On 14 April Tim Arheit wrote:...."some big operators even go so far as testing a sample (several hives) from each
apiary [for mites], then treat the whole apiary based on the results".
This is the sort of commercial practice that leads to excessive use of chemicals and accelerates development of resistance to miticides. Varooa infestation within an apiary is very variable indeed - due to robbing of weakened colonies and following back.  Nowadays every hive needs a screen floor for individual monitoring, so you catch the just the ones needing treatment early.  Otherwise you can miss the big one until too late to avoid the mites spreading. Every Long Deep Hive has a permanent floor of mesh.  
Robin Dartington 

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