Varroa

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A DANGEROUS BUT CONTROLLABLE PARASITE

 

Much is heard now about Colony Collapse Disorder and colony losses.  In one manifestation a formerly strong colony suddenly decamps, often in winter, or at least the great majority of bees leave, with just the queen and a few workers remaining. Such a colony is probably destined to dwindle away despite the presence of larvae and ample food to raise the next generation had enough bees remained to properly tend the young. Normally, immediate robbing and invasion by pests would be common in such weak nests, but not in the reported cases of CCD.  Such episodes of disappearing or dwindling colonies are not totally new; periods of significant colony losses have been reported at various times throughout modern beekeeping history.  Unfortunately, the exact cause(s) remain undetermined.  Several possible agents such as viruses, or a more lethal species of the nosema microsporidian have been identified, but whatever the truth it is accepted that a major contributor to bee ill-health is the varroa mite, either in combination with other elements, or alone. Varroa helps the transmission of viruses and other pathogens as it feeds on the bee.

Varroa is now resistant to the approved pyrethroid treatments and so these should not be used as they are no longer effective and will not reduced varroa mite numbers within the colony.

 

Detection and Monitoring

The easiest way to detect varroa is by placing an insert on the floorboard, preferably below a mesh so that the bees cannot clear out the debris.  The insert should be examined every few days.  Dead mites can be seen with the naked eye or with the help of a magnifying glass, say of x5 magnification.  For those uncertain of recognising the mite, ask an experienced colleague to look.  Alternatively, the mites’ presence may be revealed by uncapping some sealed drone brood.

Resistance to Acaricide Treatment

Varroa mites are resistant to the two synthetic pyrethroid treatments used in Britain (trade names Apistan and Bayvarol).  Neither of these products should be used . Apiguard, a thymol gel, and Apilife Var, a thymol and essential oil biscuit, are the only authorized treatment for varroa in the U.K. at present. However, with care, some organic acids may be used as “hive cleansers”. Whichever product is used, it is extremely important to follow the manufacturers’ instructions. Failure to do so may result in further resistance problems or contamination of honey.