Carlos,
 
Some authors say the process goes like this in the tropics:
 
When it´s nectar time and the colony has a "high" infestation rate,
 
* The queen has almost no place to lay, because the bees are filling 
cells with nectar
* The varroas stay on the adult bees
*When the honey is harvested and there´s anymore nectar, the queen 
starts laying again 
*All the varroa get into these new larvae (that are needed to replace 
the now old adult bees)
* The larvae are so heavily infested that it dies and there´s no 
replacement of bees, so they die too
*The colony dissappears.
 
In temperate regions, maybe the reason why the colony cannot survive 
winter is because the infested bees live less time than the healthy 
bees.
 
The drone larvae has a longer biological cycle (longer time capped 
brood), so it allows the varroa to reproduce more efficiently, it also 
seems to have a pheromone that attracts more varroas than worker larvae. 
 
Tere