Hygienic Bees Do Not Remove Healthy Brood By Mistake

Research Paper Results

​​Could hygienic behaviour harm a colony? One possibility is that in addition to removing dead or diseased brood, hygienic workers remove healthy brood by mistake. This study shows that this does not happen. There is no correlation between the removal of freeze killed brood (FKB) from sealed cells (hygienic behaviour) and the removal of healthy brood.

 10 colonies in normal hives were studied in Sussex, UK. All colonies were tested 3 times at weekly intervals in July and August 2012 using the FKB removal test. The 10 colonies showed a wide range in hygienic behaviour, removing as few as 22.2% to as high as 100% of the FKB within 48 hours.
 
As the FKB tests were made, other areas of the FKB test frame containing untreated brood with no visible signs of disease were photographed and monitored over the same 48 hour period. The untreated brood were put into four categories: eggs, young larvae in uncapped cells, older larvae in uncapped cells, and capped cells. These brood were all more than 2 cm from the patches of capped brood that were killed with liquid nitrogen during the FKB test, and so were unharmed.
 
In total, 8588 cells containing non-frozen brood were monitored. Of these, 11.9% were empty 48 hours later showing that a considerable proportion of apparently healthy brood were removed.
 
Statistical tests showed that there was no correlation between the removal of FKB from capped cells (i.e., hygienic behaviour) and the removal of healthy brood in any of the 4 categories (eggs, young larvae etc.). In addition, there was not even a consistent trend in this direction. Colonies that were more hygienic (greater FKB removal) actually removed less healthy brood in the case of young and old larvae in open cells, but removed more eggs and brood from capped cells.

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Reference
Bigio, G., Al Toufailia, H., Ratnieks, F. L. W. 2014a. Honey bee hygienic behaviour does not incur a cost via removal of healthy brood. Journal of Evolutionary Biology 27: 226-230.
 
Open access
http://onlinelibrary.wiley.com/doi/10.1111/jeb.12288/full
 
F. Ratnieks, April 2016