Since late 2006, honeybees in Europe and North America have been mysteriously disappearing. Once abuzz with activity, hives suddenly turned into honeycombed Marie Celestes. They still had plentiful supplies of honey, pollen and youngsters but the adult workers vanished with no traces of their bodies. The phenomenon has been dubbed colony collapse disorder (CCD). In the first winter when it struck, US hive populations crashed by 23% and in the next winter, they fell again by a further 36%.
Eager to avert the economic catastrophe that a bee-less world, scientists have been trying to find the cause behind the collapse. Amid wackier explanations like mobile phone radiation and GM crops, the leading theories include sensitivity to pesticides, attacks by the vampiric Varroa mite or a parasitic fungus called Nosema, infections by various viruses, or combinations of these threats.
In 2007, US scientists thought they had revealed the main villain in the piece, by showing that the an imported virus – Israeli acute paralysis virus (IAPV)- was strongly linked to empty hives. But since then, another group showed that IAPV arrived in the US many years before the first signs of CCD were reported. Other related viruses have also been linked to CCD hives, including Kashmir bee virus (KBV) and deformed wing virus (DWV).
To pare down these potential culprits, Reed Johnson from the University of Illinois compared the genetic activity of bees from over 120 colonies, including some affected by CCD and healthy ones that were sampled before the vanishing began. He looked at their digestive systems – one of the most places where infections and environmental toxins would start wreaking havoc.
The analysis didn’t offer any simple answers, but Johnson found some evidence to suggest that CCD bees have problems with producing proteins. In animal cells, proteins are manufactured in molecular factories called ribosomes. These factories assemble proteins by translating instructions encoded within molecules of RNA. Ribosomes themselves are partially built form a special type of RNA known as rRNA. And when Johnson looked at the guts of CCD bees, he found unusually high levels of fragmented rRNA.
This article is reposted from the old WordPress incarnation of Not Exactly Rocket Science. There’s been more work on CCD since, but I’m reposting this mainly because of some interesting follow-up research that will I will post about tomorrow.
In 2006, American and European beekeepers started noticing a strange and worrying trend – their bees were disappearing. Their hives, usually abuzz with activity, were emptying. There were no traces of the workers or their corpses either in or around the ghost hives, which still contained larvae and plentiful stores of food. It seemed that entire colonies of bees had apparently chosen not to be.
The cause of the aptly named ‘Colony Collapse Disorder’, or CCD, has been hotly debated over the last year. Fingers were pointed at a myriad of suspects including vampiric mites, pesticides, electromagnetic radiation, GM crops, climate change and poor beekeeping practices. And as usual, some people denied that there was a problem at all.
But a large team of US scientists led by Diana Cox-Foster and Ian Lipkin have used modern genomics to reveal a new villain in this entomological whodunnit – a virus called Israeli Acute Paralysis Virus or IAPV. By and large, the team found that where there was IAPV, there was CCD. The virus and the affliction were so stongly connected that Cox-Foster and Lipkin estimated that a hive infected with IAPV had a 96% chance of suffering from CCD. Once infected, the chances of a colony collapsing shot up by 65 times.
Earlier today, I published a post on how Japanese honeybees defend themselves from hornets with a mass defence that relies on heat and carbon dioxide. This article was originally written two years ago, and describes the slightly different tactic of Cyprian honeybees.
When Oriental hornets attack, Cyprian honeybees mob them in a huge ball that targets the breathing apparatus in the hornet’s abdomen. The hornets can’t breathe without expanding their abdomens and with sheer numbers, the bees strangle the hornets to death.
Hornets are giant wasps that pack a powerful sting. To most people, they can be a painful nuisance, but to honeybees, they’re killing machines. Hornets greatly outsize and overpower honeybees and a few individuals can decimate entire colonies.
Asian honeybees have developed a remarkable defence called ‘heat-balling’ against their local hornet, Vespa velutina. A giant ball of bees piles onto the predator, weighing it down while vibrating their wing muscles. The frenetic activity greatly increases the temperature inside the ball to about 46C – hot enough to cook the hornet alive, but five degrees under the bees’ maximum tolerated temperature.
Cyprian honeybees face a different predator, the Oriental hornet Vespa orientalis and unlike its wimpier cousin V.velutina, this species can take the heat. The Oriental hornet lives in hot, dry climates ranging from Central Asia to the Mediterrenean and it tolerates temperatures just as high as honeybees.
