by Dave Goulson
There is one final twist to this tale. When out and about watching bees it soon becomes obvious that different species of bumblebee visit different species of flower. For example, almost the only visitors to foxgloves are garden bumblebees, plus the occasional common carder bumblebee, as only these species have a long enough tongue to reach the nectar. Similar but more subtle differences in floral preferences can be found within species, according to variation in size, not least because this relates to tongue length. Although foraging bees tend to be larger than nest bees, there is a lot of size variation within the foragers. In buff-tails, the tongues of the smallest foragers are just 4 millimetres long, while those of the largest are nearly twice this length.26 James caught and measured the size of hundreds of wild, foraging buff-tails in and around Southampton, and found that the average size and tongue length varied greatly depending on which flower he caught them on. White clover, bramble and oilseed rape attracted the smallest bees, greater knapweed and field beans the largest. The latter two flowers have deep corollas. He also recorded how long it took bees of different sizes to extract the nectar from particular flowers. Lo and behold, large bees with long tongues were quicker at getting nectar from deep flowers than smaller bees, but the converse was true on shallow flowers, where small bees came into their own.
James noticed that the floral preferences of bees of a particu-lar size were also influenced by the sturdiness of the flower. The biggest workers are pretty chunky beasts, the largest insects likely to land on most flowers. Some flowers simply cannot cope with their weight. Occasionally, a big buff-tailed bumblebee will land on a white clover, at which point the stalk of the flower often gives way and it collapses to the ground. The bee is left struggling to feed while lying on her back under the flower, which looks neither comfortable nor particularly efficient. They usually give up on white clover pretty quickly and go to find something else to feed on. In contrast, other flowers have very sturdy stems: viper’s bugloss and knapweed flowers can easily support the weight of large bees, and so provide them with a more attractive proposition.
All of this means that it makes absolute sense for a colony to produce foragers ranging in size, for this allows it to efficiently exploit a broad range of flowers in the surrounding area: small, short-tongued bees for shallow and weak-stemmed flowers, and bigger, longer-tongued bees for the sturdier and deeper flowers.
You might by now be wondering as to the relevance of the Darwin quotation at the start of this chapter. It was taken from a letter to his friend John Lubbock on 3 September 1862. The context is that the day before, Darwin had written to Lubbock with a request:
‘I write now in great Haste to beg you to look (though I know how busy you are, but I cannot think of any other naturalist who wd be careful) at any field of common red clover (if such a field is near you) & watch the Hive Bees: probably (if not too late) you will see some sucking at the mouth of the little flowers & some few sucking at the base of the flowers, at holes bitten through the corollas. All that you will see is that the Bees put their Heads deep into the head & rout about. Now if you see this, do for Heaven sake catch me some of each & put in spirits & keep them separate. I am almost certain that they belong to two castes, with long & short probosces. This is so curious a point that it seems worth making out. I cannot hear of a clover field near here. Pray forgive my asking this favour, which I do not for one moment expect you to grant, unless you have clover field near you & can spare 1/2 hour.’
Darwin had been watching honeybees foraging in a field of red clover near Southampton, where he had recently been staying, and had noticed that some were robbing the flowers through holes chewed at the base, while others were feeding from the conventional entrance to the flower. Darwin was familiar with ant species in which castes with different morphology perform different jobs, and he came to the notion that this might also apply to honeybees; he supposed that those feeding conventionally had long tongues, while the short-tongued bees robbed flowers from the side. He then fired off the request to Lubbock to test this idea for him. It seems that after sending this request, Darwin himself must have decided to sample some bees and measure their tongues. He realised that he had sent his friend on a wild goose chase – as we now know, honeybee workers are all of much the same size and tongue length – and so he sent his angst-ridden apology the very next day, finishing with, ‘I hate myself, I hate clover and I hate bees.’ It seems a little over the top, for so far as we know Lubbock never found time to look into this in the day between the arrival of the two letters. Of course, had Darwin asked his friend to carry out the same exercise with bumblebees, he might very well have found a positive result.
