Winter Colony Loss

I’ed  like to discuss two scientific articles on the possible cause of colony loss over the winter period (referred to as colony collapse disorder (CCD) in English speaking countries). The first article was published in the peer reviewed online publication PLOS ONE this month.

In this study the researchers (and the beekeepers) collected and analysed data from a total of 86 colonies using the following scheme (abbreviated copy from the article);

  • During the last week of July 2011; >35 forager bees were collected from the closed hive entrance and tested for Nosema spp. presence.
  • During the first 2 weeks of August 2011 a sample of 50 bees was taken– 25 from frames with brood and 25 from frames without brood for pesticide residue analysis.
  • A minimum of 30 bees were sampled in an identical way for virus analysis.
  • Further a minimum of 50 cells with bee bread were sampled for pesticide and palynological (determine plant species from pollen) analysis.
  • Mature and half-ripe honey was sampled from each colony for pesticide residue analysis.
  • During the last week of July 2011 and last week of October 2011 approximately 200–250 bees per colony were sampled by the beekeeper for varroa infestation analysis.

From the analysis of these 6 data points the researchers come to a number of results some of which I’ll discuss here.

A weird result presented in the “Losses related to plant species” paragraph, seems the correlation between the presence of rapeseed and field mustard pollen in bee bread and colony loss over the winter period. Although this may be attributed to the higher prevalence of these species in rural areas where other factors will be prevalent, factors like neonicotinoids and other pesticides. Still, this is a weird result as wild mustard seed, for instance, is often included in seed mixtures advertised as bee friendly. I suspect it must be a “correlation does not imply causation” issue.

An other result that I thought surprising was under the “Virus and Nosema spp. related losses” heading. The study didn’t find a correlation between the presence of various viruses or Nosema and winter colony loss. I would have thought that there would be a clear connection between some viruses and CCD. Deformed wing virus (DWV) has a connection to Varroa destructor [link]. So if a colony has a high prevalence of DWV, it is safe to assume there is a Varroa infestation. The study did find a strong link (p<0.001) between Varroa mite load (in October) and winter colony loss, presented under the heading “Varroa mite related effects”. Nothing surprising about that result.

A result that is perhaps not as surprising is that the study found a link between neonicotinoids (neonics) and CCD. The study makes a distinction between where the neonics were found. The link was found in colonies where the neonics were found in either the honey or in the bees but not when it was found in the bee bread. That last result I think is slightly surprising as bee bread is fed to developing bees. Apparently neonic presence during development isn’t important but only neonic levels in adult bees is important.

The study concludes that the presence of Varroa mites the hives is the most important indication when it comes to winter colony loss or CCD and neonics second then rape/mustard seed then hive location.

The second article is slightly older (2014),  from the publication Bulletin of Insectology. I must say that the publications website doesn’t really inspire much confidence. Beside that, the scale of the study doesn’t really allow to be very confident on the verisimilitude (I like that word) of the conclusions. However I do wish to include the conclusions, you can read the article and you come to your own conclusions on the trustworthiness of the article.

Long story short the article comes to the conclusion that two neonicotinoids alone are capable of causing CCD. When six different hives were each given nonlethal doses of one of the two different neonics, those hives either didn’t survive winter or came out of winter crippled. Compared to six other hives that were treated “normaly”.

There was no difference between the two groups of colonies over the bee season and the lead up to winter, but during winter the difference was drastic. The authors pose that the differences are significant. The study doesn’t check for Varroa on the bees themselves and treats all the colonies equally for Varroa, so in essence removes the Varroa from the equation. The study gives me the impression that the conclusion was built into the design of the research.

I think I have more confidence in the results/conclusion of the first study. Not that I think that neonics/pesticides don’t play an important part but I don’t think there was ever any doubt about that. Beekeepers have little control over neonics but they are able to do something about Varroa. So I guess that is where beekeepers should focus their attention, I know I try to.


Other articles:
Multiple Routes of Pesticide Exposure for Honey Bees Living Near Agricultural Fields
Bee Experts Dismantle Touted ‘Harvard’ Neonics-Colony Collapse Disorder Study As ‘Activist Science’

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