Heat-balling shouldn’t work on them. And yet, Cyprian bees still encase Oriental hornets in large balls. Surprisingly, the strategy works – despite their heat tolerance, the hornets still die. The bees’ stings are useless against the hornet’s tough cuticle and they barely use them. What could they be doing instead?
Rising temperatures and high carbon dioxide emissions are the means through which humans are inadvertently causing the decline of several species. But one animal actively uses both heat and carbon dioxide as murderous weapons – the unassuming honeybee.
With their stings and numbers, bees already seem to be well-defended but they are completely outgunned by giant hornets (right). These two-inch long monsters are three times longer than several times heavier than tiny honeybees and raiding parties can decimate entire hives. European bees mount little in the way of an effective defence, but Japanese bees aren’t so helpless. When their hives are invaded, they launch a mass counterattack.
Swarms of workers dogpile the hornet, pinning it down while vibrating their wing muscles. At the centre of this “heatball”, the frenetic buzzing heats up the hornet to a roasting 45 degrees Celsius.
Scientists have long thought that this manoeuvre bakes the hornet alive, for the bees that surround it are more resistant to high temperatures. But Michio Sugahara and Fumio Sakamoto from Kyoto Gakuen University have found that this isn’t the whole story.
Their astounding selflessness is driven by an unusual way of handing down their genes, which means that females actually have more genes in common with their sisters than they do with their own daughters. And that makes them more likely to put the good of their colony sisters over their own reproductive legacy.
The more related the workers are to each other, the more willing they will be to co-operate. So you might expect colonies of social insects with fairly low genetic diversity to fare best. But that’s not the case, and Heather Matilla from Cornell University has found that exactly the opposite is true for bees.
Bee queens will often mate with several males (a strategy called polyandry). It’s an unexpected tactic, for it means that the queen’s daughters will be more genetically diverse and slightly less related to each other than they would be if they all shared the same father. And that could mean that selfless co-operation becomes less likely.
Despite this potential pitfall, social insect queens do frequently sleep with many males, and all species of honey bee do this. There must be some benefit, and Mattila has found it. Together with Thomas Seeley, she showed that a genetically diverse colony is actually a more productive and a stronger one.
Chimps are known to make a variety of tools to aid their quest for food, including fishing sticks to probe for termites, hammers to crack nuts and even spears to impale bushbabies. But a taste for honey has driven one group of chimps in Gabon’s Loango National Park to take tool-making to a new level.
To fulfil their sweet tooth, the chimps need to infiltrate and steal from bee nests, either in trees or underground. To do that, they use a toolkit of up to five different implements: thin perforators to probe for the nests; blunt, heavy pounders to break inside; lever-like enlargers to widen the holes and access the different chambers; collectors with frayed ends to dip into the honey; and swabbers (elongated strips of bark) to scoop it out.
Some of the tools are even fit for the Swiss army, combining multiple functions into the same stick. For example, some were obviously modified at both ends, but one was blunt while the other was frayed, suggesting that they doubled as enlargers and collectors.
These observations were made by Christophe Boesch from the Max Planck Institute for Evolutionary Anthropology and they emphasise yet again the extraordinary brainpower of chimpanzees. It takes an uncommon intellect to be able to design and manufacture a suite of tools and use them in sequence to extract a foodstuff that’s hidden from sight.
Many plants depend so heavily on visits from bees that they go to great lengths to attract them, using brightly coloured flowers baited with sweet nectar. But some of their tricks are much subtler and are designed not to attract six-legged visitors, but to make their stay more convenient.
The majority of flowering plants have evolved special conical cells that line the surface of their petals and are found nowhere else. These cells provide the flower with a rougher texture that is indistinguishable to human fingers, but that provide just enough purchase for the claws of landing insects. Heather Whitney from the University of Cambridge found that these conical cells turn the petal into a more conducive landing pad, and bees can tell if a petal has these bonus features or not by the way it reflects light.
About 80% of flowering plants possess these conical cells, but some develop mutations that do away with them. The snapdragon can develop a fault in the MIXTA gene, which prevents petal cells from developing into a conical shape. The lack of cones means that more white light reflects from the flowers’ surface, giving them a paler pink colour and making them stand out from the rich magenta of their peers. Honeybees tend to ignore these paler flowers, even though they smell the same as the normal variety.