> > >It was always my belief that there were stocks of EHB that had had a > sufficiently long evolutionary exposure to tmites for a balanced > host/parasite adaption to occur. Dan, the bee stocks in the U.S. were established from stocks that apparently had not been exposed to tracheal mite, and imports were cut off around 1920. So I question whether there were alleles that had been naturally selected for Tmite resistance extant in our population when the Tmite invaded. A point to keep in mind is that genes involved in resistance to parasites tend to be the most rapidly evolving genes, due to the Red Queen Hypothesis, which describes the continual battle between parasites and their hosts. Parasites tend to evolve more quickly than do other changes in the environment, hence the rapid evolution of resistance mechanisms. But there is a large element of randomness (stochasticity) involved. The rapidity of natural evolution of a host against the pressure of a novel parasited depends largely upon what potential "tools" a species already contains in its genome (preadaptation). And then there is a huge amount of chance involved--whether such tools happen to get passed on to the next generation, and whether they have a downside (such as, in humans, sickle cell anemia vs resistance to malaria). So whether resistance develops quickly or slowly depends upon a number of factors, mainly: 1. The degree of selective pressure (how badly the parasite is hurting the host). 2. The existing toolbox of genes and alleles in the host's genome. 3. The roulette-type chance of a beneficial random mutation occurring, and then actually getting passed to the next generation. As Pete has pointed out previously, evolution does not have a direction or goal. It is the result of largely random trial and error. The end result is not necessarily the "best" or "most efficient" result, but rather one that tended "to solve the problem" (to an adequate extent). Returning to varroa resistance, the ancestral and most genetically diverse honey bee populations (from Africa) happened to possess traits that preadapted them for resistance to varroa. And perhaps even more importantly, humans stepped aside and allowed natural selection to take its course. The result is various bee races in Africa and the Americas (in the same species as our domestic stocks) that are strongly resistant to varroa. This fact alone is strong evidence that *Apis mellifera *has the clear potential to develop resistance to varroa via natural selection. -- Randy Oliver Grass Valley, CA www.ScientificBeekeeping.com *********************************************** The BEE-L mailing list is powered by L-Soft's renowned LISTSERV(R) list management software. For more information, go to: http://www.lsoft.com/LISTSERV-powered.html