CHAPTER FOURTEEN
Ketchup and Turkish Immigrants
Time is honey.
Bernd Heinrich (American entomologist and marathon runner)
It is a common misapprehension that there is just one species of bee: they have yellow and black stripes and they sting; they live in wooden boxes, where they are looked after by bearded old men in funny hats and white suits; they pollinate crops and wild flowers; and they produce honey. Of course by now you know that much of this is untrue. There are perhaps 25,000 species of bee in the world. The bees kept by beekeepers are honeybees, and they don’t have yellow and black stripes – they are, in fact, largely tan-coloured. Some beekeepers themselves often believe or assume that all crop pollination is carried out by their honeybees, but in reality honeybees are absolutely hopeless at pollinating some crops such as runner beans or tomatoes, whilst they are good at pollinating others such as oilseed rape or kiwi fruit. Depending on their size, shape, behaviour and the length of their tongues, different bee species are suited to pollinating different types of flowers, and some plants are better pollinated by moths, or flies, or beetles.
It has long been known that bumblebees are effective pollinators of many crops and wild flowers. It was for this reason that they were taken to New Zealand (to pollinate red clover), and why the commercial rearing of bumblebees was developed by Dutch scientists in 1988, initially for tomato pollination. Breeding of bumblebees en masse is a tricky business. Back in 1912, Frederick Sladen described how to get queens to build nests in captivity, but he did not have the facilities to mate bumblebees or to hibernate the queens through the winter, so he could only get them to complete part of their life cycle. Since then, dozens of scientists and amateur enthusiasts have played around with rearing bumblebees. Sladen found that imprisoning queens for brief periods in a nest box with food would sometimes induce them to start nesting. He also discovered that putting two queens together seemed to help. One generally became subservient to the other, and the dominant one was likely to start laying eggs. Adding workers of the same or closely related species, or some pupae from another nest, also seemed to encourage queens to lay. Peculiarly, later scientists found that adding young honeybee workers also helped to stimulate the bumblebee queen into action; this technique is still widely used, and it is an odd sight to see a huge bumblebee queen in her nest being attended by relatively tiny and slender honeybees.
Sladen’s facilities were limited to what he could build in his father’s garden shed, but the widespread availability of equipment for maintaining controlled environmental conditions made life much easier for prospective bumblebee rearers in the second half of the twentieth century. It was discovered that queens seem to nest much more readily if kept at a constant 28°C and high humidity. Mating proved to be fairly easy so long as young queens and males were confined in reasonable numbers in brightly lit cages, and it was discovered that newly mated queens would readily hibernate in loose soil and could then be stored for months in a refrigerator.
By the 1970s enough had been learned to make it possible to take some bumblebee species through an entire year in captivity. Buff-tails seem to be particularly easy to rear, but other species such as the short-haired bumblebee are much more stubborn and even today very few people have managed to rear so much as a single nest in captivity.
The commercial possibilities of bumblebee rearing were not immediately realised. Most of those who had helped to develop the techniques were scientists who simply wanted nests to study and use in experiments. Rearing bumblebees was still highly labour intensive, and there seems to have been considerable scepticism that artificial rearing of nests could be commercially viable. This changed rather rapidly in 1985, when a Belgian veterinarian and amateur bumblebee enthusiast named Dr Roland De Jonghe found that placing a buff-tailed bumblebee nest in a glasshouse full of tomatoes provided a remarkably effective pollination service. Some crops, such as tomatoes and peppers, require buzz-pollination, the rapid vibration of the flower. The pollen-producing anthers are rather like an inverted pepper pot – they have to be shaken to release the pollen, and bumblebees are particularly adept at this. They grasp the anthers in their mandibles and then use their flight muscles to madly vibrate their body and the flower, at the same time adroitly catching the pollen as it falls out. Up until that time, tomato growers had been hand-pollinating tomatoes – employing teams of labourers with vibrating wands to touch every flower three times a week. The labour costs were enormous, amounting to about €10,000 per hectare per year. At that price, the effort of rearing a few bumblebee nests is comparatively trivial. What is more, De Jonghe found that both the quality and quantity of fruit produced was higher when pollinated by bumblebees. He realised he was on to a gold mine, and began rearing bumblebees for sale.
