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According to the web site of the film Vanishing of the Bees:
Bees are dying in their billions. In the UK, around one fifth of honeybee hives were lost in the winter of 2008/2009.
Is there evidence of bees disappearing and what are scientific theories on this subject?
I would hesitate to say that "bees are disappearing". But yes, there is a problem.
It's called Colony Collapse Disorder and there is nothing certain about why it happens. It's probably a combination of factors. The Wikipedia article is good. I've recently read some articles claiming that they have found a definitive link to some disease, but I can't find it right now, so I don't know if there is any good basis for the claim.
Update: The claims blaming the pesticide Imidacloprid seems promising and seem to be the strongest claims of a cause at the moment.
Current research by Jeff Pettis [1] shows that the most widely used pesticide, imidacloprid, compromises bees’ immune system even when present in sub-lethal doses. Bees thus weakened are very susceptible to infection with other pathogens.
Both of the groups that had been exposed to imidacloprid harboured an average of 700,000 parasite spores in each bee. Bees from the control colonies, by contrast, harboured fewer than 200,000 spores in their bodies. The insecticide, in other words, was exposing bees to infestation, and thus to a much greater chance of dying prematurely.
Other research [2,3,4] had similar findings. In fact, the pesticide may be enough in producing colony collapse disorder even without the presence of a pathogen, merely by affecting their nervous system, as suggested by Lu & al. [2]:
[T]o test the effect of even small amounts of these pesticides on western honeybees …, Harvard researchers treated 16 hives with different levels of imidacloprid, leaving four hives untreated. After 12 weeks, the bees in all twenty hives—treated and untreated—were alive, though those treated with the highest does of imidacloprid appeared weaker. But by 23 weeks everything had changed: 15 out of the 16 hives (94 percent) treated with imidacloprid underwent classic Colony Collapse Disorder: hives were largely empty with only a few young bees surviving. The adults had simply vanished. The hives that received the highest doses of imidacloprid collapsed first. Meanwhile the four untreated hives were healthy
They manage to replicate the exact conditions of colony collapse disorder. This suggests that their explanation is likely the correct one.
[1] Jeffery S. Pettis, Dennis vanEngelsdorp & al., Pesticide exposure in honey bees results in increased levels of the gut pathogen Nosema, Naturwissenschaften, Jan 2012. DOI 10.1007/s00114-011-0881-1
[2] Chensheng Lu, Kenneth M. Warchol, Richard A. Callahan. In situ replication of honey bee colony collapse disorder. Bulletin of Insectology. 2012.
[3] Penelope R. Whitehorn, Stephanie O’Connor, & al., Neonicotinoid Pesticide Reduces Bumble Bee Colony Growth and Queen Production, Science, Mar 2012. DOI: 10.1126/science.1215025
[4] Mickaël Henry, Maxime Béguin, & al., A Common Pesticide Decreases Foraging Success and Survival in Honey Bees, Science, Mar 2012. DOI: 10.1126/science.1215039
2 Studies have linked a pesticide (named only as a neonicotinoid) to CCD (NY Times: 2 Studies Point to Common Pesticide as a Culprit in Declining Bee Colonies)
Clothianidin is a Neonicotinoid so may be the chemical referred to in the article. (Wikipedia article has a NPOV warning but presumably that Clothianidin is a Neonictinoid is not disputed)
The Wikipedia article and a leaked EPA memo show that the EPA permitted only conditional registration because of fears about the toxicity to bees.
Clothianidin has not been used in Germany since 2009, but I have not seen any studies that show whether or not this has had an effect on the rate of CCD in Germany.
It might be the Varroa Mite.
The influx of tracheal and Varroa mites (particularly the latter), however, poses problems far greater than any faced before. From all indications, we can breed strains of tracheal mite-resistant bees and can do so ever better as we gain greater understanding of the interaction of those parasites with their bee hosts. Varroa mites, by contrast, feed on the blood of larvae, pupae and adults and can reproduce astonishingly fast; faster, that is, than the rate at which bee colonies can replace their losses.
The effect is called Colony Collapse Disorder.
Theres research that suggests that a pesticide named clothianidin is responsible for it.
