of Perthshire, most farmers now buy in dozens, in some cases hundreds, of buff-tail nests each year. The majority are placed in polytunnels to pollinate raspberries, while some are used outdoors for strawberries. The raspberry polytunnels have open ends and the plastic on the sides is rolled up in summer, so both raspberries and strawberries could be pollinated by wild bumblebees if there were enough. Clearly most farmers think that there are not.

  I was a little suspicious about this. On the one hand, it is hard to imagine a Scottish farmer spending £40 per nest on bumblebees if he didn’t have to. On the other, strawberry and raspberry yields vary a lot from year to year, and it would be very difficult for a farmer to know for sure what benefit he was getting from commercial bumblebee nests unless he did a proper experiment. There are u
mpteen examples of clever marketing persuading folk to buy products that are no use whatsoever. The cosmetics industry depends upon it.

  So it was that in 2010 I employed one of my former PhD students, Gillian Lye, to look into this, funded by a little money I had left over from a previous grant. She placed four commercial bumblebee nests next to a half-hectare plot of raspberries near Dundee, mimicking the recommended density of six to nine nests per hectare of crop. She opened and shut the doors on the nests at weekly intervals so that we could compare fruit set and raspberry yield in weeks with and without the aid of commercial bees. Lots of wild bumblebees came to pollinate the raspberries – white-tails, buff-tails, early bumblebees, common carders, even the beautiful bilberry bumblebees which have enormous red bottoms. (I admit, an enormous red bottom doesn’t sound beautiful, but reserve judgement until you’ve seen one.) Quite a few honeybees turned up, presumably from nearby hives. Yet despite all these bees, the yield increased on average by 8.3 per cent when the commercial nest boxes were opened. I must confess that I was dismayed by this result, although I shouldn’t have been. Scientists are supposed to do experiments without looking for a particular result; we are meant to strive to be impartial at all times, else we risk subconsciously biasing our results in some way. Nonetheless, I had hoped that the commercial bees would prove to be unnecessary; if they had, I could have used the evidence to persuade farmers not to buy them.

  Of course 8.3 per cent doesn’t sound very much, but when translated into cash the figures are more impressive, for raspberries are a valuable crop. Gillian estimated that the commercial bumblebees increased yield from this half-hectare plot by 63 kilograms per week, and since the colonies last about six weeks this equates to an extra 378 kilograms of raspberries, worth approximately £2,259, for an outlay of about £160. Of course commercial farms are much larger than this, and the larger the stand of crop, the less able wild bees are likely to be to provide anywhere near adequate pollination, so on the basis of this study, purchasing commercial bumblebees looks like a very sensible option for raspberry farmers.