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We have a large garden in Bedfordshire, UK, next to woods and to arable fields currently planted with intensively farmed rape. We usually have many bees in the garden. Earlier this year, things were humming along as usual. A cotoneaster bush in flower had perhaps a hundred bees on it at once, of at least 6 different species.

Now, in July, we have lavender and clover in full bloom, normally swarming with bees. But, not now. This morning (overcast and warm) there were two bees on a lavender bush covering two square metres. I can walk for minutes in the garden without seeing a single bee. The leafcutter bees have left no holes in our rose leaves this year.

The nearest managed hives are about 800m away. It's not just a managed hive that has gone, the bumblebees that nest in our garden have gone too.

The rape flowers are long past. I don't know what might have been sprayed on the rape. Our garden is organic.

Wasps are down too. This is the first year in the last twenty that there are no wasp nests in our outbuildings. There are, however, plenty of flies.

What might have caused such a sudden and unusual population change? Among multiple species of bee from multiple sources, between April and July?

Could it be our globally-warmed weather? June and July have been wetter and warmer than usual, although not exceptionally so.

Are UK farmers allowed to use an insecticide on rape that could kill most bees?

Or is a dramatic in-year population change in bees a routine, if uncommon, event?

Thanks!

Update August 17 2016

Our garden bees do seem to be gradually recovering - nothing like most years, but a few bees are coming back. Other nearby houses, at least 400m from the nearest rape field, have plenty of bees.

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    $\begingroup$ Welcome to BiologySE - thanks for your question... though I think there could be numerous reasons and it may be very difficult to answer in this format. Do you have any specific ideas that someone could address in an answer? $\endgroup$ – Vance L Albaugh Jul 22 '16 at 17:24
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    $\begingroup$ This does seem to be a global phenomenon. In Poland, I was recently surprised to find a beekeeper travel across half the country to pick up a colony from a tree in an orchard. Said there were very few this year. I'd say I've observed fewer yellowjackets, too, but I could be mistaken. See Remi.b's answer about CCD. $\endgroup$ – kaay Aug 18 '16 at 8:40
  • $\begingroup$ relevant article in today's PloS Pathogens, oddly enough: journals.plos.org/plospathogens/article?id=10.1371/… $\endgroup$ – arboviral Aug 19 '16 at 17:37
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We call it Colony Collapse Disorder (CCD).

Consequences

The phenomenon is observed worldwide and is pretty serious. Northern Ireland lost 50% of its beehives for example. Between 1997 and 2003, 10 millions beehives were lost. Many cultivated crops are pollinated by bees and we don't quite have an alternative today. In 2005 a study showed that the worth of crops that are pollinated by bees is around 200 billions dollars.

Causes

Why? The short answer is "we don't know". There are a number of possible factors and the general consensus is to think that there is not a single factor that is causing the decline but it is a combination of different factors. Possible factors include:

  • Pesticides
  • Pathogens
  • Fungicides
  • Antibiotics
  • Miticides
  • Climate Change
  • migratory beekeeping
  • loss of genetic diversity through too intense selective breeeding
  • malnutrition
  • parasitic phlorid fly

More information

The wikipedia article for CCD is very complete. You should have a look at it!

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    $\begingroup$ I'm familiar with CCD, but can that affect all species of bees, multiple swarms of multiple species, in a small area, from a healthy population in spring to a low population in summer? Plus, I'm guessing that the population has dropped to a few percent of its usual value. Wouldn't that be extreme for CCD? $\endgroup$ – emrys57 Jul 22 '16 at 19:06
  • $\begingroup$ The first reference cited by the Wikipedia page (dx.doi.org/10.1371/journal.pbio.0050168) is a very accessible (though now slightly outdated) review of possible explanations for CCD. PloS Biology Unsolved Mysteries are a really interesting article format and mostly quite readable, even if you don't normally read primary scientific papers (and of course are all open access!). $\endgroup$ – arboviral Aug 19 '16 at 9:00
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Insecticides in the form of neonicotinoids (and possibly similar substances) can certainly be a factor, and they can affect a wide range of pollinating insects. It is also commonly used on rape seed. Have a look at this paper for some background:
Rundlöf et al. 2015. Seed coating with a neonicotinoid insecticide negatively affects wild bees. Nature (written partly by people from my department).

In it, they report that honey bees, solitary wild bees and bumble bees all are negatively effected by neonicotinoid-treated fields nearby, using paired fields in replicated landscapes. The effects could be seen in both population density, colony growth and reproductive success.

Much more has been written about this (check out references in paper above), and sorry for the short answer, but I don't have time for more at the moment. Other factors (weather, natural fluctuations etc) are certainly relevant as well. Also, from what I know, there is a neonicotinoid moratorium in the EU, so this might not be an issue where you live. I don't know if the ban is absolute, and to what extent it is enforced.

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    $\begingroup$ It's going to be hard to prove anything, but I am leaning towards this conclusion. These links: Independent, Nature show that neonicotinoids on rape are particularly harmful. Spraying this year seems to be illegal, but, who knows? Local bees about 800m distant from the nearest rape fields seem to be OK. $\endgroup$ – emrys57 Aug 17 '16 at 18:08
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The causes are multi factorial. Sick bees usually leave the hive and this behaviour may explain some cases of CCD, where a small number of bees and the queen are found with all other colony members missing. A colony can also leave "en masse" if they are about to starve in a last resort to find better forage. Pollinators are no longer able to adapt rapidly to the numerous threats facing them in 2017. The human activities listed in previous posts have caused the massive decline in all pollinators. Monoculture and pesticide useage being the main contributory factors. As a child I recall many dead insect on the car windscreen on weekend car journeys, this is a rare today.

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    $\begingroup$ as before - can you add some references so that others can read more about your answer and this topic in general? $\endgroup$ – Vance L Albaugh Feb 2 '17 at 22:36

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