Varroa

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Varroa

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Varroa is originally a parasite of the Asian bee race Apis cerana. Following the import of Apis mellifera in Asia to develop honey production there and a growing bee races commerce exchange throughout de world, varroa has become invasive in other bee species to become a pandemic problem.[1]

Varroa is omnipresent when beekeepers expose their problems.[2]

Apis cerana maintains a "balanced" relationship with the varroa mite, in which this bee race keeps varroa infestations at a level that is non-damageable for the colony thanks to a number of mechanisms developed in the course of its evolution that are explained in the following.

Apis cerana has an extremely developed hygiene behaviour, as far as both grooming and hive cleaning are concerned. Each bee intensively grooms itself and the other bees in the hive to knock down the mites. This behaviour is also observed in other races, but it is less intensive or targeted. Apis cerana immediately eliminates contaminated workers' brood as soon a contamination is detected. Consequently, varroa can develop in Apis cerana exclusively on drone larvae. This behaviour has not been observed in other bee races, which allows varroa to parasite also on female larvae in these races, even it has generally kept preferring drone cells.[3]

The brood times are markedly shorter in Apis cerana that in the European honeybee and leaves thus less time to varroa to successfully develop. Moreover, the drone brood period is restricted to a very short period of the year in Apis cerana, which restrict further the chances of the parasite to develop successfully.[3]

When a drone cell is infested by two varroas or more, the drone is not able to develop properly and will not hatch, thus the varroas will be kept trapped in the cell. The workers even sometimes add a supplementary "plug" on these cells. This behaviour as also been observed for cells infested by foul brood.[3]

Numerous other animals have been observed to coexist with the bees in Apis cerana hives, including pseudoscorpions.[4], which might be belong to the defence strategies of this bee race against varroa. It is not yet known if and in which measure Apis cerana "intentionally" raises or fosters pseudoscorpions in the hive.

These strategies have developed in Apis cerana over millennia in the course of its evolution, but, as varroa is a relatively new parasite in Apis mellifera, this race has not yet learnt a defensive behaviour as extensive or as systematic as the one of Apis cerana, which has allowed varroa to develop in an uncontrolled manner in the Western world.


References

  1. Wikipedia, 2009a: Varroa Destructor. http://fr.wikipedia.org/wiki/Varroa_destructor
  2. Granger G., 2009 : Survey on bee mortality in European bees, interviews wit beekeepers from different European countries, from December 2008 to June 2009. The results of the survey are not published and only available on demand.
  3. 3.0 3.1 3.2 Boecking O., 1999: How Apis cerana keep Varroa in check. Bees for development. http://www.beesfordevelopment.org/portal/article.php?id=1149
  4. Bérubé C., 2007: Himalayan ceranaid: Development assistance to preserve and promote Apis cerana beekeeping in Nepal. http://www3.telus.net/conrad/nepalbee.htm




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