On Thu, 25 Mar 2010 22:06:53 -0400, Allen Dick <[log in to unmask]> wrote:

>>Maybe with those Louisiana bees, but not here... 

Quite possibly not if you are selecting or the winter is doing it for you.

Here are some quotes and another link: http://www.ars.usda.gov/Services/docs.htm?docid=2744&page=12

-- begin quote ---

Eight commercial queen producers from five states submitted brood from 6 to 19 breeder colonies each so that emerging bees could be evaluated for relative resistance to tracheal mites. Young, uninfested bees from each colony of an individual queen producer, and also from colonies of two reference stocks (one known to be resistant to tracheal mites and one known to be susceptible), were marked and then simultaneously exposed to mites in infested colonies. They were retrieved after 4-6 days and dissected to determine resulting mite infestations. Results for the breeder colonies were adjusted to the average results of the resistant and susceptible reference colonies with which they were tested.

The 83 breeder colonies varied widely in their responses to tracheal mites. About two-thirds were statistically similar to the resistant reference and one-fourth were similar to the susceptible reference. Three queen producers had 30 of 31 breeder colonies that were classified as resistant. The other five queen producers had breeder colonies that were very variable and of which 40% were susceptible.

The most striking result of this survey was the variability in levels of tracheal mite resistance among colonies of U.S. commercial breeding stock. This breeding population can be expected to yield propagated queens that range widely in quality: some queens will be useful in improving stock by imparting resistance, while others will predispose their colonies to damaging mite infestations. In the absence of knowledge about the resistance levels of individual breeder colonies, the performance (vis-vis tracheal mites) of production colonies headed by commercial queens becomes largely a matter of the chance associated with a queen producer=s random selection of a grafting source from  among his or her breeder colonies.   

--- begin second quote --- 

During the last ten years we have evaluated the genetic resistance of colonies from eleven sources using bioassays of newly emerged workers exposed to tracheal mites in infested colonies...

...The levels of resistance in four of the six sources appear to have deteriorated or not improved through time, with their most recent mean resistance indices being higher than 0.5 (Figure). Beekeepers should be aware of the fact that uniformly high resistance to tracheal mites is not found in all commercial sources. Active selection for resistance by breeders and purchasing of resistant breeding material by queen producers is recommended to solve these persistent problems with tracheal mites.

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