Fairly independent hypotheses relate to the whole matter. Each one has an accumulated mix of experimental results, quantified validations, experiences and anecdotes. Eventually, if we add that most inevitable test of time, reality will prevail and it may all be clearer. Here are some obvious hypotheses: 1) Defined defense mechanisms of resistance in bees (e.g. hygiene, grooming) make mite populations decrease or not grow significantly in colonies. 2) These defense mechanisms are genetically based, such that environmental influences are minor and the traits work uniformly regardless of environment. 3) Life history traits of colonies (seasonal growth patterns, swarming, timing of drone production) give colonies an advantage in dealing with varroa. 4) These life history traits may be more influenced by environment and not as reliable in making colonies uniformly resistant. 5) Isolation of colonies selects for avirulent mites. 6) Crowding of colonies eliminates any advantage of defense mechanisms or life history traits in colonies. 7) Outcrossing dilutes the usefulness of different traits at different rates. (This one in itself can be broken down many ways) What does reality say about each one of these? *********************************************** 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