In 1987 De Jonghe founded the company Biobest, which remains today one of the largest commercial producers of bumblebees. In 1988 they produced enough bumblebees to pollinate just forty hectares of tomatoes. By the following year they were exporting to Holland, France and the UK. Others wanted in on the action; the Dutch company Koppert Biological Systems began rearing bumblebees in 1988, followed by Bunting Brinkman Bees, also Dutch, in 1989. The competition led to improvements in rearing techniques, which are jealously guarded by each of the producers, and drove down the cost of the nests. By 1990, the Canadians were using commercial bumblebees; the next year the USA and Israel joined them. Japan and Morocco soon followed suit. By the end of the millennium, bumblebee pollination had become the industry standard for tomatoes in almost every country in the world (excluding Australia, as we saw earlier).
Today, there are at least thirty factories in the world producing bumblebees, mainly buff-tails. Many of them originate from Turkey – for some reason Turkish buff-tails seem to be particularly amenable to mass production. The European factories produce well in excess of a million nests per year, and there are shipped all over the globe. I am one of very few people who have been inside several of the major rearing facilities, but I had to sign confidentiality agreements to get in, and hence, sadly, I am not at liberty to describe them in any detail. Suffice it to say that the scale of the operations is staggering – imagine vast white rooms the size of football pitches, with tall stacked ranks of bumblebee nests on shelves in row after row stretching into the distance, tended by teams of technicians in white lab coats sweating in the warm, sticky conditions.
From an environmental point of view, the switch to using bumblebees for tomato pollination has one substantial advantage. Growers have to be extremely careful in their use of pesticides, or else they risk killing their bees. This has forced many to turn to natural control agents, such as predatory insects, against the many pests that attack tomatoes – for example parasitic wasps to deal with whitefly – thereby substantially reducing pesticide use and providing healthier food for us to consume. Unfortunately there are also several downsides to commercial bumblebees, some of which will have become apparent from my description of the consequences of the arrival of bumblebees in Tasmania. In the Antipodes, there are serious risks that escaped bumblebees might worsen weed problems, but elsewhere there are other issues which are perhaps even more worrying.
Rearing and distributing bumblebees has a substantial carbon footprint; the factories themselves are vast and require heating and lighting. The nests are housed in disposable boxes made of a plastic inner box surrounded by polystyrene, in turn encased in cardboard. These boxes are often burned by farmers – they are not intended to be recycled. The nests are transported thousands of miles, sometimes across continents, to the places where they are used. None of this is good for the environment.
A second concern relates to the risk of these bees escaping into the wild and competing against or hybridising with native bees. Some of the commercial suppliers have argued that bumblebees can be contained within glasshouses so they won’t escape. This argument was put forward by the horticulture industry when lobbying the Australian government to allow the introduction of bumblebees to mainland Australia. Presumably fur farmers in the UK said the same thing before their mink escaped and ate most of our water voles. It is ludicrous to argue that bumblebees will not escape if tens of thousands of nests are imported and distributed across hundreds of farms, even if they are used in glasshouses. Glasshouses have to have vents for warm days, and doors for people to go in and out, and windows get broken, so of course bees will escape. In the UK, imported nests come with advice recommending that they should be destroyed after use by incineration or freezing, but in my experience many farmers throw them on a skip or simply leave them in place until all the bees have gone. Few farmers have sufficient freezer space to fit in the nests, and burning plastic and polystyrene boxes full of live bees is smelly, creates a cloud of toxic fumes, and seems rather cruel – poor thanks for the pollination services the bees have provided.
