>I must question the hypothesis that the feral population was the main source of AFB

A couple of studies posted a couple of months ago here on the pages of Bee-L seem to question this position as well:

https://www.tandfonline.com/doi/pdf/10.1080/03014223.1994.9517996

https://www.researchgate.net/publication/14540789_Bacillus_larvae_carrier_status_of_swarms_and_feral_colonies_of_honeybees_Apis_mellifera_in_Australia

The Goodwin paper in particular makes reference to historical studies in the US and UK that mirror their own findings.

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