A Sting in the Tale (24 page)

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.