In Japan they have brought in laws insisting that all glasshouses in which bumblebees are to be used have netted vents and double doors, but since buff-tailed bumblebees have already escaped into the wild in Japan and are thriving there, this seems to be very much a case of shutting the glasshouse door after the furry black-and-yellow ‘horse’ has bolted. In any case, netting vents greatly reduces their effectiveness, increasing humidity and leading to fungal disease on the crops, so farmers are not keen to go down this route.
Just as in the UK, native Japanese bumblebee species seem to be having a hard time of it, for Japan is a similarly small and crowded island. Some Japanese researchers have suggested that the arrival of non-native buff-tails is adversely affecting some native bumblebees, but it is too early to be sure. The biggest threat may be to Bombus hypocrita,27 a relative of the buff-tail. It seems that young Bombus hypocrita queens are all too easily wooed by the suave foreigners, and readily mate with them despite their being of the wrong species. Such liaisons are disastrous for the queen for she only mates once, and sperm from buff-tailed males are unable to fertilise her eggs, so she is doomed to sterility. Recent studies suggest that 30 per cent of Bombus hypocrita queens suffer this fate in areas where buff-tails have become abundant.
Similar problems may be occurring in Britain and Ireland, where we have a distinct subspecies of buff-tailed bumblebee, formally known as Bombus terrestris audax, found nowhere else in the world (apart from New Zealand and Tasmania, to which they were introduced). The most obvious difference is the tail colour of the queens – our queen buff-tails have, as you might surmise, buff-coloured tails, although the workers’ tails are more or less white. In Europe, both the queens and the workers have white tails. The bees being imported to the United Kingdom, roughly 60,000 nests per year, are from Turkey and Greece and belong to the subspecies Bombus terrestris dalmatinus, although some of them may also be from France and Germany, in which case they would be Bombus terrestris terrestris – some of the factories are no longer quite sure of the origins of their stock, and to my eye they look much the same. In cages, British buff-tails readily mate with their Continental cousins, be they from Turkey or France, but unlike the situation with Bombus hypocrita this results in viable, hybrid offspring. Whether this is happening in the wild in Britain we do not yet know, but it seems likely. The hybrid offspring would not be obvious, since the buffness of the tails of our native queens is quite variable anyway. Hybrids
might have buff tails, white tails, or something in between – we don’t know, and I very much doubt anyone would notice whichever it was. It may be the case that Continental Bombus terrestris have escaped into the wild in the UK and established their own populations. They might compete with our native bees for food and nest sites, or they might not – we simply don’t know. If anyone spotted a queen bee in the UK with two yellow stripes and a pure white tail they would assume it was Bombus lucorum, the species we call the white-tailed bumblebee.
The only way to get a handle on this issue is to do extensive genetic testing. Lucy Woodall, a postdoctoral researcher in my lab at Stirling, has recently been doing some work on this in her spare time. She has found a genetic marker that appears to distinguish between our native buff-tails and those from the Continent, but she has also detected small numbers of the Continental type in samples taken from the wild in Britain. She has looked at only one gene so far, so we cannot say whether these are hybrids or pure-bred European bees. We also cannot be certain that bees of the European type don’t naturally occur in Britain – they might occasionally make it over the Channel. There is a simple way to find out though – by using museum specimens. If the Continental types currently in the UK result from the commercial trade, there shouldn’t be any of them among samples of buff-tailed bumblebees caught before 1988. Modern genetic techniques make it pretty easy to get DNA from old, dried specimens, provided the museum staff agree to let us chop a foot off some of the bees in their collections28. With luck we may have a definitive answer soon, although I’ll have to find someone to do the work as Lucy has just left Stirling for a job at the Natural History Museum in London, where she will be studying the DNA of deep-sea worms. My grant applications to fund work on this have thus far been rejected, but I shall keep trying.
