Aaron Morris' "Varroa Answer" speculates on the way a mite-less colony gets infested. Here in British Columbia, we have witnessed a progressive spread of Varroa from the most southern areas close to the US border northward. Due to BC's topography marked by mountain ranges running north-south, Varroa has been following the valley floors where bees are kept, and where bees are being transported. We have seen the typical 'leaps & bounds' phenomenon of finding incidental Varroa infestations in apiaries that by themselves are pretty isolated (from other bee populations) but are always close to the highway. Clear proof of infested bees escaping from trucks moving colonies from southern BC to the far north. The other form of spread is more localized but rapid nonetheless, which can only be explained through drifting and drone visitations. I commented sometime ago on the distance of flight of bees, and referred to research done by Tibor Szabo in the early eighties. Drones with free access to other colonies, coupled with their 'high motivation' (ie. sex drive) and physical ability to fly fast and far, are overwhelming likely playing a critical role as vectors of Varroa. Your question about how Varroa distinguishes between a drone cell/larva and a worker cell/larva is intriquing. I have often wandered about that also, but perhaps some chemical or pheremonal cues may play an important role. Paul van Westendorp Provincial Apiculturist BC Ministry of Agriculture Fisheries & Food 17720 - 57th Avenue Surrey, B.C. V3S 4P9 CANADA