>>They have been exacerbated the past couple of years by the freezing over of the Great Lakes, which creates an enormous cold sink,-- which keeps the temperatures cold well into spring. You look at a map of losses last winter and the worst losses were clustered around the Great Lakes. 

Yes, and the corn and soy growing areas in Ontario tend to follow the great lakes as well.  We have had a couple of cold winters here, but the that doesn't explain the overall trend of winter losses in those areas: http://www.omafra.gov.on.ca/english/food/inspection/bees/2014winterloss.htm - see Figure 3 starting in 2007.  Previous winters have been much milder.  You can add this years average loss of 38% to the chart.  Large portions of the rest of Canada have also experienced these same winters - many of these regions are much harsher than the southern Ontario corridor facing the highest losses, yet when you remove Ontario the average country-wide winter-losses have been trending downwards to below 20%.   While the Ontario losses do not correlate well with the winter climate, they do correlate the with the wide-spread use of neonic coated corn and soy beans in this region.  There are of course other factors.  One is the sharp increase in the number of colonies sent to Easter Canada for blueberry pollination.  10000 roughly (10% of all colonies) in 2010, rising to 30000(or 30%) in 2014 and I am sure it is even higher this year.  I am sure the transportation, nutritional stress and exposure to fungicides is contributing as well.  This really isn't enough on its own, with double number colonies lost in 2013/14 than were sent for pollination.

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