> bees in temperate climates are ravaged more by Varroa than those in tropical climates, even when the hives are headed up by sister queens.  

I heard Dave DeJong talk at the EAS 2003 when it was in Ithaca. He mentioned this then. He pointed out that temperate bees have a much steeper annual curve between the high and low populations, coupled with a varroa population explosion in late summer while tropical bees have a more gradual population curve, minus the big surge. 

If you combine this with the much more benign conditions of winter in the tropics or even the subtropics, you will see why beekeepers in these regions may have a less difficult time managing varroa populations. My friend Tom Glenn, from Southern California, told me he didn't struggle with varroa. But he also bred varroa resistant bees. 

On the other hand, colonies need to be very healthy to successfully winter over in the North, and the effects of varroa infestation with the associated viruses undoubtedly greatly increase winter mortality. Much hay has been made from the notion that we need northern bred bees, but that ignores the fact that most US honey bee stock came from in the Alps. 

Pete

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