a Mr Borst snip..
What might cause low sperm viability? Possibly inbreeding but more likely it’s the use of chemicals in the queen producer’s hives. I would be hesitant to accuse them of this, but I might try a different producer, or try raising some queens locally just to see the difference. Of course, it’s too late for that now, unless you are moving bees south for the winter.

My comments (largely formed by various experience at the Texas A&M 'Rangel' Lab)... 
I think it would be good to explore the possibilities here....   Certainly we know that chemical of various kinds will dramatically impact the queens viability and potential total life (ie early superscedure).  I have also sometimes wondered about the large number of very small time beekeeper (quite often with little experience in rearing queens and quite often limited bee stock) who are now distributing 'local' or 'survivor' stock and the large potential here for creating inbred stock?    

As to sperm viability... this is also a larger concern.  Don't know if the stuff is published yet but Dr Rangel (Texas A&M Bee Lab) and some students have done some interesting work on testing for drone sperm viability.  The study is ongoing with much of the data being obtained from various apiary sites of mine in Central Texas (+ three other beekeepers at one site each).  To my understanding from a purely technical aspect the same equipment that is used for equine sperm viability is used to test the drone sperm (basically the sperm is stained and the viability of the sperm rated as viable,  not viable or intermediate).  The phd student doing the study is now wrestling with the data and apply some GPS type programming to look for patterns in the data.  Personally I would not exclude nutrition as a contributing cause.      

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