>> I'm not sure whether it is simply because I am running more hygienic >> bees, because there is less feral population, or what. But it sure is >> curious. > May be the widespread adoption of Tylosin. If most commercial beekeepers > are using it and have stamped down foulbrood in their outfits, this would > tend to reduce the incidence of foulbrood in general, irrespective of > whether smaller beekeepers use it or not. I agree with Peter. The loss of sulfathiazole some time back meant that there was only one preventative available legally until Tylosin came on the scene. That in itself is a recipe for developing resistance, so having a back-up is bound to have an impact. Tylosin is also very persistent which makes it a good drug for suppressing AFB, but also potentially problematic in the wrong hands in regard to honey purity in this time of extremely sensitive lab tests and a critical public. Sulfa was a miracle drug, partly due to its persistence, but its persistence was also a curse, especially since some people are very sensitive to it. OTC (oxytetracycline) is effective against most AFB, but is quite short-lived and as a result, under-dosing is common, even when the initial dose is as prescribed. Maintaining the control dose over a brood cycle is critical to achieving and maintaining control. With OTC, this can be difficult and OTC was never very good at reliably suppressing AFB. What OTC lacks in persistence has had to be made up in beekeeper persistence and repeated applications. Tylosin, unlike OTC is very long-lived as are its metabolites. Each dose maintains its activity over sufficient time to make it very effective, and several dosings are apparently sufficient to drive AFB levels down to where even average bees do not break down, assuming that scale has been removed and all other things are equal. As far as I know, we never saw any resistance develop to sulfa, but shortly after it was banned, some AFB strains showed resistance to OTC. Will we see AFB resistant to Tylosin? That is a good question. In my opinion, the resistance that developed to OTC came about by horizontal gene transfer from other, already resistant bacteria, not spontaneously. However, IMO, the process was accelerated and somewhat enabled by the fact that maintaining a controlling level of OTC in hives at critical times is difficult. As a result of the quick fading of OTC potency over a short time under hive conditions, bacteria had ample opportunity to be selected for those which could tolerate OTC. So, yes, I agree that Tylosin has been a factor and also think that the breeding efforts aimed at hygienic behaviour have had an effect as well. *********************************************** 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 Guidelines for posting to BEE-L can be found at: http://honeybeeworld.com/bee-l/guidelines.htm