Years ago when both tracheal and varroa mites were beginning to show up in  
US bees, I did a 48 month, large scale study for EPA placing  relatively 
large numbers of colonies at several apiaries near a lead smelter and  
sulfuric acid plant.  These were non-migratory, commercial colonies placed  in 
groups at apiaries in different compass directions and distances from  the 
industrial complex. 
 
Each month, we sampled each colony for both mites.  After 48 months we  
found - bee colonies exposed to the highest levels of heavy metals from the  
industrial complex succombed faster to mites.  Both species of mites  
increased in population density at the fastest rates at the sites closest  too and 
down wind from the smelter.  By end of 48 months, the mites wiped  out the 
colonies nearest the smelter (at the sites with the highest exposures to  
metals).
 
At the start of the trial, we anticipated that the metals (lead, arsenic,  
copper) might possibly have a differential effect on the bees and on  the 
mites.  We even considered it possible that mites  might be more susceptible 
to the metals than the bees, in which case,  mite populations would have 
slowed in growth or diminished.  No such luck,  mites over ran bee colonies.  
 
 In the end, mites gained in numbers, bees lost colonies, and of  course, 
the lost colonies  thenalso took their mites to the grave (so to  speak) with 
them.  We did not see any evidence that the metals  affected the mites more 
than the bees.  Mite populations increased for both  species, bee colonies 
died quicker, closer to the smelter.
 
My point, it was a classic scenario - metals exacerbated  the  mite 
problem.  In a sense, we might have concluded that heavy metals  increased 
fecundity - but I suspect it was more of a shift in the rates of  reproduction and 
mortality of the host and the parasitoids.  Bee  reproduction tends to be 
reduced and overall mortality rate with shortened life  spans were a common 
consequence of heavy metal exposure (we did this kind of  work for nearly 20 
years).  Metal problems and bee losses  were particularly bad in dry years and 
windy conditions, where the  surfacial contamination of soils, re-entrained 
dusts containing high metal  levels tended to result in higher exposures to 
the brood via metals in  pollen.  Bee populations slowed growth, bee colony 
age structures were  altered.  Mites on the other hands tended to  thrive.

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